This document summarizes the analysis of periodic variable stars in the open cluster NGC 3766 based on a 7-year monitoring campaign. The authors detected a new class of 36 variable stars located between the instability strips for slowly pulsating B stars and delta Scuti stars, where no variability was previously predicted. The majority of these new variables have periods between 0.1-0.7 days and amplitudes of 1-4 millimagnitudes. The properties of this new class are discussed and the authors argue they are likely pulsating variables sustained by stellar rotation. Additionally, the authors identify other periodic variables such as eclipsing binaries, slowly pulsating B stars, delta Scuti stars, and gamma Doradus candidates.
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
Detection of magnetic_fields_in_both_b_type_components_of_epsilon_lupi_system...Sérgio Sacani
Uma equipe de astrônomos detectou um chamado campo magnético fóssil em ambos os componentes de um sistema estelar binário, chamado de Epsilon Lupi.
Epsilon Lupi, também conhecida como HD 136504, é uma estrela binária brilhante, localizada na constelação do hemisfério sul de Lupus.
O par de estrelas está localizado a aproximadamente 500 anos-luz de distância da Terra, e cada estrela tem entre 7 e 8 vezes a massa do Sol, e combinadas, elas têm cerca de 6000 vezes a luminosidade do Sol.
Os astrônomos sabem de muito tempo que a Epsilon Lupi é um sistema binário, mas não tinham ideia de que as duas estrelas pudessem possuir campos magnéticos.
“A origem do magnetismo entre estrelas massivas é um mistério e essa descoberta pode ajudar a trazer uma luz numa questão de por que essas estrelas possuem campos magnéticos”, disse Matt Shultz da Universidade de Queen no Canadá, e o principal autor do artigo aceito para publicação no Monthly Notices of the Royal Astronomical Society e que descreve a descoberta.
08 gray asymmetries in the spectral ines of evolved halo starsLeonardo García
This document summarizes a study of asymmetries in the spectral lines of evolved halo stars. The key findings are:
1) Metal-poor stars hotter than 4100 K showed C-shaped line bisectors similar to solar-metallicity stars below the granulation boundary.
2) Metal-poor stars cooler than 4100 K, or higher up the red giant branch, showed reversed C-shaped bisectors similar to solar stars above the granulation boundary and previous observations of Betelgeuse.
3) Both the radial velocity jitter observed in high-luminosity stars and their reversed C-shaped bisectors vary together up the red giant branch, likely signatures of large convection cells.
This document summarizes a study that uses U-band photometry to determine photometric distances to young stars in the inner Galactic disk. The study focuses on the line of sight towards the Galactic longitude of 314 degrees. Photometric data is collected and calibrated using two open clusters in the field. Three groups of stars are detected at distances of 1.5, 2.5, and 5.1 kpc, which are consistent with the Carina-Sagittarius and Scutum-Crux spiral arms. The use of U-band photometry is shown to be an effective method for characterizing young star populations and making predictions about spiral structure in the Milky Way.
New m embers_of_the_tw_hydrae_association_and_two_accreting_m_dwarfs_in_scorp...Sérgio Sacani
Uma descoberta acidental de uma coleção de jovens estrelas do tipo anãs vermelhas perto do nosso Sistema Solar, poderiam nos dar uma rara ideia da formação planetária em câmera lenta. Os astrônomos da The Australian National University a ANU e a University of New South Wales, a UNSW, em Canberra, descobriram grandes discos de poeira ao redor de duas estrelas, mostrando sinais de planetas em processo de formação.
“Nós achamos que a Terra e todos os planetas se formaram de discos como esses, assim é fascinante ver um potencial novo sistema solar se formando”, disse o principal pesquisador Dr. Simon Murphy, da ANU Research School of Astronomy and Astrophysics.
“Contudo, outras estrelas dessa idade normalmente não têm mais discos. Os discos das anãs vermelhas parecem viver mais do que os de estrelas mais quentes como o Sol. Nós não entendemos por que”, disse o Dr. Murphy.
How to tell an accreting boson star from a black hole h. olivares et al (2020)SOCIEDAD JULIO GARAVITO
Abstract
The tentative evidences for late time “echoes” in LIGO gravitational
waves (GWs) have been claimed to be signatures of horizonless compact
objects rather than vacuum black holes (BHs) possessing horizons. In
general, in the past, many authors have considered the possibility that
the so-called BHs might be only BH mimickers (BHMs). And recently
it has been suggested that the true astrophysical BH having no intrinsic
magnetic fields may be differentiated from magnetized BHMs by studying
the radial variations of magnetic fields around pertinent compact objects
(Lobanov, Nat. Astron. 2017). Here we highlight that close to the surface
of BHMs, the magnetic field pattern differs significantly from the same for
non-relativistic Neutron Stars (B ∼ r −3 ). In particular, we point out that
for ultra- compact BHMs, the polar field is weaker than the equatorial field
1by an extremely large factor of ∼ z s /lnz s , where z s ≫ 1 is the surface
gravitational redshift. We suggest that by studying the of radial variation
as well as such significant asymmetry of magnetic field structure near the
compact object, future observations may differentiate a theoretical black
hole from a astrophysical BH mimicker (a compact object). This study
also shows that even if some BHMs would be hypothesized to possess
magnetic fields even stronger than that of magnetars, in certain cases, they
may effectively behave as atoll type neutron stars possessing extremely low
magnetic fields.
Keywords: X-ray Binaries; Active Galactic Nuclei; Magnetic Field;
Black Hole Mimickers; Relativistic Astrophysics.
PACS numbers: 04.40.Dg, 97.80.Jp, 97.60.Gb, 95.86.Nv.
The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in th...GOASA
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion. The discovery of the
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
Detection of magnetic_fields_in_both_b_type_components_of_epsilon_lupi_system...Sérgio Sacani
Uma equipe de astrônomos detectou um chamado campo magnético fóssil em ambos os componentes de um sistema estelar binário, chamado de Epsilon Lupi.
Epsilon Lupi, também conhecida como HD 136504, é uma estrela binária brilhante, localizada na constelação do hemisfério sul de Lupus.
O par de estrelas está localizado a aproximadamente 500 anos-luz de distância da Terra, e cada estrela tem entre 7 e 8 vezes a massa do Sol, e combinadas, elas têm cerca de 6000 vezes a luminosidade do Sol.
Os astrônomos sabem de muito tempo que a Epsilon Lupi é um sistema binário, mas não tinham ideia de que as duas estrelas pudessem possuir campos magnéticos.
“A origem do magnetismo entre estrelas massivas é um mistério e essa descoberta pode ajudar a trazer uma luz numa questão de por que essas estrelas possuem campos magnéticos”, disse Matt Shultz da Universidade de Queen no Canadá, e o principal autor do artigo aceito para publicação no Monthly Notices of the Royal Astronomical Society e que descreve a descoberta.
08 gray asymmetries in the spectral ines of evolved halo starsLeonardo García
This document summarizes a study of asymmetries in the spectral lines of evolved halo stars. The key findings are:
1) Metal-poor stars hotter than 4100 K showed C-shaped line bisectors similar to solar-metallicity stars below the granulation boundary.
2) Metal-poor stars cooler than 4100 K, or higher up the red giant branch, showed reversed C-shaped bisectors similar to solar stars above the granulation boundary and previous observations of Betelgeuse.
3) Both the radial velocity jitter observed in high-luminosity stars and their reversed C-shaped bisectors vary together up the red giant branch, likely signatures of large convection cells.
This document summarizes a study that uses U-band photometry to determine photometric distances to young stars in the inner Galactic disk. The study focuses on the line of sight towards the Galactic longitude of 314 degrees. Photometric data is collected and calibrated using two open clusters in the field. Three groups of stars are detected at distances of 1.5, 2.5, and 5.1 kpc, which are consistent with the Carina-Sagittarius and Scutum-Crux spiral arms. The use of U-band photometry is shown to be an effective method for characterizing young star populations and making predictions about spiral structure in the Milky Way.
New m embers_of_the_tw_hydrae_association_and_two_accreting_m_dwarfs_in_scorp...Sérgio Sacani
Uma descoberta acidental de uma coleção de jovens estrelas do tipo anãs vermelhas perto do nosso Sistema Solar, poderiam nos dar uma rara ideia da formação planetária em câmera lenta. Os astrônomos da The Australian National University a ANU e a University of New South Wales, a UNSW, em Canberra, descobriram grandes discos de poeira ao redor de duas estrelas, mostrando sinais de planetas em processo de formação.
“Nós achamos que a Terra e todos os planetas se formaram de discos como esses, assim é fascinante ver um potencial novo sistema solar se formando”, disse o principal pesquisador Dr. Simon Murphy, da ANU Research School of Astronomy and Astrophysics.
“Contudo, outras estrelas dessa idade normalmente não têm mais discos. Os discos das anãs vermelhas parecem viver mais do que os de estrelas mais quentes como o Sol. Nós não entendemos por que”, disse o Dr. Murphy.
How to tell an accreting boson star from a black hole h. olivares et al (2020)SOCIEDAD JULIO GARAVITO
Abstract
The tentative evidences for late time “echoes” in LIGO gravitational
waves (GWs) have been claimed to be signatures of horizonless compact
objects rather than vacuum black holes (BHs) possessing horizons. In
general, in the past, many authors have considered the possibility that
the so-called BHs might be only BH mimickers (BHMs). And recently
it has been suggested that the true astrophysical BH having no intrinsic
magnetic fields may be differentiated from magnetized BHMs by studying
the radial variations of magnetic fields around pertinent compact objects
(Lobanov, Nat. Astron. 2017). Here we highlight that close to the surface
of BHMs, the magnetic field pattern differs significantly from the same for
non-relativistic Neutron Stars (B ∼ r −3 ). In particular, we point out that
for ultra- compact BHMs, the polar field is weaker than the equatorial field
1by an extremely large factor of ∼ z s /lnz s , where z s ≫ 1 is the surface
gravitational redshift. We suggest that by studying the of radial variation
as well as such significant asymmetry of magnetic field structure near the
compact object, future observations may differentiate a theoretical black
hole from a astrophysical BH mimicker (a compact object). This study
also shows that even if some BHMs would be hypothesized to possess
magnetic fields even stronger than that of magnetars, in certain cases, they
may effectively behave as atoll type neutron stars possessing extremely low
magnetic fields.
Keywords: X-ray Binaries; Active Galactic Nuclei; Magnetic Field;
Black Hole Mimickers; Relativistic Astrophysics.
PACS numbers: 04.40.Dg, 97.80.Jp, 97.60.Gb, 95.86.Nv.
The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in th...GOASA
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion. The discovery of the
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
Discovery of a_probable_4_5_jupiter_mass_exoplanet_to_hd95086_by_direct_imagingSérgio Sacani
The document reports the discovery of a probable 4-5 Jupiter-mass exoplanet orbiting the young star HD 95086. Deep imaging observations using VLT/NaCo detected a faint source at a separation of 56 AU from the star. Follow-up observations over more than a year found the source to be co-moving with the star, suggesting it is bound. Its luminosity corresponds to a predicted mass of 4-5 Jupiter masses, making it the lowest mass exoplanet directly imaged around a star. If confirmed, this discovery could provide insights into giant planet formation and evolution.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
This document provides an overview and context for a study of the symbiotic star SS Leporis using interferometric imaging with the PIONIER instrument on the VLTI. Key points:
- SS Leporis is a long-period interacting binary system composed of an A star accreting material from an evolved M giant companion, presenting an "Algol paradox" where the more evolved star is less massive.
- Previous studies have not fully constrained the system morphology and characteristics. New interferometric observations with PIONIER were obtained to directly probe the inner parts of the system.
- The observations were used to perform aperture synthesis imaging and model the system as a binary surrounded by a circumbinary disc. This provides the
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
This document presents an analysis of transit spectroscopy observations of three exoplanets - WASP-12 b, WASP-17 b, and WASP-19 b - using the Wide Field Camera 3 instrument on the Hubble Space Telescope. The observations achieved almost photon-limited precision but uncertainties in the transit depths were increased by the uneven sampling of the light curves. The final transit spectra for all three planets are consistent with the presence of a water absorption feature at 1.4 microns, though the amplitude is smaller than expected from previous Spitzer observations possibly due to hazes. Due to degeneracies between models, the data cannot unambiguously constrain the atmospheric compositions without additional observations.
Olivine in an_unexpected_location_on_vesta_surfaceSérgio Sacani
The document reports on the discovery of olivine on the surface of the asteroid Vesta in unexpected locations, based on data from the Dawn spacecraft's VIR instrument. Specifically:
- Olivine was found in the northern hemisphere of Vesta, rather than the southern basins where mantle rocks were expected based on previous models.
- The olivine occurs in large patches hundreds of meters across mixed with howardite regolith, unlike in meteorites where it is a minor component of diogenites.
- The amount and distribution of olivine-rich material suggests a complex evolutionary history for Vesta and is not consistent with previous ideas of olivine occurrence being associated with diogenites
1) The VVV survey discovered a new globular cluster candidate, named VVV CL001, near the known globular cluster UKS 1 in the direction of the Galactic bulge.
2) Photometry of UKS 1 from the VVV survey was used to measure its reddening as E(B-V)=2.2 mag, distance modulus as (m-M)0=16.01 mag, and distance as 15.9 kpc.
3) Near-infrared color-magnitude diagrams of VVV CL001 suggest it has similar reddening as UKS 1 and is at least as metal-poor, though its distance remains uncertain. Further observations are needed to confirm if they are
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
Cold Molecular Gas in Merger Remnants. I. Formation of Molecular Gas DiscsGOASA
- 80% (24/30) of the merger remnants with robust CO detections showed kinematical signatures of rotating molecular gas disks (including nuclear rings) based on their velocity fields. The sizes of these disks varied significantly from 1.1 kpc to 9.3 kpc.
- In 54% of the sources, the size of the molecular gas disks was more compact than the K-band effective radius, possibly formed from past gas inflows triggered by dynamical instabilities during mergers.
- The remaining 46% had more extended gas disks relative to the stellar component, possibly forming late-type galaxies with central stellar bulges.
- The study suggests that nuclear and extended molecular gas disks are common in
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
The document describes measurements of the proper motion of the Andromeda Galaxy (M31) using Hubble Space Telescope imaging data from multiple fields observed at two epochs separated by 5-7 years. Background galaxies in the images are used as stationary reference objects to measure the displacement of thousands of M31 stars between epochs. This allows determining M31's absolute proper motion with an accuracy of 12 microarcseconds per year, providing crucial information about M31 and the Local Group's dynamics and future evolution.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
This document presents observations from the Keck/OSIRIS integral field unit of a galaxy detected in absorption as a damped Lyman-alpha system (DLA) along the line of sight to a background quasar. Laser guide star adaptive optics were used to achieve high spatial resolution, allowing the detection and mapping of emission from the DLA galaxy free from contamination by the quasar. Emission from H-alpha and [O III] is detected and used to measure a star formation rate, dynamical mass, velocity field, and evidence of possible metallicity gradients in the galaxy. While some irregular kinematic features are seen, no clear rotational signature is observed that would support an edge-on disk interpretation of the galaxy's structure
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
1) Global climate models that include sophisticated cloud schemes show that tidally locked planets can develop thick water clouds near the substellar point due to strong convection. These clouds greatly increase the planetary albedo and stabilize temperatures, allowing habitability at twice the stellar flux previously thought possible.
2) The cloud feedback is stabilizing, as higher stellar flux produces stronger convection and higher albedos. Substellar clouds can block outgoing radiation, reducing the day-night temperature contrast.
3) Non-tidally locked planets do not experience this stabilizing cloud feedback, as clouds only form over parts of the tropics and mid-latitudes. Their albedo decreases with increasing stellar flux, producing a destabil
A population of_fast_radio_bursts_ar_cosmological_distancesSérgio Sacani
1) Four fast radio bursts (FRBs) lasting only a few milliseconds were detected in a radio survey of the high Galactic latitude sky.
2) The bursts' properties indicate they are of celestial rather than terrestrial origin and likely originate from cosmological distances of 0.5 to 3 billion light years.
3) No coincident x-ray or gamma-ray signals were found associated with the bursts. Characterizing the population of FRBs could help determine the baryonic content of the universe.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
Discovery of a_probable_4_5_jupiter_mass_exoplanet_to_hd95086_by_direct_imagingSérgio Sacani
The document reports the discovery of a probable 4-5 Jupiter-mass exoplanet orbiting the young star HD 95086. Deep imaging observations using VLT/NaCo detected a faint source at a separation of 56 AU from the star. Follow-up observations over more than a year found the source to be co-moving with the star, suggesting it is bound. Its luminosity corresponds to a predicted mass of 4-5 Jupiter masses, making it the lowest mass exoplanet directly imaged around a star. If confirmed, this discovery could provide insights into giant planet formation and evolution.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
This document provides an overview and context for a study of the symbiotic star SS Leporis using interferometric imaging with the PIONIER instrument on the VLTI. Key points:
- SS Leporis is a long-period interacting binary system composed of an A star accreting material from an evolved M giant companion, presenting an "Algol paradox" where the more evolved star is less massive.
- Previous studies have not fully constrained the system morphology and characteristics. New interferometric observations with PIONIER were obtained to directly probe the inner parts of the system.
- The observations were used to perform aperture synthesis imaging and model the system as a binary surrounded by a circumbinary disc. This provides the
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
This document presents an analysis of transit spectroscopy observations of three exoplanets - WASP-12 b, WASP-17 b, and WASP-19 b - using the Wide Field Camera 3 instrument on the Hubble Space Telescope. The observations achieved almost photon-limited precision but uncertainties in the transit depths were increased by the uneven sampling of the light curves. The final transit spectra for all three planets are consistent with the presence of a water absorption feature at 1.4 microns, though the amplitude is smaller than expected from previous Spitzer observations possibly due to hazes. Due to degeneracies between models, the data cannot unambiguously constrain the atmospheric compositions without additional observations.
Olivine in an_unexpected_location_on_vesta_surfaceSérgio Sacani
The document reports on the discovery of olivine on the surface of the asteroid Vesta in unexpected locations, based on data from the Dawn spacecraft's VIR instrument. Specifically:
- Olivine was found in the northern hemisphere of Vesta, rather than the southern basins where mantle rocks were expected based on previous models.
- The olivine occurs in large patches hundreds of meters across mixed with howardite regolith, unlike in meteorites where it is a minor component of diogenites.
- The amount and distribution of olivine-rich material suggests a complex evolutionary history for Vesta and is not consistent with previous ideas of olivine occurrence being associated with diogenites
1) The VVV survey discovered a new globular cluster candidate, named VVV CL001, near the known globular cluster UKS 1 in the direction of the Galactic bulge.
2) Photometry of UKS 1 from the VVV survey was used to measure its reddening as E(B-V)=2.2 mag, distance modulus as (m-M)0=16.01 mag, and distance as 15.9 kpc.
3) Near-infrared color-magnitude diagrams of VVV CL001 suggest it has similar reddening as UKS 1 and is at least as metal-poor, though its distance remains uncertain. Further observations are needed to confirm if they are
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
Cold Molecular Gas in Merger Remnants. I. Formation of Molecular Gas DiscsGOASA
- 80% (24/30) of the merger remnants with robust CO detections showed kinematical signatures of rotating molecular gas disks (including nuclear rings) based on their velocity fields. The sizes of these disks varied significantly from 1.1 kpc to 9.3 kpc.
- In 54% of the sources, the size of the molecular gas disks was more compact than the K-band effective radius, possibly formed from past gas inflows triggered by dynamical instabilities during mergers.
- The remaining 46% had more extended gas disks relative to the stellar component, possibly forming late-type galaxies with central stellar bulges.
- The study suggests that nuclear and extended molecular gas disks are common in
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
This document presents a sample of 151 dwarf galaxies that exhibit optical spectroscopic signatures of accreting massive black holes. The sample was identified by systematically searching ~25,000 emission-line galaxies from the Sloan Digital Sky Survey with stellar masses comparable to or less than the Large Magellanic Cloud. Many of the galaxies show narrow-line signatures of black hole accretion, and some also exhibit broad H-alpha emission, indicating gas orbiting in the deep potential of a massive black hole. This increases the number of known active galaxies in this low stellar mass range by over an order of magnitude. The median stellar mass of the host galaxies is around 108.5 solar masses, around 1-2 magnitudes fainter than previous samples of
The document describes measurements of the proper motion of the Andromeda Galaxy (M31) using Hubble Space Telescope imaging data from multiple fields observed at two epochs separated by 5-7 years. Background galaxies in the images are used as stationary reference objects to measure the displacement of thousands of M31 stars between epochs. This allows determining M31's absolute proper motion with an accuracy of 12 microarcseconds per year, providing crucial information about M31 and the Local Group's dynamics and future evolution.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
This document presents observations from the Keck/OSIRIS integral field unit of a galaxy detected in absorption as a damped Lyman-alpha system (DLA) along the line of sight to a background quasar. Laser guide star adaptive optics were used to achieve high spatial resolution, allowing the detection and mapping of emission from the DLA galaxy free from contamination by the quasar. Emission from H-alpha and [O III] is detected and used to measure a star formation rate, dynamical mass, velocity field, and evidence of possible metallicity gradients in the galaxy. While some irregular kinematic features are seen, no clear rotational signature is observed that would support an edge-on disk interpretation of the galaxy's structure
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
1) Global climate models that include sophisticated cloud schemes show that tidally locked planets can develop thick water clouds near the substellar point due to strong convection. These clouds greatly increase the planetary albedo and stabilize temperatures, allowing habitability at twice the stellar flux previously thought possible.
2) The cloud feedback is stabilizing, as higher stellar flux produces stronger convection and higher albedos. Substellar clouds can block outgoing radiation, reducing the day-night temperature contrast.
3) Non-tidally locked planets do not experience this stabilizing cloud feedback, as clouds only form over parts of the tropics and mid-latitudes. Their albedo decreases with increasing stellar flux, producing a destabil
A population of_fast_radio_bursts_ar_cosmological_distancesSérgio Sacani
1) Four fast radio bursts (FRBs) lasting only a few milliseconds were detected in a radio survey of the high Galactic latitude sky.
2) The bursts' properties indicate they are of celestial rather than terrestrial origin and likely originate from cosmological distances of 0.5 to 3 billion light years.
3) No coincident x-ray or gamma-ray signals were found associated with the bursts. Characterizing the population of FRBs could help determine the baryonic content of the universe.
Voyager 1 observed changes in cosmic ray intensities on August 25, 2012 when it was 122 AU from the Sun, indicating it had entered a new region outside the heliosphere still dominated by the Sun's magnetic field. Energetic particles from inside the heliosphere disappeared, while intensities of low-energy galactic cosmic rays increased. Analysis of cosmic ray spectra revealed hydrogen and helium spectra peaking between 10-40 MeV/nucleon, consistent with abundances in the solar photosphere. This provides the first direct measurements of low-energy galactic cosmic rays outside of Earth's environment.
Herschel galactic plane_survey_the_global_distribution_of_ism_gas_componnentSérgio Sacani
This document summarizes a study using Herschel observations of the [C ii] 158μm line to analyze the distribution of different gas components in the Milky Way galaxy. The observations provide high-resolution maps of [C ii] emission across the Galactic plane. By comparing these maps to observations of HI, CO, and other tracers, the study finds that [C ii] emission is associated with spiral arms between 4-10 kpc from the Galactic center. It estimates that [C ii] traces dense photon-dominated regions (47%), CO-dark H2 gas (28%), cold atomic gas (21%), and ionized gas (4%). The study also analyzes the distribution of cold neutral medium versus
Global collapse of_molecular_clouds_as_a_formation_mechanism_for_the_most_mas...Sérgio Sacani
This document summarizes observations of the massive star-forming cloud SDC335 made using Spitzer, Herschel, Mopra, and ALMA. It finds that SDC335 contains over 5500 solar masses of gas distributed in a network of filaments that converge on a central hub region. ALMA observations reveal two massive cores within this hub region, the most massive of which contains over 500 solar masses of gas. Kinematic analysis of molecular line data from Mopra and ALMA indicates that the cloud is undergoing global collapse, with infalling gas bringing additional material at a rate of over 2.5 solar masses per year to the central region, which could double its mass within the next few million years and allow
The deep blue_color_of_hd189733b_albedo_measurements_with_hst_stis_at_visible...Sérgio Sacani
The document summarizes a study that measured the geometric albedo of the exoplanet HD 189733b across visible wavelengths using Hubble Space Telescope observations. It found an albedo of 0.40 ± 0.12 at 290-450 nm that decreased to below 0.12 at 450-570 nm, suggesting optically thick clouds reflecting light at shorter wavelengths and sodium absorption suppressing reflection beyond 450 nm. This wavelength-dependent albedo implies HD 189733b would appear deep blue in color at visible wavelengths.
Hubble Space Telescope observations of the globular cluster NGC 6752 reveal a broadened and asymmetric main sequence, indicative of a large binary population. Artificial star experiments show that photometric errors and chance star superpositions alone cannot account for the observed broadening. A Monte Carlo technique is used to estimate the binary fraction, which is likely 15-38% in the inner core but less than 16% beyond that radius. The discovery of a significant main-sequence binary population provides constraints on the dynamical evolution and stellar populations of globular clusters.
This document summarizes a 1.3 mm continuum survey of protoplanetary disks in the 2-3 Myr old IC348 star cluster using the Submillimeter Array. 10 disks out of 85 young stars were detected with masses ranging from 2-6 Jupiter masses. This distribution is shifted to lower masses by a factor of 20 compared to younger regions like Taurus and Ophiuchus. The results reveal a rapid decline in the number of small dust grains in disks after 1 Myr, likely due to grain growth. The few detected disks may be the best candidates in IC348 to study planet formation.
Magnetic field observations_as_voyager1_entered_the_heliosheath_depletion_regionSérgio Sacani
1) Voyager 1 encountered an unexpected region in 2012 between 120-122 AU from the sun, entering it five times between days 210-238 based on magnetic field measurements.
2) When it entered this region, called the heliosheath depletion region (HDR), the magnetic field strength increased from around 0.2 nT to 0.4 nT and remained high, while energetic particle counts dropped significantly.
3) The direction of the magnetic field did not change significantly during the boundary crossings, indicating Voyager 1 likely did not cross the heliopause but remained in the heliosheath.
Detection of the_central_star_of_the_planetary_nebula_ngc_6302Sérgio Sacani
The document summarizes the detection of the central star of the planetary nebula NGC 6302 using new observations from the Hubble Space Telescope's Wide Field Camera 3. Key points:
1) The central star is directly detected for the first time at the center of the nebula, confirming its location but not at the center of the inner dust torus.
2) Photometry of the central star yields a reddening value of c=3.1, corresponding to AV=6.6 magnitudes of extinction, mostly from circumstellar dust.
3) Estimates of the stellar temperature, luminosity, and distance suggest a fairly massive central star of around 0.64 solar masses that is evolving rapidly and fading over time
This document summarizes the results of an MHD simulation coupled with a radiation transport model to simulate X-ray spectra from an accreting black hole. Key points:
- For the first time, the simulation is able to reproduce the main components seen in observed X-ray spectra, including a thermal peak, power-law tail, reflection hump, and iron line, by varying only the mass accretion rate.
- The temperature in the corona varies from 10 keV near the disk to over 100 keV in low-density regions, producing the hard X-ray emission through inverse-Compton scattering.
- Even as the disk's reflection edge varies from the horizon out to 6 gravitational radii with decreasing accretion
Insects live fascinating lives and play important roles in ecosystems. Marco Belzoni gave a presentation in 2010 about the magical world of insects, sharing photos and music to educate others. While the presentation materials were copyrighted, insects deserve our appreciation for their amazing diversity and contributions to the natural world.
Search for the_exit_voyager1_at_heliosphere_border_with_the_galaxySérgio Sacani
Voyager 1 has detected changes in energetic particle intensities that suggest it has reached the outer boundary of the heliosphere and entered interstellar space. Measurements show a sudden decrease in particles of solar origin by over 100 times on August 25, 2012, while galactic cosmic rays increased by 9.3% at the same time. This indicates Voyager 1 has reached a region dominated by interstellar plasma rather than heated solar plasma. The spacecraft is now detecting unexpected anisotropies in cosmic rays and temporary increases that may be associated with large solar storms, implying it is still within a transitional region to the local interstellar medium.
Dust in the_polar_region_as_a_major_contributor_to_the_infrared_emission_of_a...Sérgio Sacani
The mid-infrared emission of the active galactic nucleus NGC 3783 was observed using interferometry over multiple epochs, providing dense coverage of position angles and baselines. The emission was found to be strongly elongated along a position angle of -52 degrees, closely aligned with the polar axis orientation of -45 degrees. The half-light radii were measured to be 20.0 mas by 6.7 mas, corresponding to an axis ratio of 3:1. This implies that 60-90% of the 8-13 micron emission is from the polar-elongated component. The observations support a scenario where the majority of mid-infrared emission in Seyfert galaxies originates from a dusty wind in the polar region,
The sombrero galaxy_modelling_the_dust_contentSérgio Sacani
The document repeatedly lists the reference "1995A&A...303..673E" 18 times without providing any other context or information. It is unclear what the document is about based on the limited reference listing provided.
A dynamically packed_planetary _system_around_gj667_c_with_three_superearths_...Sérgio Sacani
This document summarizes the discovery of six potentially habitable super-Earth planets orbiting the red dwarf star GJ 667C. Analyzing new Doppler measurements from HARPS and previous data from other spectrographs, the authors detect six planetary candidates with orbital periods of 7, 28, 92, 62, 39, and 260 days. They validate the signals against stellar activity and find the system could be dynamically stable. Three or four of the planets may be located within the star's habitable zone where liquid water could exist, making this one of the first exoplanetary systems discovered with multiple Earth-sized planets in the habitable zone of an M-dwarf star.
The document lists various natural elements such as species, ecosystems, habitats, soils, clouds, lakes, rivers, mountains, humans, insects, mammals, oceans, birds, fishes, worms, plants, and flowers in repetitive phrases without any connecting context.
Insects have developed various ways to communicate, including through sight, smell, touch, dancing, and sound. They communicate to find food, defend their nests, and find mates. Sight is used by dragonflies and fireflies to recognize each other. Smell involves glands producing odors detected by antennae. Touch involves transferring chemicals through antennae contact. Bees communicate through dancing. Sound methods are used by cicadas, crickets, and mosquitoes.
This document discusses insect migration in three paragraphs or less:
Insects migrate to escape unfavorable conditions like temperature extremes, lack of food or water, or overcrowding. Common migratory insects include monarch butterflies, dragonflies, locusts, and aphids. Migration can occur over long distances of hundreds to thousands of kilometers and is often driven by seasonal changes and availability of resources across environments. Remote sensing technologies like radar are useful for monitoring large-scale insect migrations.
This document summarizes different types of communication used by insects, including visual, chemical, tactile, and acoustic communication. It discusses how insects communicate through color patterns, pheromones, touch, dance, sounds, and vibrations to recognize others of their species, find mates, locate food, warn of danger, and more. The key forms of communication are chemical signals like pheromones that convey information between individuals of the same species, and visual signals from patterns, flashes of light, or dances that help with tasks like attracting mates or locating food sources. Insects rely on these innate communication abilities to survive and thrive in their environments.
The gaia eso_survey_stellar_content_and_elemental_abundances_in_the_massive_c...Sérgio Sacani
Estudo sobre o conteúdo estelar e os elementos que estão presentes no aglomerado estelar aberto NGC 6705, também conhecido como Aglomerado do Pato Selvagem.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Three Ultra-...Sérgio Sacani
We present deep Hubble Space Telescope (HST) imaging of five faint dwarf galaxies associated with the nearby
spiral NGC 253 (D ≈ 3.5 Mpc). Three of these are newly discovered dwarf galaxies, while all five were found in
the Panoramic Imaging Survey of Centaurus and Sculptor, a Magellan+Megacam survey to identify faint dwarfs
and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data
reach 3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances,
structural parameters, and luminosities. All five systems contain mostly old, metal-poor stellar populations
(age ∼12 Gyr, [M/H] −1.5) and have sizes (rh ∼ 110–3000 pc) and luminosities (MV ∼ −7 to −12 mag) largely
consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered
beyond the Local Group. We also use archival H I data to place limits on the gas content of our discoveries. Deep
imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity
function and its scatter across a range of galaxy masses, morphologies, and environments in the decade to come
This document reports the first detections of Blue Straggler Stars (BSS) in the Milky Way bulge. Proper motions and variability measurements from Hubble Space Telescope observations were used to separate a clean bulge sample and identify BSS candidates. Of 42 candidate BSS identified, variability measurements indicate that at least 18 are genuine BSS, while contamination estimates suggest the true BSS population could be as high as 37 objects. This establishes for the first time that BSS exist as a population in the Milky Way bulge.
A three-dimensional map of the Milky Way using 66,000 Mira variable starsSérgio Sacani
We study the three-dimensional structure of the Milky Way using 65,981 Mira variable stars discovered
by the Optical Gravitational Lensing Experiment (OGLE) survey. The spatial distribution of the Mira
stars is analyzed with a model containing three barred components that include the X-shaped boxy
component in the Galactic center (GC), and an axisymmetric disk. We take into account the distance
uncertainties by implementing the Bayesian hierarchical inference method. The distance to the GC is
R0 = 7.66 ± 0.01(stat.) ± 0.39(sys.) kpc, while the inclination of the major axis of the bulge to the
Sun-GC line-of-sight is θ = 20.2
◦ ± 0.6
◦
(stat.) ± 0.7
◦
(sys.). We present, for the first time, a detailed
three-dimensional map of the Milky Way composed of young and intermediate-age stellar populations.
Our analysis provides independent evidence for both the X-shaped bulge component and the flaring
disk (being plausibly warped). We provide the complete dataset of properties of Miras that were used
for calculations in this work. The table includes: mean brightness and amplitudes in nine photometric
bands (covering a range of wavelength from 0.5 to 12 µm), photometric chemical type, estimated
extinction, and calculated distance with its uncertainty for each Mira variable. The median distance
accuracy to a Mira star is at the level of 6.6%.
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared
imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in
four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger
than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise
coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and
photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical
spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass
assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher
and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and
multimessenger astronomical events; and more.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
This document summarizes the identification of two young objects, TYC 9486-927-1 and 2MASS J21265040−8140293, as a likely very wide binary system. It presents revised astrometry showing they have common proper motion. Spectroscopy of the secondary yields a radial velocity consistent with the primary. Analysis of lithium absorption and kinematics suggests an age range of 10-45 Myr, with the secondary having an estimated mass in the planetary mass regime. If confirmed, this would be the widest known exoplanet system at over 4500 AU separation.
The Sparkler: Evolved High-redshift Globular Cluster Candidates Captured by JWSTSérgio Sacani
This document discusses compact red sources detected around a strongly lensed galaxy ("the Sparkler") at a redshift of 1.378 using JWST data. Photometry and morphological fits of the sources suggest they are spatially unresolved, very red, and consistent with old stellar populations. Spectroscopy shows emission from the galaxy but no signs of star formation in the red sources. The sources are most likely evolved globular clusters dating back to formation redshifts between 7-11, corresponding to ages of 3.9-4.1 billion years at the time of observation. If confirmed, these would be the first observed globular clusters at high redshift, opening a window into early globular cluster formation in the first billion years of
This document discusses a study that used difference imaging techniques to search for variable stars and microlensing events in the elliptical galaxy Centaurus A. The study obtained deep photometric data over almost two months using the Wide Field Imager on the ESO/MPG 2.2 m telescope. It detected 271 variable stars in Centaurus A with a detection limit of magnitude 24.5. Based on a simple model of Centaurus A's halo, the study estimated it could detect around 4 microlensing events per year, but a higher sensitivity is needed for a meaningful microlensing survey. The spatial distribution of any microlensing events could help constrain the shape of Centaurus A's dark matter halo.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
The Population of the Galactic Center Filaments: Position Angle Distribution ...Sérgio Sacani
This document analyzes the position angle (PA) distribution of filaments observed in radio images of the Galactic center, obtained using the MeerKAT radio telescope. It finds that short filaments (<66") have PAs concentrated along the Galactic plane (60-120 degrees), pointing radially towards the supermassive black hole Sgr A*. This suggests the filaments have been aligned by a collimated outflow from Sgr A* extending along the Galactic plane. The outflow pressure is estimated to require an outflow rate of 10^-4 solar masses per year over ~6 million years to align the filaments. Longer filaments (>66") show a broader PA distribution, with a peak around -3 degrees
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
Reionization and the ISM/Stellar Origins with JWST and ALMA (RIOJA): The Core...Sérgio Sacani
The protoclusters in the epoch of reionization, traced by galaxy overdensity regions, are ideal laboratories for
studying the process of stellar assembly and cosmic reionization. We present the spectroscopic confirmation of the
core of the most distant protocluster at z = 7.88, A2744-z7p9OD, with the James Webb Space Telescope NIRSpec
integral field unit spectroscopy. The core region includes as many as four galaxies detected in [O III] 4960 and
5008 Å in a small area of ∼3″ × 3″, corresponding to ∼11 × 11 kpc, after the lensing magnification correction.
Three member galaxies are also tentatively detected in dust continuum in Atacama Large Millimeter/submillimeter
Array Band 6, which is consistent with their red ultraviolet continuum slopes, β ∼ −1.3. The member galaxies
have stellar masses in the range of log(M*/Me) ∼7.6–9.2 and star formation rates of ∼3–50 Me yr−1
, showing a
diversity in their properties. FirstLight cosmological simulations reproduce the physical properties of the member
galaxies including the stellar mass, [O III] luminosity, and dust-to-stellar mass ratio, and predict that the member
galaxies are on the verge of merging in a few to several tens of Myr to become a large galaxy with
M* ∼ 6 × 109
Me. The presence of a multiple merger and evolved galaxies in the core region of A2744-z7p9OD
indicates that environmental effects are already at work 650 Myr after the Big Bang.
Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
Third epoch magellanic_clouud_proper_motionsSérgio Sacani
The document analyzes proper motion data from the Hubble Space Telescope to study the three-dimensional rotation field of the Large Magellanic Cloud (LMC) galaxy. It finds that:
1) The proper motion data implies a stellar dynamical center that coincides with the HI dynamical center from previous studies.
2) Combining the proper motion and line-of-sight velocity data provides insights into the LMC's rotation curve, disk viewing angles, and circular rotation speed of 91.7 km/s outside the central region.
3) The data paint a consistent picture of LMC rotation and yield improved constraints on the galaxy's distance, mass profile, and orbital history around the Milky Way.
Similar to Stellar variability in_open_clusters_new_class_in_ngc3766 (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
Generating privacy-protected synthetic data using Secludy and MilvusZilliz
During this demo, the founders of Secludy will demonstrate how their system utilizes Milvus to store and manipulate embeddings for generating privacy-protected synthetic data. Their approach not only maintains the confidentiality of the original data but also enhances the utility and scalability of LLMs under privacy constraints. Attendees, including machine learning engineers, data scientists, and data managers, will witness first-hand how Secludy's integration with Milvus empowers organizations to harness the power of LLMs securely and efficiently.
Full-RAG: A modern architecture for hyper-personalizationZilliz
Mike Del Balso, CEO & Co-Founder at Tecton, presents "Full RAG," a novel approach to AI recommendation systems, aiming to push beyond the limitations of traditional models through a deep integration of contextual insights and real-time data, leveraging the Retrieval-Augmented Generation architecture. This talk will outline Full RAG's potential to significantly enhance personalization, address engineering challenges such as data management and model training, and introduce data enrichment with reranking as a key solution. Attendees will gain crucial insights into the importance of hyperpersonalization in AI, the capabilities of Full RAG for advanced personalization, and strategies for managing complex data integrations for deploying cutting-edge AI solutions.
CAKE: Sharing Slices of Confidential Data on BlockchainClaudio Di Ciccio
Presented at the CAiSE 2024 Forum, Intelligent Information Systems, June 6th, Limassol, Cyprus.
Synopsis: Cooperative information systems typically involve various entities in a collaborative process within a distributed environment. Blockchain technology offers a mechanism for automating such processes, even when only partial trust exists among participants. The data stored on the blockchain is replicated across all nodes in the network, ensuring accessibility to all participants. While this aspect facilitates traceability, integrity, and persistence, it poses challenges for adopting public blockchains in enterprise settings due to confidentiality issues. In this paper, we present a software tool named Control Access via Key Encryption (CAKE), designed to ensure data confidentiality in scenarios involving public blockchains. After outlining its core components and functionalities, we showcase the application of CAKE in the context of a real-world cyber-security project within the logistics domain.
Paper: https://doi.org/10.1007/978-3-031-61000-4_16
Your One-Stop Shop for Python Success: Top 10 US Python Development Providersakankshawande
Simplify your search for a reliable Python development partner! This list presents the top 10 trusted US providers offering comprehensive Python development services, ensuring your project's success from conception to completion.
How to Get CNIC Information System with Paksim Ga.pptxdanishmna97
Pakdata Cf is a groundbreaking system designed to streamline and facilitate access to CNIC information. This innovative platform leverages advanced technology to provide users with efficient and secure access to their CNIC details.
AI-Powered Food Delivery Transforming App Development in Saudi Arabia.pdfTechgropse Pvt.Ltd.
In this blog post, we'll delve into the intersection of AI and app development in Saudi Arabia, focusing on the food delivery sector. We'll explore how AI is revolutionizing the way Saudi consumers order food, how restaurants manage their operations, and how delivery partners navigate the bustling streets of cities like Riyadh, Jeddah, and Dammam. Through real-world case studies, we'll showcase how leading Saudi food delivery apps are leveraging AI to redefine convenience, personalization, and efficiency.
“An Outlook of the Ongoing and Future Relationship between Blockchain Technologies and Process-aware Information Systems.” Invited talk at the joint workshop on Blockchain for Information Systems (BC4IS) and Blockchain for Trusted Data Sharing (B4TDS), co-located with with the 36th International Conference on Advanced Information Systems Engineering (CAiSE), 3 June 2024, Limassol, Cyprus.
Let's Integrate MuleSoft RPA, COMPOSER, APM with AWS IDP along with Slackshyamraj55
Discover the seamless integration of RPA (Robotic Process Automation), COMPOSER, and APM with AWS IDP enhanced with Slack notifications. Explore how these technologies converge to streamline workflows, optimize performance, and ensure secure access, all while leveraging the power of AWS IDP and real-time communication via Slack notifications.
Essentials of Automations: The Art of Triggers and Actions in FMESafe Software
In this second installment of our Essentials of Automations webinar series, we’ll explore the landscape of triggers and actions, guiding you through the nuances of authoring and adapting workspaces for seamless automations. Gain an understanding of the full spectrum of triggers and actions available in FME, empowering you to enhance your workspaces for efficient automation.
We’ll kick things off by showcasing the most commonly used event-based triggers, introducing you to various automation workflows like manual triggers, schedules, directory watchers, and more. Plus, see how these elements play out in real scenarios.
Whether you’re tweaking your current setup or building from the ground up, this session will arm you with the tools and insights needed to transform your FME usage into a powerhouse of productivity. Join us to discover effective strategies that simplify complex processes, enhancing your productivity and transforming your data management practices with FME. Let’s turn complexity into clarity and make your workspaces work wonders!
GraphRAG for Life Science to increase LLM accuracyTomaz Bratanic
GraphRAG for life science domain, where you retriever information from biomedical knowledge graphs using LLMs to increase the accuracy and performance of generated answers
AI 101: An Introduction to the Basics and Impact of Artificial IntelligenceIndexBug
Imagine a world where machines not only perform tasks but also learn, adapt, and make decisions. This is the promise of Artificial Intelligence (AI), a technology that's not just enhancing our lives but revolutionizing entire industries.
TrustArc Webinar - 2024 Global Privacy SurveyTrustArc
How does your privacy program stack up against your peers? What challenges are privacy teams tackling and prioritizing in 2024?
In the fifth annual Global Privacy Benchmarks Survey, we asked over 1,800 global privacy professionals and business executives to share their perspectives on the current state of privacy inside and outside of their organizations. This year’s report focused on emerging areas of importance for privacy and compliance professionals, including considerations and implications of Artificial Intelligence (AI) technologies, building brand trust, and different approaches for achieving higher privacy competence scores.
See how organizational priorities and strategic approaches to data security and privacy are evolving around the globe.
This webinar will review:
- The top 10 privacy insights from the fifth annual Global Privacy Benchmarks Survey
- The top challenges for privacy leaders, practitioners, and organizations in 2024
- Key themes to consider in developing and maintaining your privacy program
Programming Foundation Models with DSPy - Meetup SlidesZilliz
Prompting language models is hard, while programming language models is easy. In this talk, I will discuss the state-of-the-art framework DSPy for programming foundation models with its powerful optimizers and runtime constraint system.
1. A&A 554, A108 (2013)
DOI: 10.1051/0004-6361/201321065
c ESO 2013
Astronomy
&
Astrophysics
Stellar variability in open clusters
I. A new class of variable stars in NGC 3766 ,
N. Mowlavi, F. Barblan, S. Saesen, and L. Eyer
Astronomy Department, Geneva Observatory, chemin des Maillettes, 1290 Versoix, Switzerland
e-mail: Nami.Mowlavi@unige.ch
Received 8 January 2013 / Accepted 16 April 2013
ABSTRACT
Aims. We analyze the population of periodic variable stars in the open cluster NGC 3766 based on a 7-year multiband monitoring
campaign conducted on the 1.2 m Swiss Euler telescope at La Silla, Chili.
Methods. The data reduction, light curve cleaning, and period search procedures, combined with the long observation time line,
allowed us to detect variability amplitudes down to the millimagnitude (mmag) level. The variability properties were complemented
with the positions in the color–magnitude and color–color diagrams to classify periodic variable stars into distinct variability types.
Results. We find a large population (36 stars) of new variable stars between the red edge of slowly pulsating B (SPB) stars and the
blue edge of δ Sct stars, a region in the Hertzsprung-Russell (HR) diagram where no pulsation is predicted to occur based on standard
stellar models. The bulk of their periods ranges from 0.1 to 0.7 d, with amplitudes between 1 and 4 mmag for the majority of them.
About 20% of stars in that region of the HR diagram are found to be variable, but the number of members of this new group is
expected to be higher, with amplitudes below our mmag detection limit.
The properties of this new group of variable stars are summarized and arguments set forth in favor of a pulsation origin of the
variability, with g-modes sustained by stellar rotation. Potential members of this new class of low-amplitude periodic (most probably
pulsating) A and late-B variables in the literature are discussed.
We additionally identify 16 eclipsing binary, 13 SPB, 14 δ Sct, and 12 γ Dor candidates, as well as 72 fainter periodic variables. All
are new discoveries.
Conclusions. We encourage searching for this new class of variables in other young open clusters, especially in those hosting a rich
population of Be stars.
Key words. Hertzsprung-Russell and C-M diagrams – stars: oscillations – open clusters and associations: individual: NGC 3766 –
binaries: eclipsing – stars: variables: general
1. Introduction
Stars are known to pulsate under certain conditions that trans-
late into instability strips in the Hertzsprung-Russell (HR) or
color–magnitude (CM) diagram (see reviews by, e.g., Gautschy
& Saio 1995, 1996; Eyer & Mowlavi 2008). On the main se-
quence (MS), δ Sct stars (A- and early F-type stars pulsating in
p-modes) are found in the classical instability strip triggered by
the κ mechanism acting on H and He. At higher luminosities,
β Cep (p-mode) and slowly pulsating B (SPB; g-mode) stars are
found with pulsations triggered by the κ mechanism acting on the
iron-group elements, while γ Dor stars (early F-type; g-mode)
lie at the low-luminosity edge of the classical instability strip,
with pulsations triggered by the “convective blocking” mecha-
nism (Pesnell 1987; Guzik et al. 2000).
The detection and analysis of the pulsation frequencies of
pulsating stars lead to unique insights into their internal struc-
ture and the physics in play. Asteroseismology of β Cep stars,
for example, has opened the doors in the past decade to study
their interior rotation and convective core (Aerts et al. 2003;
Appendices are available in electronic form at
http://www.aanda.org
Reduced photometry of the variable stars is only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/554/A108
Dupret et al. 2004; Ausseloos et al. 2004; Lovekin & Goupil
2010; Briquet et al. 2012, and references therein). SPB stars
also offer high promise for asteroseimology, with their g-modes
probing the deep stellar interior (De Cat 2007). For those stars,
however, determining the degrees and orders of their modes is
complex because, as pointed out by Aerts et al. (2006), a) the
predicted rich eigenspectra lead to non-unique solutions and b)
stellar rotation splits the frequencies and causes multiplets of ad-
jacent radial orders to overlap. Space-based observations by the
MOST satellite have shown the advantage of obtaining contin-
uous light curves from space (e.g. Balona et al. 2011b; Gruber
et al. 2012), and the data accumulated by satellites like CoRoT
and Kepler may bring important breakthroughs in this field in the
near future (McNamara et al. 2012). The same is true for γ Dor
stars (see Uytterhoeven et al. 2011; Balona et al. 2011a; Pollard
2009, for a review of γ Dor stars), as well as for δ Sct stars
(e.g. Fox Machado et al. 2006). CoRoT has observed hundreds
of frequencies in a δ Sct star (Poretti et al. 2009), and yet, mode
selection and stellar properties derivation remain difficult. Much
effort continues to be devoted to analyzing the light curves of all
those pulsating stars, considering the good prospects for aster-
oseismology. Obviously, increasing the number of known pul-
sators like them is essential.
Another aspect of stellar variability concerns the question
why some stars pulsate and others do not. As a matter of fact,
not all stars in an instability strip pulsate. Briquet et al. (2007),
Article published by EDP Sciences A108, page 1 of 29
2. A&A 554, A108 (2013)
Table 1. NGC 3766.
Parameter Value Ref.
(α2000, δ2000) (11h
36m
14s
, 61d
36m
30s
)
(l, b) (294.117 deg, −0.03 deg)
Angular size 9.24 (V < 17 mag) 1
Minimum mass content 793 M 1
Distance 1.9 to 2.3 kpc 2
Distance modulus (V − MV )0 11.6 ± 0.2 2, 3
Age 14.5 to 25, 31 Myr 2, 3
Reddening E(B − V) 0.22 ± 0.03 mag 2, 3
References. (1) Moitinho et al. (1997); (2) McSwain et al. (2008);
(3) Aidelman et al. (2012).
for example, address this question for pulsating B stars, while
Balona & Dziembowski (2011) note that the identification of
constant stars, observed by the Kepler satellite, in the δ Sct
instability strip is not due to photometric detection threshold.
Ushomirsky & Bildsten (1998) provide an interesting view of
this issue in relation with SPB stars, arguing that stellar rota-
tion, combined with the viewing angle relative to the rotation
axis, may be at the origin of not detecting pulsations in stars that
are nevertheless pulsating. Conversely, pulsations are observed
when not expected. A historical example is given by the unex-
pected discovery of rapidly oscillating Ap (roAp) stars (Kurtz
1982), the pulsation of which has been attributed to strong mag-
netic fields (Kochukhov 2007, for a review). The potential exis-
tence of pulsators in regions outside instability strips must also
be addressed. Such a gap exists on the MS in the region be-
tween δ Sct and SPB stars, as shown in Fig. 3 of Pamyatnykh
(1999), in Fig. 22 of Christensen-Dalsgaard (2004), or in Fig. 4
of Pollard (2009), but we show in this paper evidence for the
presence of periodic variables in this region of the HR diagram.
Stellar clusters are ideal environments to study stellar vari-
ability because some basic properties and the evolutionary sta-
tus of individual star members can be derived from the prop-
erties of the cluster. It, however, requires extensive monitoring
on an as-long-as-possible time base line. This requirement may
explain why not many clusters have been studied for their vari-
ability content so far, compared to the number of known and
characterized clusters. To fill this shortcoming, an observation
campaign of twenty-seven Galactic open clusters was triggered
by the Geneva group in 2002. It ended in 2009, resulting in a
rich database for a wide range of cluster ages and metallicities
(Greco et al. 2009; Saesen et al., in prep.). Preliminary explo-
rations of the data have been published in Cherix et al. (2006)
for NGC 1901, Carrier et al. (2009) for NGC 5617, and Greco
et al. (2009, 2010) for IC 4651.
In this paper, we present an extensive analysis of the peri-
odic variables in NGC 3766. It is the first paper in a series an-
alyzing in more details the variability content of the clusters in
our survey. The characteristics of NGC 3766 are summarized in
Table 1. Among the first authors to have published photometric
data for this cluster, we can cite Ahmed (1962) for UBV pho-
tometry, Yilmaz (1976) for RGU photometry, Shobbrook (1985,
1987) for uvbyβ photometry, Moitinho et al. (1997) for charge
coupled device (CCD) UBV photometry and Piatti et al. (1998)
for CCD VI photometry. Thanks to the relative closeness of the
cluster, lying at ∼2 kpc from the Sun, the upper main sequence
in the HR diagram stands rather clearly out from field stars,
making the identification of cluster members easier. With an age
of about 20 Myr, the cluster is very rich in B stars, and a good
Fig. 1. Reference image of NGC 3766 used in the data reduction
process.
fraction of them have been identified to be Be stars (McSwain
et al. 2008; McSwain 2008; Aidelman et al. 2012). Strangely, al-
most no information about the metallicity of the cluster exists in
the literature. Authors studying this cluster usually assume so-
lar metallicity (e.g., Moitinho et al. 1997; McSwain et al. 2008).
The only metallicity determination available in the literature to
date, to our knowledge, is [Fe/H] = −0.47 proposed by Tadross
(2003) and repeated by Paunzen et al. (2010), based on the mean
ultraviolet excess δ(U −B) of bright dwarfs from the photometry
of Moitinho et al. (1997). The reliability of the estimation cannot
be easily established, though (membership of the dwarfs, uncer-
tainty of the metallicity estimate), and we therefore do not report
this value in Table 1. No blue straggler is known in this cluster,
the only candidate reported in the literature (Mermilliod 1982)
having since then been re-classified as a Be star (McSwain et al.
2009). Finally, it must be mentioned that no in depth study of
periodic variable stars (which we simply call periodic variables
in the rest of this paper) has been published so far for this cluster.
We describe our data reduction and time series extraction
procedures in Sect. 2, where we also present the overall pho-
tometric properties of the cluster. Section 3 describes the vari-
ability analysis procedure, the results of which are presented
in Sect. 4 for eclipsing binaries, and in Sect. 5 for other peri-
odic variables. Various properties of the periodic variables are
discussed in Sect. 6. The nature of the new class of MS peri-
odic variables in the variability “gap” in between the regions of
δ Sct and SPB stars in the HR diagram is addressed in Sect. 7.
Conclusions are finally drawn in Sect. 8.
A list of the periodic variables and of their properties is given
in Appendices A and B, together with their light curves.
2. Observations and data reduction
Observations of NGC 3766 have been performed from 2002 to
2009 on the 1.2 m Swiss Euler telescope at La Silla, Chile.
CCD images have been taken in the Geneva V, B and U pho-
tometric bands, centered on α = 11h
36m
14s
and δ = −61d
36m
30s
with a field of view of 11.5 × 11.5 (Fig. 1). Those bands are
A108, page 2 of 29
3. N. Mowlavi et al.: Stellar variability in open clusters
not strictly identical to the standard Geneva system, which were
defined in the era of photomultipliers. While the filter+CCD re-
sponses have been adjusted to reproduce as closely as possible
the standard Geneva system, they are not identical. A calibration
would thus be necessary before using the photometry to charac-
terize stars. We however do not perform such a (delicate) cali-
bration in this study, and solely focus on the variability analysis
of the time series, where differential photometric quantities are
sufficient. To keep in mind the uncalibrated nature of the time
series, we hereafter note by V , B and U the reduced CCD mea-
surements in the Geneva V, B and U filters, respectively.
The program was part of a wider observational campaign
of 27 open clusters, 12 in the Southern and 15 in the Northern
hemispheres (Greco et al. 2009; Saesen et al. in prep.). Several
observation runs per year, each 10 to 15 nights long, were sched-
uled in La Silla for the Southern open clusters, during which all
observable clusters were monitored at least once every night. In
addition, two clusters were chosen during each observation run
for a denser follow-up each night. For NGC 3766, the denser
follow-ups occurred at HJD-2 450 000 = 1844–1853, 2538–2553
and 2923–29361
. In total, 2545 images were taken in V , 430
in B and 376 in U , with integration times chosen to minimize
the number of saturated bright stars while performing an as-
deep-as-possible survey of the cluster (typically 25 s in V , 30 s
in B and 300 s in U , though a small fraction of the observations
were made with shorter and longer exposure times as well). As
a result, stars brighter than V 11 mag were saturated.
All images were calibrated, stars therein identified and their
light curves obtained with the procedure described in Sect. 2.1.
Stars with potentially unreliable photometric measurements
were flagged and disregarded, and the light curves of the remain-
ing stars cleaned from bad points (Sect. 2.2). Good light curves
in V , B and U are finally selected from the set of cleaned
light curves based on the number of their good and bad points
(Sect. 2.3). They form the basis for the variability analysis of
the paper. A summary of our data in the color–magnitude and
color–color diagrams is given in Sect. 2.4.
2.1. Data reduction
The data reduction process is presented in Saesen et al. (2010),
and we summarize here only the main steps. First, the raw sci-
ence images were calibrated in a standard way, by removing the
bias level using the overscan data, correcting for the shutter ef-
fects, and flat fielding using master flat fields. Then, II
(Stetson 1987) and (Stetson & Harris 1988) were used
to extract the raw light curves. We started with the construction
of an extensive master star list, containing 3547 stars, which was
converted to each frame taking a small shift and rotation into ac-
count. The magnitudes of the stars in each frame were calculated
with an iterative procedure using a combined aperture and point
spread function (PSF) photometry. Multi-differential photomet-
ric magnitudes and error estimates were derived, using about
40 reference stars, to reduce the effects of atmospheric extinction
and other non-stellar noise sources. The light curves were finally
de-trended with the Sys-Rem algorithm (Tamuz et al. 2005) to
remove residual trends.
2.2. Star selection and light curve cleaning
Three procedures are used to disregard potentially problematic
stars and wrong flux estimates. The first procedure tackles stars
1
All epochs in this paper are given in days relative to
HJD0 = 2 452 000.
05001,0001,5002,000
CCD Y pos. (pixels)
0
250
500
750
1,000
1,250
1,500
1,750
2,000
CCDXpos.(pixels)
Fig. 2. Location on the CCD of all stars with more than 100 good points
in their light curve. The seventy brightest stars are plotted in blue, with
the size of the marker proportional to the brightness of the star. Stars
that lie closer than 50 pixels on the CCD from one of those bright stars
are plotted in red. Crosses identify stars that have more than 20% bad
points in their light curves (see Sect. 2.3).
polluted by neighboring bright stars, the second deals with stars
whose flux distributions are badly determined on individual im-
ages, and the third cleans the light curves from their outliers.
Stars contaminated by bright stars: The analysis of individual
light curves reveals a pollution of stars located close to bright
stars (we consider here the “bright” stars to be the –somehow
arbitrarily defined– seventy brightest stars, the other ones being
“faint” stars). This is especially true if the bright star is saturated.
We then disregard all faint stars that lie closer than 50 pixels to
one of the bright stars. Their distribution on the CCD is shown
in Fig. 2.
Stars offset from expected position in selected images: The
flux of a star measured in a given image can be unreliable if the
position of the star on the CCD is not accurate enough, e.g. due
to a wrong convergence in the iterative PSF fitting. We therefore
disregard a flux measure if the position offset of a certain star
in a certain image relative to the reference image deviates more
than 5σ sigma from the position offset distribution of all stars
in that image. The procedure is iterated five times in each im-
age, removing each time from the list of all stars the ones with
large position offsets. We also remove measurements of stars in
a given image that fall closer than eleven pixels to one of the
borders of the CCD.
Light curve cleaning: In addition to the two cleaning steps de-
scribed above that involve the position of the stars in the images,
we remove all points in a given light curve that have a magnitude
error larger than 0.5 mag or that are at more than 3 sigmas above
the mean error. We also disregard measurements if the magni-
tude deviates more than 5 sigmas from the mean magnitude. This
last step, classically called sigma clipping on the magnitudes, is
A108, page 3 of 29
4. A&A 554, A108 (2013)
0 500 1,000 1,500 2,000 2,500
number of good points in lc
500
1,000
1,500
NumStars
V'
NGC 3766
500
1,000
1,500
NumStars
B'
500
1,000
1,500
NumStars
U'
Fig. 3. Histogram of the number of good points in the V (top panel),
B (middle panel) and U (bottom panel) time series. Dashed lines give
the histograms considering all stars (see Sect. 2.2). Continuous lines
give the histograms of selected light curves (see Sect. 2.3).
iterated twice. We however keep the points if at least four of
them would be disregarded in a row, in order to avoid removing
good points in eclipsing binaries.
The light curve cleaning is applied to each V , B and U time
series. The histograms of the resulting number of good points for
the three photometric bands are shown in dashed lines in Fig. 3.
2.3. Light curve selection
The light curve cleaning procedure described in Sect. 2.2 re-
moves a certain number of bad points in each V , B and U time
series. The number of points disregarded in this way is actually
a relevant indication of the quality of the time series of a given
star. The more points disregarded, the more problematic the flux
computation may be in the images, whether it be due to a posi-
tion issue on the CCD (closeness to a bright source for example),
CCD issues (bad pixels for example), or data reduction difficul-
ties (in a crowded region for example). We therefore disregard all
time series that contain more than 20% of bad points if the star is
fainter than 10.5 mag. Their distribution on the CCD is shown in
Fig. 2. We do not apply this filter to brighter stars because they
may have a larger number of bad points due to saturation while
the remaining good points may still be relevant. The histograms
of the number of good points for all good time series are shown
in solid lines in Fig. 3. The tails of the histograms at the side
of small numbers of points are seen to be significantly reduced,
especially in U . In total, there are 2858 good times series in V ,
2637 in B and 1907 in U . The U time series are expected to
provide the least reliable measurements. This however does not
affect our variability study, which mainly relies on the V time
series.
The photometric precisions reached in V , B and U can be
estimated from the standard deviations σ of the time series as a
function of magnitude. These are shown in Fig. 4 for the three
photometric bands. The lower envelopes in those diagrams give
the best precisions obtained from our data at any given magni-
tude. We call them the envelopes of constant stars (ECSs), as
80.0
82.5
85.0
87.5
90.0
92.5
95.0
97.5
100.0
%goodpointsinV'
7 8 9 10 11 12 13 14 15 16 17 18 19
V' (mag)
0.01
0.1
1
stdev(V')(mag)
NGC 3766
80.0
82.5
85.0
87.5
90.0
92.5
95.0
97.5
100.0
%goodpointsinB'
7 8 9 10 11 12 13 14 15 16 17 18 19 20
B' (mag)
0.01
0.1
1
stdev(B')(mag)
NGC 3766
80.0
82.5
85.0
87.5
90.0
92.5
95.0
97.5
100.0
%goodpointsinU'
7 8 9 10 11 12 13 14 15 16 17 18 19
U' (mag)
0.01
0.1
1
stdev(U')(mag)
NGC 3766
Fig. 4. Standard deviations of the time series of good points as a func-
tion of magnitudes in the V (top), B (middle) and U (bottom) bands.
The percentage of good points in the original light curves is shown in
color according to the color scales displayed on the right.
they identify the location expected for constant stars in those
diagrams.
A precision better than 3 mmag is reached around V =
11−12 mag, as seen in Fig. 4 (we note that the precision reached
in amplitude detection of periodic variables reaches 1 mmag,
see Sect. 5). For brighter stars, the standard deviation increases
with increasing brightness, due to both photometric saturation
and intrinsic variability. Stars fainter than V = 12 mag have
worse precisions, as expected. The precisions are about 10, 30
and 60 mmag at V = 15.2, 17 and 18 mag, respectively. They
are about similar in B , though the dispersion in σ of the ECS
at a given magnitude is larger in B than in V . The U time
series have the least precise photometry, though still good for
bright stars, with a precision of ∼3 mmag at U = 11−12 mag.
It is less good for faint stars, reaching a precision of 100 mmag
at U = 18 mag. We can thus expect to have reliable B − V
colors, but much less reliable U − B colors for fainter stars. We
have also to keep in mind that there are much fewer good time
series in U than in V and B .
2.4. Summary diagrams
The color–magnitude diagram (B − V , V ) is shown in Fig. 5.
Stars which have good light curves in all three bands are shown
in black, those with only good V and B light curves in blue.
The upper MS is rather clear and well detached from background
A108, page 4 of 29
5. N. Mowlavi et al.: Stellar variability in open clusters
0.0 0.5 1.0 1.5 2.0 2.5 3.0
B'-V' (mag)
7
8
9
10
11
12
13
14
15
16
17
18
19
V'(mag)
NGC 3766
Fig. 5. Color–magnitude diagram (B − V , V ) of stars with good light
curves in both V and B . Black points have good U time series as well,
blue points don’t.
field stars due to the relative closeness of the cluster to us. Based
on the density of stars on the red side of the MS in the diagram,
we may expect field stars to start contaminating the MS mainly
at magnitudes above V 15 mag. Of course, only radial veloc-
ities, proper motions and good parallaxes will be able to distin-
guish members from field stars. The future Gaia mission of the
European Space Agency, to be launched end of 2013, will be a
key contributor in this respect.
The color–color diagram (B − V , U − B ) constructed with
all stars brighter than V = 15.5 mag is shown in Fig. 6. The
S shape (rotated 45o
anti-clockwise) characteristic of that dia-
gram is well visible. Stars located below the S shape at 0.3 mag
B −V 1 mag and 0.5 mag U −B 1 mag are expected to be
field stars behind the cluster that are more reddened by interstel-
lar extinction (reddening moves a point to the lower-right direc-
tion in the diagram). This statement is supported by the thinness
of the sequence of B stars in the diagram, which indicates no
important differential reddening for cluster members.
3. Periodic variability analysis
Variability detection and characterization is based on V time se-
ries only, which are much better sampled than the B and U ones
and with better precisions. The identification of periodic vari-
able candidates is performed in two ways. The method is adapted
and simplified from the one described in Sect. 6 of Saesen et al.
(2010), where it was used to find variable stars in data from a
multisite campaign on a cluster.
In a first step, we calculate the generalized Lomb-Scargle
diagrams (Zechmeister & Kürster 2009), weighted with the in-
verse square of each measurement error, for each of the stars
from 0 to 50 d−1
. We pick stars that have at least one significant
peak, i.e. with a signal-to-noise ratio (S/N) above 4.5, and for
which the selected frequency does not occur in several stars (at
least 3), pointing to unwanted instrumental effects. We calculate
the S/N as the ratio of the amplitude of a frequency to the noise
7
8
9
10
11
12
13
14
15
V'(mag)
0.0 0.5 1.0 1.5 2.0 2.5
B'-V' (mag)
-0.5
0.0
0.5
1.0
1.5
2.0
U'-B'(mag)
349
1428
NGC 3766
Fig. 6. Color–color diagram (B −V , U −B ) of stars brighter than V =
15.5 mag and with good light curves in V , B and U . The V magnitude
is color coded according to the color scale on the right.
level, where the noise is computed as the mean amplitude around
this frequency. The interval over which we evaluate the average
changes according to the frequency value. We use an interval
of 1 d−1
for f ∈ [0–3] d−1
, of 1.9 d−1
for f ∈ [3–6] d−1
, of 3.9 d−1
for f ∈ [6–11] d−1
and of 5 d−1
for f ∈ [11–50] d−1
. This is done
in order to account for the increasing noise at lower frequencies.
All of the retained stars are then checked manually for variabil-
ity to remove remaining spurious detections (see Sect. 5). The
light curves of all other stars are visually examined to identify
missing eclipsing binaries and other non-periodic variables.
In a second step, the stars where one genuine frequency peak
was detected are submitted to an automated frequency analysis
to deduce all significant frequencies till 50 d−1
present in the
light curves. The procedure uses the same frequency search pa-
rameters as described above and is based on standard prewhiten-
ing. When no significant peaks are present any more in the pe-
riodogram of the residuals, the frequency search is stopped. All
extracted frequencies are however not necessarily relevant or in-
dependent of each other and therefore a manual check for each
star is performed to assess the validity of each frequency and to
identify the non-independent frequencies, e.g., harmonic or alias
frequencies. In this way, we obtain a final frequency list for each
of the periodic variables.
We exclude from the variability analysis all stars brighter
than V = 10 mag because their light curves are affected by
pixel saturation effects. This includes all potential β Cep stars
of the cluster. The study of those stars would require a specific
light curve analysis procedure that we may perform in a future
study. The distributions of the detected periodic variables in the
(B − V , V ), (B − V , U − B ) and (V , σ(V )) diagrams are
shown in Figs. 7–9, respectively. The eclipsing binaries among
them are presented in Sect. 4 and the other periodic variables
analyzed in Sect. 5.
4. Eclipsing binaries
Eclipsing binaries are of great interest in the fields of stellar
formation, stellar evolution and distance determinations, to cite
only a few of them. For stellar formation studies, the analysis of
populations of binary systems versus those of single stars pro-
vides information on the initial conditions in star forming re-
gions. For stellar evolution, precise photometric and radial ve-
locity curves of binary stars enable derivation of the masses,
radii, surface gravities and densities of both components with
a high precision, and confront them with stellar evolution model
A108, page 5 of 29
6. A&A 554, A108 (2013)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
B'-V' (mag)
7
8
9
10
11
12
13
14
15
16
17
18
19
V'(mag)
349
NGC 3766
Fig. 7. Distribution in the color–magnitude diagram of the periodic
variables studied in this paper. Filled colored and black circles rep-
resent stars with secured periods, while open circles locate periodic
variables whose periods need confirmation. Their colors identify the
different groups of variable stars identified in Sect. 5. Black crosses
identify eclipsing binaries. Light-gray points locate all other stars with
good light curves in V and B . The horizontal dashed line indicates
the V magnitude above which periodic variables have been searched
for. The location of red giant star 349 is also indicated.
predictions. Analysis of the spectra of both components would
further allow the determination of their effective temperatures,
whereby their luminosities can be inferred. The distance to the
system can then be derived (e.g. Southworth 2012). The study
of eclipsing binaries in clusters is particularly interesting in this
respect since it benefits from the determination of the cluster
properties such as the age, chemical composition and distance,
if their membership is ensured. Conversely, they can also con-
tribute to characterize the host clusters (e.g. Grundahl et al.
2008). Despite the efforts invested in this area (e.g. Thompson
et al. 2001, 2010, and references therein), not many cluster
eclipsing binaries have so far been analyzed with high precision,
probably due to both stringent observational and data analysis re-
quirements, such as well sampled photometric and radial veloc-
ity curves, high resolution spectra, and the need to disentangle
both components in the blended spectra. We refer for example
to Yıldız (2011) and Brogaard et al. (2012) for some relatively
well characterized eclipsing binaries in open clusters in the past
two years. While it is obviously out of the scope of this article to
perform such detailed analysis for the eclipsing binaries found
in our data, it is worth listing them, which we do here.
Sixteen eclipsing binaries are identified in our FOV of
NGC 3766, with one of them being uncertain (eclipsing bi-
nary 693 in our identification numbering scheme). They are
marked by crosses in Figs. 7 to 9. All of them are new discov-
eries. From the morphology of their folded light curves, nine
0.0 0.5 1.0 1.5 2.0 2.5 3.0
B'-V' (mag)
-1.25
-1.00
-0.75
-0.50
-0.25
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
U'-B'(mag)
295
349
576
582
1584
NGC 3766
Fig. 8. Color–color diagram, with symbols as in Fig. 7. Only stars with
good light curves in V , B and U are plotted, except for binary stars
which are plotted in red if their U light curve is not good. Individual
periodic variables whose variability classification are debated in Sect. 5
are labeled with their star id next to the marker.
7 8 9 10 11 12 13 14 15 16 17 18 19
V' (mag)
0.01
0.1
stdev(V')(mag)
NGC 3766
Fig. 9. (V , σ(V )) diagram, with symbols as in Fig. 7. The vertical
dashed line indicates the V magnitude above which periodic variables
have been searched for.
are classified as Algol-type (EA), four as β Lyrae-type (EB) and
three as W Ursae Majoris-type (EW) binary candidates. Their
characteristics are summarized in Table A.1, and their folded
light curves displayed in Fig. A.1. The question of their mem-
bership to NGC 3766 is important if one wants to study them in
combination with the cluster properties. From their position in
the color–magnitude (Fig. 7) and color–color (Fig. 8) diagrams,
five of them may be cluster members, three of which are of type
EA, one of type EB and one of type EW.
5. Periodic variable stars
There are 159 stars (excluding purely eclipsing binaries) for
which at least one significant frequency is found in the peri-
odogram with the procedure described in Sect. 3. A visual check
of the frequencies and periodograms of those stars led us to
A108, page 6 of 29
7. N. Mowlavi et al.: Stellar variability in open clusters
10 11 12 13 14 15 16 17 18 19
V' (mag)
0,1
1
10
100
1000
P(d)
1
10
100
A(mmag)
NGC 3766
Fig. 10. Periods (top panel) and associated pulsation amplitudes
(bottom panel) of the periodic variables (other than purely eclipsing bi-
naries) as a function of their V magnitude. Multiple periods of the same
object are connected with solid lines. The color of each marker indicates
the group to which the star belongs: red for group 1 (SPB), green and
cyan for group 2 (new class, see text), blue for group 3 (δ Sct), magenta
for group 4 (γ Dor) and black for either red giants or periodic variables
fainter than V = 15.5 mag, unless clearly belonging to one of groups 1
to 4 (see text).
consider the values of the frequencies as reliable for 147 of them.
The remaining 12 stars have frequencies that are either too close
to each other for a given star (they differ by less than the fre-
quency resolution ∼1/T, with T being the duration of the obser-
vation campaign), or separated by frequency intervals reminis-
cent of aliases. Their periods need confirmation, possibly based
on additional observations to be performed, and are excluded
from the rest of this study. All those 12 stars, except one, are
fainter than V = 16 mag. They are identified by open circles in
Figs. 7 to 9.
Among the periodic variables with presumably secured fre-
quencies, 85 stars are detected with one significant (i.e. with
S/N > 4.5) frequency, 45 stars with two, 13 with three, 3 with
four and 1 with five independent frequencies. The values of the
periods are shown in Fig. 10 as a function of V . The majority of
the periods are longer than 0.1 d, except for a group of stars at V
between 14.0 and 14.9 mag, which have periods that can be as
low as 1/2 h. These stars with low periods are δ Sct candidates,
and offer a nice way to differentiate the different groups of peri-
odic variables. Two groups, that we note 1 and 2, are identified
at the brighter side of the δ Sct candidates, which is itself labeled
group 3. Two other groups, 4 and 5, are identified at their fainter
side. They are color-coded in Fig. 10 and defined according to
their V magnitude and period P in the following way:
– group 1: V < 12.5 mag and P > 1.1 d (red points in Fig. 10).
They are two magnitudes or more brighter than the most
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
S/N
10 11 12 13 14 15
V' (mag)
0.1
1
10
P(d)
1
10
100
A(mmag)
NGC 3766
Fig. 11. Periods (top panel) and associated pulsation amplitudes
(bottom panel) of the periodic variables brighter than V = 15.5 mag,
as a function of their V magnitude. Multiple periods of the same object
are connected with solid lines (note that the period separations of mul-
tiperiodic variables are often much smaller than the periods themselves,
resulting in the vertical solid lines being reduced to a black point inside
the markers in the top panel). The color of each point indicates the S/N
of the peak in the periodogram corresponding to the given frequency,
according to the color scale displayed on the right of the figure. When
overlapping, the marker of the highest S/N appears in the plot.
luminous δ Sct candidate. One fainter star at V = 13.86 mag
is also added to this group (see Sect. 5.1);
– group 2: 11 < V < 14 mag and 0.1 d < P < 1.1 d (green and
cyan points). They fill the magnitude range between the δ Sct
and group 1 stars;
– group 3: 14 < V < 14.9 mag and P < 0.1 d (blue points).
It is the group of δ Sct candidates. Two fainter stars at V
15.3 mag are also added to this group (see Sect. 5.3);
– group 4: 14.9 < V < 15.5 mag and P > 0.1 d (magenta
points). One fainter star at V 17 mag is also added to this
group (see Sect. 5.4);
– group 5: all other periodic variables (black points), i.e. those
fainter than V = 15.5 mag and the red giants that were ex-
cluded from the other groups.
The distributions of those groups in the color–magnitude and
color–color diagrams are shown in Figs. 7 and 8, respectively.
Thanks to the closeness of NGC 3766 to us, all periodic variables
brighter than V = 15 mag have a high probability to belong to
the cluster. This covers groups 1 to 4. Their periods and ampli-
tudes as a function of V are shown in more detail in Fig. 11,
with the S/N of each detected frequency color coded.
The properties of the periodic variables are listed in
Table B.1. In the next sections, we analyze each group in more
details, starting with the most luminous one.
5.1. Group 1 of periodic variables: SPB candidates
Thirteen stars belong to group 1. Their folded light curves are
shown in Figs. B.1 and B.2. All are monoperiodic, to our mmag
detection limit, except two. The two exceptions are stars 36,
which has two periods, and 51, with three periods. The succes-
sive periodograms of the biperiodic variable 36 (P = 1.7631
and 1.5127 d) are shown in Fig. 12 as an illustration.
A108, page 7 of 29
8. A&A 554, A108 (2013)
Fig. 12. Successive periodograms of the multiperiodic variable 36 of
group 1. The top panel gives the spectral window. The second panel
gives the periodogram of the original light curve. The next panels give
the periodograms from the subsequent pre-whitening steps. In each pe-
riodogram, the red line gives the background noise at 1σ and the orange
line the limit at 4.5σ. The yellow vertical bands in the second and third
panels locate the dominant frequency in the respective periodogram.
All periodic variables in our field of view that are brighter
than V = 11 mag belong to this group. Periodic variables
with V between 11 and 11.3 mag, on the other hand, contain
a mixture of group 1 and 2 stars. The two groups are never-
theless distinct in the (V , P) diagram (Fig. 10). Interestingly,
star 51 is a hybrid star belonging to both groups 1 and 2, with
two periods in group 1 (P = 3.4692 and 1.9777 d) and one pe-
riod in group 2 (P = 0.23111 d). We also note that star 107,
while having V = 12.15 mag, well in the range of magnitudes
expected for group 2, has a period of P = 4.536 d reminiscent
of group 1 stars. We therefore assign it to this group, but keep in
mind that it could, instead, be a spotted or binary star.
Star 295 is also added to this group. Its magnitude of V =
13.86 mag makes it an outlier in this respect. Inspection of its
position in the color–color diagram (Fig. 8) reveals that it is
a highly reddened star located behind NGC 3766 and not be-
longing to the cluster. De-reddening would bring it back, in
that diagram, among the population of group 1 stars on the se-
quence of B stars. Its period of 1.70109 d is compatible with this
conclusion.
The magnitudes of group 1 stars fall in the range expected
for SPB stars. From Fig. 3 of Pamyatnykh (1999), SPB stars are
predicted to have luminosities log(L/L ) 1.8. Observed SPBs
reported in this figure even start at higher luminosities. δ Sct
stars, on the other hand, are expected to have log(L/L ) 1
in NGC 3766 (in which they must be located at beginning of
their MS phase given the age of the cluster). SPB stars are thus
expected to be at least 2 mag (∆ log L = 0.8) brighter than δ Sct
stars. The magnitudes of our group 1 stars in Fig. 10 agree with
this statement.
The periods of group 1 stars also fall in the range expected
for SPB stars. They pulsate in g-modes (κ mechanism on iron-
group elements) with periods that are generally between 0.5
and 5 d and amplitudes of few mmags (De Cat 2002). This is
consistent with our group 1 stars.
Fig. 13. Same as Fig. 12, but for star 78 of group 2.
5.2. Group 2 of periodic variables
The second group of periodic variables falls in the range V =
11−14.3 mag, with periods between ∼0.1 and ∼1.1 d (but see
remark below). Thirty-six stars belong to this group. Twenty-
three of them are monoperiodic, 11 biperiodic and 2 have three
frequencies. Their folded light curves are shown in Figs. B.3
to B.5. The periodogram of the biperiodic variable 78 (with P =
0.189088 and 0.38845 d) is shown in Fig. 13 as an example.
Two characteristics of this group must be mentioned. First,
the group extends over more than three magnitudes, from
V = 11 to 14.3 mag, and partly overlaps with the adjacent
groups. The overlap with group 1 was already mentioned in the
previous section. The overlap with group 3 (δ Sct candidates) oc-
curs at V = 14.0−14.3 mag. The two groups are however clearly
distinct in the (V , P) diagram (Fig. 10), as was the case between
groups 1 and 2. We find no hybrid case of a multiperiodic vari-
able with periods that would make it belong to groups 2 and 3 at
the same time. Second, about one third of the stars of this group
(13 out of 36 members) are detected as being multiperiodic.
The period distribution of group 2 stars shows a clear con-
centration between 0.1 and 0.7 d (see Fig. 19 in Sect. 7.1), with
only 4 stars having periods between 0.7 and 1.1 d. We have there-
fore distinguished, in all figures, the bulk of group 2 stars from
those four “outliers” by plotting the former ones in green and the
latter ones in cyan.
No classical type of pulsating star is expected on the MS be-
tween SPB and δ Sct stars in the HR diagram (see, e.g., Fig. 22
of Christensen-Dalsgaard 2004). The origin of our group 2 stars
thus requires investigation. Their periods fall between the ones
expected for the p-mode pulsating δ Sct and the g-mode pulsat-
ing SPB stars. The case is further discussed in Sect. 7.
5.3. Group 3 of periodic variables: δ Sct candidates
The third group contains 14 stars, 6 of which are monoperiodic,
3 biperiodic, 2 triperiodic, 2 quadriperiodic and 1 has five peri-
ods. Their folded light curves are shown in Figs. B.6 to B.9.
They are δ Sct candidates, pulsating in p-modes (κ mecha-
nism mainly on the second partial ionization zone of He) with
periods between 0.02 and 0.25 d. They are often multiperiodic.
A108, page 8 of 29
9. N. Mowlavi et al.: Stellar variability in open clusters
Fig. 14. Same as Fig. 12, but for star 423 of group 3.
An example of a periodogram typical of those stars is shown
in Fig. 14 with the quadriperiodic star 423. The magnitudes
of the δ Sct candidates in NGC 3766 range between V = 14
and 14.9 mag (Fig. 10). All periodic variables in our field of view
within this magnitude range belong to this group, except two.
The first exception is star 349 at V = 14.12 mag, with a period
of 61.51 d. It is a red giant not belonging to NGC 3766, as shown
by its position in the color–magnitude diagram (Fig. 7). It is put
in group 5. The second exception is star 364 at V = 14.25 mag.
With P = 0.91772 d, it belongs to group 2.
In addition to stars with magnitudes between V = 14
and 14.9 mag, two fainter stars are added to group 3. The
first one, star 576 at V = 15.28 mag, has three periods,
at P = 0.0761747, 0.0770839 and 0.0773966 d, reminiscent of
δ Sct pulsators. In the color–color diagram (Fig. 8), it stands
at B − V = 0.857 and U − B = 0.783. It is thus not a
member of NGC 3766, but a reddened star located behind the
cluster in the Galaxy. De-reddening would bring it back on the
S-shape sequence in that diagram, among the population of δ Sct
candidates.
The second star, star 582, is also reddened according to
its position in the color–color diagram. Both its inferred de-
reddened position in that diagram and the values of its four pe-
riods, ranging between 0.16 and 0.21 d, make it a strong δ Sct
candidate.
5.4. Group 4 of periodic variables: γ Dor candidates
The fourth group identified in Fig. 10 contains 12 stars, 5 of
which are monoperiodic, 5 biperiodic and 2 triperiodic. Their
light curves are shown in Figs. B.10 to B.12. They are at the
faint side of the δ Sct candidates and cover only half a magnitude
from V = 14.9 to 15.2 mag. Their periods range between 0.3
and 2 d, and their amplitudes from few to ∼30 mmag.
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
S/N
15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0
V' (mag)
0.1
1
10
100
1000
P(d)
10
100
A(mmag)
NGC 3766
Fig. 15. Same as Fig. 11, but for the faint periodic variables.
Among them, star 1584 is an apparent exception at V =
17 mag. It is actually a reddened star not member of the cluster.
De-reddening would bring it in the color–color diagram in the
region of group 4 stars (Fig. 8), in agreement with its period
of 0.54271 d.
Those stars are γ Dor candidates pulsating in g-modes. Their
periods range from 0.3 to 1.7 d, though two cases are known at
longer periods, up to 2.7 d (Henry et al. 2007, 2011). Our periods
are compatible with this range.
Finally, we remark the very narrow range in magnitudes
(of 0.26 magnitudes) covered by the γ Dor candidates that are
members of the cluster, compared to the magnitude ranges of
each of the δ Sct, group 2 and SPB candidates (of 0.77, 3.2
and >1.3 mag, respectively).
5.5. Group 5 of periodic variables
Group 5 contains 72 stars, of which 40 are monoperiodic,
25 biperiodic, 6 triperiodic and 1 star has four periods. It gath-
ers all periodic variables fainter than the γ Dor candidates. Their
periods and amplitudes are shown in Fig. 15 as a function of V ,
with the S/N of each detected frequency color coded. No special
feature comes out from the period distribution in the figure. They
all have periods shorter than 10 days, except star 1428, a long
period variable (LPV), with a period of 887 d and an amplitude
of 206 mmag. The other LPV, star 349 mentioned in Sect. 5.3
at V = 14.12 mag and with P = 61.51 d, is also added to this
group. None of those two LPVs belong to the cluster. Their light
curves are shown in Fig. B.13.
The nature of the faint periodic variables is not easy to deter-
mine due to, among other reasons, the lack of stellar characteri-
zation and cluster membership confirmation. We therefore omit
their further classification.
6. General properties of the periodic variables
We discuss in this section several properties of the periodic vari-
ables found in the previous section. Section 6.1 presents the
period–amplitude diagram, Sect. 6.2 the frequency separations
A108, page 9 of 29
10. A&A 554, A108 (2013)
0.02 0.1 0.2 1 2 3 4 5 7
Period (d)
1
10
100
Amplitude(mmag)
NGC 3766
Fig. 16. Period–amplitude diagram, in logarithms, of all periodic vari-
ables. Multiple periods of a same star are connected with straight lines.
Colors indicate the group to which the period belongs, coded as in
Fig. 10 except for group 5 which is plotted in small gray points instead
of black. The X-axis range has been truncated at 7 d for sake of clarity.
Only two stars fall outside this range, stars 349 and 1428 with P = 61.5
and 888 d, respectively, both belonging to group 5.
of the multiperiodic variables, and Sect. 6.3 the amplitudes in
different photometric bands.
6.1. Periods versus amplitudes
A classical visualization diagram of periodic variables is the pe-
riod versus amplitude diagram. This is shown in Fig. 16 for our
periodic variables. Ignoring group 5 of faint stars which are dif-
ficult to classify, we see that groups 1 (red points, SPB candi-
dates), 2 (green and cyan points) and 3 (blue points; δ Sct can-
didates) occupy rather distinct regions in this diagram. They all
have amplitudes below ∼10 mmag, down to 2 mmag for δ Sct
and SPB candidates, and down to 1 mmag for group 2 stars,
but they have quite distinct periods. δ Sct candidates have peri-
ods shorter than ∼0.1 d, group 2 stars between ∼0.1 and ∼1.1 d,
(with the bulk between ∼0.1 and ∼0.7 d), and SPB candidates
longer than ∼1.5 d. Group 4 (magenta points; γ Dor candidates),
on the other hand, has periods similar to group 2. γ Dor candi-
dates have larger amplitudes, on the average, than group 2 stars,
but the distribution of the amplitudes of the members of the two
groups overlap significantly between 2.5 and 10 mmag. There
is, however, a clear difference in V , of at least one magnitude,
between those two groups.
Figure 16 also reveals an overall trend of increasing ampli-
tude with period within groups 2, 3 and 4. In group 2, for exam-
ple, stars with small amplitudes of ∼1 mmag all have periods less
than 0.5 d, while those with A > 5 mmag all have P 0.5 days.
6.2. Multiperiodic variables
The frequency separations |∆ f| between the frequencies of mul-
tiperiodic variables are shown in Fig. 17. Group 2 stars are seen
to have frequency separations on line with those of γ Dor and
δ Sct candidates. The relative frequency separations ∆f/ f range
from ∼0.01 to ∼1 for all stars from group 1 to 4, with no dis-
tinctive feature characterizing any of those four groups relative
to the others.
The multiperiodic variables among the faint stars (group 5),
on the other hand, have very small frequency separations for the
0.2 1 2 3 4 5 10 20 30
f (1/d)
0.001
0.01
0.1
1
10
Deltaf(1/d)
NGC 3766
Fig. 17. Frequency separations of all frequency pairs belonging to mul-
tiperiodic variables, as a function of the mean of the considered pair
of frequencies. The data for stars with more than two frequencies are
connected with a line. Colors in all panels indicate the group to which
the star belongs, coded as in Fig. 10, except for group 5 stars which are
colored in gray (small points) instead of black.
majority of them, with ∆f < 0.01 d−1
. This may be attributed to
noise in the light curves of those stars. We note that seven years
of observations lead to a typical peak width in the Fourier space
of 0.5 × 10−3
d−1
.
6.3. Multiband variability properties
The wavelength dependency of the amplitude of a pulsating
star has been considered since the late seventies as an obser-
vational tool to identify the degree l of pulsation modes (e.g.
Dziembowski 1977; Buta & Smith 1979; Stamford & Watson
1981; Watson 1988). The amplitude ratios at different wave-
lengths depend on the degree l of the pulsation modes (e.g.
Heynderickx et al. 1994; Dupret et al. 2003). Recent applica-
tions of this technique to derive the modes of individual stars
include, for example, Aerts & Kolenberg (2005), Tremblay et al.
(2006), Daszy´nska-Daszkiewicz (2008), Handler et al. (2012).
The A(B )/A(V ) amplitude ratios as a function of the phase
differences ϕ(B ) − ϕ(V ) are shown in Fig. 18 for the dominant
period of all our periodic variables, color coded according to the
group to which they belong. The A(B ) amplitude in B is com-
puted by fitting a sine to the B time series using the dominant
period in V . The majority of the stars have A(B )/A(V ) 1, as
expected. The existence of a few stars with amplitudes smaller
in B than in V is understood by the larger uncertainties in
the B amplitudes compared to those in V . Indeed, the mmag
level of the amplitudes requires a sufficient number of obser-
vations to be made in order to be detected, but the number of
observations in B is smaller than that in V by a factor of about
six (see Fig. 3).
The more than 1500 observations in V , combined with the
stability of the periodic variability over the seven-year duration
of the survey, is a key factor in the detection of the variability.
Such a detection could not reliably be achieved in the B band
for the small amplitude variables. This is especially true for the
subset of group 2 stars with amplitudes below 3 mmag. Stars 259
and 527, for example, which have the smallest A(B )/A(V ) ra-
tios among group 1 to 4 stars (0.61 and 0.38, respectively, see
Fig. 18), have amplitudes in V as small as 1.8 and 3.3 mmag,
respectively, and only 1.2 and 1.3 mmag, respectively, in B .
This explains why group 2 stars, which have on average the
smallest amplitudes among our periodic variables, also have the
A108, page 10 of 29
11. N. Mowlavi et al.: Stellar variability in open clusters
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
phi(B')-phi(V')
0.5
1.0
1.5
2.0
2.5
3.0
A(B')/A(V')
259
527
NGC 3766
Fig. 18. Ratio of the amplitude in B over that in V versus phase dif-
ference in those two bands. The color of each point indicates the group
to which the star belongs, coded as in Fig. 10, except for group 5 stars
which are colored in gray (small points) instead of black. The horizon-
tal and vertical dotted lines are added as eye guides to locate identical
amplitudes and phases, respectively, in the two photometric bands.
largest number of members with A(B )/A(V ) < 1 in Fig. 18. It
is therefore not possible at this stage to perform a deeper pulsa-
tion study based on the multiband variability properties of our V
and B time series. The situation is worse with the U time series,
which have both larger uncertainties and fewer observations than
the B time series. Additional observations at those short wave-
lengths are necessary to conduct such a study.
The multiband data displayed in Fig. 18 nevertheless reveal
an important fact, that there is no significant difference in the
distribution of groups 1 to 4 stars in the A(B )/A(V ) versus
ϕ(B ) − ϕ(V ) diagram. This supports the idea that the variability
of group 2 stars may be of a similar nature than that of group 1,
3 and 4 stars, i.e. that it may originate from pulsation as well.
7. The nature of group 2 stars
The nature of group 2 stars is mysterious. As mentioned in
Sect. 5.2, no classical type of pulsating star is expected on the
MS of the HR diagram in the region between δ Sct and SPB
stars, which is out of all known instability strips. This is exactly
where group 2 stars are found.
In this section, we thus further analyze those stars. We start
with a summary of their properties in Sect. 7.1, and discuss the
possible origin of their variability in Sect. 7.2. Section 7.3 briefly
explores the literature for potential stars showing similar proper-
ties. Section 7.4 finally discusses whether they form a new class
of variable stars.
7.1. Summary of their variability properties
The main properties of group 2 stars from our photometric vari-
ability analysis of NGC 3766 can be summarized as follows:
1. They are MS stars with magnitudes between those of δ Sct
and SPB candidates (Fig. 7).
2. They are numerous in NGC 3766. There are 36 such stars,
which represent about 20% of all stars in their magnitude
range.
3. The bulk of their periods ranges from 0.1 to 0.7 d, with a
peak around 0.3 d, as shown in the histogram displayed in
Fig. 19 (top panel). Only four stars have periods between 0.7
and 1.1 d.
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
Period (day)
0.0
2.5
5.0
7.5
10.0
Numberofstars
NGC 3766
0 1 2 3 4 5 6 7 8 9 10 11
Amplitudes (mmag)
0.0
2.5
5.0
7.5
10.0
12.5
Numberofgroup2stars
NGC 3766
Fig. 19. Histograms of the periods (top panel) and amplitudes (bottom
panel) of group 2 stars. Solid lines give the histograms for the periods
and amplitudes of the dominant detected frequency, while dotted lines
show the histograms considering all frequencies of the multiperiodic
group 2 variables. The bulk of stars with periods between 0.1 and 0.7 d
are shown in dark green, while the few stars with periods between 0.7
and 1.1 d are displayed in cyan, in agreement with the color codes
adopted in Fig. 10.
4. One third of them are multiperiodic, at our 1 mmag variabil-
ity detection limit. Their frequency separations are similar to
those of δ Sct and γ Dor candidates (Fig. 17).
5. Their amplitudes are at the mmag level. The histogram of
the amplitudes (Fig. 19, bottom panel) shows that all, except
one, of the bulk stars (i.e. with periods less than 0.7 d) have
amplitudes below 5 mmag. It also suggests that the iden-
tification of group 2 stars in our data base is instrument-
sensitivity limited. The number of group 2 stars is thus
expected to be higher than what we find, with sub-mmag
amplitudes.
6. There is an overall trend of increasing amplitudes with in-
creasing periods (Fig. 16).
7. Their amplitudes of variability are generally larger in
the B band than in the V (Fig. 18). There is no significant
phase shift between the two bands.
8. The found periods are stable over at least the seven years
of our monitoring campaign, which enabled their detection
despite their small amplitudes.
The overall distribution of group 2 stars in the (log P, log A) dia-
gram (Fig. 16) places them at periods longer than those of δ Sct
and shorter than those of SPB stars (their periods are actually
similar to those of β Cep stars). The periods are similar to or
slightly below those of γ Dor candidates, but at smaller am-
plitudes, on average. Obviously, the key attribute to distinguish
group 2 stars from γ Dor candidates (and from β Cep stars) is
their magnitude.
A108, page 11 of 29
12. A&A 554, A108 (2013)
7.2. Origin of their variability
The properties of group 2 stars, summarized in the previous
section, suggest a pulsation origin for their variability. Among
them is the multiperiodic nature of one third of the members of
that group, with periods stable over seven years. The amplitude
dependency on wavelength is also compatible with pulsations.
Nevertheless, no pulsation is expected to be sustained in the re-
gion of the HR diagram where they are found.
A fraction of the bright stars in NGC 3766 are known to
be rapid rotators, a fact supported by the known high number of
Be stars present in the cluster. We can then wonder whether rota-
tion plays a role in sustaining pulsation in group 2 stars. Studies
of the interplay between fast rotation and non-radial pulsations
have shown that rotation does impact pulsation in SPB stars.
Ushomirsky & Bildsten (1998), in particular, get to interesting
predictions. First, they show that “rapid rotation stabilizes some
of the g-modes that are excited in a nonrotating star and, con-
versely, excites g-modes that are damped in the absence of ro-
tation”. This provides a potential explanation of why pulsating
stars can be found outside the instability strips, though detailed
models need to confirm the pulsation modes that can be sus-
tained by rotation, if any. Second, these authors find that “the
fluid velocities and temperature perturbations are strongly con-
centrated near the equator for most g-modes in rapidly rotating
stars, which means that a favorable viewing angle may be re-
quired to observe the pulsations”. This can potentially explain
the existence, inside or outside instability strips, of “observa-
tionally non-pulsating” stars that, in reality, do pulsate while
rotating.
While Ushomirsky & Bildsten (1998) illustrate their find-
ings in models of SPB stars, their conclusions are not restricted
to those stars. Townsend (2005) also predicts unstable modes
as a result of rotation. Using a non-adiabatic pulsation code, he
finds that “retrograde mixed modes are unstable in mid- to late-
B-type stars, as a result of the same iron-bump opacity mecha-
nism that is usually associated with SPB and β Cep stars”. This
even leads him to claim the “discovery of a wholly new class of
pulsational instability in early-type stars”. The periods he pre-
dicts range from 100 days down to a fraction of a day, depending
on the azimuthal order m of the mode. His lowest predicted peri-
ods are in agreement with the periods found in our group 2 stars,
which would be compatible with m = 3 and 4.
To further explore the nature of group 2 stars requires the
characterization of their stellar properties. Not many studies
helping in this direction are available in the literature. One of
them is the work by McSwain et al. (2008), who analyzed the
spectra of 42 B stars in NGC 3766, including 16 Be stars. Thirty-
nine of them are present in our list of stars, and ten of them
are periodic variables. Six of them belong to group 1 (stars 31,
36, 40, 49, 61 and 107) and four to group 2 (stars 50, 62, 66
and 145)2
. They are all B stars, except star 50 which is classified
as a Be star by McSwain et al. (2008).
From the spectra of their stars, McSwain et al. (2008) de-
rived, among other stellar parameters, the effective tempera-
tures Teff, the surface gravities g, and the projected rotational ve-
locities v sin(i), where v is the equatorial rotational velocity and i
is the inclination angle, i.e. the angle between the line of sight
and the rotation axis. They then derived the expected critical ro-
tational velocity by comparison with stellar evolutionary models.
They also estimated the surface gravities gpolar at the pole of the
stars, a quantity that should be less affected by rotation than g is.
2
The correspondence between our star identification numbers and the
ones used by McSwain et al. (2008) is given in Table B.1.
0
1
2
3
4
5
6
P(d)
10,00012,50015,00017,50020,000
Teff (K)
3.25
3.50
3.75
4.00
4.25
4.50
logg_polar(cm/s2)
34579
NGC 3766
Fig. 20. Location in the (Teff, log gpolar) HR diagram of the B (squares)
and Be (diamonds) stars of McSwain et al. (2008) that fall in our field of
view. Open markers identify non-periodic variables, and filled markers
periodic variables with the color of the marker related to the period (the
dominant one for multiperiodic variables) according to the color scale
on the right. The four dark blue markers represent group 2 stars (peri-
ods less than 1 day), the other six color markers representing SPB can-
didates. Tracks of non-rotating stellar evolution models are shown by
continuous lines for various initial stellar masses, as labeled next to the
tracks. Tracks with initial models rotating at 40% the critical rotational
velocity are shown by dashed lines. All tracks are taken from Ekström
et al. (2012).
The thirty-nine stars in common between their list of stars and
ours are shown in the (Teff, log gpolar) diagram in Fig. 20. We also
plot in the figure solar metallicity stellar evolution tracks, both
with and without rotation, computed by Ekström et al. (2012).
The ten periodic variables in common between the list of stars
of McSwain et al. (2008) and ours are highlighted in color in the
figure.
The periods of our stars are plotted in Fig. 21 as a function
of the projected equatorial velocity obtained by McSwain et al.
(2008), for the stars in common in the two studies. We see that
the four stars among them that belong to group 2 are spinning
at rotation velocities of at least 50% the critical velocity. The
actual rotation velocities v may be higher than the measured pro-
jected velocities, depending on the inclination angle i, but they
are limited by the critical velocity. The range of possible ve-
locities for each star between those two limits is shown by the
horizontal lines in Fig. 21. Four stars are of course not enough to
draw firm conclusions, but that all four of them are fast rotators
strongly supports the potential role of rotation in explaining the
existence of MS pulsators in the luminosity range between δ Sct
and SPB stars. Analysis of more stars from group 2 is of course
needed to check the validity of this conclusion, but this requires
more spectroscopic data. Star 51, with two periods reminiscent
of SPB stars (at 3.47 and 1.98 d) and one of group 2 (at 0.23 d)
is an interesting case to be studied in this context.
7.3. Link with known variables in the literature
In the fifties, Struve (1955) hypothesized the presence of a se-
quence of variable stars in the region of the HR diagram between
the locations of the currently known SPB and δ Sct stars. The
suggestion was based on the detection of radial velocity vari-
ations in the B8-type star Maia of the Pleiades, with a period
A108, page 12 of 29
13. N. Mowlavi et al.: Stellar variability in open clusters
0.2
0.3
0.4
0.5
0.6
0.7
0.8
v*sin(i)/v_crit50 100 150 200 250 300 350 400 450
v sin(i) (km/s)
0
1
2
3
4
5
6
P(d)
31, MG54
36, MG41
40, MG170
49, MG94
50, MG139
61, MG57
62, MG77
66, MG42
107, MG197
145, MG36
NGC 3766
Fig. 21. Period as a function of v sin(i) for the periodic variables in
common with the stars spectroscopically observed by McSwain et al.
(2008). The projected rotational velocity v sin(i) is taken from those au-
thors. The markers have the same meaning as those in Fig. 20, with the
colors related to the v sin(i)/vcrit ratio according to the color scale plot-
ted on the right of the figure, vcrit being the critical rotational velocity.
The four group 2 stars are the ones having P < 1 d, the other ones
belonging to group 1. Horizontal lines indicate the range of possible ro-
tational velocities v for each star, i.e. from v sin(i) to vcrit. Our star id is
indicated next to each marker, followed by the star id from McSwain &
Gies (2005).
of ∼4 h, and in the A-type star γ Ursae Minoris, with a period
of 2.5 h. He called those variable stars Maia stars. The variability
of the Maia star itself was however disclaimed two years later,
by himself (Struve et al. 1957), and the very existence of “Maia
variables” became since then a source of debate (McNamara
1987). In the late nineties, Scholz et al. (1998), despite assess-
ing unambiguous detections of multiperiodic short-term radial
velocity variations in two A-type stars, state that “no proof for
the existence of a separate class of variables, designated as Maia
variables, are found”.
The high precision of the photometric data gathered by
the H satellite gave a new impetus in the search for
Maia stars, but resulted in inconclusive results. Percy & Wilson
(2000), for example, conclude after a careful analysis of several
hundred H variables that “the Maia variables, if they ex-
ist, are very rare and very elusive”. Seven years later, De Cat
et al. (2007) monitored from ground 35 B-type stars during a
3-year high-quality observation campaign. In their variability
analysis, “all the Maia candidates were reclassified into other
variability classes”.
These few examples show the difficulty to confirm the hy-
pothetical sequence of “Maia variables”. The trouble is not so
much to find variable stars in that region of the HR diagram –
individual cases are found –, but that they are rather rare. The
non-prediction of pulsations in this part of the HR diagram, at
least based on classical stellar models, did not help to support
for a new class of variables either.
The fact that we find in NGC 3766 so many variables at
spectral types between those of δ Sct and SPB stars – there
are 36 stars in our group 2 variables, which represent about 20%
of the stars in that magnitude range –, and with variability prop-
erties that distinguish them from their neighboring δ Sct and
SPB candidates, calls for a new attention. Whether the “Maia”
candidates considered in the past and with confirmed short-
period variability are of the same nature as our group 2 stars
is not clear. But we believe that we found a new class of variable
stars, and that at least some variables discussed in the literature
belong to this class.
HD 121190 is an example of a known variable that we be-
lieve belongs to our new group 2 stars. It is of spectral type B9V
and has been classified as an SPB star by Waelkens et al. (1998),
with a period of 0.38 d derived from H epoch photome-
try. This makes it an unusually short period SPB star, as recog-
nized by Aerts & Kolenberg (2005), the periods of SPB variables
being predicted to be above 0.5 d (Pamyatnykh 1999). Aerts
& Kolenberg (2005) confirm the short-term periodic variabil-
ity of this star, with three significant periods detected in mul-
ticolor Geneva photometry light curves, at P = 0.3727, 0.3817
and 0.4046 d and with amplitudes of a few mmag. They fur-
ther derive a projected rotation velocity of v sin i = 118 km s−1
from spectroscopic observations, which implies a rotational ve-
locity of at least 26% of its critical velocity. This, those authors
state, may explain the pulsations found in this star because “such
rotation velocities imply that the effects of the Coriolis force
may come into play and that this force introduces significant
frequency shifts for the low-frequency gravity modes”, quoting
Townsend (2003). They also note that HD 121190 is “the coolest
single star of that class (SPB) known to date”. In view of our
findings, we consider HD 121190 to be a member of our new
group 2 variables. It also supports the conclusion of Sect. 7.2
that rotation may play a key role in explaining the pulsations of
those stars. The important point to raise here is that group 2 stars
lie in the HR diagram out of any classical instability strip, and
thus cannot be easily linked to known variability types.
The small amplitudes of 1 to 3 mmag of the group 2 vari-
ables may explain why those stars have been hardly detected
until now from ground-based photometry. Among the published
studies of variability in open clusters, the analysis performed
by one of us on NGC 884 (Saesen et al. 2010), based on
an 800 days multisite campaign gathering more than 77 500
CCD images from 15 different instruments, also reached vari-
ability detection limits down to the mmag level. NGC 884, with
an age of about 13 My, is a little younger than NGC 3766, but
shares with our cluster the property of being rich in B stars. In
NGC 884, the δ Sct stars are found at V magnitudes between 15
and 16 mag, roughly one magnitude fainter than in NGC 3766.
According to our results, thus, the equivalents of our group 2
stars should be observed in NGC 844, if they exist, at magnitudes
between V = 12 and 15 mag. Interestingly, Saesen et al. (2010)
also find many periodic variables in that “forbidden” range of
magnitudes corresponding to the region between δ Sct and SPB
stars. Furthermore, many of them have periods between 0.15
and 1 d, and amplitudes of few mmags, like our group 2 stars.
But they also find such variables at brighter magnitudes, down
to V = 9 mag, where SPB stars are expected to be found, as well
as variables with periods up to 3 to 10 days at all magnitudes. It
is thus difficult to classify their periodic stars and to analyze their
properties in the way we did, without further studies with com-
plementary data. But one conclusion, we believe, emerges from
their database as well, that the range of magnitudes between the
δ Sct and the SPB instability strips in NGC 884 is definitely
well populated with periodic variables, contrary to expectations
from standard pulsation model predictions. It must be noted that
NGC 884 is also known to hold Be stars. We refer to Saesen
et al. (2010) for more information on the variability content of
this cluster.
A108, page 13 of 29
14. A&A 554, A108 (2013)
Space-based missions such as CoRoT and Kepler provided
new opportunities in the detection of small amplitude variables.
Very interestingly, Degroote et al. (2009) report on the “evidence
for a new class of low-amplitude B-type pulsators between the
SPB and δ Sct instability strips”. The amplitudes of the main
peaks in the periodograms of the new B-type pulsators found
by those authors are ∼0.1%, with periods between 0.1 and 1 d
on average. The variability properties are thus very similar to
those of our group 2 stars. But a negative conclusion seems to
be reached by Balona et al. (2011b) from Kepler data, as they
state that “no evidence of pulsation is found in the B-type stars
located between the cool edge of the SPB and the hot edge of
the δ Sct instability strips”. Balona (2011), however, reports on
the detection of low-frequency (0.2 d < P < 5 d), low-amplitude
(∼40 ppm) variability in most Kepler A-type stars. He tries to
explain those periodic variations through known classes of vari-
ability, assuming that the variable A-type stars “are just the hot-
ter counterparts of the spotted F-type stars, since there is no pul-
sation mechanism which can account for the low frequencies in
these stars”. But he recognizes that, if this is the explanation,
“the idea that A-type atmospheres are quiescent would need to
be revised”. He also detects low frequencies in “hot A-type δ Sct
stars”, of about twice the rotational frequency, for which he can-
not find any explanation. We believe that those Kepler A-type
stars and the CoRoT new B-type pulsators may be of the same
nature as our new group 2 variables.
7.4. A new class of variable stars?
Group 2 stars fall in a region of the HR diagram where no pulsa-
tion is predicted to occur. Their classification in a known class of
pulsating stars is therefore not possible. If we consider a typical
member of group 2 stars, for example a pulsating early A-type
star with a period of 0.3 d, it cannot be a δ Sct star both because
the period is too long and because it stands out of the classical
instability strip. It cannot be an SPB star either, which are B-type
stars and with longer periods.
Of course, a nonpulsating origin for some of these selected
stars is not excluded, and this must certainly be the case. Spots,
for example, are known to exist on the surface of A-type stars.
Some group 2 stars may also be ellipsoidal variables. But many
of the group 2 stars are most probably pulsators, as discussed in
the previous sections. The impossibility of classifying them in
one of the known classes of variable stars thus calls for a new
class of low-amplitude (multi-)periodic stars that contains main
sequence A and late B type stars variable at the mmag level (at
least in the optical bands) with periods between 0.1 and 0.7 d.
The definition of a new variability class does not imply the need
for a new pulsation mechanism, but some physics must be spe-
cific to those stars in order to be able to excite pulsation modes
outside the borders of known instability strips. The previous sec-
tions have suggested that the interaction between stellar rotation
and pulsation (based on standard κ-mechanism) may fulfill the
requirements.
The same conclusion is reached by Degroote et al. (2009)
based on CoRoT data. Thanks to the high photometric precisions
achieved by this space mission, those authors even conclude that
this new class may not be uniform. They suggest the existence
of four groups within the class, based on the structure of the
frequency spectra of the stars. In their database, each group con-
tains four to six candidates.
The detection of group 2 stars in an open cluster has the great
advantage to enable the identification of stellar types by compar-
ing the location of the stars in the color–magnitude diagram with
the locations of identified SPB and δ Sct members (membership
is relatively secured in our case of NGC 3766). This is not the
case for the ∼16 CoRoT candidates of this new class, the stel-
lar parameters of which had to be estimated using a procedure
that is not straightforward (Degroote et al. 2009). They never-
theless concluded those stars to be of type A. Our analysis of
group 2 stars in NGC 3766 does not suffer from these difficulties
and directly supports the claim for a new class of variable stars
on the MS between SPB and δ Sct stars.
Eventually, a suitable name for this new group of variables
should be found. We think that the elusiveness of these vari-
ables results from their small amplitudes. Given furthermore that
the distribution of their amplitudes may extend to the sub-mmag
range, we would propose calling them “low amplitude periodic
A and late-B variables”, which may actually become “low am-
plitude pulsating A and late-B variables”, if confirmed so.
8. Conclusions
This paper presents the periodic variables detected in the field
of view of NGC 3766 from a seven-year monitoring campaign
performed with the 1.2-m Swiss Euler telescope in La Silla,
Chili. We reach the mmag variability detection level for pe-
riodic variables, allowing the discovery of a large number of
low-amplitude pulsators. We find 13 SPB (group 1), 14 δ Sct
(group 3) and 12 γ Dor (group 4) candidates, as well as 16 eclips-
ing binaries and 72 various periodic variables fainter than the
γ Dor candidates (group 5), not all belonging to the cluster. All
variable stars presented in this paper are new discoveries. It must
be noted that our search does not include any β Cep star, even
though such stars may be present in NGC 3766, because we ex-
cluded from our analysis the brightest, saturated, stars.
Most importantly, we find 36 MS variable (group 2) stars
between the red edge of SPB stars and the blue edge of δ Sct
stars, where no pulsation is predicted with standard stellar mod-
els. These form a new group of variables with properties distinct
from those of the adjacent SPB and δ Sct candidates. About 20%
of the MS stars of NGC 3766 in that magnitude range are found
to be group 2 variable candidates, and they represent the most
numerous group of variable stars (excluding group 5 of faint
stars). The true number of variable stars in that new group is
however expected to be larger, our results being limited by our
mmag detection limit.
The properties of this new group of variables, which are sum-
marized in Sect. 7.1, support a pulsation origin. Among those
properties are the multiperiodic nature of more than one third
of its members and the stability of their variability properties on
a time scale of at least seven years. If pulsation is indeed re-
sponsible for their photometric variability, rotation is believed
to provide the necessary physical conditions to excite the pulsa-
tion modes. Indeed, four of our candidates in this new group, for
which spectra are available in the literature, do rotate at least
at half their critical velocity. Pulsation predictions in models
of rotating stars, computed in the last decade, also support this
conclusion.
Several observations in the literature support the existence of
the new class of variables we find in NGC 3766. The evidence
from ground-based observation is rare, most probably because
of the low, mmag level, variability amplitude of those objects,
but such evidence is much more convincing from the data gath-
ered by the CoRoT and Kepler satellites. We find it remarkable
that our ground-based observations, performed with a one-meter
class telescope, is able to provide evidence of that new class of
variables at such small amplitudes. This, we believe, is thanks
A108, page 14 of 29
15. N. Mowlavi et al.: Stellar variability in open clusters
to the high quality of the observations and of the data reduc-
tion, combined with the seven-year baseline of our monitoring
campaign.
We encourage searching for this new class of variables in
other young open clusters. That there are so many candidates
for this new class in NGC 3766 may be analogous to the large
number of Be stars observed in this cluster. This would be un-
derstandable if both phenomena are indeed related to high rota-
tional velocities characterizing the stellar population of the clus-
ter. If this is true, then the search would be the most efficient in
other clusters that are already known to have rich populations of
Be stars as well. Variables of this new class may, for example,
already be present in the data of NGC 884 gathered by Saesen
et al. (2010) for NGC 884.
Finally, we propose (Sect. 7.4) the name of “low amplitude
periodic (or pulsating) A and late-B variables” for this new class
of variable stars.
Acknowledgements. We would like to thank A. Gautschy for his careful reading
and commenting on an early version of the paper. We also thank G. Burki, F.
Carrier and A. Blecha for having set up the Geneva Open Clusters monitoring
campaign ten years ago, as well as all the observers that devoted their times to
build the resulting high-quality data base of photometric light curves. The ob-
servers include, in alphabetic order, G. Burki, F. Carrier, M. Cherix, C. Greco,
M. Spano and M. Varadi in addition to ourselves, as well as other people who
occasionally contributed to the monitoring campaign while performing other ob-
servation runs at the telescopes.
References
Aerts, C., & Kolenberg, K. 2005, A&A, 431, 615
Aerts, C., Thoul, A., Daszy´nska, J., et al. 2003, Science, 300, 1926
Aerts, C., De Cat, P., Kuschnig, R., et al. 2006, ApJ, 642, L165
Ahmed, F. 1962, Publ. Roy. Obs. Edinburgh, 3, 60
Aidelman, Y., Cidale, L. S., Zorec, J., & Arias, M. L. 2012, A&A, 544, A64
Ausseloos, M., Scuflaire, R., Thoul, A., & Aerts, C. 2004, MNRAS, 355, 352
Balona, L. A. 2011, MNRAS, 415, 1691
Balona, L. A., & Dziembowski, W. A. 2011, MNRAS, 417, 591
Balona, L. A., Guzik, J. A., Uytterhoeven, K., et al. 2011a, MNRAS, 415, 3531
Balona, L. A., Pigulski, A., De Cat, P., et al. 2011b, MNRAS, 413, 2403
Briquet, M., Hubrig, S., De Cat, P., et al. 2007, A&A, 466, 269
Briquet, M., Neiner, C., Aerts, C., et al. 2012, MNRAS, 427, 483
Brogaard, K., VandenBerg, D. A., Bruntt, H., et al. 2012, A&A, 543, A106
Buta, R. J., & Smith, M. A. 1979, ApJ, 232, 213
Carrier, F., Saesen, S., Cherix, M., et al. 2009, Commun. Asteroseismol., 158,
199
Cherix, M., Carrier, F., Burki, G., & Blecha, A. 2006, Mem. Soc. Astron. It., 77,
328
Christensen-Dalsgaard, J. 2004, in SOHO 14 Helio- and Asteroseismology:
Towards a Golden Future, ed. D. Danesy, ESA SP, 559, 1
Daszy´nska-Daszkiewicz, J. 2008, Commun. Asteroseismol., 152, 140
De Cat, P. 2002, in IAU Colloq. 185: Radial and Nonradial Pulsationsn as Probes
of Stellar Physics, eds. C. Aerts, T. R. Bedding, & J. Christensen-Dalsgaard,
ASP Conf. Ser., 259, 196
De Cat, P. 2007, Commun. Asteroseismol., 150, 167
De Cat, P., Briquet, M., Aerts, C., et al. 2007, A&A, 463, 243
Degroote, P., Aerts, C., Ollivier, M., et al. 2009, A&A, 506, 471
Dupret, M.-A., De Ridder, J., De Cat, P., et al. 2003, A&A, 398, 677
Dupret, M.-A., Thoul, A., Scuflaire, R., et al. 2004, A&A, 415, 251
Dziembowski, W. 1977, Acta Astron., 27, 203
Ekström, S., Georgy, C., Eggenberger, P., et al. 2012, A&A, 537, A146
Eyer, L. & Mowlavi, N. 2008, J. Phys. Conf. Ser., 118, 012010
Fox Machado, L., Pérez Hernández, F., Suárez, J. C., Michel, E., & Lebreton, Y.
2006, A&A, 446, 611
Gautschy, A., & Saio, H. 1995, ARA&A, 33, 75
Gautschy, A., & Saio, H. 1996, ARA&A, 34, 551
Greco, C., Mowlavi, N., Eyer, L., et al. 2009, in AIP Conf. Ser. 1170, eds. J. A.
Guzik, & P. A. Bradley, 318
Greco, C., Mowlavi, N., Eyer, L., et al. 2010, in IAU Symp. 264, eds. A. G.
Kosovichev, A. H. Andrei, & J.-P. Roelot, 87
Gruber, D., Saio, H., Kuschnig, R., et al. 2012, MNRAS, 420, 291
Grundahl, F., Clausen, J. V., Hardis, S., & Frandsen, S. 2008, A&A, 492,
171
Guzik, J. A., Kaye, A. B., Bradley, P. A., Cox, A. N., & Neuforge, C. 2000, ApJ,
542, L57
Handler, G., Shobbrook, R. R., Uytterhoeven, K., et al. 2012, MNRAS, 424,
2380
Henry, G. W., Fekel, F. C., & Henry, S. M. 2007, AJ, 133, 1421
Henry, G. W., Fekel, F. C., & Henry, S. M. 2011, AJ, 142, 39
Heynderickx, D., Waelkens, C., & Smeyers, P. 1994, A&AS, 105, 447
Kochukhov, O. 2007, Commun. Asteroseismol., 150, 39
Kurtz, D. W. 1982, MNRAS, 200, 807
Lovekin, C. C., & Goupil, M.-J. 2010, A&A, 515, A58
McNamara, B. J. 1987, in Stellar Pulsation (Berlin: Springer Verlag), eds. A. N.
Cox, W. M. Sparks, & S. G. Starrfield, Lecture Notes in Physics, 274, 92
McNamara, B. J., Jackiewicz, J., & McKeever, J. 2012, AJ, 143, 101
McSwain, M. V. 2008, ApJ, 686, 1269
McSwain, M. V., & Gies, D. R. 2005, ApJS, 161, 118
McSwain, M. V., Huang, W., Gies, D. R., Grundstrom, E. D., & Townsend,
R. H. D. 2008, ApJ, 672, 590
McSwain, M. V., Huang, W., & Gies, D. R. 2009, ApJ, 700, 1216
Mermilliod, J.-C. 1982, A&A, 109, 37
Moitinho, A., Alfaro, E. J., Yun, J. L., & Phelps, R. L. 1997, AJ, 113, 1359
Montgomery, M. H., & Odonoghue, D. 1999, Delta Scuti Star Newsletter, 13,
28
Pamyatnykh, A. A. 1999, Acta Astron., 49, 119
Paunzen, E., Heiter, U., Netopil, M., & Soubiran, C. 2010, A&A, 517,
A32
Percy, J. R., & Wilson, J. B. 2000, PASP, 112, 846
Pesnell, W. D. 1987, ApJ, 314, 598
Piatti, A. E., Claria, J. J., & Bica, E. 1998, ApJS, 116, 263
Pollard, K. R. 2009, in AIP Conf. Ser. 1170, eds. J. A. Guzik, & P. A. Bradley,
455
Poretti, E., Michel, E., Garrido, R., et al. 2009, A&A, 506, 85
Saesen, S., Carrier, F., Pigulski, A., et al. 2010, A&A, 515, A16
Scholz, G., Lehmann, H., Hildebrandt, G., Panov, K., & Iliev, L. 1998, A&A,
337, 447
Shobbrook, R. R. 1985, MNRAS, 212, 591
Shobbrook, R. R. 1987, MNRAS, 225, 999
Southworth, J. 2012, in Proc. of the workshop Orbital Couples: Pas de Deux in
the Solar System and the Milky Way. Held at the Observatoire de Paris, 10–12
October 2011, eds. F. Arenou, & D. Hestroffer, 51
Stamford, P. A., & Watson, R. D. 1981, Ap&SS, 77, 131
Stetson, P. B. 1987, PASP, 99, 191
Stetson, P. B., & Harris, W. E. 1988, AJ, 96, 909
Struve, O. 1955, S&T, 14, 461
Struve, O., Sahade, J., Lynds, C. R., & Huang, S. S. 1957, ApJ, 125, 115
Tadross, A. L. 2003, New Astron., 8, 737
Tamuz, O., Mazeh, T., & Zucker, S. 2005, MNRAS, 356, 1466
Thompson, I. B., Kaluzny, J., Pych, W., et al. 2001, AJ, 121, 3089
Thompson, I. B., Kaluzny, J., Rucinski, S. M., et al. 2010, AJ, 139, 329
Townsend, R. H. D. 2003, MNRAS, 343, 125
Townsend, R. H. D. 2005, MNRAS, 364, 573
Tremblay, P.-E., Fontaine, G., Brassard, P., Bergeron, P., & Randall, S. K. 2006,
ApJS, 165, 551
Ushomirsky, G., & Bildsten, L. 1998, ApJ, 497, L101
Uytterhoeven, K., Moya, A., Grigahcène, A., et al. 2011, A&A, 534, A125
Waelkens, C., Aerts, C., Kestens, E., Grenon, M., & Eyer, L. 1998, A&A, 330,
215
Watson, R. D. 1988, Ap&SS, 140, 255
Yıldız, M. 2011, PASA, 28, 66
Yilmaz, F. 1976, A&AS, 26, 1
Zechmeister, M., & Kürster, M. 2009, A&A, 496, 577
Pages 16 to 29 are available in the electronic edition of the journal at http://www.aanda.org
A108, page 15 of 29
16. A&A 554, A108 (2013)
Appendix A: Eclipsing binaries
The list of eclipsing binaries found in our FOV of NGC 3766
is provided in Table A.1. We give, in the order of the columns
presented in the table, their identification number in our num-
bering scheme, their mean V magnitude, their colors, their pe-
riod, their binarity type and their potential cluster membership.
Membership is evaluated from the position of the star in the
color–magnitude and color–color diagrams (Figs. 7 and 8, re-
spectively, in the main body of the paper).
The folded light curves of the eclipsing binaries are shown
in Fig. A.1.
The eclipsing binary system candidate 50 requires further
discussion. Its light curve, displayed in Fig. A.2, shows only two
eclipsing event candidates, that occurred respectively during the
nights 2552.5 and 1858.5 d. The eclipse durations, if both events
are indeed due to an eclipse, are of the order of several hours to
half a day. The third dimming event, around 1410 d, spans two
nights and seems less probably due to an eclipsing event. We
therefore assume here that only the first two events are due to an
eclipse. The first of them shows a very nice V-shape light curve,
while the second one has only two sets of measurements on the
brightening side of event.
It is difficult to estimate a period of an eclipsing binary
with only two eclipses. Furthermore, and unfortunately, no B
Table A.1. Eclipsing binaries in our field of view of NGC 3766.
GvaId RA Dec V B − V U − B Period Type Potential
(hour) (deg) (mag) (mag) (mag) (day) member
50 11.611636 –61.631599 11.079 –0.016 –0.398 (100.63957) EA yes
444 11.589491 –61.649919 14.734 0.513 0.240 1.194975 EB yes
504 11.609959 –61.689997 15.092 0.847 0.418 3.082914 EA no
542 11.610533 –61.680373 15.150 0.883 0.947 3.182190 EA no
545 11.602196 –61.690321 15.209 0.505 0.249 7.716726 EA yes
626 11.590774 –61.582517 15.511 0.758 0.363 1.358385 EA no
685 11.609402 –61.601084 15.352 0.561 0.234 1.078387 EA yes
693 11.601583 –61.558911 15.646 0.653 0.689 2.990783 EA no
719 11.608576 –61.616905 15.464 0.931 0.796 2.138442 EB no
934 11.591592 –61.650848 16.117 1.160 1.012 2.533318 EB no
1125 11.607174 –61.661810 16.007 0.777 –0.016 3.218536 EA no
1443 11.595281 –61.552545 16.837 1.066 0.561 0.887205 EW yes
2000 11.600740 –61.562226 17.170 1.228 0.361 0.366388 EW no
2076 11.594144 –61.679395 17.553 1.238 0.110 4.175527 EA no
2336 11.589583 –61.580192 18.016 1.183 –1.088 0.316234 EW no
2663 11.613256 –61.597650 17.993 1.018 –0.197 0.476018 EB no
or U measurement is available at the times of the two events.
We therefore proceeded in the following way. We first deter-
mined the most probable period PV from the V light curve. No
bright (i.e. at the out-of-eclipse level) measurement should be
present at eclipse times, as easily checked in the folded light
curves. This led to PV = 6.291223 d. We then search the small-
est multiple n PV, n being an integer, for which the folded
light curves in B and U are compatible with the two eclipses
at their relevant phases. The final period is thereby estimated
to P = 100.63957 d.
The folded light curve is shown in the upper-left panel of
Fig. A.1, and a zoom on the two eclipses in Fig. A.3. The minima
of the two eclipses are seen to be distant, in phase, by only 0.1
from each other, pointing to a very eccentric system.
To shed some further light on the binary nature of star 50,
we took spectra of it with the Euler telescope. From its loca-
tion on the MS in the HR diagram, we expected the star to be of
spectral type around B3. Its spectra, however, showed the pres-
ence of many iron lines, thus revealing the presence of an A-type
companion, possibly of spectral type A3. We thus conclude on a
double system with a B-type primary and an A-type secondary.
More observations are required to better characterize this sys-
tem. We further note that this binary candidate 50 is also a mem-
ber of group 2 stars.
A108, page 16 of 29
19. N. Mowlavi et al.: Stellar variability in open clusters
Appendix B: Group 1 to 5 periodic variables
The list of group 1 to 5 periodic variables with secured fre-
quencies is provided in Table B.1. We give, in the order of the
columns presented in the table, their identification number in
our numbering scheme, their mean V magnitude and colors, the
group to which they belong (as defined in Sect. 5), the period,
amplitude, uncertainty on the amplitude, and S/N of each of their
frequencies determined from their V time series (one line per
period), and the star identification number given by McSwain &
Gies (2005) and used in McSwain et al. (2008), if available.
The number of digits printed in Table B.1 for the periods
is computed from the uncertainty εP on the period P, estimated
with the formula, derived by Montgomery & Odonoghue (1999),
εP =
√
6
Π
√
Nobs
1
Tobs
σnoise
A
P2
, (B.1)
where Nobs is the number of observations in the time series of du-
ration Tobs, A is the amplitude and σnoise the mean uncertainty of
the measurements. The uncertain digit is written in parenthesis.
The uncertainty on the amplitude is estimated, also from
Montgomery & Odonoghue (1999), with the formula
σ(A) =
√
2
√
Nobs
σnoise. (B.2)
The folded light curves of group 1 stars are shown in Figs. B.1
and B.2, of group 2 stars in Figs. B.3 to B.5, of group 3 stars
in Figs. B.6 to B.9, and of group 4 stars in Figs. B.10 to B.12.
The outliers seen in the folded light curve of star 49 (Fig. B.1)
are due to an outburst occurring at the end of our observation
campaign. It will be studied in more details in a forthcoming
paper (Mowlavi et al., in prep.).
The light curves of the two LPV stars in our sample are
shown in Fig. B.13.
A108, page 19 of 29