This document analyzes a spectrum of V838 Monocerotis obtained in October 2005 using the Keck/HIRES instrument. The analysis yields the following key findings:
1) The spectrum shows evidence of an intense mass outflow from V838 Mon with velocities up to 215 km/s and a mass loss rate of 10^-6 to 10^-5 solar masses per year. Some lines also show evidence of infalling matter.
2) Emission lines of [Fe II] and an eclipse-like event in 2006 are explained by interactions between the expanding matter ejected in 2002 and radiation from the B3V companion star.
3) Modeling of the [Fe II] line profiles allows
Propagation of highly_efficient_star_formation_in_ngc7000Sérgio Sacani
This document summarizes observations of molecular gas and star formation in the NGC 7000 molecular cloud and HII region. The key points are:
1. Five dense molecular clumps were identified in NGC 7000 based on NH3 emission, with sizes of 0.2-1 pc and masses of 9-452 solar masses.
2. The clumps have similar gas temperatures of 11-15K but different levels of star formation activity, from concentrations of T-Tauri stars to associations with H2O maser sources.
3. The star formation activities appear related to the geometry of the HII region, with the clump near the HII region boundary having the highest star formation efficiency of 36
Ultraviolet signposts of resonant dynamics in the starburst ringed sab galaxy...Sérgio Sacani
1) The document analyzes ultraviolet images of the starburst-ringed galaxy M94, finding emission from the nucleus, inner disk, bright inner ring of H II regions, and two outer knots of hot stars.
2) Optical and ultraviolet spectroscopy of the nucleus and inner disk indicate a 107-108 year old stellar population with some low-level star formation and LINER activity.
3) Analysis of multi-wavelength data suggests that star formation in M94 is being driven by ring-bar dynamics involving structures like the nuclear mini-bar, inner ring, oval disk, and outer ring.
The document summarizes information about the Lagoon Nebula and its surrounding regions. It is located in the Sagittarius-Carina Arm of the Milky Way, about 1.3 kpc away. The Lagoon Nebula contains the young open cluster NGC 6530 (1-3 Myr old), which has several O and B type stars. Younger star formation is ongoing in regions like the Hourglass Nebula and M8 E. The complex structure of the region has been shaped by interactions between massive stars and molecular gas over multiple episodes of star formation.
An energetic stellar_outburst_accompanied_by_circumstellar_light_echoesSérgio Sacani
1) V838 Monocerotis (V838 Mon) underwent an energetic stellar outburst in early 2002, temporarily becoming the brightest star in the Milky Way. 2) Hubble Space Telescope images revealed expanding light echoes in the circumstellar dust surrounding V838 Mon, allowing astronomers to set a minimum distance of over 6 kiloparsecs. 3) The light echoes, combined with the object's high luminosity and evidence that it resides in a binary system, indicate that V838 Mon represents a new class of stellar outburst not fully explained by current models.
This document summarizes a study on the formation of polar ring galaxies through two proposed scenarios: the merging scenario and the accretion scenario. The merging scenario involves a head-on collision between two galaxies, where one becomes the host galaxy and the other's gas forms the polar ring. The accretion scenario involves tidal interactions that allow gas from one galaxy to be accreted by another galaxy to form a polar ring. Through simulations, the study finds that both scenarios can produce stable polar rings, but that the accretion scenario better matches observed properties of polar ring galaxies, such as the frequency and morphology of the rings. The study concludes the accretion scenario is both more likely and more supported by observations to explain how most polar ring galaxies form.
Analysis of most_light_curves_of_five_young_stars_in_taurus_auriga_and_lupus_3...Sérgio Sacani
This document analyzes light curves from the MOST satellite of five young stars in star-forming regions. Light curves of three spotted weak-line T Tauri stars (V410 Tau, V987 Tau, and Lupus 3-14) show small values of the solar-type differential rotation parameter, indicating slightly non-rigid rotation. Light curves of another spotted weak-line T Tauri star (Lupus 3-48) are consistent with rigid rotation. Three similar flares were detected in the light curve of Lupus 3-14. The light curve of the classical T Tauri star RY Tau showed continuous decreasing brightness over three weeks of observation with variable modulation and no obvious periodic signal.
Unique Meteorite from Early Amazonian Mars: Water-Rich Basaltic Breccia North...Carlos Bella
1) NWA 7034 is a 319.8g martian meteorite found in Morocco in 2011. It is a porous basaltic breccia composed of feldspar and pyroxene phenocrysts in a fine-grained groundmass.
2) Chemical and isotopic analyses indicate it formed on Mars 2.089 billion years ago from a magma enriched in the martian crust. It contains over 6000ppm water, more than most martian meteorites.
3) NWA 7034 matches basalts analyzed at Gusev Crater by the Mars Exploration Rover and the average martian crust measured by orbiters, unlike other martian meteorites. Its composition suggests
1) NWA 7034 is a 319.8g martian meteorite found in Morocco in 2011. It is a porous basaltic breccia composed of feldspar and pyroxene phenocrysts in a fine-grained groundmass containing magnetite.
2) Chemical and isotopic analyses indicate NWA 7034 formed on Mars 2.089 billion years ago from a geochemically enriched crustal source. It contains over 6000ppm water, more than most martian meteorites.
3) NWA 7034's composition is unlike SNC meteorites but matches basalts analyzed at Gusev Crater and the average martian crust measured by orbiters, providing the
Propagation of highly_efficient_star_formation_in_ngc7000Sérgio Sacani
This document summarizes observations of molecular gas and star formation in the NGC 7000 molecular cloud and HII region. The key points are:
1. Five dense molecular clumps were identified in NGC 7000 based on NH3 emission, with sizes of 0.2-1 pc and masses of 9-452 solar masses.
2. The clumps have similar gas temperatures of 11-15K but different levels of star formation activity, from concentrations of T-Tauri stars to associations with H2O maser sources.
3. The star formation activities appear related to the geometry of the HII region, with the clump near the HII region boundary having the highest star formation efficiency of 36
Ultraviolet signposts of resonant dynamics in the starburst ringed sab galaxy...Sérgio Sacani
1) The document analyzes ultraviolet images of the starburst-ringed galaxy M94, finding emission from the nucleus, inner disk, bright inner ring of H II regions, and two outer knots of hot stars.
2) Optical and ultraviolet spectroscopy of the nucleus and inner disk indicate a 107-108 year old stellar population with some low-level star formation and LINER activity.
3) Analysis of multi-wavelength data suggests that star formation in M94 is being driven by ring-bar dynamics involving structures like the nuclear mini-bar, inner ring, oval disk, and outer ring.
The document summarizes information about the Lagoon Nebula and its surrounding regions. It is located in the Sagittarius-Carina Arm of the Milky Way, about 1.3 kpc away. The Lagoon Nebula contains the young open cluster NGC 6530 (1-3 Myr old), which has several O and B type stars. Younger star formation is ongoing in regions like the Hourglass Nebula and M8 E. The complex structure of the region has been shaped by interactions between massive stars and molecular gas over multiple episodes of star formation.
An energetic stellar_outburst_accompanied_by_circumstellar_light_echoesSérgio Sacani
1) V838 Monocerotis (V838 Mon) underwent an energetic stellar outburst in early 2002, temporarily becoming the brightest star in the Milky Way. 2) Hubble Space Telescope images revealed expanding light echoes in the circumstellar dust surrounding V838 Mon, allowing astronomers to set a minimum distance of over 6 kiloparsecs. 3) The light echoes, combined with the object's high luminosity and evidence that it resides in a binary system, indicate that V838 Mon represents a new class of stellar outburst not fully explained by current models.
This document summarizes a study on the formation of polar ring galaxies through two proposed scenarios: the merging scenario and the accretion scenario. The merging scenario involves a head-on collision between two galaxies, where one becomes the host galaxy and the other's gas forms the polar ring. The accretion scenario involves tidal interactions that allow gas from one galaxy to be accreted by another galaxy to form a polar ring. Through simulations, the study finds that both scenarios can produce stable polar rings, but that the accretion scenario better matches observed properties of polar ring galaxies, such as the frequency and morphology of the rings. The study concludes the accretion scenario is both more likely and more supported by observations to explain how most polar ring galaxies form.
Analysis of most_light_curves_of_five_young_stars_in_taurus_auriga_and_lupus_3...Sérgio Sacani
This document analyzes light curves from the MOST satellite of five young stars in star-forming regions. Light curves of three spotted weak-line T Tauri stars (V410 Tau, V987 Tau, and Lupus 3-14) show small values of the solar-type differential rotation parameter, indicating slightly non-rigid rotation. Light curves of another spotted weak-line T Tauri star (Lupus 3-48) are consistent with rigid rotation. Three similar flares were detected in the light curve of Lupus 3-14. The light curve of the classical T Tauri star RY Tau showed continuous decreasing brightness over three weeks of observation with variable modulation and no obvious periodic signal.
Unique Meteorite from Early Amazonian Mars: Water-Rich Basaltic Breccia North...Carlos Bella
1) NWA 7034 is a 319.8g martian meteorite found in Morocco in 2011. It is a porous basaltic breccia composed of feldspar and pyroxene phenocrysts in a fine-grained groundmass.
2) Chemical and isotopic analyses indicate it formed on Mars 2.089 billion years ago from a magma enriched in the martian crust. It contains over 6000ppm water, more than most martian meteorites.
3) NWA 7034 matches basalts analyzed at Gusev Crater by the Mars Exploration Rover and the average martian crust measured by orbiters, unlike other martian meteorites. Its composition suggests
1) NWA 7034 is a 319.8g martian meteorite found in Morocco in 2011. It is a porous basaltic breccia composed of feldspar and pyroxene phenocrysts in a fine-grained groundmass containing magnetite.
2) Chemical and isotopic analyses indicate NWA 7034 formed on Mars 2.089 billion years ago from a geochemically enriched crustal source. It contains over 6000ppm water, more than most martian meteorites.
3) NWA 7034's composition is unlike SNC meteorites but matches basalts analyzed at Gusev Crater and the average martian crust measured by orbiters, providing the
Stars and gas_in_the_very_large_interacting_galaxy_ngc6872Sérgio Sacani
This document summarizes observations of stars and gas in the interacting galaxy NGC 6872 using radio telescope data and numerical simulations. It finds:
1) NGC 6872 contains 1.4x1010 solar masses of atomic hydrogen gas distributed in an extended rotating disk.
2) Massive gas concentrations of about 109 solar masses are detected at the tips of both tidal tails and in the northern optical arm near a companion galaxy.
3) Simulations reproducing the galaxy's morphology, inner bar, tidal tail extent and thinness support a gravitational interaction scenario with a small nearby companion galaxy.
Modulations in the_radio_light_curve_of_the_typeiib_supernova_2001igSérgio Sacani
This document summarizes radio observations of the Type IIb supernova SN 2001ig made with the Australia Telescope Compact Array and Very Large Array over 700 days. The observations found periodic deviations from the standard model of radio light curves that are consistent with recurring density modulations in the circumstellar medium with a period of around 150 days. This provides evidence that the progenitor was a Wolf-Rayet star in a binary system with an eccentric 100 day orbit, causing regular build-up of circumstellar material. Such binary systems are thought to produce Type Ib/c supernovae through envelope stripping, linking these events to Type IIb supernovae.
This document presents the results of a study of 32 Bok globules, which are small, isolated molecular clouds that often contain young stellar objects. Millimeter and submillimeter continuum images were used to detect dust emission from star-forming cores within the globules. These data, along with infrared images and spectral energy distributions, were analyzed to determine the physical properties and evolutionary stages of the embedded sources. Submillimeter dust emission was detected in 26 globules, and the analysis identified 9 starless cores, 9 Class 0 protostars, and 12 Class I young stellar objects. The study found evidence that at least two-thirds of the globules studied were forming multiple stars within distances of 1,000-50,000 AU of each
This document discusses observations of extended X-ray and H-alpha emission about 11 arcminutes (11.6 kpc) north of the starburst galaxy M82. The total H-alpha flux from this region is 1.5×10−13 erg s−1 cm−2, comprising about 0.3% of M82's total H-alpha flux. Diffuse soft X-ray emission is also seen in the same region. The X-ray spectrum is well fit by a thermal plasma model with a temperature of 0.80±0.17 keV. The total unabsorbed X-ray flux is 1.4×10−13 erg s−1 cm−2, comprising about 0
Hard xray emission_in_the_star_formation_region_on2Sérgio Sacani
This document reports on XMM-Newton observations of the star-forming region ON 2 and the massive star cluster Berkeley 87. Diffuse hard X-ray emission was detected from two regions within ON 2 - the northern region ON 2N, encompassing the H II regions GAL 75.84+0.40 and GAL 75.84+0.36, and the southern region ON 2S adjacent to the ultra-compact H II region Cygnus 2N. The emission from ON 2N has a luminosity of 10^32 erg/s and can be fit by either a thermal plasma model above 30 MK or a power-law model with gamma=-2.6. The emission from ON 2S has a
Star formation history_in_the_smc_the_case_of_ngc602Sérgio Sacani
This document summarizes a study of the star formation history in the NGC 602 region of the Small Magellanic Cloud based on Hubble Space Telescope observations. Deep photometry reveals numerous pre-main sequence stars as well as young stars on the main sequence, allowing the study of star formation into recent times. New pre-main sequence stellar evolutionary tracks are presented. A stellar population synthesis code is used to derive the best estimate of the star formation history by comparing observed and synthetic color-magnitude diagrams. The star formation rate in the region has increased over the past tens of Myr, reaching 0.3-0.7×10−3 M☉ yr−1 in the last 2.5 Myr, comparable to
Dust production and_particle_acceleration_in_supernova_1987_a_revealed_with_almaSérgio Sacani
This document presents spatially resolved submillimeter observations of supernova remnant SN 1987A using the Atacama Large Millimeter/Submillimeter Array (ALMA). The observations reveal that at longer wavelengths (2.8 mm - 1.4 mm), the emission is from a torus associated with the supernova shock wave, while at shorter wavelengths (870 μm - 450 μm) the emission is dominated by the inner supernova ejecta. For the first time, the dust emission is unambiguously shown to originate from the inner ejecta rather than from the surrounding material, supporting theoretical models of significant dust production in supernovae. The observations also allow separation of synchrotron emission from shock-accelerated particles in
This document summarizes observations of IGR J12580+0134, a newly discovered hard X-ray source associated with the Seyfert 2 galaxy NGC 4845, which underwent an unusual X-ray flare. Follow-up observations with XMM-Newton, Swift, MAXI, and INTEGRAL are presented and analyzed. The spectrum is well described by an absorbed power law plus soft excess. The hard X-ray flux increased over weeks and decreased over a year as expected for a tidal disruption event. Fast variations near peak allowed estimating the black hole mass as ∼3×105 M⊙, indicating disruption of ∼10% of a 14-30 Jupiter mass object. Hard X-ray emission is from a corona forming
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
Three newly discovered_globular_clusters_in_ngc6822Sérgio Sacani
This document describes the discovery of three new globular clusters in the Local Group dwarf irregular galaxy NGC 6822. The authors present optical photometry of the clusters from archival CFHT/Megacam data. Two clusters are luminous and compact, while the third is a lower luminosity diffuse cluster. The positions of the new clusters are consistent with the linear alignment of previously known clusters in NGC 6822. Studying globular cluster systems in dwarf galaxies provides insights into the formation of larger galaxies through accretion and mergers.
1. VFTS 682 is a very massive star located 29 pc in projection from the young massive cluster R136 in the Tarantula Nebula of the LMC.
2. Spectral modeling finds it has an unusually high luminosity of log(L/L) = 6.5, corresponding to a present-day mass of ~150 solar masses.
3. Its isolation and mass pose the question of whether it formed in situ, which would profoundly impact theories of massive star formation, or if it was ejected from R136, making it the most massive runaway star known.
A possible carbonrich_interior_in_superearth_55_cancrieSérgio Sacani
1) The document analyzes the possibility that the interior of the super-Earth exoplanet 55 Cancri e could be carbon-rich rather than oxygen-rich.
2) Models that assume an oxygen-rich interior with iron, silicates, and a water envelope cannot fully explain 55 Cancri e's mass and radius measurements. However, a carbon-rich interior containing iron, silicon carbide, and/or carbon could explain the observations without needing a volatile envelope.
3) A carbon-rich interior for 55 Cancri e is plausible given the reported carbon-rich composition of its host star, though more data is needed on the star's elemental abundances and the planet's atmosphere.
Multi wavelenth observations and surveys of galaxy clustersJoana Santos
This document provides an overview of galaxy clusters, focusing on their baryonic components (intracluster medium and galaxies) and how they relate to the cluster's physical properties like mass. It discusses that galaxy clusters form hierarchically through gravitational collapse. The intracluster medium, which makes up most of the baryonic mass, emits X-rays and has been heated to temperatures of millions of degrees. The document reviews properties of the intracluster medium like density, temperature, metallicity, and how they can be measured from X-ray spectra. It also discusses upcoming surveys that will advance the study of galaxy clusters.
This document summarizes an X-ray study of the supernova remnant G352.7-0.1 using data from XMM-Newton and Chandra observations. Prior observations revealed G352.7-0.1 has a shell-like radio morphology but center-filled thermal X-ray morphology, classifying it as a mixed-morphology supernova remnant. The new observations confirm the X-ray emission comes from the interior and is dominated by ejecta. Spectra from XMM-Newton are fit by a single thermal component with enhanced silicon and sulfur. Some Chandra spectra require a second thermal component to fit, with solar abundances providing a better physical model. No evidence of overionization was found. A neutron
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.
Early optical spectra_of_nova_v1369_cen_show_the_presence_of_lithiumSérgio Sacani
O elemento químico lítio foi encontrado pela primeira vez em material ejetado por uma nova. Observações da Nova Centauri 2013 obtidas com o auxílio de telescópios no Observatório de La Silla do ESO e perto de Santiago do Chile, ajudaram a explicar por que é que muitas estrelas jovens parecem ter mais quantidade deste elemento químico do que o esperado. Esta nova descoberta acrescenta uma importante peça que faltava ao quebra-cabeças que representa a evolução química da nossa Galáxia e é um enorme passo em frente na compreensão das quantidades dos diferentes elementos químicos nas estrelas da Via Láctea.
O elemento químico leve lítio é um dos poucos elementos que se prevê ter sido criado pelo Big Bang, há 13,8 bilhões de anos atrás. No entanto, tentar compreender as quantidades de lítio observadas nas estrelas que nos rodeiam hoje tem sido um processo muito difícil. Estrelas mais velhas possuem menos lítio do que o esperado [1] e algumas estrelas jovens têm dez vezes mais lítio do que o que pensávamos [2].
Desde os anos 1970 que os astrônomos especulam que a enorme quantidade de lítio encontrado nas estrelas jovens poderá vir de novas — explosões estelares que libertam material para o espaço entre as estrelas, contribuindo assim para a matéria que forma a próxima geração de estrelas. No entanto, observações cuidadas de várias novas não tinham, até agora, fornecido resultados claros.
Uma equipe liderada por Luca Izzo (Universidade Sapienza de Roma e ICRANet, Pescara, Itália) utilizou o instrumento FEROS montado no telescópio MPG/ESO de 2,2 metros instalado no Observatório de La Silla, assim como o espectrógrafo PUCHEROS montado no telescópio de 0,5 metros do ESO, no Observatório da Pontificia Universidad Catolica de Chile em Santa Marina, perto de Santiago, para estudar a nova Nova Centauri 2013 (V1369 Centauri). Esta estrela explodiu no céu austral perto da estrela brilhante Beta Centauri em dezembro de 2013, tratando-se, até agora, da nova mais brilhante deste século — facilmente observada a olho nu [3].
This document summarizes a study that used optical, infrared, and submillimeter data to examine star formation in the region surrounding the IC 348 star cluster and the nearby Flying Ghost Nebula. The study identified 13 protostars driving protostellar outflows in the region, including HH 211 which had not previously been detected at visible wavelengths. The region surrounding the Flying Ghost Nebula shows ongoing star formation with outflows similar to other areas of moderate star formation in Perseus. A candidate bent jet was also found, which may have been ejected from a multiple star system near IC 348.
1) The VMC survey is using the VISTA telescope to survey the Magellanic Cloud system, including the LMC, SMC, Magellanic Bridge, and Magellanic Stream, in the near-infrared Y, J, and Ks bands.
2) The goals of the survey are to determine the spatially resolved star formation history and three-dimensional structure of the Magellanic system by observing faint stars, including the oldest main sequence turnoff points and pulsating variables.
3) This paper presents first results from observations of 7% of planned LMC fields from November 2009 to March 2010, which show the data agree with sensitivity expectations and derive uncertainties and completeness. Preliminary
Planetary system disruption_by_galactic _perturbations_to_wide_binary_starsSérgio Sacani
The document summarizes simulations showing that perturbations from the Milky Way can disrupt planetary systems in wide binary star systems (average separations over 1,000 AU) by driving variations in the binary orbit.
Specifically:
- Simulations found that 30-60% of planetary systems in wide binaries experience instabilities causing planetary ejections over 10 billion years due to low binary pericentre passages driven by Galactic tides.
- The eccentricity distribution of giant exoplanets in wide binaries is significantly higher than around single stars, consistent with additional scattering triggered by time-varying binary companions.
- Additional simulations reproduced the observed eccentricity distributions by assuming similar initial planetary systems that undergo scattering both in isolation and with a distant
Stars and gas_in_the_very_large_interacting_galaxy_ngc6872Sérgio Sacani
This document summarizes observations of stars and gas in the interacting galaxy NGC 6872 using radio telescope data and numerical simulations. It finds:
1) NGC 6872 contains 1.4x1010 solar masses of atomic hydrogen gas distributed in an extended rotating disk.
2) Massive gas concentrations of about 109 solar masses are detected at the tips of both tidal tails and in the northern optical arm near a companion galaxy.
3) Simulations reproducing the galaxy's morphology, inner bar, tidal tail extent and thinness support a gravitational interaction scenario with a small nearby companion galaxy.
Modulations in the_radio_light_curve_of_the_typeiib_supernova_2001igSérgio Sacani
This document summarizes radio observations of the Type IIb supernova SN 2001ig made with the Australia Telescope Compact Array and Very Large Array over 700 days. The observations found periodic deviations from the standard model of radio light curves that are consistent with recurring density modulations in the circumstellar medium with a period of around 150 days. This provides evidence that the progenitor was a Wolf-Rayet star in a binary system with an eccentric 100 day orbit, causing regular build-up of circumstellar material. Such binary systems are thought to produce Type Ib/c supernovae through envelope stripping, linking these events to Type IIb supernovae.
This document presents the results of a study of 32 Bok globules, which are small, isolated molecular clouds that often contain young stellar objects. Millimeter and submillimeter continuum images were used to detect dust emission from star-forming cores within the globules. These data, along with infrared images and spectral energy distributions, were analyzed to determine the physical properties and evolutionary stages of the embedded sources. Submillimeter dust emission was detected in 26 globules, and the analysis identified 9 starless cores, 9 Class 0 protostars, and 12 Class I young stellar objects. The study found evidence that at least two-thirds of the globules studied were forming multiple stars within distances of 1,000-50,000 AU of each
This document discusses observations of extended X-ray and H-alpha emission about 11 arcminutes (11.6 kpc) north of the starburst galaxy M82. The total H-alpha flux from this region is 1.5×10−13 erg s−1 cm−2, comprising about 0.3% of M82's total H-alpha flux. Diffuse soft X-ray emission is also seen in the same region. The X-ray spectrum is well fit by a thermal plasma model with a temperature of 0.80±0.17 keV. The total unabsorbed X-ray flux is 1.4×10−13 erg s−1 cm−2, comprising about 0
Hard xray emission_in_the_star_formation_region_on2Sérgio Sacani
This document reports on XMM-Newton observations of the star-forming region ON 2 and the massive star cluster Berkeley 87. Diffuse hard X-ray emission was detected from two regions within ON 2 - the northern region ON 2N, encompassing the H II regions GAL 75.84+0.40 and GAL 75.84+0.36, and the southern region ON 2S adjacent to the ultra-compact H II region Cygnus 2N. The emission from ON 2N has a luminosity of 10^32 erg/s and can be fit by either a thermal plasma model above 30 MK or a power-law model with gamma=-2.6. The emission from ON 2S has a
Star formation history_in_the_smc_the_case_of_ngc602Sérgio Sacani
This document summarizes a study of the star formation history in the NGC 602 region of the Small Magellanic Cloud based on Hubble Space Telescope observations. Deep photometry reveals numerous pre-main sequence stars as well as young stars on the main sequence, allowing the study of star formation into recent times. New pre-main sequence stellar evolutionary tracks are presented. A stellar population synthesis code is used to derive the best estimate of the star formation history by comparing observed and synthetic color-magnitude diagrams. The star formation rate in the region has increased over the past tens of Myr, reaching 0.3-0.7×10−3 M☉ yr−1 in the last 2.5 Myr, comparable to
Dust production and_particle_acceleration_in_supernova_1987_a_revealed_with_almaSérgio Sacani
This document presents spatially resolved submillimeter observations of supernova remnant SN 1987A using the Atacama Large Millimeter/Submillimeter Array (ALMA). The observations reveal that at longer wavelengths (2.8 mm - 1.4 mm), the emission is from a torus associated with the supernova shock wave, while at shorter wavelengths (870 μm - 450 μm) the emission is dominated by the inner supernova ejecta. For the first time, the dust emission is unambiguously shown to originate from the inner ejecta rather than from the surrounding material, supporting theoretical models of significant dust production in supernovae. The observations also allow separation of synchrotron emission from shock-accelerated particles in
This document summarizes observations of IGR J12580+0134, a newly discovered hard X-ray source associated with the Seyfert 2 galaxy NGC 4845, which underwent an unusual X-ray flare. Follow-up observations with XMM-Newton, Swift, MAXI, and INTEGRAL are presented and analyzed. The spectrum is well described by an absorbed power law plus soft excess. The hard X-ray flux increased over weeks and decreased over a year as expected for a tidal disruption event. Fast variations near peak allowed estimating the black hole mass as ∼3×105 M⊙, indicating disruption of ∼10% of a 14-30 Jupiter mass object. Hard X-ray emission is from a corona forming
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
Three newly discovered_globular_clusters_in_ngc6822Sérgio Sacani
This document describes the discovery of three new globular clusters in the Local Group dwarf irregular galaxy NGC 6822. The authors present optical photometry of the clusters from archival CFHT/Megacam data. Two clusters are luminous and compact, while the third is a lower luminosity diffuse cluster. The positions of the new clusters are consistent with the linear alignment of previously known clusters in NGC 6822. Studying globular cluster systems in dwarf galaxies provides insights into the formation of larger galaxies through accretion and mergers.
1. VFTS 682 is a very massive star located 29 pc in projection from the young massive cluster R136 in the Tarantula Nebula of the LMC.
2. Spectral modeling finds it has an unusually high luminosity of log(L/L) = 6.5, corresponding to a present-day mass of ~150 solar masses.
3. Its isolation and mass pose the question of whether it formed in situ, which would profoundly impact theories of massive star formation, or if it was ejected from R136, making it the most massive runaway star known.
A possible carbonrich_interior_in_superearth_55_cancrieSérgio Sacani
1) The document analyzes the possibility that the interior of the super-Earth exoplanet 55 Cancri e could be carbon-rich rather than oxygen-rich.
2) Models that assume an oxygen-rich interior with iron, silicates, and a water envelope cannot fully explain 55 Cancri e's mass and radius measurements. However, a carbon-rich interior containing iron, silicon carbide, and/or carbon could explain the observations without needing a volatile envelope.
3) A carbon-rich interior for 55 Cancri e is plausible given the reported carbon-rich composition of its host star, though more data is needed on the star's elemental abundances and the planet's atmosphere.
Multi wavelenth observations and surveys of galaxy clustersJoana Santos
This document provides an overview of galaxy clusters, focusing on their baryonic components (intracluster medium and galaxies) and how they relate to the cluster's physical properties like mass. It discusses that galaxy clusters form hierarchically through gravitational collapse. The intracluster medium, which makes up most of the baryonic mass, emits X-rays and has been heated to temperatures of millions of degrees. The document reviews properties of the intracluster medium like density, temperature, metallicity, and how they can be measured from X-ray spectra. It also discusses upcoming surveys that will advance the study of galaxy clusters.
This document summarizes an X-ray study of the supernova remnant G352.7-0.1 using data from XMM-Newton and Chandra observations. Prior observations revealed G352.7-0.1 has a shell-like radio morphology but center-filled thermal X-ray morphology, classifying it as a mixed-morphology supernova remnant. The new observations confirm the X-ray emission comes from the interior and is dominated by ejecta. Spectra from XMM-Newton are fit by a single thermal component with enhanced silicon and sulfur. Some Chandra spectra require a second thermal component to fit, with solar abundances providing a better physical model. No evidence of overionization was found. A neutron
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.
Early optical spectra_of_nova_v1369_cen_show_the_presence_of_lithiumSérgio Sacani
O elemento químico lítio foi encontrado pela primeira vez em material ejetado por uma nova. Observações da Nova Centauri 2013 obtidas com o auxílio de telescópios no Observatório de La Silla do ESO e perto de Santiago do Chile, ajudaram a explicar por que é que muitas estrelas jovens parecem ter mais quantidade deste elemento químico do que o esperado. Esta nova descoberta acrescenta uma importante peça que faltava ao quebra-cabeças que representa a evolução química da nossa Galáxia e é um enorme passo em frente na compreensão das quantidades dos diferentes elementos químicos nas estrelas da Via Láctea.
O elemento químico leve lítio é um dos poucos elementos que se prevê ter sido criado pelo Big Bang, há 13,8 bilhões de anos atrás. No entanto, tentar compreender as quantidades de lítio observadas nas estrelas que nos rodeiam hoje tem sido um processo muito difícil. Estrelas mais velhas possuem menos lítio do que o esperado [1] e algumas estrelas jovens têm dez vezes mais lítio do que o que pensávamos [2].
Desde os anos 1970 que os astrônomos especulam que a enorme quantidade de lítio encontrado nas estrelas jovens poderá vir de novas — explosões estelares que libertam material para o espaço entre as estrelas, contribuindo assim para a matéria que forma a próxima geração de estrelas. No entanto, observações cuidadas de várias novas não tinham, até agora, fornecido resultados claros.
Uma equipe liderada por Luca Izzo (Universidade Sapienza de Roma e ICRANet, Pescara, Itália) utilizou o instrumento FEROS montado no telescópio MPG/ESO de 2,2 metros instalado no Observatório de La Silla, assim como o espectrógrafo PUCHEROS montado no telescópio de 0,5 metros do ESO, no Observatório da Pontificia Universidad Catolica de Chile em Santa Marina, perto de Santiago, para estudar a nova Nova Centauri 2013 (V1369 Centauri). Esta estrela explodiu no céu austral perto da estrela brilhante Beta Centauri em dezembro de 2013, tratando-se, até agora, da nova mais brilhante deste século — facilmente observada a olho nu [3].
This document summarizes a study that used optical, infrared, and submillimeter data to examine star formation in the region surrounding the IC 348 star cluster and the nearby Flying Ghost Nebula. The study identified 13 protostars driving protostellar outflows in the region, including HH 211 which had not previously been detected at visible wavelengths. The region surrounding the Flying Ghost Nebula shows ongoing star formation with outflows similar to other areas of moderate star formation in Perseus. A candidate bent jet was also found, which may have been ejected from a multiple star system near IC 348.
1) The VMC survey is using the VISTA telescope to survey the Magellanic Cloud system, including the LMC, SMC, Magellanic Bridge, and Magellanic Stream, in the near-infrared Y, J, and Ks bands.
2) The goals of the survey are to determine the spatially resolved star formation history and three-dimensional structure of the Magellanic system by observing faint stars, including the oldest main sequence turnoff points and pulsating variables.
3) This paper presents first results from observations of 7% of planned LMC fields from November 2009 to March 2010, which show the data agree with sensitivity expectations and derive uncertainties and completeness. Preliminary
Planetary system disruption_by_galactic _perturbations_to_wide_binary_starsSérgio Sacani
The document summarizes simulations showing that perturbations from the Milky Way can disrupt planetary systems in wide binary star systems (average separations over 1,000 AU) by driving variations in the binary orbit.
Specifically:
- Simulations found that 30-60% of planetary systems in wide binaries experience instabilities causing planetary ejections over 10 billion years due to low binary pericentre passages driven by Galactic tides.
- The eccentricity distribution of giant exoplanets in wide binaries is significantly higher than around single stars, consistent with additional scattering triggered by time-varying binary companions.
- Additional simulations reproduced the observed eccentricity distributions by assuming similar initial planetary systems that undergo scattering both in isolation and with a distant
This document summarizes the discovery of two planetary companions orbiting the metal-poor star HIP 11952 based on radial velocity measurements. The star HIP 11952 was observed over a period of 16 months using the FEROS spectrograph. Analysis of the spectra revealed periodic radial velocity variations of 6.95 days and 290 days, indicating the presence of two planets with minimum masses of 0.78 MJup and 2.93 MJup orbiting at 0.07 AU and 0.81 AU, respectively. HIP 11952 is a metal-poor star with [Fe/H] of -1.95, making it one of the few known systems with planets orbiting a star with such low metallicity
Evidence for water_ice_near_mercury_north_pole_from_messenger_neutron_spectro...Sérgio Sacani
The MESSENGER spacecraft's Neutron Spectrometer detected decreases in the flux of epithermal and fast neutrons from Mercury's north polar region. This is consistent with the presence of water ice in permanently shadowed craters near the north pole. Analysis of the neutron data indicates the polar deposits contain a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer 10 to 30 cm thick that is less rich in hydrogen. The buried layer likely consists of nearly pure water ice, while the upper layer contains less than 25% water by weight. The total mass of water at Mercury's poles is estimated to be between 2×1016 and 1018 grams.
1) Lunar Orbiter tracking data revealed large mass concentrations (mascons) beneath the lunar maria.
2) The largest mascons were found beneath Mare Imbrium, Mare Serenitatis, Mare Crisium, Mare Humorum, and Mare Nectaris.
3) The mascons suggest a relationship between the formation of the maria and large impact events on the lunar surface.
The document summarizes observations of two giant radio lobes emanating from the center of the Milky Way galaxy. The lobes extend about 60 degrees from the galactic center and correspond closely with previously observed gamma-ray "Fermi bubbles". The lobes contain three ridge-like substructures that curve towards the galactic west as they extend away from the center. Strong magnetic fields of up to 15 microgauss permeate the lobes. The observations indicate that the radio lobes originate from a biconical outflow driven by intense star formation in the galactic center, rather than activity from the supermassive black hole, and have transported a huge amount of magnetic energy into the galactic halo over at least the past 10 million years.
The document presents evidence for azimuthal variations in cosmic ray ion acceleration at the blast wave of the supernova remnant SN 1006. Using radio, X-ray, and optical observations, the researchers find that the ratio of radii between the blast wave and contact discontinuity varies azimuthally, being smallest in the brightest synchrotron emission regions, indicating more efficient cosmic ray acceleration. They interpret this as evidence that the injection rate, magnetic field strength, and turbulence level - which influence cosmic ray acceleration - all vary azimuthally and are highest in the brightest regions.
This document reports the detection of five planets orbiting the star Kepler-62, including two super-Earth-size planets (Kepler-62e and Kepler-62f) in the habitable zone of the star. Kepler-62e receives 1.2 times the solar flux at Earth's orbit, while Kepler-62f receives 0.41 times the solar flux. Theoretical models suggest that both planets could be solid, with either a rocky composition or composed mostly of solid water.
The MESSENGER mission aims to study Mercury through flybys in 2008-2009 and orbital observations beginning in 2011. It launched in 2004 and will use gravity assists at Earth and Venus to reach Mercury's orbit. The spacecraft faces challenges from Mercury's intense solar radiation and requires a large velocity change to achieve orbit. It carries 7 miniaturized instruments to characterize Mercury's composition, geology, magnetic field, exosphere, and magnetosphere. The flybys and orbital phase aim to address outstanding questions about Mercury's formation and evolution.
Glaciers and ice caps (GICs), excluding those in Greenland and Antarctica, lost mass at a rate of 148 +/- 30 Gt yr-1 from 2003 to 2010 according to a study using GRACE satellite gravity measurements. This contributed 0.41 +/- 0.08 mm yr-1 to global sea level rise. The GIC loss rate was about 30% lower than previous estimates. Additionally, Greenland and Antarctic ice sheets, including peripheral GICs, contributed 1.06 +/- 0.19 mm yr-1 to sea level rise. In total, all ice-covered regions contributed 1.48 +/- 0.26 mm yr-1 to sea level rise over this period according to the study.
Evidence for a_complex_enrichment_history_of_the_stream_from_fairall_9_sightlineSérgio Sacani
This study analyzes absorption spectra of the Magellanic Stream (MS) toward the quasar Fairall 9, obtained using the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) and the Very Large Telescope Ultraviolet and Visible Echelle Spectrograph (VLT/UVES). The spectra reveal absorption from multiple velocity components of the MS, indicating multiphase gas. Surprisingly, the sulfur abundance is found to be high ([S/H] = -0.30), five times higher than other MS sightlines, while the nitrogen abundance is lower ([N/H] = -1.15). This points to a complex enrichment history, where the gas toward Fair
Ancient igneous intrusions_and_early_expansion_of_the_moon_revealed_by_grailSérgio Sacani
1) Application of gravity gradiometry to data from the GRAIL mission revealed numerous linear gravity anomalies on the Moon with lengths of hundreds of kilometers.
2) Inversion of the anomalies indicates they are dense vertical intrusions or dikes formed by ancient magmatism during extension of the lunar lithosphere before the end of heavy bombardment.
3) The distribution, orientation, and size of the intrusions suggest they formed as the Moon's radius increased by 0.6-4.9 km early in its history, consistent with predictions of thermal evolution models.
Shaping the glowing_eye_planetary_nebula_ngc6751Sérgio Sacani
This document presents a comprehensive study of the planetary nebula NGC 6751 using spectroscopic observations and imaging. It finds:
1) NGC 6751 has a thick equatorial ring fragmented into knots enclosing a central bubble, surrounded by faint envelope and bipolar lobes with filaments.
2) Kinematic data identify distinct velocities for different components: the outer halo at -15 km/s, inner halo at -31 km/s, and bipolar lobes at ±30 km/s.
3) A 3D morpho-kinematic model is constructed using the SHAPE code that closely matches the observed images and spectra, providing insight into the nebula's complex structure.
The BEER algorithm identified Kepler-76b, a hot Jupiter orbiting an F star, from its Kepler light curve. The light curve showed evidence of the beaming, ellipsoidal, and reflection effects consistent with a planetary companion. Follow-up spectroscopy confirmed Kepler-76b with a mass of 2.0 ± 0.26 MJup and orbital period of 1.5449 days. Analysis of the light curve effects provided evidence that Kepler-76b exhibits atmospheric superrotation, or an eastward jet stream that shifts the hottest atmospheric region.
Diagnostic line ratios_in_the_ic1805_optical_gas_complexSérgio Sacani
This document discusses diagnostic line ratios observed in the IC 1805 optical gas complex, a giant H II region containing at least 10 O-stars. The authors used an imaging Fourier transform spectrometer to obtain spectral information from ionic lines including Hα, [N II], and [S II]. Diagnostic diagrams were used to identify portions of the nebula subject to shock excitation from stellar winds versus those dominated by photoionization. Density ratios of [S II] lines indicate gas compression from supersonic shocks. An anomalous [N II] line ratio is explained by collisional de-excitation affecting the [N II] line.
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.
The document summarizes the first results published by the Alpha Magnetic Spectrometer (AMS) Collaboration. Key points:
- AMS has been collecting data on cosmic rays on the International Space Station since 2011, measuring over 30 billion cosmic rays up to trillions of electron volts.
- In its first 18 months of operations, AMS analyzed 25 billion primary cosmic ray events, including an unprecedented 6.8 million unambiguously identified as electrons and positrons between 0.5-350 GeV.
- AMS precisely measured the positron fraction across this energy range, finding it decreases from 0.5-10 GeV then increases steadily up to 250 GeV before flattening at higher energies. The data shows no
The Curiosity rover analyzed samples of Martian fines from the Rocknest site using its Sample Analysis at Mars (SAM) instrument suite. SAM detected water, sulfur dioxide, carbon dioxide, and oxygen as the major gases released when heating the fines. The water content and release temperature suggest the water is bound in amorphous materials. Much of the carbon dioxide was likely released from the decomposition of fine-grained iron or magnesium carbonates. Elevated levels of deuterium indicate recent interaction with the atmosphere. Several simple organic compounds were detected but are not definitively of Martian origin.
X ray emission-from_strongly_asymmetric_circumstellar_material_in_the_remnant...Sérgio Sacani
This document summarizes a study of X-ray emission from circumstellar material (CSM) in the remnant of Kepler's supernova. The researchers used a statistical technique to isolate X-ray emission from CSM versus ejecta based on spectral characteristics. They found that most CSM is distributed along the bright north rim, but substantial amounts are also projected against the center, indicating a disk-like distribution of CSM from the progenitor system before the supernova. Hydrodynamic simulations support an AGB star companion as the origin of the asymmetric CSM. Quantitative analysis of magnesium emission identifies CSM and requires Kepler to have originated from a close binary system.
Matter ejections behind the highs and lows of the transitional millisecond pu...Sérgio Sacani
Transitional millisecond pulsars are an emerging class of sources linking low-mass X-ray binaries to millisecond radio pulsars in
binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active
state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray
to optical pulsations are observed only during the high mode. Knowledge of the root reason for this puzzling behaviour remains
elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar
prototype, PSR J1023+0038, covering from radio to X-rays. The campaign was carried out over two nights in June 2021, and involved
12 different telescopes and instruments including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA and FAST.
By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by
changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on
top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with A
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.
Rapid disappearance of a warm dusty circumstellar diskCarlos Bella
- The star TYC 8241 2652 1 was observed to have a factor of 30 decrease in mid-infrared dust emission over less than two years, indicating the rapid disappearance of warm, dusty material orbiting the star.
- Observations before 2009 showed significant mid-infrared excess emission, but 2010 observations and later showed the excess had reduced to barely detectable levels.
- No currently available physical model can satisfactorily explain these rapid changes, which suggest a phase of very rapid evolution of dusty planetary collision ejecta that had not been previously predicted or observed.
X rays and-protostars_in_the_trifid_nebulaSérgio Sacani
This document summarizes an astronomical study of the Trifid Nebula using X-ray and infrared observations. The ROSAT X-ray image revealed over a dozen X-ray sources in the nebula, including the bright O7 star that provides most of the ionization. Infrared observations identified 85 young star candidates. Ten X-ray sources had infrared counterparts. Spectroscopy of the brightest X-ray source with ASCA showed unusually hot plasma up to 10 keV, suggesting interaction between winds or flares from embedded young stars.
Jack Oughton - Quark Star Journal 01.pdfJack Oughton
A quark star is a hypothetical type of neutron star that may form if the intense gravitational pressure is enough to overcome nuclear forces, causing neutrons to break down into their constituent quarks. Quark stars are theorized to be even denser than neutron stars, with matter composed of "free quarks" or strange quark matter. They may form from certain massive neutron stars collapsing when beyond the Tolman-Oppenheimer-Volkoff limit. Quark stars could potentially be detected from being over-dense compared to neutron stars of the same mass, through energetic "quark nova" explosions, or by their relationship to mysterious magnetars and superluminous supernovae. However, direct evidence of strange quark matter has
A super earth transiting a naked-eye starSérgio Sacani
This document summarizes the detection of transits of an exoplanet orbiting the star 55 Cnc, using photometry from the MOST space telescope. The transits match the period, phase, duration, and depth predicted for the innermost planet of 55 Cnc, designated 55 Cnc e. Analysis of the transit data indicates the planet has a mass of 8.57 Earth masses, a radius of 1.63 Earth radii, and a dense composition of rock and iron. This makes 55 Cnc e similar to other dense super-Earth exoplanets in short orbits, unlike lower-density super-Earths further from their stars. The brightness of 55 Cnc will enable further study of this transiting exoplanet system.
First detection of_molecular_gas_in_shells_in_cena_galaxySérgio Sacani
This document reports the first detection of molecular gas (CO) in the shells of the galaxy Centaurus A (Cen A), located 15 kpc from the galaxy's center. The ratio of CO to HI emission in the shells matches what is found in the galaxy's central regions, which is unexpected given typical metallicity gradients in galaxies. The detection of molecular gas in the shells provides evidence that molecular gas in galaxy mergers may be spread further from nuclear regions than previously thought. The dynamics of the gas can be understood if the interstellar medium is considered clumpy and less dissipative than assumed, allowing dense gas to orbit with stars and form shells.
This document presents aluminum abundances for about 100 red giant stars in each of the Galactic globular clusters 47 Tuc and M 4. The abundances were derived from intermediate-resolution FLAMES/GIRAFFE spectra, focusing on the Al I doublet at 8772-8773 Å. Previous homogeneous abundances of O, Na, Mg, and Si were also analyzed to study multiple stellar populations in these clusters. The data confirm two stellar populations are visible in M 4, while 47 Tuc shows evidence of at least three distinct stellar groups based on the abundances of O, Na, Mg, Al, and N.
1. Chandra observations of the galaxy NGC 3351 revealed X-ray emission from its circumnuclear star-forming ring that is composed of numerous point-like sources embedded in diffuse hot gas.
2. The morphology of the X-ray emission is similar to but not identical with UV and H-alpha hot spots in the ring, which can be understood if star formation occurs through intermittent starbursts around the ring with different emissions tracing later evolutionary stages.
3. X-ray emission also extends beyond the ring, which is interpreted as outflowing gas from the ring into the disk and halo of NGC 3351, providing evidence for confined outflow near the plane but less restricted outflow perpendicular to
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068Sérgio Sacani
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from
their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both
phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino
emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission
from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the
case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we
show that the entire spectrum of multimessenger data—from radio to γ-rays including the neutrino constraint—can
be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission
region is not sufficient.
A LUMINOUS Be+WHITE DWARF SUPERSOFT SOURCE IN THE WING OF THE SMC: MAXI J0158...Carlos Bella
This document summarizes a study of the X-ray source MAXI J0158-744, which was detected by the MAXI instrument in November 2011. It exhibited an unusually bright and brief X-ray flare with a luminosity exceeding 10^39 erg/s, approaching ultraluminous X-ray source levels. Follow-up observations with Swift and other instruments over subsequent months found the source had a very soft X-ray spectrum characteristic of a supersoft source. Optical spectra of the counterpart revealed emission and absorption features consistent with a B1/2IIIe spectral type star in the Small Magellanic Cloud. The authors propose MAXI J0158-744 is a luminous supersoft source associated with
1) Researchers have developed a new technique called mechanophotopatterning (MPP) that uses light irradiation and mechanical deformation to precisely control the topology of light-responsive elastomers, establishing a new patterning method.
2) Using MPP, a variety of surface topologies can be produced, making it potentially useful for applications. When optically thick samples are irradiated, they bow into 3D shapes with promising applications in advanced optics.
3) The intrinsic material properties of the polymers remain unchanged after deformation, allowing for diverse applications at the interface of cell biology and tissue engineering through dynamic control of mechanical feedback to cells.
Herschel space telescope observations reveal cold dust emitting from Supernova 1987A at a temperature of 17-23 K, indicating a dust mass of 0.4-0.7 solar masses. The dust must originate from the supernova ejecta, requiring efficient precipitation of refractory elements into dust. This implies that supernovae can produce the large dust masses seen in early galaxies.
A polarimetric survey for dust in 47 tucanae (ngc 104)Sérgio Sacani
This document summarizes a polarimetric survey of the globular cluster 47 Tucanae to search for evidence of dust. Polarization measurements were made for 77 stars in the cluster field and 14 star-free regions, as well as multi-color observations of the cluster nucleus. Small but systematically higher polarization residuals were found toward the south of the cluster. Most variable stars showed significant intrinsic polarization. A dark patch located 1200 from the cluster center appeared to have slightly different polarization and is a candidate dust globule within the cluster. The observations set an upper limit on any smooth intracluster light polarization but could not rule out some dust located in the nucleus illuminated by a bright blue star.
A deep dive: Chandra observations of the NGC 4839 group falling into the Coma...Sérgio Sacani
Cosmological simulations of structure formation predict that galaxy clusters continue to grow and evolve through ongoing
mergers with group-scale systems. During these merging events, the ram pressure applied by the intracluster medium acts to strip
the gas from the infalling groups, forming large tails of stripped gas, which eventually become part of the main cluster. In this
work, we present a detailed analysis of our new deep Chandra observations of the NGC 4839 group falling into the nearby Coma
cluster, providing a unique opportunity to explore the way galaxy clusters in the local universe continue to grow. Our analysis
reveals a cold front feature at the leading head of the group, preceded by a bow shock of hot gas in front with a Mach number
of ∼ 1.5. The power spectrum of surface brightness fluctuations in the tail shows that the slope gets less steep as the distance
from the leading head increases, changing from −2.35+0.07
−0.06 at the inner part of the tail to −1.37+0.09
−0.07 at the outermost part of
the tail. These values are shallower than the slope of the Kolmogorov 2D power spectrum, indicating that thermal conduction is
being suppressed throughout the tail, enabling long-lived small-scale turbulence, which would typically be washed out if thermal
conduction was not inhibited. The characteristic amplitude of surface brightness fluctuations in the tail suggests a mild level of
turbulence with a Mach number in the range of 0.1–0.5, agreeing with that found for the infalling group in Abell 2142.
1. The spectrum of the bright Kuiper Belt object 2005 FY9 is dominated by methane absorption features in the near-infrared region. However, the methane absorption lines are significantly broader than seen on any other solar system body, indicating unusually long optical path lengths through methane grains on 2005 FY9, estimated to be around 1 cm in size.
2. In addition to methane, the spectrum also shows clear evidence for ethane, which is expected to form from UV photolysis of methane. No evidence is found for nitrogen or carbon monoxide, both known to be present on Pluto.
3. The differences between 2005 FY9's spectrum and those of Pluto and 2003 UB313 are suggested
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.
Rings in the_haloes_of_planetary_nebulaeSérgio Sacani
This document presents the discovery of ring structures in the haloes of eight planetary nebulae, tripling the number known to have such rings. The rings are analyzed using image processing techniques to enhance their visibility. They find ring spacings range from less than 0.01 pc to 0.06 pc. This suggests ring spacing increases with time after the asymptotic giant branch phase. The properties of the rings support predictions of dust-driven wind instability models of mass loss but do not rule out other models. Analyzing the new detections provides insights into mass modulation processes late in stellar evolution.
Similar to An analysis of_a_spectrum_of_v838_monocerotis_in_october_2005 (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.
Continuum emission from within the plunging region of black hole discs
An analysis of_a_spectrum_of_v838_monocerotis_in_october_2005
1. Astronomy & Astrophysics manuscript no. PAP˙II˙AA c ESO 2013
February 20, 2013
An analysis of a spectrum of V838 Monocerotis in October 2005
R. Tylenda, T. Kami´ ski, and M. Schmidt
n
Department for Astrophysics, N. Copernicus Astronomical Center, Rabia´ ska 8, 87-100 Toru´ , Poland
n n
e-mail: tylenda@ncac.torun.pl, tomkam@ncac.torun.pl, schmidt@ncac.torun.pl
arXiv:0907.0572v1 [astro-ph.SR] 3 Jul 2009
Received; accepted
ABSTRACT
Context. V838 Mon erupted at the beginning of 2002 becoming an extremely luminous star with L = 106 L⊙ . Among various
scenarios proposed to explain the nature of the outburst, the most promising is a stellar merger event.
Aims. We attempt to obtain information about the structure and evolution of the object in the decline from the 2002 eruption.
Methods. The results of spectroscopic observations of the object obtained in October 2005 with the Keck/HIRES instrument,
presented in detail in Paper I, are analysed and discussed. Modelling of the observed line profiles has been used to constrain the
physical parameters of the system.
Results. The kinematics of the atmosphere of V838 Mon is very complex. Our analysis of the molecular bands and the P-Cyg profiles
of atomic lines shows that the object loses matter with a velocity of up to 215 km s−1 and a rate of 10−6 − 10−5 M⊙ yr−1 . In the
profiles of some atomic lines, we have, however, found evidence of matter infall. Moreover, a narrow absorption component, which
is particularly strong in some P-Cyg profiles, may indicate that a jet-like outflow has also been formed.
We show that the observed emission in the [Fe II] lines and an eclipse-like event observed in November/December 2006 was probably
caused by interactions of the expanding matter, ejected by V838 Mon in 2002, with radiation from the B3V companion. In particular,
the observed profiles of the [Fe II] lines can be easily modelled in this scenario and allow us to estimate parameters of the system,
such as the position of the B3V companion relative to V838 Mon and the line of sight, density in the outflowing matter, and mass lost
in the 2002 eruption. The observed appearance of strong Hα emission, just before and during the eclipse-like event, can be interpreted
as a result of the accretion of the outflowing matter onto the B3V companion: the accreted matter, shocked above the stellar surface,
can be a source of extreme-UV and soft X-ray radiation capable of ionizing and exciting H in the outflow.
Key words. stars: individual: V838 Mon – stars: late-type – stars: mass loss – stars: peculiar – stars: winds, outflows – line: profiles
1. Introduction 2. Evolution of V838 Mon during the decline after
The eruption of V838 Monocerotis was discovered at the the 2002 eruption
beginning of January 2002. As observed in the optical, A few months after the eruption, discovered at the beginning
the eruption lasted about three months (Munari et al., 2002a; of January 2002, V838 Mon entered a relatively calm decline
Kimeswenger et al., 2002; Crause et al., 2003). During the phase. V838 Mon then resembled a very cool oxygen-
event, the object reached a luminosity of ∼ 106 L⊙ . After rich (C/O < 1) supergiant slowly declining in luminosity
developing an A–F supergiant spectrum at the maximum (Evans et al., 2003; Tylenda, 2005; Munari et al., 2007b). It
in the beginning of February 2002, the object evolved to dominated the observed spectrum at green, red and infrared
lower effective temperatures and in April 2002 was practically wavelengths. The blue part of the spectrum was dominated by
unable to be detected in the optical, remaining very bright the light of the B3V companion.
however in the infrared. Optical spectroscopy acquired at
that time discovered a B3V companion of the erupted object Late in 2004, narrow emission lines, belonging mostly
(Munari et al., 2002b). Tylenda (2005) analysed the evolution of to [Fe II], appeared mainly in the blue part of the spectrum
V838 Mon during outburst and early decline. (Barsukova et al., 2006), and strengthened in time (Munari et al.,
Different outburst mechanisms, including an unusual nova, 2007a). During November–December 2006, an eclipse-like
a He-shell flash, and a stellar merger, were proposed to explain event of the B3V companion was observed (Bond, 2006;
the eruption of V838 Mon. These mechanisms were critically Munari et al., 2007a). At the epoch of the event, the [Fe II]
discussed by Tylenda & Soker (2006), the authors conclude that emission lines reached their maximum strength and strong
the only mechanism that could satisfactorily account for the emission in Balmer lines appeared (Munari et al., 2007a).
observational data was a collision and merger of a low-mass pre- In October 2005, we obtained an optical spectrum of
main-sequence star with an ∼ 8 M⊙ main-sequence star. V838 Mon using the Keck/HIRES instrument. Results of these
In Kami´ ski et al. (2009) (hereinafter referred to as Paper I),
n observations were presented in Paper I. The star V838 Mon itself
a high resolution spectrum of V838 Mon acquired with the is seen as a very cool supergiant that dominates the green and red
Keck I telescope in October 2005 was presented. In the present parts of the spectrum. Numerous, often very deep and complex,
paper, we analyse and discuss the results obtained from this molecular absorption bands are the main spectral characteristics
spectrum. of this component. All the bands are from oxides and include
TiO, VO, AlO, ScO, and YO. The excitation temperature derived
Send offprint requests to: R. Tylenda from the bands ranges from ∼ 2500 K, identified also as the
2. photospheric temperature of V838 Mon, down to ∼ 500 K,
which presumably corresponds to outflowing matter at a few
stellar radii. The most positive (heliocentric) radial velocity
derived from the bands is ∼ 58 km s−1 , which we propose
to be the radial velocity of V838 Mon itself. Several atomic
lines, mostly resonance, display P-Cyg profiles. They provide
evidence of an intense mass outflow with a typical velocity of
∼ 150 km s−1 . The blue part of the spectrum is dominated by the
spectrum of the B3V companion. The values of T eff and log g
derived from the spectrum agree well with those implied by the
spectral type. The star is a rapid rotator (V sin i ≃ 250 km s−1 )
and its (heliocentric) radial velocity is ∼ 40 km s−1 . Numerous
emission lines were identified, mainly in the blue part of the
spectrum. They correspond predominantly to [Fe II] and exhibit
the same profile, which can be fitted well with a Lorentzian
profile. The lines are centred on a heliocentric radial velocity
of ∼ 13 km s−1 and have a FWHM of ∼ 80 km s−1 . Fig. 1. A sketch of the scenario considered in modelling the
Munari et al. (2007a) propose that the appearance of the [Fe II] line profile in Sect. 4.
[Fe II] emission lines and the eclipse-like event observed in
November/December 2006 were unrelated, and that the eclipse-
like event was caused by an eclipse in a binary system. We argue
that both events were strongly related and produced by matter 3. The radial velocity of V838 Mon
ejected from V838 Mon during the 2002 outburst and reaching
the vicinity of the B3V companion (see also Barsukova et al., Several molecules observed in the spectrum of V838 Mon reveal
2006; Bond, 2006). bands formed from high excitation-energy levels (see Sect. 5
in Paper I). They are usually indicative of a radial heliocentric
In principle, one can consider that because of a certain velocity of 58 ± 5 km s−1 (see also Sect. 5.1). It is reasonable to
mechanism (e.g., dissipation of mechanical energy), the outer assume that they arise very close to the photosphere and have a
parts of the present V838 Mon wind become excited, producing velocity close to the stellar one. Earlier determinations of the
the observed [Fe II] emission lines. In this case, however, the stellar velocity in Kolev et al. (2002) and Kipper et al. (2004)
radial velocity of the lines would be close to that of V838 Mon. implied a value of 59–62 km s−1 , i.e., close to our result.
This is certainlly not the case. The [Fe II] lines have a radial However, the SiO maser emission observed in V838 Mon
velocity of 13.3 ± 0.7 km s−1 (Sect. 4.1.1 in Paper I), while the (Deguchi et al., 2005; Claussen et al., 2007; Deguchi et al.,
radial velocity of V838 Mon is at least 53 km s−1 (see Sect. 3). In 2009) is at a heliocentric velocity of 71 km s−1 . In the case of
this case, it would also be difficult to explain the observed [Fe II] late-type stars, the SiO masers usually have a reliable measure
profiles. of their stellar radial velocity.
All the observed characteristics of the [Fe II] emission lines There are two possible explanations of this discrepancy. If
can, however, be easily explained, if they are assumed to be the SiO maser emission really originates at the stellar velocity
produced by the matter ejected during the 2002 eruption that then the estimate made in Paper I may indicate that we do
approaches the B3V companion. As shown in Sect. 4, the not measure molecular bands deep enough that are to reach
observed line profiles as well as their radial velocities can then hydrostatic levels of the V838 Mon atmosphere, i.e., even the
be well accounted for. The continuous strengthening of the highest excitation bands are formed in already expanding layers.
lines in 2005–2006 is also easy to understand: larger and larger The other possibility is that the optical spectroscopic studies
amounts of matter become excited as it approaches the source provide a correct estimate of the stellar velocity but that the
of excitation. Excitation by radiation from the B3V companion SiO maser is not at the stellar velocity. We note that the radial
then explains why the emission line spectrum is dominated by velocity and width of the main component of the SiO maser are
Fe II. In the spectrum of a B3V star, there are enough photons very close to those of the CO rotational lines observed in diffuse
capable of ionizing species with an ionization potential of ∼ matter in the close vicinity of V838 Mon (Kami´ ski, 2008). This
n
7 eV, e.g., Fe, Ni, while there are very few photons capable of point certainly deserves further investigation.
ionizing the most abundant elements such as H, He or CNO. In the present paper, we usually adopt the radial velocity
Finally, the idea easy explains the ∼ 70 day eclipse-like event derived from the SiO maser, i.e., 71 km s−1 , as the radial velocity
observed in November/December 2006 as an occultation by a of V838 Mon. One has, however, to keep in mind that the results
dense cloud of the matter ejected in 2002 and now crossing the from optical spectroscopy infer a value 10–15 km s−1 lower.
line of sight of the B3V companion. If this is the case, one can
expect that the 2006 eclipse should be followed by similar events
when other fragments of the 2002 ejecta cross the line of sight.
Indeed, a few months later V838 Mon entered another eclipse- 4. An analysis of the [Fe II] line profile
like event.1 We note that the latter would be, at least, difficult to
explain as a phenomenon typical of an eclipsing binary system. As discussed in Sect. 2, we assume that the [Fe II] emission lines
are formed in the matter ejected by V838 Mon during its 2002
outburst, which is now approaching the B3V companion and
ionized by the UV radiation of the companion. In this section,
1
See e.g., the website of V. Goranskij using simplified modelling, we show that the observed profiles
(http://jet.sao.ru/∼goray/v838mon.htm). of the [Fe II] lines can be easily explained by this scenario.
2
3. 4.1. The model
We consider a system of two stars, S 1 and S 2 , with a separation
A (see Fig. 1). We assume that the star S 1 is a source of a steady,
spherically symmetric wind, that forms an expanding envelope
with a r−2 density distribution. We allow for the possibility that
matter in the form of clumps or filaments fills a ξ part of the
envelope volume, i.e., ξ ≤ 1. The wind started a certain time
ago, so the envelope has an outer boundary, r0 . The wind has
not yet reached star S 2 , so r0 < A. Star S 2 is a source of
ionizing radiation and emits Nph ionizing photons isotropically
per unit time and unit solid angle. The radiation produces an
ionized region in the wind whose boundaries can be determined
assuming ionization equillibrium.
We consider ionization along a given direction from star S 2
forming an angle α with the axis between the stars. A distance x2
from star S 2 , to which the wind matter is ionized, can be found
from
Nrec = Nph dω, (1)
where
x2
Nrec = ξ x2 dω αrec Ni2 dx (2)
x1
is a number of recombinations in a cone of solid angle dω along Fig. 2. A model profile (full curve) compared to the observed
the considered direction, αrec is a recombination coefficient, profile of [Fe II] 4287 Å (points). The model parameters are
while Ni = N0 (A/r)2 is an ion number density (electron density discussed in the text.
is assumed to be equal to ion density). In the following, we
assume that A is a unit length, so all the r and x are expressed in
terms of A, and x is then related to r and α via profile is Gaussian characterized by a thermal and/or turbulent
velocity, Vt . Integrating the intrinsic line profile over the ionized
r2 = 1 + x2 − 2 x cos α. (3) region and taking into account the kinematic properties of the
ionized wind, a final emission-line profile can be obtained.
In Eq. (2), x1 is a distance from star S 2 to the wind outer Apart from the above-mentioned parameters determining the
boundary along the considered direction, given by ionization front, the resultant line profile depends on kinematic
parameters of the wind and the stellar system, which are: the
x1 = cos α − 2
cos2 α − (1 − r0 ). (4) wind expansion velocity, Vwind ; the velocity of star S 1 (source of
the wind) relative to the observer, Vs ; and the angle between the
Equation (1) can be rewritten as stars separation axis and the line of sight, αs .
x2
Nph x2
C0 ≡ 2
= dx, (5) 4.2. Fitting the model to the observations
A3 ξ N0 αrec x1 r4
which, using Eq. (3), can be evaluated to give Some of the parameters in the above problem can be estimated
from observations. As discussed in Sect. 2, we assume that
C0 = I(x2 ) − I(x1 ), (6) close to the time of the November/December 2006 eclipse,
matter ejected during the 2002 eruption of V838 Mon reached
where the vicinity of the B3V companion. Our observations were
x cos 2α − cos α 1 x − cos α completed in October 2005, so we can estimate that r0 ≃
I(x) ≡ + arctan . (7) 0.75. During the 2002 outburst of V838 Mon, expansion
2r 2 sin2 α 3
2 sin α sin α
velocities observed reached ∼ 600 km s−1 , although most of
Equation (6) can be solved numerically to obtain x2 . Along the mass loss occurred at 150–400 km s−1 (Munari et al., 2002a;
separation axis, i.e., when α = 0, x1 = 1 − r0 , while Eq. (7) Crause et al., 2003; Kipper et al., 2004; Tylenda, 2005). As
reduces to discussed in Tylenda (2005), the most intense mass loss
1 1 1 occurred in March 2002, which was observed as an expanding
I(x) = − 2
+ . (8) photosphere of velocity ∼ 270 km s−1 . We therefore assume
1 − x (1 − x) 3(1 − x)3 Vwind ≃ 250 km s−1 in the present calculations. We also assume
Solving Eq. (6) for a grid of α values in the range 0 ≤ α ≤ that the heliocentric radial velocity of V838 Mon is Vs =
arcsin r0 , allows us to obtain the shape and position of the 71 km s−1 (see Sect. 3). Thus, there remain 3 free parameters,
ionization front in the wind. Matter is ionized between the wind i.e., C0 , αs , and Vt , which can be obtained by fitting the model
outer boundary and the ionization front. We note that the star profile to the observed profile of the [Fe II] emission lines.
separation axis is a symmetry axis of the ionized region. There A fit of this kind is presented in Fig. 2. Points show the
are two free parameters in the above problem, i.e., r0 and C0 . observed profile of the [Fe II] 4287 Å line. This is one of the
We assume that the ionized region is isothermal, so that the strongest emission lines of [Fe II] in our spectrum. Its profile is
emission line coefficient varies as Ni2 , and that the intrinsic line free of blending with other lines and affected little by noise. The
3
4. local continuum was subtracted and the flux was normalized to
the peak value. (Note that the profile of [Fe II] 4287 Å shown in
Fig. 2 is practically the same as the mean profile derived from
7 [Fe II] lines displayed in Fig. 4 of Paper I.) The model profile
was obtained with the following values of the free parameters:
C0 = 0.35, αs = 77◦ , and Vt = 11.5 km s−1 . If Vs = 58 km s−1 is
assumed (as discussed in Sect. 3), the results of the profile fitting
remain unchanged, except αs , which increases to 80◦ .
We note that there is little ambiguity in determining the
values of the above free parameters, because each of them affects
different characteristics of the model line profile. The value of C0
determines the size of the ionized region, so, for a fixed Vwind ,
it affects the wings of the line profile (the higher the value of
C0 , the more extended and stronger the wings). If Vwind and Vs
are fixed, αs defines the position of the line peak. Finally, Vt
determines the width of the line core.
4.3. Discussion
The results of the above modelling of the [Fe II] profile allows
us to estimate the parameters of the matter approaching the
B3V companion. From the profile fitting, we have C0 = 0.35.
Assuming that the matter, expanding with velocity Vwind ≃
250 km s−1 , reached the B3V companion in November or
December of 2006, we derive a distance between V838 Mon Fig. 3. The heliocentric radial velocity of individual TiO bands
and the B3V companion of A ≃ 3.7 × 1015 cm (∼ 250 AU). plotted against the excitation potential of the lower level of the
Integrating the spectrum of a standard B3V star above the band. See text for more details.
ionization potential of iron, one obtains Nph = 2.4×1046 s−1 . The
recombination coefficient of Fe I is αrec ≃ 2.5 × 10−12 cm3 s−1 (at
an electron temperature of 103 − 104 K; see Nahar et al., 1997). related to molecular bands. A simple model of a stellar
From Eq. (5), one then finds that N0 ≃ 7 × 105 ξ−1/2 cm−3 , or photosphere plus an outflowing homogeneous layer was used to
Ni ≃ 1.3 × 106 ξ−1/2 cm−3 at the outer edge of the wind envelope, identify and fit the observed structures of individual bands. In
i.e., at r0 . We note that at an electron density > 107 cm−3 ,
∼ this procedure, it was necessary to adopt various velocities for
the [Fe II] lines become collisionally de-excited. Assuming the outflowing layer to reproduce different band structures. In
spherical symmetry, a mass-loss rate during the 2002 outburst general, we found that bands originating in more excited levels
can be estimated to be correspond to higher (more positive) radial velocities than low
excitation bands. This effect is shown, in a more quantitative
˙ 4 π A2 Vwind ξ N0 1.4 mH way, in Fig. 3, which plots the heliocentric radial velocity of a
Mwind = , (9)
NFe /NH particular band versus the excitation energy, χ, of the level from
which the band arises. Only results for the TiO molecule, for
where NFe /NH is the relative-to-H number density of elements which we identified the largest number of bands, are shown.
with an ionization potential similar to or lower than that of Fe As the excitation potential plotted in Fig. 3, we have taken
(i.e., Na, Mg, Al, Si, Ca, Ni), while mH is the H atom mass. the energy of the lower level of the most blueshifted line in
Assuming solar abundances, NFe /NH ≃ 10−4 and Mwind ≃ ˙
25 1/2 −1 1/2 −1 the bandhead. Vertical error bars illustrate uncertainties in the
7 × 10 ξ g s ≃ 1 ξ M⊙ yr . The most intense period velocity. Uncertainties in the energy have been taken as a range
of mass loss lasted a month (March) in 2002 (Tylenda, 2005), of energies of lower levels of lines lying within ±35 km s−1 of
so, according to the above estimate, it produced a ∼ 0.1 ξ1/2 M⊙ the bandhead (this is the typical velocity broadening adopted in
shell. This agrees with the total mass lost in the 2002 outburst, modelling the bands in Paper I).
which was estimated to have a mass between 0.001 − 0.6 M⊙ in
As can be seen from Fig. 3, there is a clear correlation
Tylenda (2005).
between the radial velocity of a particular band and the
excitation potential of the lower level of the band. This we
5. Mass outflow in V838 Mon interpret as evidence of an outward accelerated mass outflow,
in which the observed bands are formed. The highest excitation
Munari et al. (2007b) noted presence of continuous mass loss bands can be formed in hotter regions, i.e., close to the
since the outburst. They reported that the outflow observed in photosphere, where the outflow velocity is low. Hence, we
K I 7698 Å has not much changed since 2002. The nature of its postulated in Paper I that the highest radial velocity observed
mass loss is however unclear. In this section, we analyse and in the high excitation bands, i.e., ∼ +58 km s−1 , corresponds to
discuss results from the profiles of molecular bands and atomic the radial velocity of V838 Mon. The bands originating in levels
lines observed in October 2005 and presented in Paper I. close to the ground state can be easily formed in cold outermost
layers outflowing with a large velocity.
5.1. Outflow as seen in molecular bands Figure 4 shows the same data as in Fig. 3 but in a
different, more astrophysical, way. Here, instead of the excitation
As discussed in Paper I, the spectrum of V838 Mon is dominated potential, we plot a parameter, log(g f λ) − 5040χ/T exc, where
by numerous, complex, and often very deep absorption lines g f and λ are the oscillator strength and wavelength of the
4
5. the atoms in the outer parts of the outflow. Because of the high
oscillator strength and the high atomic abundance, the opacity in
the K I λ7698 line is at least two orders of magnitude higher than
for any other resonant line observed. Consequently, this line can
be observed even with relatively low column densities expected
at high velocities. The value of terminal velocity derived from
the K I absorption is consistent with, although slightly higher
than, the outflow velocity estimated form the molecular bands
of TiO analysed in Sect. 5.1. It also agrees with the maximum
expansion velocity derived by Geballe et al. (2007) from the CO
bands observed half a year after our observations.
To obtain a deeper insight into the nature of the outflow
in V838 Mon, we performed a radiative transfer modelling
of the P-Cyg profiles. We assume that the profiles are
formed in a spherically symmetric expanding envelope. Our
modelling procedure is based on the SEI method developed by
Lamers et al. (1987), and all details concerning the solution of
radiative transfer can be found therein2 . As the velocity field of
the outflow, we adopt the standard β-law, i.e.,
β
1
w(x) = w0 + (1 − w0 ) 1 − , (10)
x
where w = V/V∞ is an outflow velocity normalized to the
Fig. 4. The heliocentric radial velocity of individual TiO bands terminal velocity, x = r/R⋆ is a dimensionless radial distance
plotted against log(g f λ) − 5040χ/T exc. See text for more details. from the star with a photospheric radius R⋆ , while w0 is the
normalized initial velocity at the stellar photosphere (taken to
be w0 =0.01 in our calculations).
band, respectively. Within a constant factor, this parameter is As already pointed out in Paper I (Sect. 4.2), the observed P-
equivalent to the logarithm of the absorption coefficient in a Cyg absorption components have velocity structure. A majority
given band. As an excitation temperature, T exc , we adopted of the absorption profiles have narrow absorption components
500 K, which is a typical value in the outflow, as inferred in (NACs) that appear at different velocities. The most striking
Paper I (Sect. 5). The horizontal error bars show uncertainties example of NAC is seen in the Rb I line at Vh = –82 km s−1 (see
related to the spread in the excitation energy and oscillator Fig. 6 in Paper I). Some lines, e.g., those of Cr I and Ba I, seem to
strength for the lines present within 35 km s−1 of the bandhead. exhibit many NACs at once, which dominate the appearance of
As Fig. 3, Fig. 4 can be interpreted as evidence of the profiles. On the other hand, there are also absorption profiles,
an increasing outflow velocity with the distance from the e.g., those of Ca I λ6572 and K I λ7698, which are very smooth
photosphere. Bands with a small absorption coefficient require and do not seem to be affected by discrete components. The
large column densities to be visible in the observed spectrum. question is whether the narrow components seen in our profiles
Thus, they must be formed deep in the outflow. More opaque are superimposed on a broad P-Cyg absorption profile formed
bands are effectively formed in more distant layers and their in a bulk flow, or whether the entire absorption profile consists
profiles provide information about the kinematics well above the of several discrete and strong absorption components that are
photosphere. blended and together form a more or less continuous profile.
From the span of the radial velocities observed in the TiO As a first attempt, we assumed a distribution of optical
bands, shown in Figs. 3 and 4, we can conclude that the wind in thickness in the form
V838 Mon is accelerated at least to a velocity of ∼ 180 km s−1 .
α2
τ(w) = Ttot (w/w1 )α1 1 − (w/w1 )1/β , (11)
5.2. An analysis of the P-Cyg profiles w1
where Ttot = w τ(w) dw is the integrated optical thickness
0
The presence of lines showing P-Cyg profiles in the spectrum and w1 is the normalized velocity at which opacity vanishes
of an observed object is usually considered as strong evidence (usually taken to be 1). The values of Ttot , w1 , α1 , and α2
of an ongoing mass outflow from the object. In our spectrum were treated as free parameters in our modelling procedure.
of V838 Mon, we found about ten atomic lines exhibiting The radial distribution given by Eq. (11) is known to reproduce
these characteristics (see Sect. 4.2 in Paper I). All of them but ultraviolet (UV) resonant lines formed in winds of hot stars
one originate from resonant transitions. Below we analyse the (Castor & Lamers, 1979). Our attempts to reproduce the smooth
profiles of these lines in an attempt to investigate the physics profiles of Ca I, K I, and the overall profile of Rb I (neglecting
and nature of the outflow. the NAC), showed that it was impossible to reproduce
The terminal velocity of the outflow from V838 Mon can satisfactorily any of these lines with the opacity distribution
be obtained from the observed K I λ7698 absorption profile (see in the form of Eq. (11). The best set of the parameters found
Fig. 6 in Paper I). If we take V s = 71 km s−1 to be the stellar
radial velocity (see discussion in Sect. 3), then the terminal 2
Aware of limitations of the SEI method we have also
velocity of the outflow is V∞ = 215 ± 5 km s−1 . The observed performed modelling in the more accurate comoving frame formalism
absorption components in other P-Cyg profiles do not reach this (Mihalas et al., 1975). It confirms the results obtained with the former
velocity, most probably because of the low column density of method.
5
6. within this approach resulted in profiles that were too narrow 1.4
with respect to the observed ones.
We, therefore, modified the optical depth distribution by Rb I 7800 Å
adding multiple Gaussian components, τi (w), to Eq. (11) 1.2
parameterized by central velocities, widths, and weights
according to which they are added. We note that, for the sake of 1
convenience, the Gaussian components are parameterized in the
normalized flux
velocity domain, so the corresponding distributions as functions 0.8
of radial distance, τi (x), are in general not Gaussian (the profile
is modified by the adopted velocity field).
In this multi-component approach, we were able to 0.6
successfully reproduce the observed profiles. Results for the
Rb I λ7800 line are shown in Fig. 5. At least three discrete 0.4
components (“shells”) of different widths are needed to obtain a
profile that reproduces the observations well. These components,
0.2
which are clearly present in all the profiles, are located at outflow
velocities of about 50, 110, and 150 km s−1 (with respect to
V s = 71 km s−1 ). 0
We attempted to model all the prominent P-Cyg lines −1 −0.5 0 0.5 1
independently and, while the central velocities and widths of w=V/V∞
different components were found to be consistently determined −2
for different lines, the relative contributions of the components β = 0.4
log (M/(M⊙ yr−1))
differ considerably from line to line. This implies that the relative −3
ion opacities differ considerably between consecutive “shells”.
This can be understand either as changes in excitation conditions −4
or different atomic abundances (chemical composition) in the
⋅
discrete outflow components. Although the latter seems to be −5
less likely, the changing atomic fractions due to interchanges of
atoms with molecules and/or dust grains may play an important −6
role. An extreme case of this effect is observed in the resonant 1 1.5 2 2.5 3
absorption lines of Ti I. Apart from the main component seen x=r/R★
close to the stellar velocity (but see Sect. 5.3), these lines appear
only in one of the outflowing “shells” (see Fig. 6 in Paper I).
Our modelling allows us to place general constraints on Fig. 5. Top: The P-Cygni profile of Rb I λ7800. The observed
the velocity field in the outflow. The adopted value of β has profile is drawn with a filled grey curve while the result of the
a strong influence on the relative strengths of absorption and SEI modelling is shown with a black line. Bottom: The mass
emission components in a P-Cyg profile (for a given radial loss rate corresponding to the fitted profile. The modelling was
distribution of optical thickness). We found that the outflow performed with β = 0.4 and V∞ = 215 km s−1 .
in V838 Mon can be characterized well by β =0.35±0.05.
This result was obtained assuming that collisional deexcitation
non-monotonicities, were proposed to explain the winds of hot
and photospheric contamination to the P-Cyg profile can be
stars (Prinja & Howarth, 1986; Puls et al., 1993). The possible
neglected. An influence of collisional de-excitation on the
existence of similar features in the outflow of V838 Mon is
emission component cannot be properly recognized because of
a tentative conclusion, which should be examined by time-
unknown electron densities in the outflow. We believe that it is
dependent observations of the P-Cyg profiles in the spectrum of
small, at least for lines with high transition probabilities (e.g.,
V838 Mon. The derived radial distributions of optical thickness
the lines of Rb I, K I, and Ba I with an Einstein coefficient
for different ions can be used to provide a rough estimate of the
Aul of the order of 107 –108 s−1 ). We did not find any signs of
mass-loss rate in V838 Mon. For a given stellar radius, R⋆ , the
photospheric contamination in the observed spectrum and we
mass-loss rate can be estimated from (Groenewegen & Lamers,
therefore neglected this effect in our modelling.
1989)
The value of β derived above implies that the acceleration
of material is very rapid and at the distance of 4R⋆ , the dw(x) 2 4 me c µ mH
wind has a velocity of 0.99 V∞ . This steep velocity gradient
˙
M(x) = τ(x) w(x) x2 V∞ R⋆ , (12)
dx e2 AE flu λ0
requires very high densities of material to be able to reproduce
strong absorption features at low velocities. Therefore, to where µ is the mean molecular weight, mH is the hydrogen mass,
reproduce the absorption component at the outflow velocity of AE is the abundance of an element with respect to hydrogen, flu
50 km s−1 (which corresponds to r = 1.03 R⋆ for β = 0.4), it is the oscillator strength, λ0 is the laboratory wavelength of the
was necessary to include an inner narrow shell with a very line, and the symbols me , e, and c have their usual meanings. In
high optical thickness. For several lines, e.g., the K I line, it Eq. (12), it is assumed that all the atoms of a given element are
was even impossible to reproduce the central parts of the P- in the ground state and that there is no ionization nor any other
Cyg profile without incorporating unreasonably high values of form of ion depletion. Taking as the stellar radius R⋆ = 103 R⊙
optical thickness. This made us conclude that in the velocity (see Sect.5 in Paper I), adopting β = 0.4, and assuming solar
field, generally well described by the β-law, a sort of a plateau abundances, the mass-loss rate derived from the lines of Rb I
(or plateaus) may exist, i.e., a region of nearly constant velocity λ7800 is on average of 10−6 − 10−5 M⊙ yr−1 , with individual
extended in the radial direction. These velocity plateaus, or mass-loss events reaching 10−3 M⊙ yr−1 (see Fig. 5).
6
7. 5.3. Signatures of an infall radiation pressure absorbed in molecular bands was proposed
as a mechanism accelerating cold circumstellar envelopes (see
The redward broad absorption components seen in the Ti I lines Jørgensen & Johnson, 1992, and references therein).
(see Sect. 4.3 in Paper I) can be interpreted as a signature of The analysis of the P-Cyg profiles reported in Sect. 5.2
an infall in V838 Mon. Similar absorption components also was completed assuming spherical symmetry and a monotonicly
contaminate the profiles of the 5060 and 5110 Å lines of Fe I. increasing outflow velocity described by Eq. (10). Within this
These absorption features in the Ti I lines have wings approach, the general shape of the observed profiles can be
extending out to about Vh = 120 km s−1 . Thus, regardless of the satisfactorily reproduced. This shows that the general pattern of
velocity of the star in the range 58–71 km s−1 (see Sect. 3), the outflow is more or less spherically symmetric. The profiles
the red wings of these features are evidently redshifted with however show, at least some of them, narrow structures, which
respect to the photosphere. The maximum infall velocity inferred we called NACs. The structure at Vh = −82 km s−1 is particularly
from these wings is 50–60 km s−1 , which agrees very well with striking. In the spherically symmetric, approach the only way
the free fall velocity of an 8M⊙ star (Tylenda et al., 2005) at a to explain the NACs is to assume that the mass-loss rate varies
photospheric radius of ∼ 900R⊙ (Sect. 5 in Paper I). with time and produces dense shells expanding with a thinner
Signatures of an infall were previously observed in wind. As can be seen in Fig. 5, to explain the strong NAC
V838 Mon. Rushton et al. (2005) observed inverse P-Cyg at Vh = −82 km s−1 it is necessary to postulate a short lived
profiles of Ti I lines in their spectra obtained in the near infrared enhancement in the mass loss rate by two orders of magnitude.
in December 2003. From the separation of the absorption and However, if the above assumptions are relaxed, the NACs can
emission components, an infall velocity of ∼ 20 km s−1 can be explained in other ways. One possibility is that the NACs
be deduced. These authors also argue that the infalling matter, are produced by mass loss being more intense in certain, more
compressed, and heated when colliding with the atmospheric or less discrete, directions. For instance, the NAC at Vh =
material, provide conditions necessary to excite the SiO lines −82 km s−1 would then be understood as a stream-like or jet-
that they observe. Observations of the ro-vibrational bands like outflow with a projected velocity of ∼ 153 km s−1 (adopting
of CO by Geballe et al. (2007) in April 2006 revealed a the radial velocity of V838 Mon of 71 km s−1 ; see Sect. 3). Jets
photospheric component redshifted by 15 km s−1 with respect usually have counter-jets. The observed lack of any counter-jet
to the velocity of the SiO maser. This suggests, according to the in our spectrum as well as the position of the NAC close to the
authors, the presence of gas infalling onto the star or contraction terminal velocity of the P-Cyg profiles suggests that the jet, if
of the stellar photosphere. responsible for producing the NAC at −82 km s−1 , is not far from
the line of sight.
5.4. Discussion Another possibility is that the NAC at Vh = −82 km s−1
has nothing to do with the presently ongoing mass outflow, but
As mentioned above, the mass outflow in V838 Mon has been is produced in the matter lost during the 2002 eruption that is
observed continously since the 2002 eruption. Our analysis now in front of the object. This interpretation would imply the
confirms this statement and provides new results. The question existence of a dense shell at a distance of ∼ 1.7 × 1015 cm
that arises is what drives this outflow. It consists of cold neutral (∼ 2.5 × 104 R⊙ ) from the object expanding with a velocity
matter that is rich in molecules, and possibly also dust, which of ∼ 153 km s−1 . However, during the 2002 eruption the matter
is similar to the composition of the winds of cool stars, e.g., was ejected with velocities ranging from ∼ 100 to ∼ 600 km s−1
objects in the asymptotic giant branch. Velocity fields of these (Munari et al., 2002a; Crause et al., 2003; Kipper et al., 2004).
cool winds are usually well described by the β-law with β ≃ 0.5, Thus, the matter, or at least part of it, would have to have been
which is close to the value derived above for V838 Mon. These condensed into a shell at later epochs. This can occur if matter
cool winds are believed to be dust-driven. They usually do ejected later catches up with slower matter ejected earlier. In
not reach the high terminal velocities found for V838 Mon. the case of V838 Mon, this mechanism does not seem to have
A possible reason is that dust is destroyed in collisions, when worked, since the outflow velocity observed during the 2002
the outflow is faster than about 30 km s−1 (Olofsson, 2004). eruption tended to decrease with time (Munari et al., 2002a;
From this reason, it seems that the outflow in V838 Mon Crause et al., 2003). A NAC at Vh = −90 km s−1 is seen in
cannot be driven by dust only, since we observe material our spectrum in the Ti I 5147 and 5152 Å lines, which do not
being accelerated at much higher velocities than 30 km s−1 . This display P-Cyg profiles (see panel c in Fig. 6 in Paper I). The
driving mechanism can, however, play a role at the base of the close radial velocity and line width suggest that this component
outflow, where velocities are low enough. is produced in the same enviroment as the NAC in the P-Cyg
One can consider a mechanism similar to that driving winds profiles. If this is the case, our interpretation presented above
in hot stars, i.e., by radiation pressure absorbed in atomic would have to be excluded. The Ti I lines arise from the levels
resonant lines. However, the small number and relative weakness lying 2.3–2.4 eV above the ground state. Thus, they must arise
of lines of this type in our spectrum (they are typically 10 in a rather warm matter (of temperature comparable to that in the
times narrower than those in the OB stars) does not support photosphere), while the matter lost in 2002 and now at a distance
the idea that these lines could be effective in driving mass loss of ∼ 30 photospheric radii is expected to be cold (∼ 500 K, if
from V838 Mon. More promising is the possibility that the estimated from pure geometric dilution of the radiative energy
outflow is driven by radiation pressure absorbed in molecular density). In conclusion, we consider that the interpretation that
bands in the optical and infrared. The object is very bright in the NAC at Vh = −82 km s−1 is related to matter lost in 2002 is
these wavelength ranges and the observed number and strength less probable than the other two, i.e., varying mass-loss rate in
of molecular bands, as seen in our spectrum (some of them the present wind or jet-like ouflow.
absorb practically all the radiation available in their wavelength Spectroscopic data allowing analyses of the time-dependent
ranges – see Paper I), clearly shows that a significant part behaviour of the P-Cyg profiles would help to discriminate
of the momentum carried out in radiation is indeed absorbed between interpretations involving varying mass-loss rate, jet-
in the outflowing matter. A process of driving winds by like outflow, or distant matter lost in 2002. In the first case,
7
8. the NACs are expected to migrate in the profile with time, strongest [Fe II] lines in our spectrum obtained in October 2005
while in the two other cases the NACs should be rather stable increased by a factor of ∼ 3.5 in the measurements completed
features. It is worth noting that Geballe et al. (2007) in their by Munari et al. (2007a) in December 2006. At the moment of
high-resolution spectra obtained in the K band in April 2006, our observations, the outer boundary of the expanding envelope
i.e., half a year after our spectroscopy, indentified several was presumably at a distance of ∼ 0.75 times the separation
velocity components in the CO absorption line profiles. Apart between V838 Mon and its B3V companion. Thus, only ∼ 17%
from the photospheric component (mentioned in Sect 5.3) the of the radiation flux of the B3V companion should then interact
authors found components at expansion velocities of 15, 85, and with the matter. At the moment of the eclipse-like event in
150 km s−1 . The last feature is practically at the same velocity November/December 2006, the matter presumably reached the
as our NAC at Vh = −82 km s−1 suggesting that this is a closest vicinity of the companion and the portion of the stellar
persistent component. However, the feature in the CO lines is radiation capable of exciting the matter increased to 50 − 100%.
much wider than the NAC, so the conclusion is unclear. The two Apart from the [Fe II] emission lines, Munari et al. (2007a)
other components in the CO lines do not match other NACs in also observed strong Balmer lines in emission. In particular, they
our P-Cyg profiles, which are seen at the expansion velocities of discussed in detail the profile of Hα observed in December 2006
50 and 110 km s−1 (see Sect. 5.2). This suggests that these NACs – April 2007. No Hα was seen in our spectrum in October 2005.
are transient and produced by varying mass-loss rates. However, in the absorption cores of higher members of the
Balmer series (in the spectrum of the B3V companion), we have
detected weak emission components (see Sect. 4.1.2 in Paper I).
6. Summary and discussion In particular, the emission component in the Hβ line was
Our analysis of both the positions of the molecular bands estimated to have an observed flux of ∼ 3 × 10−16 erg cm−2 s−1 .
(Sect. 5.1) and the P-Cyg profiles (Sect. 5.2) have shown that We note that the profile of the Hβ emission component (see
V838 Mon loses matter with a terminal velocity of ∼ 215 km s−1 Fig. 5 in Paper I) was remarkably similar to that of the Hα line
at a rate of 10−6 − 10−5 M⊙ yr−1 . Thus, the object loses of the observed by Munari et al. (2007a) in December 2006. Moreover,
order of 10 L⊙ in the form of the kinetic energy of the wind. the parameters of the emission component in Hβ in our spectrum
This is small compared to the radiation luminosity of the object, and of the Hα emission component in Munari et al. (2007a)
which is ∼ 2.4 × 104 L⊙ (see Sect. 5 in Paper I). However, the (radial velocity and FWHM) are close to those of the [Fe II]
momentum carried out in the wind is comparable to that in the lines derived in Paper I. This implies that all these lines probably
radiation. Thus, the wind in V838 Mon is likely to be radiation originate in the same region, i.e., in the part of the V838 Mon
driven, probably due to absorption in the molecular bands, as envelope (ejected in 2002) approaching the B3V companion.
discussed in Sect. 5.4. The point is, however, that while in the spectrum of a B3V
The kinematic pattern of the matter in the atmosphere of star there are enough photons capable of ionizing iron and
V838 Mon is very complex. Both expansion and wind outflow exciting the [Fe II] lines, there are very few photons, capable of
dominate. Most of the outflow is more or less spherically ionizing hydrogen. Between October 2005 and December 2006,
symmetric as suggested by our modelling of the observed P-Cyg the flux in the Hβ emission also increased by a factor of ∼ 7,
profiles (Sect. 5.2). However, as discussed in Sect. 5.4, it is quite while that in Hα increased by at least two orders of magnitude.
possible that we also observe a jet-like outflow. As shown in This large increase cannot be explained by a purely geometric
Sect. 5.3, certain regions, perhaps initially accelerated but not effect, as discussed above in the case of the [Fe II] lines.
sufficiently to allow them to leave the object, also fall back to Therefore, an additional source of excitation of the Balmer lines
the photosphere. We note that simultaneous signatures of infall is necessary, a source, whose intensity significantly increased
and outflow have been observed in the winds of hot stars (e.g., between October 2006 and December 2007. We suggest that this
Howk et al., 2000) and often in protostars. A possible scenario is provided by matter accretion from the outflowing V838 Mon
for creating coexisting mass outflow and infall in asymptotic envelope on the B3V companion. We now complete simplified
giant branch stars was discussed in Soker (2008) and may also estimates for this scenario.
work in the remnant of the V838 Mon outburst. We assume that matter flows with a velocity, Vwind , in the
As discussed in Tylenda (2005), the evolution of V838 Mon vicinity of a star of mass, MB3V . An accretion radius, racc , can be
in the post-outburst state is probably dominated by gravitational estimated from the standard formula (see e.g., Frank et al., 2002)
contraction, i.e., is closely related to that of protostars. If,
2 G MB3V
as argued in Tylenda & Soker (2006), the 2002 outburst of racc ≃ 2
≃ 3 × 1012 cm ≃ 43 R⊙, (13)
V838 Mon was produced by a stellar merger, then a significant Vwind
amount of angular momentum should have been stored in
the remnant of the event (see also Soker & Tylenda, 2007). where we adopted MB3V = 7 M⊙ and Vwind = 250 km s−1 . An
Gravitational contraction may then result in the flattening of the accretion rate can then be estimated from
envelope, eventually leading to the formation of an accretion 2
π racc
disc (as in protostellar objects). The possibility discussed in ˙
Macc ≃ Mwind ≃ 1 × 1019 ξ1/2 g s−1 ,
˙ (14)
Sect. 5.4, namely that we observe a jet in the spectrum, (4 π A2)
if confirmed, may imply that a disc has already formed in ˙
where we used the values of Mwind and A estimated in Sect. 4.3.
V838 Mon. This implies an accretion luminosity,
As shown in Sect. 4, the observed profile of the [Fe II] lines
can be easily understood as having been produced by matter ˙
G MB3V Macc
lost by V838 Mon in the 2002 eruption and now excited by Lacc = ≃ 9 ξ1/2 L⊙ , (15)
RB3V
the radiation of the B3V companion. As the matter approaches
the companion, a larger and larger proportion of the flux from where RB3V = 4.5 R⊙ has been assumed. This luminosity is
the star can interact with the matter causing an increase in small compared to the intrinsic luminosity of a standard B3V star
the [Fe II] emission, as observed. Indeed, the flux in the 20 (∼ 1.9×103 L⊙ , Schmidt-Kaler, 1982). Thus, no significant effect
8
9. is expected to be observed in the global energetics of the B3V Soker, N. 2008, New Astronomy, 13, 491
companion, e.g., in the visual brightness. However, after being Soker, N. & Tylenda, R. 2007, MNRAS, 375, 909
dissipated via an accretion shock3 and thus producing a hot layer Tylenda, R. 2005, A&A, 436, 1009
Tylenda, R. & Soker, N. 2006, A&A, 451, 223
above the star surface, the accretion luminosity is expected to be Tylenda, R., Soker, N., & Szczerba, R. 2005, A&A, 441, 1099
emitted mainly in the far-UV and/or soft X-rays. This can affect
the ionization of the expanding envelope of V838 Mon, i.e.,
produce significant ionization of hydrogen. The accretion from
the expanding matter is expected to become effective just before
and during the November/December 2006 eclipse. We suggest
that this is the reason for the rapid increase in emission of the
Balmer lines, particularly in Hα, observed in the second half of
2006. We note that the luminosity in the Balmer emission lines,
dominated by Hα, as observed by Munari et al. (2007a) during
the eclipse, was ∼ 3.5 L⊙ (assuming E B−V = 0.9 and a 8 kpc
distance to V838 Mon). Thus, the accretion, as estimated above,
can provide enough energy to explain the observed luminosity
in the Balmer lines.
Acknowledgements. The research reported on in this paper has been supported
by the Polish Ministry of Science and Higher Education under grant no. N203
004 32/0448, for which the authors are grateful.
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3
The specific angular momentum accreted with the matter is
negligible in this case and there is no chance to create an accretion
disc arround the B3V companion, contrary to the suggestion of
Goranskij et al. (2008).
9