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.
Extended x ray emission in the h i cavity of ngc 4151- galaxy-scale active ga...Sérgio Sacani
The document summarizes the discovery of diffuse soft X-ray emission extending about 2 kpc from the active nucleus of NGC 4151, filling the cavity of H i material. The X-ray emission has a luminosity of about 1039 erg s-1 and can be fit with either a thermal plasma model with a temperature of around 0.25 keV, or a photoionized model. This interaction between the AGN and interstellar medium implies the last episode of high nuclear activity occurred relatively recently, around 104 years ago.
The stellar content_of_the_ring_in_ngc660Sérgio Sacani
The document summarizes the results of a stellar photometry study of the polar ring galaxy NGC 660 using archival Hubble Space Telescope images. Over 550 stars were resolved, including many blue and red supergiants belonging to the polar ring. Analysis of the color-magnitude diagram for polar ring stars showed they are best represented by isochrones with a metallicity of Z=0.008. Star formation in the polar ring appears to have been continuous, with the youngest detected stars having an age of about 7 million years.
The central star_of_the_planetary_nebula_ngc_6537Sérgio Sacani
1) HST images of the planetary nebula NGC 6537 fail to detect its central star, placing an upper limit on its magnitude of fainter than 22.4.
2) This limit is used to derive a lower limit for the star's temperature of at least 500,000 K based on Zanstra temperature analysis.
3) The energy balance temperature method, which does not require direct observation of the star, yields a temperature consistent with 500,000 K, as does the ionization state of the nebula.
Off nuclear star_formation_and_obscured_activity_in_the_luminous_infrared_gal...Sérgio Sacani
The document summarizes observations of the luminous infrared galaxy NGC 2623 from multiple telescopes. Hubble Space Telescope images reveal over 100 bright star clusters in a 3.2 kpc extension south of the galaxy's nucleus, making it one of the richest concentrations of clusters observed. The clusters have ages between 1-100 Myr based on their optical colors. Archival GALEX data show the extension is very bright in far-ultraviolet but less significant at longer wavelengths. Spitzer data detect [Ne V] emission, confirming the presence of an active galactic nucleus. The off-nuclear star formation corresponds to a rate of 0.1-0.2 solar masses per year, while the bulk of the infrared
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
This document reports the discovery of the central star of the planetary nebula IC 4663, which exhibits spectral properties that mimic a nitrogen-rich Wolf-Rayet star of spectral type [WN3]. This makes it the first unambiguous case of a planetary nebula central star taking on the properties of a Wolf-Rayet star. The central star is dominated by broad helium and nitrogen emission lines. The surrounding nebula is definitively a planetary nebula based on its morphology and chemical abundances. The discovery provides evidence for an alternative evolutionary pathway for some hydrogen-deficient, helium-rich post-asymptotic giant branch stars.
Investigating the nuclear_activity_of_ngc1672Sérgio Sacani
1) The document investigates the nuclear activity of the barred spiral galaxy NGC 1672 using X-ray data from Chandra and XMM-Newton, as well as optical data from Hubble and infrared data from Spitzer.
2) It detects 28 X-ray sources within NGC 1672, with nine being ultraluminous X-ray sources located at the ends of the galaxy's bar.
3) For the first time, it shows NGC 1672 possesses a hard nuclear X-ray source surrounded by an X-ray bright circumnuclear star-forming ring, which dominates the central X-ray emission of the galaxy. The data indicates the nuclear source is a low-luminosity active gal
This document summarizes a study of the galaxy NGC 3801 using panchromatic data from radio, ultraviolet, optical and infrared wavelengths. The study finds that NGC 3801 is a post-merger early-type galaxy that shows evidence of recent star formation in spiral wisps as well as feedback from active galactic nucleus jets. Specifically, the galaxy has a young radio jet that has not yet impacted the outer gaseous regions, but will likely quench star formation within the next 10 million years and further transform the galaxy into a red elliptical. The multi-wavelength data reveal complex gas and dust structures that may be due to a kinematically decoupled core or warped disk.
Extended x ray emission in the h i cavity of ngc 4151- galaxy-scale active ga...Sérgio Sacani
The document summarizes the discovery of diffuse soft X-ray emission extending about 2 kpc from the active nucleus of NGC 4151, filling the cavity of H i material. The X-ray emission has a luminosity of about 1039 erg s-1 and can be fit with either a thermal plasma model with a temperature of around 0.25 keV, or a photoionized model. This interaction between the AGN and interstellar medium implies the last episode of high nuclear activity occurred relatively recently, around 104 years ago.
The stellar content_of_the_ring_in_ngc660Sérgio Sacani
The document summarizes the results of a stellar photometry study of the polar ring galaxy NGC 660 using archival Hubble Space Telescope images. Over 550 stars were resolved, including many blue and red supergiants belonging to the polar ring. Analysis of the color-magnitude diagram for polar ring stars showed they are best represented by isochrones with a metallicity of Z=0.008. Star formation in the polar ring appears to have been continuous, with the youngest detected stars having an age of about 7 million years.
The central star_of_the_planetary_nebula_ngc_6537Sérgio Sacani
1) HST images of the planetary nebula NGC 6537 fail to detect its central star, placing an upper limit on its magnitude of fainter than 22.4.
2) This limit is used to derive a lower limit for the star's temperature of at least 500,000 K based on Zanstra temperature analysis.
3) The energy balance temperature method, which does not require direct observation of the star, yields a temperature consistent with 500,000 K, as does the ionization state of the nebula.
Off nuclear star_formation_and_obscured_activity_in_the_luminous_infrared_gal...Sérgio Sacani
The document summarizes observations of the luminous infrared galaxy NGC 2623 from multiple telescopes. Hubble Space Telescope images reveal over 100 bright star clusters in a 3.2 kpc extension south of the galaxy's nucleus, making it one of the richest concentrations of clusters observed. The clusters have ages between 1-100 Myr based on their optical colors. Archival GALEX data show the extension is very bright in far-ultraviolet but less significant at longer wavelengths. Spitzer data detect [Ne V] emission, confirming the presence of an active galactic nucleus. The off-nuclear star formation corresponds to a rate of 0.1-0.2 solar masses per year, while the bulk of the infrared
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
This document reports the discovery of the central star of the planetary nebula IC 4663, which exhibits spectral properties that mimic a nitrogen-rich Wolf-Rayet star of spectral type [WN3]. This makes it the first unambiguous case of a planetary nebula central star taking on the properties of a Wolf-Rayet star. The central star is dominated by broad helium and nitrogen emission lines. The surrounding nebula is definitively a planetary nebula based on its morphology and chemical abundances. The discovery provides evidence for an alternative evolutionary pathway for some hydrogen-deficient, helium-rich post-asymptotic giant branch stars.
Investigating the nuclear_activity_of_ngc1672Sérgio Sacani
1) The document investigates the nuclear activity of the barred spiral galaxy NGC 1672 using X-ray data from Chandra and XMM-Newton, as well as optical data from Hubble and infrared data from Spitzer.
2) It detects 28 X-ray sources within NGC 1672, with nine being ultraluminous X-ray sources located at the ends of the galaxy's bar.
3) For the first time, it shows NGC 1672 possesses a hard nuclear X-ray source surrounded by an X-ray bright circumnuclear star-forming ring, which dominates the central X-ray emission of the galaxy. The data indicates the nuclear source is a low-luminosity active gal
This document summarizes a study of the galaxy NGC 3801 using panchromatic data from radio, ultraviolet, optical and infrared wavelengths. The study finds that NGC 3801 is a post-merger early-type galaxy that shows evidence of recent star formation in spiral wisps as well as feedback from active galactic nucleus jets. Specifically, the galaxy has a young radio jet that has not yet impacted the outer gaseous regions, but will likely quench star formation within the next 10 million years and further transform the galaxy into a red elliptical. The multi-wavelength data reveal complex gas and dust structures that may be due to a kinematically decoupled core or warped disk.
No signature of_ejecta_interaction_with_a_stellar_companion_in_three_type_ia_...Sérgio Sacani
ARtigo descreve estudos de supernovas feitos com o Kepler e mostram que explosões podem ser geradas por estrelas anãs brancas simples, se chocando com outras ou se fundindo com outras.
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.
The exceptional soft_x_ray_halo_of_the_galaxy_merger_ngc6240Sérgio Sacani
The document summarizes a recent 150-ks Chandra observation of the galaxy merger NGC 6240. Extended soft X-ray emission is detected over a 110x80 kpc region around NGC 6240. Spectral analysis finds the emission comes from hot gas with a temperature of around 7.5 million K and a total mass of about 10^10 solar masses. The gas properties suggest widespread star formation over the past 200 Myr rather than a recent nuclear starburst. The fate of the diffuse hot gas after the galaxy merger is uncertain but it may be retained and evolve into the halo of an elliptical galaxy.
A estrela KIC 8462852 voltou a ser comentada na mídia astronômica essa semana, e vamos entender porque. Mas antes uma pequena recordação.
Provavelmente, você já ouviu falar da estrela KIC 8462852, que recebeu o nome carinhoso de Estrela de Tabby, em homenagem a Tabetha Boyajian que liderou a equipe que descobriu o seu estranho comportamento. Essa foi a estrela que chamou muito a atenção da imprensa no final do último ano. Os astrônomos utilizaram observações feitas com o Kepler e mediram as variações no brilho da estrela. Algumas dessas variações eram significativas, com uma queda de brilho de cerca de 20%.
Isso é muito. Não poderia ser um planeta passando em frente a estrela, pois as quedas dos brilhos também não eram periódicas, e a quantidade de luz bloqueada era diferente a cada vez. Além disso, até um planeta do tamanho de Júpiter, bloqueia menos de 1% da luz da estrela.
No artigo original, Boyajian e sua equipe discutiu uma série de hipóteses e possíveis cenários que poderiam causar a queda de brilho, eliminando algumas delas e levantando outras. Entre as hipóteses, aquela que ganhou uma força foi a de uma família de cometas passando na frente da estrela, com alguns deles colidindo entre si e gerando uma nuvem espessa que poderia bloquear a luz da estrela.
The document summarizes two Chandra X-ray observations of the Type IIn supernova SN 2010jl taken around two months and one year after explosion. The first observation revealed a high temperature (10 keV) and very high absorption column density (1024 cm-2) from circumstellar matter. The second observation, one year later, showed the absorption column had decreased by a factor of three as expected from shock propagation. Both observations detected an unabsorbed luminosity of 7×1041 erg s-1. The Fe line detected in the first observation was not present in the second.
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
A young protoplanet_candidate_embedded_in_the_circumstellar_disk_of_hd100546Sérgio Sacani
This document summarizes observations of HD100546 using high-contrast imaging techniques. A faint emission source was detected near the star at a projected separation of about 47 AU. The position of the source coincides with a deficit in polarization observed from the circumstellar disk. This suggests a physical link between the source and the disk. Considering various scenarios, the authors favor interpreting the source as a young protoplanet currently forming within the disk. Follow-up observations could distinguish between different possible explanations for the observed features. If confirmed, it would be a unique opportunity to study giant planet formation within an optically thick disk.
Type iax supernovae_a_new_class_of_stellar_explosionSérgio Sacani
Type Iax supernovae are a new class of stellar explosions that are spectroscopically similar to Type Ia supernovae but have lower maximum light velocities and peak magnitudes. They typically have lower ejecta masses and hotter photospheres than Type Ia. The progenitor system is likely a carbon-oxygen white dwarf that accretes matter from a helium star companion, resulting in a deflagration explosion that does not fully disrupt the white dwarf. Type Iax events occur about 31 times as frequently as Type Ia supernovae.
A rapidly spinning_supermassive_black_hole_at_the_centre_of_ngc1365Sérgio Sacani
1) XMM-Newton and NuSTAR observed the galaxy NGC 1365 simultaneously over 130 ks, detecting broadband X-ray emission from 3-79 keV.
2) The observations revealed variable absorption below 10 keV and prominent broad emission features between 5-7 keV and 10-30 keV, indicative of relativistic reflection from an accretion disk near a spinning supermassive black hole.
3) Time-resolved spectral analysis was able to disentangle the variable absorption component from the relativistic reflection component. Absorption-dominated models without reflection could be ruled out statistically and on physical grounds.
Apartes de la conferencia de la SJG del 14 y 21 de Enero de 2012: Gravitation...SOCIEDAD JULIO GARAVITO
1) The document discusses the potential detection of gravitational waves from the ejection of superluminal jet components and precession of accretion disks dynamically driven by the Bardeen-Petterson effect around spinning black holes.
2) It suggests that ejection of ultrarelativistic jet components may be associated with the precession of the accretion disk induced by the black hole's spin and fragmentation of the tilted disk due to the Bardeen-Petterson effect.
3) It computes the characteristic amplitude and frequency of gravitational wave bursts that could be produced during the early acceleration phase of launching superluminal jet components, finding they may be detectable by the gravitational wave observatory LISA.
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
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
50 Years of the Astronomy Centre at the University of SussexPeter Coles
This summarizes about 50 research papers and other notable events, approximately one for each year of existence of the Astronomy Centre at the University of Sussex (1966-2016). Shown at a special event on 15th October 2016. to mark the 50th Anniversary
Herman mosquera2011 nonlinear electrodynamics and the pioneer 1011 spacecraftSOCIEDAD JULIO GARAVITO
1) The document discusses the unexplained "Pioneer anomaly" - an anomalous blueshift in radio signals from the Pioneer 10/11 spacecraft that suggests they are accelerating under an unexplained force.
2) Conventional explanations like gravitational effects, solar radiation pressure, and modified dynamics have been ruled out. The anomaly appears to be related to the electromagnetic sector rather than gravity.
3) The document proposes that nonlinear electrodynamics (NLED), where the electromagnetic field depends nonlinearly on the field strength, could explain an anomalous frequency shift in photons as they propagate through space without interacting with matter. This effect is called "photon acceleration".
The document summarizes a study that presents the first panoramic view of the outskirts of the Milky Way analogue galaxy NGC 891 based on ground-based imaging. The key findings are:
1) Numerous stellar overdensities and coherent substructures were detected out to distances of ~90 kpc from the center of NGC 891, including a giant stream looping around the galaxy up to ~50 kpc.
2) A previously undetected large, flat, and thick cocoon-like stellar structure was found surrounding the bulge and disk of NGC 891 out to radial distances of ~40 kpc and vertical distances of ~15 kpc.
3) The properties of the substructures suggest NGC
This document summarizes an analysis of high resolution infrared spectra from the Cassiopeia A supernova remnant taken by the Spitzer Space Telescope. The analysis finds:
1) The reverse shock of the remnant is spherical to within 7%, though offset from the geometric center by 810 km/s.
2) Nucleosynthetic layers of Si and O show velocities differing by up to 500 km/s in some directions, indicating separation during the supernova.
3) Small-scale corrugated velocity structures seen in the ejecta likely formed during the supernova rather than by later instabilities at the remnant's reverse shock.
This document summarizes the discovery of Kepler-413b, a Neptune-sized circumbinary planet orbiting the eclipsing binary star system Kepler-413. The planet has an orbital period of approximately 66 days and an eccentric orbit with a semimajor axis of 0.355 AU. Analysis of the Kepler light curve revealed the planet's orbit is misaligned with the binary star plane by about 2.5 degrees, causing it to sometimes fail to transit one of the stars. The orbital configuration of the system places the planet interior to the habitable zone but its obliquity may undergo fluctuations on precession timescales.
Discrete and broadband electron acceleration in Jupiter’s powerful auroraSérgio Sacani
The most intense auroral emissions from Earth’s polar regions,
called discrete for their sharply defined spatial configurations, are
generated by a process involving coherent acceleration of electrons
by slowly evolving, powerful electric fields directed along the
magnetic field lines that connect Earth’s space environment to its
polar regions1,2. In contrast, Earth’s less intense auroras are generally
caused by wave scattering of magnetically trapped populations of
hot electrons (in the case of diffuse aurora) or by the turbulent or
stochastic downward acceleration of electrons along magnetic field
lines by waves during transitory periods (in the case of broadband
or Alfvénic aurora)3,4. Jupiter’s relatively steady main aurora has a
power density that is so much larger than Earth’s that it has been
taken for granted that it must be generated primarily by the discrete
auroral process5–7. However, preliminary in situ measurements of
Jupiter’s auroral regions yielded no evidence of such a process8–10.
Here we report observations of distinct, high-energy, downward,
discrete electron acceleration in Jupiter’s auroral polar regions. We
also infer upward magnetic-field-aligned electric potentials of up to
400 kiloelectronvolts, an order of magnitude larger than the largest
potentials observed at Earth11. Despite the magnitude of these
upward electric potentials and the expectations from observations
at Earth, the downward energy flux from discrete acceleration is less
at Jupiter than that caused by broadband or stochastic processes,
with broadband and stochastic characteristics that are substantially
different from those at Earth.
The high albedo of the hot jupiter kepler 7 bSérgio Sacani
This document summarizes the analysis of Kepler photometry data for the exoplanet Kepler-7b. Key findings include:
1) The occultation depth is measured to be 44±5 ppm, translating to a Kepler geometric albedo of 0.32±0.03, the most precise value measured for an exoplanet.
2) The planetary orbital phase lightcurve is characterized with an amplitude of 42±4 ppm.
3) Atmospheric modeling finds it unlikely that the high albedo is due to a dominant thermal component. Two possible explanations are proposed: excess reflection from clouds/hazes, or depleted atmospheric sodium and potassium allowing Rayleigh scattering to dominate.
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.
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
For their production group, the document discusses how conducting a risk assessment is required by law to identify potential hazards during filming and minimize risks. It will consider hazards like slipping or equipment issues and place results in a table. The goal is to make the film crew as safe as possible and avoid injuries that could hinder production. The risk assessment should be completed before filming begins.
No signature of_ejecta_interaction_with_a_stellar_companion_in_three_type_ia_...Sérgio Sacani
ARtigo descreve estudos de supernovas feitos com o Kepler e mostram que explosões podem ser geradas por estrelas anãs brancas simples, se chocando com outras ou se fundindo com outras.
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.
The exceptional soft_x_ray_halo_of_the_galaxy_merger_ngc6240Sérgio Sacani
The document summarizes a recent 150-ks Chandra observation of the galaxy merger NGC 6240. Extended soft X-ray emission is detected over a 110x80 kpc region around NGC 6240. Spectral analysis finds the emission comes from hot gas with a temperature of around 7.5 million K and a total mass of about 10^10 solar masses. The gas properties suggest widespread star formation over the past 200 Myr rather than a recent nuclear starburst. The fate of the diffuse hot gas after the galaxy merger is uncertain but it may be retained and evolve into the halo of an elliptical galaxy.
A estrela KIC 8462852 voltou a ser comentada na mídia astronômica essa semana, e vamos entender porque. Mas antes uma pequena recordação.
Provavelmente, você já ouviu falar da estrela KIC 8462852, que recebeu o nome carinhoso de Estrela de Tabby, em homenagem a Tabetha Boyajian que liderou a equipe que descobriu o seu estranho comportamento. Essa foi a estrela que chamou muito a atenção da imprensa no final do último ano. Os astrônomos utilizaram observações feitas com o Kepler e mediram as variações no brilho da estrela. Algumas dessas variações eram significativas, com uma queda de brilho de cerca de 20%.
Isso é muito. Não poderia ser um planeta passando em frente a estrela, pois as quedas dos brilhos também não eram periódicas, e a quantidade de luz bloqueada era diferente a cada vez. Além disso, até um planeta do tamanho de Júpiter, bloqueia menos de 1% da luz da estrela.
No artigo original, Boyajian e sua equipe discutiu uma série de hipóteses e possíveis cenários que poderiam causar a queda de brilho, eliminando algumas delas e levantando outras. Entre as hipóteses, aquela que ganhou uma força foi a de uma família de cometas passando na frente da estrela, com alguns deles colidindo entre si e gerando uma nuvem espessa que poderia bloquear a luz da estrela.
The document summarizes two Chandra X-ray observations of the Type IIn supernova SN 2010jl taken around two months and one year after explosion. The first observation revealed a high temperature (10 keV) and very high absorption column density (1024 cm-2) from circumstellar matter. The second observation, one year later, showed the absorption column had decreased by a factor of three as expected from shock propagation. Both observations detected an unabsorbed luminosity of 7×1041 erg s-1. The Fe line detected in the first observation was not present in the second.
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
A young protoplanet_candidate_embedded_in_the_circumstellar_disk_of_hd100546Sérgio Sacani
This document summarizes observations of HD100546 using high-contrast imaging techniques. A faint emission source was detected near the star at a projected separation of about 47 AU. The position of the source coincides with a deficit in polarization observed from the circumstellar disk. This suggests a physical link between the source and the disk. Considering various scenarios, the authors favor interpreting the source as a young protoplanet currently forming within the disk. Follow-up observations could distinguish between different possible explanations for the observed features. If confirmed, it would be a unique opportunity to study giant planet formation within an optically thick disk.
Type iax supernovae_a_new_class_of_stellar_explosionSérgio Sacani
Type Iax supernovae are a new class of stellar explosions that are spectroscopically similar to Type Ia supernovae but have lower maximum light velocities and peak magnitudes. They typically have lower ejecta masses and hotter photospheres than Type Ia. The progenitor system is likely a carbon-oxygen white dwarf that accretes matter from a helium star companion, resulting in a deflagration explosion that does not fully disrupt the white dwarf. Type Iax events occur about 31 times as frequently as Type Ia supernovae.
A rapidly spinning_supermassive_black_hole_at_the_centre_of_ngc1365Sérgio Sacani
1) XMM-Newton and NuSTAR observed the galaxy NGC 1365 simultaneously over 130 ks, detecting broadband X-ray emission from 3-79 keV.
2) The observations revealed variable absorption below 10 keV and prominent broad emission features between 5-7 keV and 10-30 keV, indicative of relativistic reflection from an accretion disk near a spinning supermassive black hole.
3) Time-resolved spectral analysis was able to disentangle the variable absorption component from the relativistic reflection component. Absorption-dominated models without reflection could be ruled out statistically and on physical grounds.
Apartes de la conferencia de la SJG del 14 y 21 de Enero de 2012: Gravitation...SOCIEDAD JULIO GARAVITO
1) The document discusses the potential detection of gravitational waves from the ejection of superluminal jet components and precession of accretion disks dynamically driven by the Bardeen-Petterson effect around spinning black holes.
2) It suggests that ejection of ultrarelativistic jet components may be associated with the precession of the accretion disk induced by the black hole's spin and fragmentation of the tilted disk due to the Bardeen-Petterson effect.
3) It computes the characteristic amplitude and frequency of gravitational wave bursts that could be produced during the early acceleration phase of launching superluminal jet components, finding they may be detectable by the gravitational wave observatory LISA.
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
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
50 Years of the Astronomy Centre at the University of SussexPeter Coles
This summarizes about 50 research papers and other notable events, approximately one for each year of existence of the Astronomy Centre at the University of Sussex (1966-2016). Shown at a special event on 15th October 2016. to mark the 50th Anniversary
Herman mosquera2011 nonlinear electrodynamics and the pioneer 1011 spacecraftSOCIEDAD JULIO GARAVITO
1) The document discusses the unexplained "Pioneer anomaly" - an anomalous blueshift in radio signals from the Pioneer 10/11 spacecraft that suggests they are accelerating under an unexplained force.
2) Conventional explanations like gravitational effects, solar radiation pressure, and modified dynamics have been ruled out. The anomaly appears to be related to the electromagnetic sector rather than gravity.
3) The document proposes that nonlinear electrodynamics (NLED), where the electromagnetic field depends nonlinearly on the field strength, could explain an anomalous frequency shift in photons as they propagate through space without interacting with matter. This effect is called "photon acceleration".
The document summarizes a study that presents the first panoramic view of the outskirts of the Milky Way analogue galaxy NGC 891 based on ground-based imaging. The key findings are:
1) Numerous stellar overdensities and coherent substructures were detected out to distances of ~90 kpc from the center of NGC 891, including a giant stream looping around the galaxy up to ~50 kpc.
2) A previously undetected large, flat, and thick cocoon-like stellar structure was found surrounding the bulge and disk of NGC 891 out to radial distances of ~40 kpc and vertical distances of ~15 kpc.
3) The properties of the substructures suggest NGC
This document summarizes an analysis of high resolution infrared spectra from the Cassiopeia A supernova remnant taken by the Spitzer Space Telescope. The analysis finds:
1) The reverse shock of the remnant is spherical to within 7%, though offset from the geometric center by 810 km/s.
2) Nucleosynthetic layers of Si and O show velocities differing by up to 500 km/s in some directions, indicating separation during the supernova.
3) Small-scale corrugated velocity structures seen in the ejecta likely formed during the supernova rather than by later instabilities at the remnant's reverse shock.
This document summarizes the discovery of Kepler-413b, a Neptune-sized circumbinary planet orbiting the eclipsing binary star system Kepler-413. The planet has an orbital period of approximately 66 days and an eccentric orbit with a semimajor axis of 0.355 AU. Analysis of the Kepler light curve revealed the planet's orbit is misaligned with the binary star plane by about 2.5 degrees, causing it to sometimes fail to transit one of the stars. The orbital configuration of the system places the planet interior to the habitable zone but its obliquity may undergo fluctuations on precession timescales.
Discrete and broadband electron acceleration in Jupiter’s powerful auroraSérgio Sacani
The most intense auroral emissions from Earth’s polar regions,
called discrete for their sharply defined spatial configurations, are
generated by a process involving coherent acceleration of electrons
by slowly evolving, powerful electric fields directed along the
magnetic field lines that connect Earth’s space environment to its
polar regions1,2. In contrast, Earth’s less intense auroras are generally
caused by wave scattering of magnetically trapped populations of
hot electrons (in the case of diffuse aurora) or by the turbulent or
stochastic downward acceleration of electrons along magnetic field
lines by waves during transitory periods (in the case of broadband
or Alfvénic aurora)3,4. Jupiter’s relatively steady main aurora has a
power density that is so much larger than Earth’s that it has been
taken for granted that it must be generated primarily by the discrete
auroral process5–7. However, preliminary in situ measurements of
Jupiter’s auroral regions yielded no evidence of such a process8–10.
Here we report observations of distinct, high-energy, downward,
discrete electron acceleration in Jupiter’s auroral polar regions. We
also infer upward magnetic-field-aligned electric potentials of up to
400 kiloelectronvolts, an order of magnitude larger than the largest
potentials observed at Earth11. Despite the magnitude of these
upward electric potentials and the expectations from observations
at Earth, the downward energy flux from discrete acceleration is less
at Jupiter than that caused by broadband or stochastic processes,
with broadband and stochastic characteristics that are substantially
different from those at Earth.
The high albedo of the hot jupiter kepler 7 bSérgio Sacani
This document summarizes the analysis of Kepler photometry data for the exoplanet Kepler-7b. Key findings include:
1) The occultation depth is measured to be 44±5 ppm, translating to a Kepler geometric albedo of 0.32±0.03, the most precise value measured for an exoplanet.
2) The planetary orbital phase lightcurve is characterized with an amplitude of 42±4 ppm.
3) Atmospheric modeling finds it unlikely that the high albedo is due to a dominant thermal component. Two possible explanations are proposed: excess reflection from clouds/hazes, or depleted atmospheric sodium and potassium allowing Rayleigh scattering to dominate.
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.
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
For their production group, the document discusses how conducting a risk assessment is required by law to identify potential hazards during filming and minimize risks. It will consider hazards like slipping or equipment issues and place results in a table. The goal is to make the film crew as safe as possible and avoid injuries that could hinder production. The risk assessment should be completed before filming begins.
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
The document discusses the characteristics of tourism as a place-oriented activity. Tourism destinations are multi-product areas that attract multi-segment markets. Local resources are essential to differentiate destinations but are sensitive to overuse. Innovation in tourism services has occurred through technologies like computer reservations systems and is increasingly knowledge-based. Tourism clusters involve many activities across accommodation, food, transportation, culture and more. Smart specialization in tourism faces challenges in combining tacit local knowledge with academic expertise.
The US solar market grew in 2009 despite the recession. Photovoltaic installations increased by 40% overall, with residential installations doubling and utility installations tripling. However, non-residential installations saw no growth. California remained the largest market, but many other states like New Jersey and Florida saw installations more than double. The outlook for continued growth in 2010 and beyond is positive due to policy incentives and new project announcements.
The document discusses how social media and the internet have enabled protests and revolutions around the world. It describes several instances where individuals' deaths were captured on video and spread online, galvanizing movements in Tunisia, Iran, London, and the US. It also discusses instances where governments have shut down internet access in an attempt to suppress protests, like in Egypt and at BART stations in San Francisco, but this tended to further energize protesters. The document argues that access to communication tools is important for protecting free speech and the ability to organize.
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 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.
Studies of ngc_6720_with_calibrated_hst_wfc3_emission_line_filter_imagesSérgio Sacani
This study uses calibrated Hubble Space Telescope images of the Ring Nebula (NGC 6720) taken 12.925 years apart to measure tangential motions within the nebula. Individual features were measured in nitrogen emission line images as well as dark knots seen against oxygen emission. The results indicate that the nebula is expanding homologously, but at a faster rate along its major axis. Dark knots were found to expand more slowly than the nebular gas. The tangential motion measurements allow estimates of the nebula's distance and dynamic age to be about 720 pc and 4000 years, respectively.
This document summarizes observations from integral field spectroscopy of the low-luminosity Seyfert galaxy NGC 5033 using the INTEGRAL system on the William Herschel Telescope. The Hβ emission line map shows a spiral or ring-like pattern of HII regions, while the [OIII] map shows a markedly asymmetric morphology, indicating ionized gas illuminated by the active galactic nucleus. Kinematic analysis reveals important deviations between the [OIII] emitters and stellar velocity field, related to the asymmetric ionization structure. The Seyfert 1 nucleus is identified by its broad Hβ emission and located in an obscured region with the bluest spectral energy distribution.
This paper presents a study of the extended X-ray emission in the Seyfert galaxy NGC 4151 using deep Chandra observations. Key findings include:
1) Emission line maps show strong OVII, OVIII, and NeIX line emission extending along the northeast-southwest direction, consistent with an ionization cone.
2) Spectral analysis finds the extended emission is well described by photoionized plasma models, supporting a dominant role for nuclear photoionization.
3) Faint extended emission is also seen perpendicular to the ionization cone, indicating some leakage of nuclear ionizing radiation through warm absorbers rather than being blocked by an obscuring torus.
This document describes observations of Cepheid variables in the host galaxies of two Type Ia supernovae, SN 1995al in NGC 3021 and SN 2002fk in NGC 1309, using the Hubble Space Telescope. The observations aim to increase the sample of reliably calibrated supernovae to improve the measurement of the Hubble constant. New Cepheids were discovered, including many with periods over 60 days. Metallicity measurements of the galaxies' H II regions were also consistent with solar metallicity. The new data on the supernovae and Cepheids will help strengthen the distance ladder and reduce systematic uncertainties in the determination of the Hubble constant.
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.
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
Alignment of th_angular_momentum_vectors_of_planetary_nebulae_in_the_galactic...Sérgio Sacani
This document analyzes the orientations of 130 planetary nebulae (PNe) in the Galactic Bulge to investigate whether there is a preferred alignment. It finds that while the full sample shows a uniform distribution, the bipolar PNe exhibit a non-uniform distribution with a mean orientation along the Galactic plane at a 90 degree position angle, significant at the 0.001 level. This indicates that the orbital planes of binary systems in old stars are oriented perpendicular to the Galactic plane, likely due to strong magnetic fields during star formation that influenced the angular momentum vectors.
This document summarizes the discovery and analysis of a Type Ia supernova (SN Ia) at a redshift of 1.71, the most distant spectroscopically confirmed SN Ia at the time. The Hubble Space Telescope was used to obtain spectroscopy and photometry of the supernova. Analysis of the spectroscopy confirms it as a SN Ia with 92% confidence. The photometry is used to determine the supernova's distance, which agrees with the predictions of the ΛCDM cosmological model. This distant supernova helps improve constraints on the nature and behavior of dark energy in the early universe.
The pillars of_creation_revisited_with_muse_gas_kinematics_and_high_mass_stel...Sérgio Sacani
The document discusses observations of the Pillars of Creation in the Eagle Nebula using integral field spectroscopy from the MUSE instrument on the VLT. For the first time, the study maps physical parameters like extinction, density, temperature, and velocity across the pillars. The data show that the pillar tips have high densities and are being photoevaporated by the massive stars in NGC 6611. The kinematics indicate a blueshifted photoevaporative flow, consistent with simulations. The 3D geometry of the pillars is inferred, with some in front of and some behind the ionizing stars. A previously unknown outflow is detected from the middle pillar, suggesting an embedded protostar.
Identification of the central compact object in the young supernova remnant 1...Sérgio Sacani
Oxygen-rich young supernova remnants1
are valuable objects
for probing the outcome of nucleosynthetic processes in massive
stars, as well as the physics of supernova explosions.
Observed within a few thousand years after the supernova
explosion2
, these systems contain fast-moving oxygen-rich and
hydrogen-poor filaments visible at optical wavelengths: fragments
of the progenitor’s interior expelled at a few thousand
kilometres per second during the supernova explosion. Here
we report the identification of the compact object in the supernova
remnant 1E 0102.2–7219 in reprocessed Chandra X-ray
Observatory data, enabled by the discovery of a ring-shaped
structure visible primarily in optical recombination lines of
Ne i and O i. The optical ring has a radius of (2.10 ± 0.35)″≡
(0.63 ± 0.11) pc, and is expanding at a velocity of 90 . 5 30
+40 − km s−1
.
It surrounds an X-ray point source with an intrinsic X-ray luminosity
Li
(1.2–2.0 keV) = (1.4 ± 0.2) × 1033 erg s−1
. The energy
distribution of the source indicates that this object is an isolated
neutron star: a central compact object akin to those
present in the Cas A3–5
and Pup A6 supernova remnants, and
the first of its kind to be identified outside of our Galaxy.
An exceptional xray_view_of_the_young_open_cluster_ngc6231Sérgio Sacani
The XMM-Newton satellite observed the young open star cluster NGC 6231 for a total of 180 kiloseconds, providing an unprecedented X-ray view. Around 600 point-like X-ray sources were detected, including many early-type O stars. The data helped refine the relationship between X-ray and bolometric luminosities for O stars, finding less scatter than previously thought, with the main exception being X-ray emission from wind interactions in binary systems. The data also provided insight into the low-mass pre-main sequence star population and star formation history of the cluster.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
This document summarizes a study of the outer rings of supernova SN 1987A using spectroscopy and archival Hubble Space Telescope images spanning 11 years. The study finds:
1) Light curves of emission lines from the outer rings show a declining behavior, consistent with initial supernova flash powering.
2) Electron densities in the outer rings are <3,000 cm-3 and have not changed in 15 years. Temperature remains at ~12,000 K.
3) Densities may be highest (~5,000 cm-3) in the southern outer ring, which shows slightly faster decline in H-alpha emission.
4) Interaction between supernova ejecta and outer rings could begin within ~
Detection of the_central_star_of_the_planetary_nebula_ngc6302Sérgio Sacani
This document reports on the first direct detection of the central star of the planetary nebula NGC 6302 using the Wide Field Camera 3 on the Hubble Space Telescope. Photometry of the central star was obtained in two narrowband filters, F469N and F673N, from which the reddening was estimated to be c=3.1, corresponding to AV=6.6 magnitudes of extinction. Comparison to evolutionary tracks suggests the central star has a temperature of around 200,000 K, luminosity of 2000 L☉, and the nebula is around 2,200 years old. The high extinction from dust in the nebula had previously prevented direct detection of the central star.
Deja vu all_over_again_the_reapperance_of_supernova_refsdalSérgio Sacani
O Telescópio Espacial Hubble das agências NASA e ESA registrou a imagem pela primeira vez da explosão prevista de uma supernova. O reaparecimento da supernova Refsdal foi calculado a partir de diferentes modelos de aglomerados de galáxias, cuja imensa gravidade está entortando a luz da supernova.
Muitas estrelas terminam a sua vida com uma explosão, mas somente poucas dessas explosões estelares têm sido registradas no ato que acontecem. Quando isso acontece, é pura sorte, pelo menos até agora. No dia 11 de Dezembro de 2015, os astrônomos não somente fizeram a imagem de uma supernova em ação, como também observaram quando e onde ela estava prevista para acontecer.
A supernova, apelidada de Refsdal, foi registrada no aglomerado de galáxias, conhecido como MACS J1149.5+2223. Enquanto que a luz do aglomerado gasta cerca de cinco bilhões de anos para chegar até nós, a supernova explodiu muito tempo antes, a aproximadamente 10 bilhões de anos atrás.
A história da Refsdal começou em Novembro de 2014, quando os cientistas registraram quatro imagens separadas da supernova num raro arranjo conhecido como Cruz de Einstein, ao redor de uma galáxia dentro do MACS J1149.5+2223. A ilusão de óptica cósmica ocorreu devido ao fato da massa de uma única galáxia dentro do aglomerado estar entortando e ampliando a luz da distante explosão estelar, num processo conhecido como lente gravitacional.
Models of the_intergalactic_gas_in_stephan_quintetSérgio Sacani
This document summarizes a numerical simulation study of the intergalactic gas in Stephan's Quintet galaxy group. The simulation uses smoothed particle hydrodynamics to model the formation of hot X-ray gas, large-scale shocks, and emission line gas seen in observations, as NGC 7318b collides with the group. The simulation reproduces the general morphology of the group, but requires adjustments to better match velocities and temperatures seen in radio, X-ray, and infrared observations. Future work will fine-tune the model parameters and cooling processes to improve agreement with multi-wavelength data.
1) NGC 474 is a lenticular galaxy surrounded by shells of matter whose origin is still debated - they could have formed from merging with a low mass galaxy or gravitational interaction with satellite galaxy NGC 470.
2) Photometric analysis of NGC 474 found its surface brightness profile is typical for a lenticular galaxy even in the center, and the color indices of the shells are consistent with NGC 474.
3) This implies the shells most likely originated from gravitational interaction with NGC 470 rather than from merging, as merging would have disturbed the central surface brightness profile.
1) NGC 474 is a lenticular galaxy surrounded by shells of matter whose origin is still debated.
2) Through surface photometry, the authors found that NGC 474's surface brightness profile is typical for a lenticular galaxy even in its central parts, and the color indices of the shells are consistent with NGC 474.
3) This implies that the shells likely originated from gravitational interaction with the nearby satellite galaxy NGC 470 rather than from the merging of two galaxies, as mergers would have disturbed NGC 474's central regions.
Similar to Shaping the glowing_eye_planetary_nebula_ngc6751 (20)
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
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.
Climate extremes likely to drive land mammal extinction during next supercont...
Shaping the glowing_eye_planetary_nebula_ngc6751
1. The Astrophysical Journal, 722:1260–1268, 2010 October 20 doi:10.1088/0004-637X/722/2/1260
C 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
SHAPING THE GLOWING EYE PLANETARY NEBULA, NGC 6751
ı ı ´
D. M. Clark, Ma. T. Garc´a-D´az, J. A. Lopez, W. G. Steffen, and M. G. Richer
Instituto de Astronom´a, Universidad Nacional Aut´ noma de M´ xico, Campus Ensenada, Ensenada, Baja California, 22800, Mexico;
ı o e
dmclark@astrosen.unam.mx, tere@astrosen.unam.mx, jal@astrosen.unam.mx, wsteffen@astrosen.unam.mx, richer@astrosen.unam.mx
Received 2010 February 23; accepted 2010 August 24; published 2010 September 28
ABSTRACT
NGC 6751 is a highly structured multiple-shell planetary nebula (PN) with a bipolar outflow. In this work, we
present a comprehensive set of spatially resolved, high spectral resolution, long-slit spectra and deep imaging from
San Pedro M´ rtir, Gemini, the Hα composite full sky survey and archive images from the Hubble Space Telescope
a
and Spitzer. This material allows us to identify all the main morphological components and study their detailed
kinematics. We find a thick equatorial structure fragmented into multiple knots that enclose a fast expanding
bubble with a filamentary surface structure. The knotty ring is surrounded by faint emission from a disk-like
envelope. Lobes with embedded filaments form a bipolar outflow. The equatorial ring is tilted with respect to
the line of sight and with respect to the bipolar outflow. A spherical halo surrounds the PN and there is material
further out identified as a fragmented outer halo. This information is used to derive a three-dimensional morpho-
kinematic model using the code SHAPE that closely replicates the observed image and long-slit spectra of the
nebula, providing a fair representation of its complex structure. NGC 6751 is located close to the galactic plane
and its large-scale surrounding environment is shown to be a gas-rich region. We find indications that the PN is
interacting with the interstellar medium. Emission components from an extended nebulosity located a couple of
arcminutes away from the nebula have radial velocities that are inconsistent with the rest of NGC 6751 and are
confirmed as originating from the ambient material, not related to the PN, in agreement with a previous suggestion.
Key words: ISM: jets and outflows – planetary nebulae: general – planetary nebulae: individual (NGC 6751)
Online-only material: color figures
1. INTRODUCTION ˙
0.13 and a mass loss rate M ∼ 10−6 M yr−1 . The stellar
surface composition is dominated by helium and carbon, which
NGC 6751 is a multiple-shell planetary nebula (PN) that has lead these authors to suggest the possible occurrence of a late
attracted attention in recent years due to spectacular images thermal pulse. Stanghellini & Pasquali (1995) point out that the
obtained by the Hubble Space Telescope (HST) that reveal a evolutionary and dynamical timescales between the shells seem
highly structured inner region, earning it the “Glowing Eye” significantly different and also suggest a possible born-again
nickname. Sabbadin (1984) describes it as a possible prolate scenario.
spheroid with an expansion velocity of 40 km s−1 . NGC 6751 In this work, we present the most comprehensive kinematic
was observed by Gieseking & Solf (1986) as part of their study of NGC 6751 to date. A total of nine spatially resolved,
pioneering work on bipolar, collimated outflows in planetary high-resolution long-slit spectra have been obtained over the
nebulae (PNe). They found a bipolar mass outflow oriented at main body of NGC 6751, its bipolar outflow system, the
a P.A. ∼ 100◦ embedded in an outer envelope. The observed inner and detached outer haloes, and the extended nebulosity
radial velocity of this bipolar outflow is ∼ ±30 km s−1 with located to the northeast of the PN. The spectroscopic data
respect to the systemic velocity and apparently slower than the are combined with imaging from HST, San Pedro M´ rtir a
expansion velocity of the main shell. Their data were insufficient (SPM), and a deep Gemini image that for the first time
to derive a spatial model though they estimate from general permit a complete morphological identification of the kinematic
arguments an inclination angle of 65◦ with respect to the line of components identified spectroscopically. The spectroscopic and
sight for an outflow velocity of ∼±70 km s−1 . Hua & Louise imaging information are used to produce a three-dimensional
(1990) in their search for haloes in PNe detected an extended morpho-kinematic model of the nebula using the program
filamentary nebulosity approximately 2 arcmin to the northeast SHAPE (Steffen & L´ pez 2006). Kinematics together with
o
of NGC 6751 and tentatively identified this material as part of Spitzer and SASHA imagery are used to reaffirm the origin of
a halo related to the PN, though they warned that additional the extended nebulosity as part of the gas-rich, local interstellar
evidence confirming the physical link between the extended environment. This paper is organized as follows. Section 2
nebulosity and the PN was needed. Chu et al. (1991) analyzed the describes the observations, Section 3 discusses the results,
different components of the nebula and found differences in the Section 4 presents the SHAPE model of the nebula, and we
kinematics and the He/H ratio of the extended nebulosity with finish with the conclusions in Section 5.
respect to the main nebula that lead them to suggest it as part of
the local interstellar material. The central star of NGC 6751 has 2. OBSERVATIONS
Wolf-Rayet (W-R) characteristics (Aller 1976). Chu et al. (1991)
classify it as a hydrogen-deficient WC 4-type star. Koesterke High-resolution spectroscopic observations and monochro-
& Hamann (1997) confirm this classification and derive from matic images of NGC 6751 were obtained at the Ob-
NLTE models a stellar temperature T 140 kK, and assume a servatorio Astron´ mico Nacional at SPM, Baja California,
o
luminosity log L/L = 5000 to derive a stellar radius R/R = M´ xico on two observing runs, 2006 September 10 and 2008
e
1260
2. No. 2, 2010 SHAPING THE GLOWING EYE PN, NGC 6751 1261
Ha+[NII] [OIII]
1’
Figure 1. Deep, Hα+[N ii] and [O iii] images of NGC 6751 obtained at SPM. The inset shows an HST image of the nebula that shows its complex inner structure.
North is up and east is to the left. Note the two prominent twisted filaments to the east and west of the nebula in the Hα+[N ii] image, also discernible in the HST
image. The inner halo is apparent in the [O iii] image.
September 7–9. The observations were obtained with the their archive. A wide field 25◦ , Hα image from the Hα full sky
Manchester Echelle Spectrometer (MES-SPM; Meaburn et al. map (Finkbeiner 2003), was obtained from the SkyView web
2003) on the 2.1 m telescope in its f/7.5 configuration. The tool.
instrument was equipped with the SITE-3 CCD detector con-
sisting of 1024 × 1024 square pixels, each 24 μm on a side. 3. RESULTS AND DISCUSSION
We used a 90 Å bandwidth filter to isolate the 87th order con-
taining the Hα and [N ii] λλ6548, 6584, nebular emission lines. 3.1. Morphology
Two-by-two binning was employed in both the spatial and spec- Figure 1 shows two deep images of NGC 6751 obtained
tral directions. Consequently, 512 increments, each 0. 624 long with MES-SPM in its imaging mode in the light of Hα+[N ii]
gave a projected slit length of 5.32 on the sky. We used a slit and [O iii]. The Hα+[N ii] image shown here is saturated in
150 μm wide (≡ 11 km s−1 and 1. 9). During the observations the central region in order to highlight the seemingly point-
the slit was oriented at slightly different position angles along symmetric filaments on the west and east side of the main
the bipolar outflow, specifically, 97. 5, 99. 5, and 101◦ and one
◦ ◦
shell. The [O iii] image clearly exhibits a bright rim and a
◦
pointing at P.A. = 0 across the center of the nebula. Narrow- surrounding spherical halo with a radius of 27 that incidentally
band images in the light of Hα and [N ii] and [O iii] λ5007 were corresponds to the “outer envelope” described by Gieseking &
also obtained with MES-SPM in its imaging mode. All spectra Solf (1986). Outside of the 27 inner halo, there is additional
and images were acquired using exposure times of 1800 s. The emission corresponding to an outer halo in the form of a
spectra were calibrated in wavelength against the spectrum of a broken filament at a radius of ∼44 –50 . In addition, extended
Th/Ar arc lamp to an accuracy of ±1 km s−1 when converted filamentary nebulosity can be appreciated up to nearly 2 away
to radial velocity. The data were reduced using IRAF1 routines, to the north and northeast of the PN in both images. The inset
to correct bias, remove cosmic rays, and wavelength-calibrate in the Hα+[N ii] image contains the HST image with the same
the two-dimensional spectra. All spectra presented in this paper orientation showing the opposite outflows and the bright, knotty
are corrected to heliocentric velocity (Vhel ). structure that encircles the rich filamentary central bubble.
Additional material. A deep Gemini image obtained with Figure 2 shows the gray-scale version of the superb Gemini
GMOS in its imaging mode has been made available to us by image where all the elements described in Figure 1 can be
Christopher Onken from the Australian Gemini Office (Gemini clearly seen. Of particular relevance are the faint bipolar lobes
Program ID GS-2009A-Q-22, PI: Terry Bridges). This image that surround the filaments and are clearly revealed here for
is the result of the winning entry in the 2009 Gemini School the first time. The filaments that appear as point symmetric in
Astronomy Contest, submitted by high school student Daniel Figure 1 are embedded in the lobes, the latter correspond to the
Tran. Image credits are Daniel Tran (PAL College), Travis Rec- “puzzling oval” described by Chu et al. (1991).
tor (University Alaska Anchorage), Terry Bridges (Queen’s
University), and the Australian Gemini Office. The origi- 3.2. Kinematics
nal color image (http://www.gemini.edu/node/11329) received
1 hr of Gemini telescope time and is the result of combining nar- In Figure 3 we present the deep, Hα+[N ii] image of
rowband images obtained in the light of Hα, [S ii], and [O iii]. NGC 6751 taken at SPM overlaid with the nine slit positions
The HST image of NGC 6751 was obtained from the STScI Web we observed. The right panel of this figure shows the location
site and is part of the Hubble Heritage Team collection.2 Images of the slits on the HST image for a better visualization of their
from the 8 μm IRAC Spitzer3 work survey were obtained from location over the central region of the nebula.
Figure 4 presents the position–velocity (P–V) arrays corre-
1 IRAF is distributed by the National Optical Astronomy Observatory, which sponding to the [N ii] line profiles for each slit position. In each
is operated by the Association of Universities for Research in Astronomy, Inc., case, the corresponding synthetic P–V array derived from the
under cooperative agreement with the National Science foundation. SHAPE model (see the next section) is shown next to the ob-
2 HST image credit: NASA, ESA, and the Hubble Heritage Team
(STScI/Aura). served line profile (see Figure 9, panel (f), for component labels).
3 The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, In slit (a) (top left in Figure 4), the emission located at offset
California Institute of Technology under contract with NASA. 165 is from the local interstellar medium (ISM; see Figure 7,
3. 1262 CLARK ET AL. Vol. 722
unprecedented coverage of the long-slit spectra together with
the Gemini and HST images allow us to separate the constituent
parts of the nebula and study them individually.
In Figure 5, we present a mosaic with each panel highlighting
different components of NGC 6751. In each panel are indicated
the slit positions corresponding to the relevant component, i.e.,
the outer halo, the inner halo, the filamentary, bipolar lobes, and
the knotty ring. The information corresponding to the extended
nebulosity is shown separately in Figure 7 since, as discussed
below, this material shows evidence of not being part of the
PN. The length and positions indicated for the slits in Figure 5
show the approximate location of the slit and the spatial extent
along which kinematic data have been extracted. The kinematic
data for each panel in Figure 5 are presented in Table 1. The
corresponding data for the slits indicated on the right panel in
Figure 7 are indicated directly on that figure. The velocities
of the central bubble, corresponding to the velocity ellipsoids
apparent in the line profiles in Figure 4 (and Figure 6, see below),
are listed directly in Table 1.
The heliocentric systemic velocity of NGC 6751 is measured
at Vsys = −31.7(±2) km s−1 , derived from both slits (g) and
(a) that pass through the central star (see Figure 6). This value
is lower than those quoted by Chu et al. (1991) and Sabbadin
(1984) of Vsys = −42 and −39 km s−1 , respectively. The origin
of this difference is unclear.
One can easily discern the distinct kinematic signature of
each component of NGC 6751 from Table 1. The outer halo
Figure 2. Gray-scale version of the Gemini image of NGC 6751 the original is characterized by heliocentric velocities of the order of
color-coded image is the result of separate exposures in the light of Hα, [S ii],
and [O iii] and is shown in the electronic version. This image shows clearly for
Vhel −15 km s−1 whereas the inner halo shows values of
the first time all the structural components of this complex nebula, as described Vhel −31 km s−1 on average. The bipolar lobes show distinct
in the text (and see also Figures 5 and 7 where these components are labeled). expansion velocities with the blueshifted side at about Vhel =
Image credits are Daniel Tran (PAL College), Travis Rector (University of 0 km s−1 and the redshifted one at Vhel = −62 km s−1 , average
Alaska, Anchorage), Terry Bridges (Queen’s University), and the Australian values. For slits (d)–(f), we were able to measure the velocity of
Gemini Office (http://www.gemini.edu/node/11329).
the lobes for regions close to but outside the brighter filaments,
(A color version of this figure is available in the online journal.)
these values are listed as the second row of values in Table 1
for those slits. The lobe velocities are very similar to those of
panel (b)) as discussed below, and the one at offset 115 is the filaments. This coincidence in velocities indicates that the
from the outer halo, the model does not include these structural filaments and lobes are part of the same bipolar outflow, i.e.,
components. Figure 4 includes all observed positions except the filaments do not seem to represent high-velocity elements
position b, which is shown in Figure 7. Slit (a) is at a P.A. of 0◦ advancing through a slower moving envelope formed by the
with north at the top and south at the bottom of the P–V profile lobes, as is sometimes observed in some PNe, but rather seem
in the figure. Slits (b) and (c) are at a P.A. of 101◦ , slits (d)–(g) to be denser filaments than the surrounding material, embedded
◦ ◦ in the bipolar outflow and flowing as part of the lobes. The
at a P.A. of 97. 5, and slits (h)–(i) at a P.A. of 99. 5. In these
slits the western side is at the top of the line profile and the Gemini image provides some hints that indicate that these denser
eastern side at the bottom of the P–V profiles in the figure. The filaments run predominantly along opposite walls of the bipolar
NGC 6751 a
a
b
c d
e
f
g
i h
1’
Figure 3. Left panel: the positions of the long slits are indicated against a deep, Hα+[N ii] image of NGC 6751 obtained at SPM. North is up, east is to the left, and
the image scale is shown at the lower left. Right panel: the HST image is used to show more clearly the location of the central long slits over the lobes, knotty ring,
and filamentary central bubble in this confined area. The HST image covers ≈ 1 ×1 .
4. No. 2, 2010 SHAPING THE GLOWING EYE PN, NGC 6751 1263
Figure 4. For each slit position there is a pair of P–V arrays, the observed [N ii]λ 6583 line profile on the left and the corresponding synthetic P–V array modeled with
SHAPE on the right side. The P–V array corresponding to slit position (b) is shown in Figure 7. See Figure 9, panel (f), for component labels. The SHAPE model does
not include the outer halo. For slit (a), north is at the top and south at the bottom, for all the others, west is at the top and east at the bottom of the P–V array.
Table 1
Vhel for the Different Components of NGC 6751
Slit Outer Halo Inner Halo Bipolar Lobes Ring Knots Bubble
Vhel (km s−1 ) Vhel (km s−1 ) Vhel (km s−1 ) Vhel (km s−1 ) Vhel (km s−1 )
(a) −19.3; −15.3 −35.8; −30.3 ··· −23.5, −53.5; −34.8 +11.2; −73.6
(c) ··· −31.5, −33.3, −35.6, −31.9 ··· ··· ···
(d) −14.3; · · · −19.8; −28.4 −3.4; −65.8 −44.4; −27.5 +0.7; −63.5
+1.6; −59.4
(e) −15.6, −16.1; · · · −33.9; −27.9 −1.0; −65.3 −43.0; −27.0 +6.7; −72.1
· · · ; −58.9
(f) −12.8, −13.7; −16.4 −31.0; −27.4 −0.5; −63.4 −40.6; −24.6 +9.1; −73.4
· · · ; −61.1
(g) −8.9, −10.2; −14.8 −33.9; · · · +3.4; −61.3 −39.4; −24.4 +5.2; −70.9
(h) −11.3 · · · ; −15.0 −33.2; · · · · · · ; −60.1 −34.1; −24.1 +2.4; −67.4
(i) · · · · · · ; −18.7 −28.2, −35.1, −31.0, ··· ··· ···
−44.6, −35.1, −30.5
Notes. Vhel measured for the segments of the slits indicated in Figure 5. The measurements are listed north first then south for slit (a)
and from east to west for all other slits. Values measured on one side of the nebula are separated from the other side by a semicolon.
5. 1264 CLARK ET AL. Vol. 722
Outer halo Inner Halo
a
a
c
f d
d h d e
e g e f
f i f
g g i
h h
a
a
Lobes Ring knots
a
d
d e d d
e f e e
f g f f
g h g g
h h
a
Figure 5. Slit positions and length over which kinematic data are extracted and tabulated in Table 1 are indicated in each panel for different main components of
NGC 6751, as indicated in each panel.
lobes, producing the point-symmetric shape apparent in ground- the main components of the inner regions of the PN that we
based images (e.g., see the Hα+[N ii] image in Figure 1) such have already discussed, namely, the velocity ellipsoid from the
as in the case of the bipolar PN Hb 5. central expanding bubble, the conspicuous, bright knots from the
A system of knotty structures defines a ring that encircles surrounding ring located at the external border of the velocity
the central bubble (see Figure 6), the velocities of these knots ellipsoid, and the bipolar lobes located outside the velocity
have predominantly radial motion away from the central star, ellipsoid showing opposite velocities (see Figure 9, panel (f), for
following the velocity ellipsoid of the central bubble and are an identification of these components on the synthetic P–V array
located at its outer border. Opposite knots in the ring show of slit (g)). Moreover, additional condensations are apparent in
however a clear velocity difference between the east and the P–V line profiles in Figure 6, along the walls of the velocity
west sides, the eastern side shows an average velocity Vhel ellipsoid, indicating that these are series of dense regions at the
−40 km s−1 and the western side a Vhel −26 km s−1 , surface of the highly structured expanding shell (see the right
indicating a tilt in the ring with respect to the line of sight, panel in Figure 3). The P–V arrays in this figure also reveal
with the eastern side on the near side and the western part on that the emission from the knots is always accompanied by
the far side. An additional indication of the spatial orientation faint radial extensions that appear to be emission from a disk-
of the ring is given by the systematic decrease in values from like envelope to this ring, perhaps formed by photoevaporated
top (north) to bottom (south) in the ring, apparent in Table 1, material and stellar wind overrunning the ring of knots. Also,
suggesting that the top (north) of the ring is also tilted forward. we detect an additional high-velocity component that manifests
The expansion velocities of the central bubble show the itself as faint, diffuse emission located between the spatial
expected monotonic decrease in values from the slits located offsets that enclose the central expanding shell. It doubles the
away from the center, though there is some deviant behavior expansion velocity described by the velocity ellipsoid, i.e., it
from the smooth velocity ellipsoid that would represent a runs approximately from Vhel −120 to +60 km s−1 .
spherically expanding bubble in some cases, such as slit (d). As for the extended nebulosity, values shown in Figure 7,
The average expansion velocity of the central bubble, taken panel (b), indicate velocities of the order of Vhel +29 km s−1 ,
as half the peak-to-peak velocity difference from the values this velocity is very different from the rest of the nebula
listed in Table 1 for slits (a) and (f) that cross the center of the and a strong indication that this gas is unrelated to the PN.
nebula, yields 42 km s−1 , this is considered an above average Further evidence in this regard is substantiated by examining
expansion value for a PN (e.g., Richer et al. 2010). the surroundings of NGC 6751. Panel (a) in Figure 7 shows a
For a further scrutiny of the kinematics of NGC 6751, a mosaic from the Spitzer Infrared Array Camera 8 μm images
close-up of the six P–V line profiles from the central region of that reveals that the extended diffuse emission seen to the
the nebula (slits (a), (d), (e), (f), (g), and (h), see Figure 3) northeast of NGC 6751 continues extending at least 10 to the
is presented in Figure 6. In these panels, one can identify north. Panel (c) shows a much wider 30◦ × 30◦ field of view of
6. No. 2, 2010 SHAPING THE GLOWING EYE PN, NGC 6751 1265
Figure 6. Close-up view of the six [N ii] P–V line profiles from the central region of the nebula. The data are displayed with a square root intensity scale to show at
the same time the bright ring knots and the faint, high-velocity material and other components discussed in the text. The continuum from the central star is apparent
in the panels for slits (a) and (f) (top and bottom left).
the region from the Hα composite full sky map (Finkbeiner Table 2
2003) with separate zoom levels at 15◦ × 15◦ and 5◦ × 5◦ Average Expansion with Respect to Vsys , Dimensions, and Timescales
around the position of NGC 6751 that make it clear that this Component Vexp = Vhel − Vsys (km s−1 ) Radius ( ) t (yr)
PN is embedded in a gas-rich environment within the disk of
Outer halo +16.9 50
the Milky Way. The present results together with those from Inner halo 2 27 1.28 × 105
Chu et al. (1991) provide plausible evidence that this extended Bipolar lobes ±31(±79) 21 2.80 × 103
nebulosity is unrelated to NGC 6751. Central bubble 41.8 12 2.72 × 103
Table 2 lists the average expansion velocities measured from Ring knots 7(40) 22 5.13 × 103
the different components of NGC 6751 with respect to the Diffuse high velocity ±90 16 1.69 × 103
systemic velocity Vsys = −31.7 km s−1 , i.e., Vexp = Vhel − Vsys , Extended nebulosity +58.7 114
their corresponding radii, and kinematic timescales. A distance
of 2 kpc (Chu et al. 1991) has been adopted. These velocities Notes. Deprojected velocities are listed within parenthesis. For the bipolar lobes,
provide the expansion pattern of the material with respect to a tilt with respect to the plane of the sky of 23◦ is considered and 10◦ for the
the nebula’s reference frame, without considering projection ring. A distance of 2 kpc to NGC 6751 has been adopted.
effects. The values in Table 2 indicate that the outer halo is
receding from the nebula, whereas the inner halo is essentially ring is 10◦ , and the deprojected value in this case is also shown
inert. The bipolar lobes have a projected outflow velocity of in parenthesis. The high-velocity, faint, diffuse material that
±31 km s−1 (in good agreement with the values derived by engulfs the ring and central bubble expands at ≈ ±90 km s−1 ,
Gieseking & Solf 1986). Table 2 also lists in parenthesis the and finally the extended nebulosity located to the northeast of
deprojected velocity for the bipolar outflow considering a tilt of the nebula shows a large receding velocity of +59 km s−1 in clear
23◦ with respect to the plane of the sky derived from our model disagreement with the values of the other components related to
(see below). The central bubble expands at 41.8 km s−1 and the nebula.
the knotty ring that surrounds it shows a velocity asymmetry
4. SHAPE MODELING
(−8.3 km s−1 on the east side and +5.7 km s−1 on the west
side) that is interpreted as a projection effect due to a tilt of the To understand the complex three-dimensional structure and
ring with respect to the sightline. The model derived tilt for the kinematics of NGC 6751, we used the program SHAPE (Steffen
7. 1266 CLARK ET AL. Vol. 722
(a) (b) b
a W
+29.9
+27.7
b
+26.3
+27.7
E
+30 c
+34.2 h
Local ISM
(c)
o 1o
5
o
5
Figure 7. Panel (a): a mosaic of two Spitzer IRAC 8 μm fields showing a wide field around NGC 6751, which is the bright source in the bottom half of the panel.
The image is saturated and the gray-scale level emphasized to bring out the faint, filamentary emission seen near this PN. The compass at the upper left corner shows
the orientation, and the length of each arrow is 1 . Panel (b): the slit positions and length over which kinematic data are extracted in the extended nebulosity. The
corresponding values of Vhel are indicated in the figure. The P–V array for slit (b) is shown in the top right corner. Panel (c): a wide field Hα image taken from the Hα
composite full sky map (Finkbeiner 2003) for three, separate zoom levels around the position of NGC 6751. The PN can be seen as the small, black dot at the center
of the last zoom level.
& L´ pez 2006). SHAPE is a morpho-kinematic modeling tool
o use the observed [N ii]P–V line profiles since they contain
that allows the user to reconstruct the three-dimensional struc- all of the main components. The model consists of five main
ture and observed spectral line profiles using diverse geomet- parts: the inner halo, the bipolar outflow, a fragmented ring,
rical forms. SHAPE uses as reference monochromatic images a disk exterior to the ring, and a central bubble with a high-
and observed P–V diagrams to reproduce the three-dimensional velocity component. The model does not include the outer halo.
structure and kinematics of the object. Particles are distributed The wire-frame model, before rendering, is shown in Figure 8
over a surface, or throughout a specified volume, and are as- where six views at different orientations (from 0◦ to 90◦ in 15◦
signed a specific velocity law and relative brightness. Several intervals) are shown. We assume that these structures obey a
particle systems can be used and each can be assigned dif- Hubble-type velocity law, except for the bubble and inner halo
ferent velocity laws to form a complex object. The resultant where we used a constant velocity. Particles were distributed on
two-dimensional image and spectral information are then ren- the surface of a sphere for the inner halo and within a volume
dered from the three-dimensional model and compared with for the bubble. For the high-velocity component, we assigned a
the real data. A key advantage of SHAPE for objects like higher velocity to the corresponding set of particles. The ring
NGC 6751 is its ability to model independent structures, each and disk are inclined by 10◦ ± 5◦ with respect to the plane
with its own velocity law, and then merge them into a sin- of the sky (western side into the plane of the sky) and exhibit
gle product. We have used velocity laws of the Hubble-type a slight warp about the north–south axis. The bipolar lobes’
v = k · r/ro , where k is a constant, r is the distance from system are formed by curved surfaces that describe the walls
the source, and ro is the distance at which the velocity k is of the opposite lobes along which run the bright filaments that
reached. The values for k and ro have been chosen to match the produce a point-symmetric appearance in the outflow. From the
observed velocities for the various components of NGC 6751 model, we derived a position angle for the bipolar outflow of
and to provide reasonable distance scales along the line of 97. 5 (277. 5) ±10◦ with an inclination of 23◦ ± 5◦ with respect
◦ ◦
sight. to the plane of the sky.
The SHAPE analysis presented here is similar to the one The results of the final rendered SHAPE model are shown in
performed by Garc´a-D´az et al. (2009) for NGC 6337. We
ı ı Figure 9, where they are compared with the basic morphology of
8. No. 2, 2010 SHAPING THE GLOWING EYE PN, NGC 6751 1267
Figure 8. Six views of the SHAPE mesh model before rendering. On the top left is the view as seen by the observer with north up and east to the left. In each successive
frame, the model has been rotated into the page by the degrees specified to the upper right. The axis of rotation is about the dotted line shown in the first image. The
outer sphere represents the inner halo and has a uniform distribution of particles (uniform emissivity). The ring and its surrounding disk are best seen in the view
tilted by 45◦ or 60◦ . The central bubble is most clearly seen in the view tilted by 90◦ . The high-velocity component is not shown but is within the bubble. The bipolar
outflow, depicted by its opposite outermost segments, is best seen in the same view tilted at 90◦ . In this same view, the particles within the bubble, above and below
the ring, represent the condensations seen in the inner regions of the velocity ellipsoids in Figure 6.
(A color version of this figure is available in the online journal.)
(a) (b) (c)
N
E
(d) (e) halo (f) halo
lobes
lobes disk
disk
bubble
ring bubble
ring
lobes lobes
halo
Figure 9. Comparisons between observations of NGC 6751 and the SHAPE models of this nebula. (a) HST image, (b) Hα+[N ii]image from SPM, (c) the observed,
[N ii] profile for slit (g), (d) SPM, [O iii] image, (e) the SHAPE model image, and (f) the synthetic, SHAPE spectrum for slit (g). In (e) and (f), we label the various
components of the nebula that we discuss in this paper. The high-velocity component is also present but it is not labeled here. All images are 1. 1 × 1. 1. The orientation
of the images is shown in panel (a).
NGC 6751 and the observed P–V line profiles (see also Figure 4). P–V array from slit position (g) that runs throughout the lobes.
The noise-like texture in the synthetic image is the result of the Panel (d) is the [O iii], MES-SPM image. The rendered, model
rendering process over the finite distribution of surface particles image is in panel (e) and the rendered model spectrum for slit
in the image. Panel (a) is the HST image and panel (b) is position (g) is in panel (f). Five main features of NGC 6751 are
the Hα+[N ii]MES-SPM image. Panel (c) shows the observed indicated in the last two panels. The images in this figure are
9. 1268 CLARK ET AL. Vol. 722
◦
rotated ∼97 counterclockwise with approximately west up and yields a deprojected velocity (±79 km s−1 ) for the bipolar
north to the left to approximately match and ease comparison of outflow.
morphological elements of the nebula with emission features in The central bubble expands at 41.8 km s−1 , and the knotty ring
the P–V arrays here and in Figures 4 and 6. The exact orientation that surrounds it shows a velocity asymmetry that is interpreted
of these images is indicated in panel (a). as a projection effect due to a tilt of the ring with respect to
The present SHAPE model successfully represents the main the plane of the sky. The model-derived tilt for the ring is ∼10◦
characteristics of the complex “Glowing Eye” nebula. It is able and the deprojected expansion velocity of the ring results in
to reproduce the basic two-dimensional morphology and the set ∼40 km s−1 , which closely matches that of the central bubble,
of complex emission line profiles that provide a representation indicating that the expansion of the ring is likely being driven by
of the third dimension of the nebula through the radial velocity the pressure from the bubble. Faint emission extending outward
component. A limitation of the model is that it cannot place from the knots is detected in the spectra and this is identified
restrictions on, for example, the exact shape of the inner halo with a disk-like extension to the knotty ring, following the same
and the central bubble, which have been assumed spherical kinematic pattern. This disk-like structure is possibly related
though a slightly prolate form is likely. In addition, the velocity to ablated material from the knots by the erosive action of
ellipsoid from the central bubble is distorted in some sections the percolating stellar wind and photoevaporation processes
due to the presence of condensations, such as filaments and producing a radial mass-loaded outflow from the knots.
knots in the inner regions of the bubble or at its surface. The The high-velocity, faint, diffuse material that engulfs the ring
model cannot disentangle the detailed differences that these and central bubble expands at ≈ ±90 km s−1 and is most
distortions produce in shape but this effect is in any case likely material directly related to the fast wind that is starting to
of minor consequence for the overall result. The model can percolate through the central regions.
neither constrain the length of the bipolar outflow, which is The timescales that result from our model indicate that the in-
considered to remain within the boundaries of the inner halo, ner halo formed some 105 years ago while the bipolar lobes, the
nor the thickness of the toroid. As discussed above, the inner central bubble, and the knotty ring occurred approximately si-
halo and central bubble are considered spheres expanding at multaneously, some (3–5) × 103 years ago, whereas the diffuse,
constant velocity, while the other components are geometrical faint, high-velocity component must be more recent. The outer
forms whose particles follow a Hubble-type velocity law (v = filamentary halo is presumably related to the mass lost during
k · r/ro ), therefore, given various values of k, one can vary the AGB stage and as such is the oldest structure of this PN, cur-
the distance, r, for a particular part of the nebula and achieve rently showing kinematic signs of an extended interaction with
a similar observed velocity. Thus, slightly different geometric the local ISM. The contrasting kinematic differences between
forms could have been used to build up the final model, but in the halos and the other structures lend credence to the hypoth-
the end there is only a very limited set of solutions that are able esis that NGC 6751 underwent a late thermal pulse (Koesterke
to replicate the complex P–V diagrams of NGC 6751. & Hamann 1997; Stanghellini & Pasquali 1995).
The extended nebulosity located to the north and northeast of
5. DISCUSSION the nebula shows a large receding velocity of +59 km s−1 in clear
We have derived a morpho-kinematic model for NGC 6751 disagreement with the values of the other components related to
that is able to replicate the main morphological and kinematic the nebula. Considering the large-scale, gas-rich environment in
components of this nebula and provides a good understanding which NGC 6751 is located, we conclude that the surrounding
of its complex structure and outflows that otherwise are rather extended nebulosity is not part of the PN.
difficult to visualize given its projected orientation on the sky.
We find six distinct structural and kinematic components in M.T.G.-D. gratefully acknowledges the support of a postdoc-
NGC 6751: outer and inner haloes, filamentary bipolar lobes, toral grant from UNAM. This research has benefited from the
a central bubble surrounded by a knotty ring, and diffuse high- financial support of DGAPA-UNAM through grants IN116908,
velocity gas. IN108506, and IN108406, and CONACYT grants 49447 and
The values in Table 2 indicate that the outer halo is receding 82066. We acknowledge the excellent support of the technical
from the nebula whereas the inner halo is essentially inert. The personnel at the OAN-SPM, particularly Gustavo Melgoza and
filaments that form the outer halo are most probably related Felipe Montalvo, who were the telescope operators during our
to the earliest stages of mass loss during the asymptotic giant observing runs.
branch (AGB) stage, and their current overall receding velocity
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