This document summarizes an astronomical study of the Trifid Nebula using X-ray and infrared observations. The ROSAT X-ray image revealed over a dozen X-ray sources in the nebula, including the bright O7 star that provides most of the ionization. Infrared observations identified 85 young star candidates. Ten X-ray sources had infrared counterparts. Spectroscopy of the brightest X-ray source with ASCA showed unusually hot plasma up to 10 keV, suggesting interaction between winds or flares from embedded young stars.
Xray and protostars_in_the_trifid_nebulaSérgio Sacani
The document summarizes X-ray observations of the Trifid Nebula using ROSAT and ASCA. ROSAT images revealed around a dozen X-ray sources in the nebula, including the bright O7 star HD 164492 that provides much of the ionization. Ten X-ray sources were correlated with near-infrared sources identified as young stars or protostars. ASCA spectroscopy of the brightest source showed hard X-ray emission up to 10 keV including an iron K line, best fit with a two-temperature thermal model and absorption. The hotter component's temperature is unusually high and may originate from interaction with another object or protostellar flares.
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
Ultraviolet signposts of resonant dynamics in the starburst ringed sab galaxy...Sérgio Sacani
1) The document analyzes ultraviolet images of the starburst-ringed galaxy M94, finding emission from the nucleus, inner disk, bright inner ring of H II regions, and two outer knots of hot stars.
2) Optical and ultraviolet spectroscopy of the nucleus and inner disk indicate a 107-108 year old stellar population with some low-level star formation and LINER activity.
3) Analysis of multi-wavelength data suggests that star formation in M94 is being driven by ring-bar dynamics involving structures like the nuclear mini-bar, inner ring, oval disk, and outer ring.
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
A candidate redshift z < 10 galaxy and rapid changes in that population at...Sérgio Sacani
The document summarizes the findings of a study searching for galaxies at redshift z > 10 using deep imaging data from the Hubble Ultra Deep Field. The key points are:
1) The study detects one possible galaxy candidate at z ~ 10.3, the earliest galaxy reported to date.
2) Regardless of detections, the star formation rate density is found to be much smaller (~10%) at z ~ 10 than just 200 million years later at z ~ 8, demonstrating rapid galaxy build-up in the first 500 million years.
3) The 100-200 million years before z ~ 10 appears to be a crucial phase in the early assembly of galaxies.
This document summarizes recent observations of Kepler's supernova remnant 400 years after the supernova was observed. The remnant remains enigmatic as the type of star that exploded is still debated and the distance is uncertain by more than a factor of two. Multiwavelength observations reveal the expanding remnant but show some inconsistencies in interpretations of the dynamics. While evidence initially pointed to a core-collapse supernova, recent X-ray analyses have alternated between supporting a Type Ia or core-collapse origin. Further observations are needed to better understand this intriguing object.
Xray and protostars_in_the_trifid_nebulaSérgio Sacani
The document summarizes X-ray observations of the Trifid Nebula using ROSAT and ASCA. ROSAT images revealed around a dozen X-ray sources in the nebula, including the bright O7 star HD 164492 that provides much of the ionization. Ten X-ray sources were correlated with near-infrared sources identified as young stars or protostars. ASCA spectroscopy of the brightest source showed hard X-ray emission up to 10 keV including an iron K line, best fit with a two-temperature thermal model and absorption. The hotter component's temperature is unusually high and may originate from interaction with another object or protostellar flares.
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
Ultraviolet signposts of resonant dynamics in the starburst ringed sab galaxy...Sérgio Sacani
1) The document analyzes ultraviolet images of the starburst-ringed galaxy M94, finding emission from the nucleus, inner disk, bright inner ring of H II regions, and two outer knots of hot stars.
2) Optical and ultraviolet spectroscopy of the nucleus and inner disk indicate a 107-108 year old stellar population with some low-level star formation and LINER activity.
3) Analysis of multi-wavelength data suggests that star formation in M94 is being driven by ring-bar dynamics involving structures like the nuclear mini-bar, inner ring, oval disk, and outer ring.
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
A candidate redshift z < 10 galaxy and rapid changes in that population at...Sérgio Sacani
The document summarizes the findings of a study searching for galaxies at redshift z > 10 using deep imaging data from the Hubble Ultra Deep Field. The key points are:
1) The study detects one possible galaxy candidate at z ~ 10.3, the earliest galaxy reported to date.
2) Regardless of detections, the star formation rate density is found to be much smaller (~10%) at z ~ 10 than just 200 million years later at z ~ 8, demonstrating rapid galaxy build-up in the first 500 million years.
3) The 100-200 million years before z ~ 10 appears to be a crucial phase in the early assembly of galaxies.
This document summarizes recent observations of Kepler's supernova remnant 400 years after the supernova was observed. The remnant remains enigmatic as the type of star that exploded is still debated and the distance is uncertain by more than a factor of two. Multiwavelength observations reveal the expanding remnant but show some inconsistencies in interpretations of the dynamics. While evidence initially pointed to a core-collapse supernova, recent X-ray analyses have alternated between supporting a Type Ia or core-collapse origin. Further observations are needed to better understand this intriguing object.
The document discusses the distance ladder, which is an attempt to determine astronomical distances by using a series of methods that build on one another. Within the Solar System, distances are measured using radar ranging. Within the galaxy, distances are measured using stellar parallax, main sequence fitting, and properties of Cepheid variable stars. Further out in the universe, distances are measured using the Tully-Fisher relation, Type Ia supernovae, brightest cluster galaxies, and Hubble's law. The document aims to answer fundamental questions about what exists in the universe and how large it is.
Astronomy - State of the Art - TelescopesChris Impey
Telescopes help us learn about the universe by collecting more light than the human eye and seeing more detail. Larger telescopes collect more light and see sharper images, but the atmosphere limits ground-based telescope resolution. Telescope size has grown exponentially over time. Adaptive optics and interferometry allow telescopes to approach the theoretical resolution limit. While space telescopes avoid many atmospheric limitations, they are much more expensive to build and operate. The Hubble Space Telescope has revolutionized astronomy through high-quality images across the electromagnetic spectrum.
Dark side ofthe_universe_public_29_september_2017_nazarbayev_shrtZhaksylyk Kazykenov
1) The document discusses the history of discoveries about the universe, from ancient cosmologies to modern precision cosmology. Key developments include realizing the sun is at the center of the solar system, discovering other galaxies and the expansion of the universe, and detecting the cosmic microwave background and dark matter.
2) Current open questions about the universe include the nature of dark matter and dark energy. Observations show dark energy is accelerating the expansion of the universe, but its underlying cause remains unknown. Precise measurements aim to distinguish between models of dark energy.
3) The standard cosmological model has been very successful in explaining observations but has fine-tuning problems regarding why the present epoch is dominated by both matter and dark energy.
This document summarizes a 1.3 mm continuum survey of protoplanetary disks in the 2-3 Myr old IC348 star cluster using the Submillimeter Array. 10 disks out of 85 young stars were detected with masses ranging from 2-6 Jupiter masses. This distribution is shifted to lower masses by a factor of 20 compared to younger regions like Taurus and Ophiuchus. The results reveal a rapid decline in the number of small dust grains in disks after 1 Myr, likely due to grain growth. The few detected disks may be the best candidates in IC348 to study planet formation.
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
A super earth transiting a naked-eye starSérgio Sacani
This document summarizes the detection of transits of an exoplanet orbiting the star 55 Cnc, using photometry from the MOST space telescope. The transits match the period, phase, duration, and depth predicted for the innermost planet of 55 Cnc, designated 55 Cnc e. Analysis of the transit data indicates the planet has a mass of 8.57 Earth masses, a radius of 1.63 Earth radii, and a dense composition of rock and iron. This makes 55 Cnc e similar to other dense super-Earth exoplanets in short orbits, unlike lower-density super-Earths further from their stars. The brightness of 55 Cnc will enable further study of this transiting exoplanet system.
The document discusses high energy astrophysical research conducted at the Maidanak Observatory in Uzbekistan. It provides historical context about the transfer of Islamic science to the region in the 11th century. It then describes the observatory's facilities, including its six telescopes and five CCD cameras. The main fields of scientific research at the observatory are also listed, such as gravitational lensing systems, active galactic nuclei, gamma-ray bursts, and blazars. Specific research on gravitational lensing systems and blazars using data from Maidanak is summarized.
The document provides information about various telescopes and their capabilities. It begins with an image and description of the Eagle Nebula taken by the Hubble Space Telescope. It then provides details about the Hubble, including its launch date, dimensions, mirror size, weight, orbital parameters, and main scientific instruments. The next generation of large ground and space-based telescopes are mentioned, including the European Extremely Large Telescope with a 37m mirror, the Atacama Large Millimeter Array, the James Webb Space Telescope, and the Large Synoptic Survey Telescope.
This document summarizes a study that identified 195 compact elliptical galaxies across different environments using data from optical and ultraviolet sky surveys. The researchers constructed the sample by selecting galaxies that were outliers from the universal color-magnitude relation and had small sizes and high stellar velocity dispersions based on spectral modeling. They found that 7 of the galaxies were isolated, not belonging to any known galaxy groups. For these isolated galaxies, the researchers identified possible host galaxies located up to 3.3 Mpc away. The stellar populations of the isolated compact elliptical galaxies were found to be similar to those in galaxy groups and clusters, suggesting a common formation mechanism.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
The document summarizes the discovery of transient bright features detected in Titan's northern sea, Ligeia Mare, by the Cassini spacecraft's radar instrument in July 2013. These features were not seen in previous or subsequent observations. The author analyzes potential explanations and argues that the features were likely ephemeral phenomena caused by surface waves, bubbles, or suspended solids. This suggests dynamic processes are starting in Titan's northern lakes and seas as summer approaches in the northern hemisphere.
Three new circumbinary planets have been discovered orbiting binary star systems, rather than single stars. This establishes a new class of planets and shows that circumbinary planets are not rare, with an estimated frequency of at least 1% for short-period binary systems, implying millions exist in the Milky Way. While the three discovered planets are too hot or cold to support life, circumbinary planets could potentially be habitable.
Herschel space telescope observations reveal cold dust emitting from Supernova 1987A at a temperature of 17-23 K, indicating a dust mass of 0.4-0.7 solar masses. The dust must originate from the supernova ejecta, requiring efficient precipitation of refractory elements into dust. This implies that supernovae can produce the large dust masses seen in early galaxies.
Comets: Delving into the Heart of the MatterRyan Laird
Ryan Laird presented on the Survey of Ensemble Physical Properties of Cometary Nuclei (SEPPCoN) project. The presentation aimed to investigate the physical properties of Jupiter-family comet nuclei, including size distribution, albedo, color, rotation, and bulk density. SEPPCoN analyzed over 100 Jupiter-family comet targets using ground-based visible and infrared observations to determine geometric albedos, sizes, and other properties to better understand the origins and evolution of comet nuclei and their connection to Kuiper belt objects. Preliminary findings from SEPPCoN showed successful detection of 64 of 91% of the targeted comet sample, with only 16 showing signs of outgassing.
A. Zakharov: Supermassive Black Hole at the Galactic CenterSEENET-MTP
The document summarizes research on the supermassive black hole at the center of the Milky Way galaxy. It discusses how Reinhard Genzel and Andrea Ghez received the 2012 Crafoord Prize in Astronomy for their observations of stars orbiting the galactic center, providing evidence of a supermassive black hole called Sagittarius A*. It also describes efforts to measure the shadow size of the black hole and constraints on its potential charge, finding that a significant negative charge is ruled out. Interferometric observations using radio telescopes aim to better understand properties of the black hole and test general relativity.
The document discusses the big bang theory and recent efforts to recreate what it may have sounded like. According to physicist John Cramer, the big bang would have produced a deep hum rather than a bang. He analyzed cosmic microwave background radiation data from the Wilkinson Microwave Anisotropy Probe satellite to calculate the frequencies of sound waves in the early universe. Cramer then scaled these frequencies up enormously to make them audible. His recording suggests the sound became more of a bass tone as the universe expanded after the big bang.
The document analyzes data from the open star cluster M11 to determine its fundamental properties. Photometry of stars in M11 was performed using images taken through two filters with a telescope. A color-magnitude diagram was created and fit with theoretical models, revealing M11 to be around 250 million years old, located 5930 light years away, and having a similar iron-to-hydrogen ratio as the sun. Analysis of independent star clusters provides insights into patterns of galaxy formation and evolution.
BETTII is an experimental infrared telescope and interferometer that will be launched via balloon to study star formation and active galactic nuclei. It aims to spatially resolve young stellar objects within dense star clusters using its high angular resolution in the far infrared spectrum. This will provide insight into the earliest stages of star formation and chemical evolution of protostars and their disks. BETTII will also observe active galactic nuclei to separate emissions from the supermassive black hole accretion disk and nearby starburst regions, improving understanding of their co-evolution.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
This document summarizes a scientific paper published in Science in 2011 about the discovery that the large, oxygen-rich halos surrounding star-forming galaxies are a major reservoir of heavy elements ejected from galaxies. The paper presents evidence that these halos contain a significant portion of metals produced by massive stars. It also describes how these findings help scientists better understand the cycling of matter on large scales throughout the universe.
Bright and dark_polar_deposits_on_mercury_evidence_for_surface_volatilesSérgio Sacani
1) Measurements from MESSENGER's Mercury Laser Altimeter revealed regions of unusually dark and bright surface deposits near Mercury's north pole.
2) These deposits are concentrated on pole-facing slopes and spatially correlate with areas exhibiting high radar backscatter, suggesting the presence of near-surface water ice.
3) Analysis found the bright deposits are consistent with surface water ice, while the dark regions likely overlie buried ice and provide thermal insulation, such as from complex organic materials delivered by comets or asteroids.
The document discusses the distance ladder, which is an attempt to determine astronomical distances by using a series of methods that build on one another. Within the Solar System, distances are measured using radar ranging. Within the galaxy, distances are measured using stellar parallax, main sequence fitting, and properties of Cepheid variable stars. Further out in the universe, distances are measured using the Tully-Fisher relation, Type Ia supernovae, brightest cluster galaxies, and Hubble's law. The document aims to answer fundamental questions about what exists in the universe and how large it is.
Astronomy - State of the Art - TelescopesChris Impey
Telescopes help us learn about the universe by collecting more light than the human eye and seeing more detail. Larger telescopes collect more light and see sharper images, but the atmosphere limits ground-based telescope resolution. Telescope size has grown exponentially over time. Adaptive optics and interferometry allow telescopes to approach the theoretical resolution limit. While space telescopes avoid many atmospheric limitations, they are much more expensive to build and operate. The Hubble Space Telescope has revolutionized astronomy through high-quality images across the electromagnetic spectrum.
Dark side ofthe_universe_public_29_september_2017_nazarbayev_shrtZhaksylyk Kazykenov
1) The document discusses the history of discoveries about the universe, from ancient cosmologies to modern precision cosmology. Key developments include realizing the sun is at the center of the solar system, discovering other galaxies and the expansion of the universe, and detecting the cosmic microwave background and dark matter.
2) Current open questions about the universe include the nature of dark matter and dark energy. Observations show dark energy is accelerating the expansion of the universe, but its underlying cause remains unknown. Precise measurements aim to distinguish between models of dark energy.
3) The standard cosmological model has been very successful in explaining observations but has fine-tuning problems regarding why the present epoch is dominated by both matter and dark energy.
This document summarizes a 1.3 mm continuum survey of protoplanetary disks in the 2-3 Myr old IC348 star cluster using the Submillimeter Array. 10 disks out of 85 young stars were detected with masses ranging from 2-6 Jupiter masses. This distribution is shifted to lower masses by a factor of 20 compared to younger regions like Taurus and Ophiuchus. The results reveal a rapid decline in the number of small dust grains in disks after 1 Myr, likely due to grain growth. The few detected disks may be the best candidates in IC348 to study planet formation.
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
A super earth transiting a naked-eye starSérgio Sacani
This document summarizes the detection of transits of an exoplanet orbiting the star 55 Cnc, using photometry from the MOST space telescope. The transits match the period, phase, duration, and depth predicted for the innermost planet of 55 Cnc, designated 55 Cnc e. Analysis of the transit data indicates the planet has a mass of 8.57 Earth masses, a radius of 1.63 Earth radii, and a dense composition of rock and iron. This makes 55 Cnc e similar to other dense super-Earth exoplanets in short orbits, unlike lower-density super-Earths further from their stars. The brightness of 55 Cnc will enable further study of this transiting exoplanet system.
The document discusses high energy astrophysical research conducted at the Maidanak Observatory in Uzbekistan. It provides historical context about the transfer of Islamic science to the region in the 11th century. It then describes the observatory's facilities, including its six telescopes and five CCD cameras. The main fields of scientific research at the observatory are also listed, such as gravitational lensing systems, active galactic nuclei, gamma-ray bursts, and blazars. Specific research on gravitational lensing systems and blazars using data from Maidanak is summarized.
The document provides information about various telescopes and their capabilities. It begins with an image and description of the Eagle Nebula taken by the Hubble Space Telescope. It then provides details about the Hubble, including its launch date, dimensions, mirror size, weight, orbital parameters, and main scientific instruments. The next generation of large ground and space-based telescopes are mentioned, including the European Extremely Large Telescope with a 37m mirror, the Atacama Large Millimeter Array, the James Webb Space Telescope, and the Large Synoptic Survey Telescope.
This document summarizes a study that identified 195 compact elliptical galaxies across different environments using data from optical and ultraviolet sky surveys. The researchers constructed the sample by selecting galaxies that were outliers from the universal color-magnitude relation and had small sizes and high stellar velocity dispersions based on spectral modeling. They found that 7 of the galaxies were isolated, not belonging to any known galaxy groups. For these isolated galaxies, the researchers identified possible host galaxies located up to 3.3 Mpc away. The stellar populations of the isolated compact elliptical galaxies were found to be similar to those in galaxy groups and clusters, suggesting a common formation mechanism.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
The document summarizes the discovery of transient bright features detected in Titan's northern sea, Ligeia Mare, by the Cassini spacecraft's radar instrument in July 2013. These features were not seen in previous or subsequent observations. The author analyzes potential explanations and argues that the features were likely ephemeral phenomena caused by surface waves, bubbles, or suspended solids. This suggests dynamic processes are starting in Titan's northern lakes and seas as summer approaches in the northern hemisphere.
Three new circumbinary planets have been discovered orbiting binary star systems, rather than single stars. This establishes a new class of planets and shows that circumbinary planets are not rare, with an estimated frequency of at least 1% for short-period binary systems, implying millions exist in the Milky Way. While the three discovered planets are too hot or cold to support life, circumbinary planets could potentially be habitable.
Herschel space telescope observations reveal cold dust emitting from Supernova 1987A at a temperature of 17-23 K, indicating a dust mass of 0.4-0.7 solar masses. The dust must originate from the supernova ejecta, requiring efficient precipitation of refractory elements into dust. This implies that supernovae can produce the large dust masses seen in early galaxies.
Comets: Delving into the Heart of the MatterRyan Laird
Ryan Laird presented on the Survey of Ensemble Physical Properties of Cometary Nuclei (SEPPCoN) project. The presentation aimed to investigate the physical properties of Jupiter-family comet nuclei, including size distribution, albedo, color, rotation, and bulk density. SEPPCoN analyzed over 100 Jupiter-family comet targets using ground-based visible and infrared observations to determine geometric albedos, sizes, and other properties to better understand the origins and evolution of comet nuclei and their connection to Kuiper belt objects. Preliminary findings from SEPPCoN showed successful detection of 64 of 91% of the targeted comet sample, with only 16 showing signs of outgassing.
A. Zakharov: Supermassive Black Hole at the Galactic CenterSEENET-MTP
The document summarizes research on the supermassive black hole at the center of the Milky Way galaxy. It discusses how Reinhard Genzel and Andrea Ghez received the 2012 Crafoord Prize in Astronomy for their observations of stars orbiting the galactic center, providing evidence of a supermassive black hole called Sagittarius A*. It also describes efforts to measure the shadow size of the black hole and constraints on its potential charge, finding that a significant negative charge is ruled out. Interferometric observations using radio telescopes aim to better understand properties of the black hole and test general relativity.
The document discusses the big bang theory and recent efforts to recreate what it may have sounded like. According to physicist John Cramer, the big bang would have produced a deep hum rather than a bang. He analyzed cosmic microwave background radiation data from the Wilkinson Microwave Anisotropy Probe satellite to calculate the frequencies of sound waves in the early universe. Cramer then scaled these frequencies up enormously to make them audible. His recording suggests the sound became more of a bass tone as the universe expanded after the big bang.
The document analyzes data from the open star cluster M11 to determine its fundamental properties. Photometry of stars in M11 was performed using images taken through two filters with a telescope. A color-magnitude diagram was created and fit with theoretical models, revealing M11 to be around 250 million years old, located 5930 light years away, and having a similar iron-to-hydrogen ratio as the sun. Analysis of independent star clusters provides insights into patterns of galaxy formation and evolution.
BETTII is an experimental infrared telescope and interferometer that will be launched via balloon to study star formation and active galactic nuclei. It aims to spatially resolve young stellar objects within dense star clusters using its high angular resolution in the far infrared spectrum. This will provide insight into the earliest stages of star formation and chemical evolution of protostars and their disks. BETTII will also observe active galactic nuclei to separate emissions from the supermassive black hole accretion disk and nearby starburst regions, improving understanding of their co-evolution.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
This document summarizes a scientific paper published in Science in 2011 about the discovery that the large, oxygen-rich halos surrounding star-forming galaxies are a major reservoir of heavy elements ejected from galaxies. The paper presents evidence that these halos contain a significant portion of metals produced by massive stars. It also describes how these findings help scientists better understand the cycling of matter on large scales throughout the universe.
Bright and dark_polar_deposits_on_mercury_evidence_for_surface_volatilesSérgio Sacani
1) Measurements from MESSENGER's Mercury Laser Altimeter revealed regions of unusually dark and bright surface deposits near Mercury's north pole.
2) These deposits are concentrated on pole-facing slopes and spatially correlate with areas exhibiting high radar backscatter, suggesting the presence of near-surface water ice.
3) Analysis found the bright deposits are consistent with surface water ice, while the dark regions likely overlie buried ice and provide thermal insulation, such as from complex organic materials delivered by comets or asteroids.
This document presents observations from the VLT X-shooter instrument of two quasars, SDSS J1106+1939 and SDSS J1512+1119. For SDSS J1106+1939, a broad absorption line (BAL) outflow is detected with a kinetic luminosity of at least 10^46 erg/s, which is 5% of the quasar's bolometric luminosity. This outflow has a velocity of ~8000 km/s and is located ~300 pc from the quasar. For SDSS J1512+1119, two separate outflows are detected using the same technique, with distances ranging from 100-2000 pc from the central source. The distances of the outflows
This document presents color-magnitude diagrams derived from Hubble Space Telescope photometry of 6 outer Galactic globular clusters: Pyxis, Ruprecht 106, IC 4499, NGC 6426, NGC 7006, and Palomar 15. The deep photometry allows the ages of the clusters to be estimated from the main sequence turnoff. Preliminary age analysis reveals that IC 4499, Ruprecht 106, and Pyxis appear 1-2 billion years younger than inner halo clusters of similar metallicity, while NGC 7006 and Palomar 5 are marginally younger. NGC 6426 and Palomar 15, the two most metal-poor clusters, appear coeval with other metal-poor clusters within
Relativistic collapse and explosion of rotating supermassive stars with therm...Sérgio Sacani
1) The document describes general relativistic simulations of collapsing supermassive stars with and without rotation using a numerical code called Nada.
2) The simulations include effects of gas pressure, radiation, electron-positron pairs, and thermonuclear energy from hydrogen and helium burning.
3) Objects with a mass of around 5×105 solar masses explode if non-rotating with a metallicity over 0.007, while rotation lowers the threshold to 0.001. More massive objects have a higher critical metallicity for explosion.
This article presents evidence for past groundwater activity on Mars that could have supported a deep subsurface biosphere. The researchers developed a conceptual model of the martian subsurface divided into four zones based on depth and predicted fluid chemistry. Evidence is presented that crustal fluids emerged at the surface of McLaughlin Crater, forming an alkaline lacustrine system. This contrasts with more acidic environments implied by other sulfate deposits and suggests groundwater activity on Mars may have occurred sporadically on a local scale rather than regionally or globally.
This document summarizes long-slit spectroscopic observations of four planetary nebulae - Hb 4, IC 4634, NGC 6369, and NGC 7354 - conducted with the Palomar 5 m telescope. The observations were aimed at investigating the spectroscopic properties of microstructures like jets and FLIERs (fast, low-ionization emission regions) seen in these planetary nebulae. Physical conditions and chemical abundances were derived from emission line ratios along the structural axes of the microstructures. In most cases, no evidence of shock activity or nitrogen-to-oxygen abundance anomalies was found, unlike some previous studies of similar structures. Microstructures appear to be a heterogeneous class of structures aside from their generally supersonic
Non mare silicic volcanism on the lunar farside at compton–belkovichSérgio Sacani
1. Images from the Lunar Reconnaissance Orbiter reveal a central feature within the Compton–Belkovich thorium anomaly on the lunar farside characterized by elevated topography and relatively high reflectance.
2. The central feature contains several volcanic domes ranging from less than 1 km to over 6 km across, as well as arcuate and irregular depressions interpreted as collapse features associated with volcanism.
3. Spectral data indicates the volcanic feature is enriched in silica and alkali-feldspar, suggesting a composition of rhyolitic volcanic materials. This provides evidence for rare non-basaltic volcanism on the lunar farside far from the Procellarum
This article discusses findings from the MESSENGER spacecraft revealing details about Mercury's dynamic atmosphere. The spacecraft found that Mercury's polar regions contain large amounts of water ice, fulfilling predictions. However, measurements also surprisingly showed that the laser altimeter detected very low reflectance of Mercury's surface in polar regions, indicating it is coated in a dark, absorbing material in addition to water ice. Further studies are needed to understand the nature and origin of this dark material.
Small dust particles escaping from Pluto's moons Nix and Hydra could temporarily form a ring around Pluto due to impacts, but the solar radiation pressure would remove about half of 1 micrometer particles within a year by causing collisions with Pluto and its moons. Numerical simulations found that a tenuous ring with an optical depth of 6×10^-11 could be maintained by dust released from Nix and Hydra.
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
This document summarizes a survey of the massive star forming region RCW 57 (NGC 3576) using JHKs and L-band (3.5 μm) infrared data. Over 50% of the sources detected showed infrared excess emission, indicating the presence of circumstellar disks. Comparison to other regions supported a very high initial disk fraction (>80%) around massive stars, though disks may dissipate faster around high-mass stars. 33 sources only detected at L-band indicated heavily embedded, massive Class I protostars. Diffuse polycyclic aromatic hydrocarbon emission was also detected throughout the region.
This document summarizes an X-ray study of the supernova remnant G352.7-0.1 using data from XMM-Newton and Chandra observations. Prior observations revealed G352.7-0.1 has a shell-like radio morphology but center-filled thermal X-ray morphology, classifying it as a mixed-morphology supernova remnant. The new observations confirm the X-ray emission comes from the interior and is dominated by ejecta. Spectra from XMM-Newton are fit by a single thermal component with enhanced silicon and sulfur. Some Chandra spectra require a second thermal component to fit, with solar abundances providing a better physical model. No evidence of overionization was found. A neutron
This document summarizes an infrared survey of the massive star forming region RCW 57 (NGC 3576) using L-band (3.5 μm) data from SPIREX and JHKs data from 2MASS. Over 50% of the 209 sources detected showed infrared excess, indicating circumstellar disks. Comparison to other surveys supports a very high initial disk fraction (>80%) around massive stars, though disks may dissipate faster around high-mass stars. 33 sources only detected at L-band indicate heavily embedded, massive Class I protostars. Diffuse PAH emission was also detected throughout RCW 57.
1. VFTS 682 is a very massive star located 29 pc in projection from the young massive cluster R136 in the Tarantula Nebula of the LMC.
2. Spectral modeling finds it has an unusually high luminosity of log(L/L) = 6.5, corresponding to a present-day mass of ~150 solar masses.
3. Its isolation and mass pose the question of whether it formed in situ, which would profoundly impact theories of massive star formation, or if it was ejected from R136, making it the most massive runaway star known.
This document discusses observations of extended X-ray and H-alpha emission about 11 arcminutes (11.6 kpc) north of the starburst galaxy M82. The total H-alpha flux from this region is 1.5×10−13 erg s−1 cm−2, comprising about 0.3% of M82's total H-alpha flux. Diffuse soft X-ray emission is also seen in the same region. The X-ray spectrum is well fit by a thermal plasma model with a temperature of 0.80±0.17 keV. The total unabsorbed X-ray flux is 1.4×10−13 erg s−1 cm−2, comprising about 0
The document describes Hubble Space Telescope observations of Hercules A that revealed two faint, dark, interlocking rings of obscuring material located near the galaxy's nucleus and aligned along the radio jet axis. The rings are interpreted as either dust or electron scattering, and several models are discussed for their origin, including entrainment of molecular clouds by the radio jets or expansion of hot gas bubbles produced by the active galactic nucleus. The rings provide new insights into the transport of energy by powerful radio jets.
Bright radio emission_from_an_ultraluminous_stellar_mass_microquasar_in_m31Sérgio Sacani
1) A new ultraluminous X-ray source (ULX) was detected in the galaxy M31 with a peak X-ray luminosity exceeding 10^39 erg s^-1.
2) Radio observations found highly variable radio emission on timescales of minutes to days, indicating an extremely compact emission region.
3) The X-ray and radio properties of this source are consistent with stellar-mass black hole accretion near or above the Eddington limit, powered by a relativistic jet as seen in Galactic microquasars.
A 100 parsec elliptical and twisted ring of cold and dense molecular clouds r...Sérgio Sacani
The document summarizes observations from the Herschel satellite that reveal a 100-parsec elliptical and twisted ring of cold, dense molecular clouds orbiting the Galactic Center. The ring has a mass of about 3 million solar masses and semi-major axes of 100 and 60 parsecs. Its major axis is inclined 40 degrees to the plane of the sky and perpendicular to the Galactic Bar. The ring appears to trace stable x2 orbits predicted for the barred Galactic potential.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
The document summarizes the timeline of major discoveries in cosmology, including Einstein's theory of general relativity, Hubble's discovery of the expanding universe, and the discovery of the cosmic microwave background radiation by Penzias and Wilson which provided evidence for the Big Bang theory. It then discusses supernovae types and their use in determining the accelerating expansion of the universe, for which three scientists - Perlmutter, Riess, and Schmidt - were awarded the 2011 Nobel Prize in Physics for their findings which suggested the universe is dominated by dark energy.
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068Sérgio Sacani
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from
their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both
phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino
emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission
from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the
case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we
show that the entire spectrum of multimessenger data—from radio to γ-rays including the neutrino constraint—can
be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission
region is not sufficient.
First detection of_molecular_gas_in_shells_in_cena_galaxySérgio Sacani
This document reports the first detection of molecular gas (CO) in the shells of the galaxy Centaurus A (Cen A), located 15 kpc from the galaxy's center. The ratio of CO to HI emission in the shells matches what is found in the galaxy's central regions, which is unexpected given typical metallicity gradients in galaxies. The detection of molecular gas in the shells provides evidence that molecular gas in galaxy mergers may be spread further from nuclear regions than previously thought. The dynamics of the gas can be understood if the interstellar medium is considered clumpy and less dissipative than assumed, allowing dense gas to orbit with stars and form shells.
This document summarizes the results of a sub-mm survey of the Carina Nebula complex conducted with the LABOCA instrument on the APEX telescope. The survey mapped an area of 1.25° × 1.25° at 870 μm, revealing the morphology and distribution of cold dust clouds with masses down to a few solar masses. The total mass of clouds detected is estimated to be around 60,000 M☉. The cloud morphologies range from large clouds of several thousand solar masses to small diffuse clouds of only a few solar masses. The distribution of sub-mm emission generally agrees with Spitzer 8 μm maps, identifying clouds interacting with massive stars as well as infrared dark clouds. The survey provides crucial
This study uses deep Chandra observations to examine the X-ray morphology of the circum-nuclear region of NGC 4151 on spatial scales down to 30 pc. Extended soft X-ray emission is detected out to 1.3 kpc from the nucleus, farther than seen in previous studies. The X-ray emission is more absorbed towards the boundaries of the ionization cone and perpendicular to the bicone, suggesting absorption by a torus. The innermost X-ray emission, coincident with H2 emission and dusty spirals, supports X-ray excitation of molecular gas. The extended X-ray emission may be due to hot gas heated by the AGN outflow or photoionized by past AGN activity.
Dust production and_particle_acceleration_in_supernova_1987_a_revealed_with_almaSérgio Sacani
This document presents spatially resolved submillimeter observations of supernova remnant SN 1987A using the Atacama Large Millimeter/Submillimeter Array (ALMA). The observations reveal that at longer wavelengths (2.8 mm - 1.4 mm), the emission is from a torus associated with the supernova shock wave, while at shorter wavelengths (870 μm - 450 μm) the emission is dominated by the inner supernova ejecta. For the first time, the dust emission is unambiguously shown to originate from the inner ejecta rather than from the surrounding material, supporting theoretical models of significant dust production in supernovae. The observations also allow separation of synchrotron emission from shock-accelerated particles in
Sdss1133 an unsually_perssitent_transient_in_a_nearby_dwarf_galaxySérgio Sacani
This document summarizes observations of SDSS1133, an unusual transient object offset from the center of a nearby dwarf galaxy. SDSS1133 has been detected in observations spanning 63 years, and exhibits broad emission lines and strong variability. While initially classified as a supernova due to its non-detection in 2005, more recent observations over the past decade show it has rebrightened over a magnitude and displays properties consistent with both an active galactic nucleus and luminous blue variable star eruptions. Its nature remains ambiguous between an extreme example of pre-supernova mass loss or a potential candidate for a recoiling supermassive black hole.
Radio imaging obserations_of_psr_j1023_0038_in_an_lmxb_stateSérgio Sacani
Uma estrela super densa formada depois da explosão de uma supernova está expelindo poderosos jatos de material no espaço, sugerem pesquisas recentes.
Num estudo publicado no dia 6 de Agosto de 2015, uma equipe de cientistas na Austrália e na Holanda descobriram poderosos jatos sendo expelidos de uma sistema estelar duplo conhecido como PSR J1023+0038.
Pensava-se anteriormente que os únicos objetos no universo capazes de formar jatos poderosos eram os buracos negros.
O sistema PSR J1023+0038 contém uma estrela extremamente densa que os astrônomos chamam de estrela de nêutrons, numa órbita próxima com uma estrela normal.
Ela foi identificada primeiro como uma estrela de nêutrons em 2009, mas foi somente quando a equipe de pesquisa observou a estrela com o rádio telescópio Very Large Array nos EUA em 2013 e 2014 que eles perceberam que a estrela estava produzindo jatos mais fortes do que se esperava.
Os astrônomos James Miller-Jones, do International Centre for Radio Astronomy Research (ICRAR), disse que as estrelas de nêutrons podem ser pensadas como cadáveres estelares.
“Elas são formadas quando uma estrela massiva esgota todo o seu combustível e vira uma supernova, e as partes centrais da estrela colapsam sobre sua própria gravidade”, disse ele.
“Essas coisas tem normalmente entre uma vez e meia a massa do Sol e somente entre 10 a 15 km de diâmetro, de modo que são extremamente densas”.
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
Similar to X rays and-protostars_in_the_trifid_nebula (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
Continuum emission from within the plunging region of black hole discs
X rays and-protostars_in_the_trifid_nebula
1. THE ASTROPHYSICAL JOURNAL, 562 : 446È455, 2001 November 20
( 2001. The American Astronomical Society. All rights reserved. Printed in U.S.A.
X-RAYS AND PROTOSTARS IN THE TRIFID NEBULA
JEONGHEE RHO
Infrared Processing and Analysis Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125 ; rho=ipac.caltech.edu
MICHAEL F. CORCORAN
NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20742
YOU-HUA CHU
Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801
AND
WILLIAM T. REACH
Space Infrared Telescope Facility Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125
Received 2001 February 19 ; accepted 2001 June 28
ABSTRACT
The TriÐd Nebula is a young H II region, recently rediscovered as a ““ pre-Orion ÏÏ star-forming region,
containing protostars undergoing violent mass ejections visible in optical jets as seen in images from the
Infrared Space Observatory and the Hubble Space T elescope. We report the Ðrst X-ray observations of
the TriÐd Nebula using ROSAT and ASCA. The ROSAT image shows a dozen X-ray sources, with the
brightest X-ray source being the O7 star, HD 164492, which provides most of the ionization in the
nebula. We also identify 85 T Tauri star and young, massive star candidates from near-infrared colors
using the JHK color-color diagram from the Two-Micron All-Sky Survey (2MASS). Ten X-ray sources
s
have counterpart near-infrared sources. The 2MASS stars and X-ray sources suggest there are potentially
numerous protostars in the young H II region of the TriÐd. ASCA moderate-resolution spectroscopy of
the brightest source shows hard emission up to 10 keV with a clearly detected Fe K line. The best model
Ðt is a two-temperature (T 1.2 ] 106 K and 39 ] 106 K) thermal model with additional warm absorb-
ing media. The hotter component has an unusually high temperature for either an O star or an H II
region ; a typical Galactic H II region could not be the primary source for such hot temperature plasma
and the Fe XXV line emission. We suggest that the hotter component originates in either the interaction
of the wind with another object (a companion star or a dense region of the nebula) or from Ñares from
deeply embedded young stars.
Subject headings : H II regions È infrared : stars È stars : formation È X-rays : individual (TriÐd Nebula)
1. INTRODUCTION
1995 ; Feigelson et al. 1993), Lupus (Krautter et al. 1997),
H II regions contain various types of X-rayÈemitting Ž
and Taurus-Auriga (Neuhuser et al. 1995 ; Wichmann et al.
sources, such as high- and low-mass stars, binaries, and 1997). Flarelike X-ray events have been detected from T
protostars. Single massive O and B stars emit soft X-rays Tauri stars (Kamata et al. 1997 ; Koyama et al. 1992). The
from shocks in their radiatively unstable, outwardly moving X-rayÈemitting sources in the Monoceros and Rosette
outer atmospheres. X-ray emission from late-type stars is molecular clouds are also mostly T Tauri and Herbig Ae/Be
attributed to magnetically heated stellar coronae and mag- stars and they typically show luminosities of L D
netically driven stellar Ñares. Protostars produce X-rays via X
1030È1032 ergs s~1 (Gregorio-Hetem et al. 1998). Recent
magnetic heating and perhaps from accretion or excretion Chandra observation of the Orion Nebula resolved a thou-
disks and/or interaction of stellar jets with the circumnebu- sand X-rayÈemitting PMS stars with a mass range of 0.05 to
lar gas. Massive binaries can produce X-ray emission from 50 M , and a combined infrared and X-ray study suggested
colliding stellar winds ; close low-mass binaries can produce _
that the X-ray luminosity depends on stellar mass, rotation-
X-rays via mass exchange and enhanced dynamo action. al history, and magnetic Ðeld (Garmire et al. 2000).
X-ray emission provides a sensitive tracer of these di†erent At a distance of 1.67 kpc (Lynds & OÏNeil 1985), the
stellar populations and, along with infrared colors, is one of TriÐd Nebula, M20, is one of the best-known astrophysical
the main probes for identifying protostars and preÈmain- objects and one of the prettiest : it glows brightly in red light
sequence (PMS) stars. and is trisected by obscuring dust lanes. At an age of
Studies of X-ray emission from H II/star-forming regions D 3 ] 105 yr, the TriÐd is one of the youngest known H II
have made signiÐcant advances because of ROSAT regions. Observations with the Infrared Space Observatory
(Casanova et al. 1995), ASCA (e.g., Koyama et al. 1996), (ISO) and the Hubble Space T elescope (HST ) show the
and, most recently, Chandra observations (Garmire et al. TriÐd as a dynamic, ““ pre-Orion ÏÏ star-forming region con-
2000). For example, in the o Oph core region, 70% of the taining young stars undergoing episodes of violent mass
near-infrared (NIR) sources associated with protostars and ejections, and protostars (like HH 399) losing mass and
molecular cores have X-ray counterparts (Casanova et al. energy to the nebula in optically bright jets (Cernicharo et
1995), and a large number of X-ray sources have been found al. 1998, hereafter CLC98 ; LeÑoch & Cernicharo 2000 ;
to be low-mass PMS stars in other star-forming regions Hester et al. 1999). The ionization of the nebular gas is
such as Orion (Alcala et al. 1996), Chamaeleon (Alcala et al. dominated by the O7.5 star HD 164492. HD 164492 is a
446
2. X-RAYS AND PROTOSTARS IN THE TRIFID NEBULA 447
luminosity class V (Levato 1975) or III (Conti & Alschuler in Figure 1. This image reveals for the Ðrst time that the
1971) star with a bolometric luminosity of L D 0.5È1.6 TriÐd Nebula contains numerous X-ray sources. We have
] 1039 ergs s~1 and an X-ray luminosity of 6 bol 1032 ergs
] identiÐed X-ray sources in the PSPC image using the
s~1 (Chlebowski et al. 1989). The mass-loss rate of this O FTOOLS task SRCDETECT and estimated the count rates
star is M 2 ] 10~6 M yr~1 (Howarth & Prinja 1989)
0 and uncertainties. The detected point sources are presented,
_
and the wind terminal velocity is V 1580 km s~1 (Prinja, in order of increasing right ascension, in Table 1 and
=
Barlow, & Howarth 1990). marked in Figure 1. Table 1 lists the position, count rate,
X-ray observations of the TriÐd o†er a unique and p of detection for 10 sources detected at greater than 3
opportunity to study the inÑuence of a massive star on star p and two possible sources (sources 11 and 12) detected with
formation in an exceptionally young star-forming region. somewhat lower conÐdence. We deÐne here new X-ray
Initially, X-ray emission from the TriÐd was reported only sources detected in the ROSAT PSPC image, as ROSAT
from the O star in the Einstein IPC catalog (Chlebowski & X-ray source in the TriÐd (RXT). Since the count rate is very
Harnden 1989). We serendipitously discovered a complex of small except for the O star HD 164492, we estimated the
X-ray emission from the TriÐd Nebula in a PSPC obser- luminosity by assuming an absorption column density
vation of the nearby supernova remnant W28 (Rho et al. N 3 ] 1021cm~2 (A D 1.5m, see ° 4 for details), and a
H V
1995). Subsequently, we started an extensive investigation thermal spectrum with kT 1 keV. The X-ray emission of
of the X-ray emission from the TriÐd Nebula. This paper PMS stars is understood to be thermal emission from gas
presents the Ðrst detection of a dozen X-ray sources in the rapidly heated to a temperature of D1 keV by violent mag-
TriÐd Nebula, and we correlate these with protostar candi- netohydrodynamic reconnection events (Feigelson &
dates identiÐed using the Two-Micron All-Sky Survey Montmerle 1999). The correspondence between the PSPC
(2MASS) data. The ROSAT images show multiple point count rate and the X-ray unabsorbed Ñux is 1 ] 10~3
sources, including HD 164492 and several T Tauri stars, PSPC counts s~1 D2.95 ] 10~14 ergs s~1 cm~2. Using this
and the ASCA spectra show hard X-ray emission, including conversion, the luminosities of the X-ray sources are com-
detection of an Fe K line. We discuss identiÐcations of the puted and given in Table 1.
X-rayÈemitting sources and the origin of the unusually hard We have examined the source list database using
X-ray emission from the TriÐd. SIMBAD, identiÐed counterparts to the X-ray sources at
other wavelengths, and marked them in Figure 1. To visual-
2. X-RAY SOURCES IN THE TRIFID ize the correspondence of X-ray sources with either optical
2.1. X-Ray Observations or radio sources, we have plotted the X-ray contours over
The TriÐd Nebula was observed using the X-ray tele- an Ha image (F. Winkler, 2001, private communication) in
Ž
scope on ROSAT (Trumper 1993) with the Position Sensi- Figure 2. Twenty-four sources from the Guide Star Catalog
tive Proportional Counter (PSPC) as the imaging detector. (GSC) are visible in the Ha image in Figure 2. The brightest
The PSPC on-axis angular resolution is 25A (FWHM, at 1 X-ray point source, RXT8 in Table 1, corresponds to the O
keV), and the PSPC covers a 2¡ Ðeld of view in the 0.1È2.4 star HD 164492. The possible X-ray source RXT11 coin-
keV energy band. Two PSPC observations were analyzed cides with the B8 star HD 313596 (R.A. 18h02m35s and decl.
for this paper : rp900375 centered on HD 164492 and [22¡59@54A), and the possible X-ray source RXT12 with the
observed on 1993 September 8 for an exposure of 9365 s
(PI : S. Snowden), and rp500236 centered on the supernova
remnant W28 and observed on 1993 April 1 for an exposure
of 10,476 s (PI : R. Pisarski ; Rho et al. 1995).
We also performed an ASCA observation (PI : J. Rho ;
sequence number 26051000) toward the center of the TriÐd
Nebula. The observation took place on 1998 September 30
to October 2. ASCA (TI & H94) has two detector pairs : Gas
Imaging Spectrometers (GIS2 and GIS3) and Solid-State
Imaging Spectrometers (SIS0 and SIS1). The SIS covers an
energy band of 0.5È10 keV and the GIS 0.6È10 keV. The
on-axis angular resolution of the GIS and SIS is about 1@È2@.
Each GIS counter has a circular Ðeld of view of 35@ diameter
while the Ðeld of view of each SIS CCD is an 11@ square ;
thus, both GIS and SIS detectors sufficiently cover the
entire TriÐd Nebula. We Ðltered the data using a few cri-
teria such as cuto† rigidity (COR) and earth elevation
(based on Revison 2 processing). After Ðltering, the expo-
sure time was 57 ks for the GIS and 53.5 ks for the SIS. The
entire TriÐd Nebula region after background subtraction
has count rates of 0.050 ^ 0.001 counts s~1 for SIS0,
0.040 ^ 0.001 counts s~1 for SIS1, 0.030 ^ 0.008 counts s~1
for GIS2, 0.039 ^ 0.009 counts s~1 for GIS3, and
0.086 ^ 0.004 counts s~1 for the ROSAT PSPC, in their
respective energy bands (integrated over all channels).
FIG. 1.ÈPSPC X-ray image and detected sources (RXT) are marked
2.2. X-Ray Source IdentiÐcation with numbers. Count rates for each source are listed in Table 1. Known
The ROSAT PSPC image of the TriÐd Nebula is shown sources are also marked with the labels.
3. 448 RHO ET AL. Vol. 562
TABLE 1
X-RAY SOURCES DETECTED IN THE PSPC IMAGE OF THE TRIFID NEBULA
Name R.A. (2000) Decl. (2000) Count Rate Detection (p) log (L )
X
RXT1 . . . . . . . 18 02 52.8 [23 02 18.1 0.0014 ^ 0.0005 5 31.12
RXT2 . . . . . . . 18 02 39.3 [22 58 34.3 0.0011 ^ 0.0004 3.5 31.02
RXT3 . . . . . . . 18 02 41. [23 03 51.8 0.0014 ^ 0.0006 3.5 31.12
RXT4 . . . . . . . 18 02 36.0 [23 01 36.3 0.0019 ^ 0.0006 4 31.05
RXT5 . . . . . . . 18 02 35.0 [23 01 29.4 0.0021 ^ 0.0006 4.5 31.29
RXT6 . . . . . . . 18 02 27.9 [22 59 47.9 0.0016 ^ 0.0006 4 31.17
RXT7 . . . . . . . 18 02 25.4 [22 59 51.4 0.0010 ^ 0.0005 3 30.97
RXT8 . . . . . . . 18 02 23.35 [23 01 47.0 0.0131 ^ 0.0013 8 (see Table 4)
RXT9 . . . . . . . 18 02 21.1 [23 03 21.5 0.0010 ^ 0.0004 4 30.97
RXT10 . . . . . . 18 02 12.38 [22 55 37.0 0.0012 ^ 0.0004 4.5 31.05
RXT11 . . . . . . 18 02 34.92 [22 59 55.6 0.0006 ^ 0.0003 2.5 30.75
RXT12 . . . . . . 18 02 31.67 [23 02 25.6 0.0007 ^ 0.0003 2.5 30.82
NOTE.ÈUnits of right ascension are hours, minutes, and seconds, and units of declination are degrees, arcmin-
utes, and arcseconds.
optical star GSC–06842–00001 (R.A. 18h02m34s 8 and decl.
. sources showing NIR color excesses and present candidate
[23¡03@06A3). None of the other GSC stars coincide with
. protostars.
X-ray peaks. A radio source, GPSR5 6.980[0.286 (R.A.
18h02m28s 1 and decl. [23¡03@46A3 ; Becker et al. 1994), is
. . 3. NEAR-INFRARED SOURCES FROM 2MASS : YOUNG
close to the X-rayÈemitting area but does not have a corre- STELLAR OBJECTS
sponding X-ray peak. Four protostars (TC0, TC1, TC3, and We have identiÐed young stellar objects (YSOs) using the
TC4 sources1 in CLC98) have been reported in the TriÐd 2MASS data (Skrutskie et al. 1997). Using identical tele-
Nebula (CLC98), which are marked in Figure 1, but only scopes in the northern and southern hemispheres, 2MASS is
one is close to the X-ray peak at HD 164492. In the mapping the entire sky in the J (1.11È1.36 km), H (1.5È1.8
next section, we correlate the PSPC X-ray sources with km), and K (2È2.32 km) bands to a limiting point-source
s
sensitivity of approximately 16.5, 16.0, and 15.5 mag,
1 The source designation TC0, TC1, etc. was assigned by CLC98. Since respectively (Cutri et al. 2000).2 The data toward the TriÐd
this designation was already in use, for indexing purposes these sources Nebula were taken on 1998 June 14 using the southern
should be referred to as [CLC98] 0, etc. telescope, and most of these data were included in the
2MASS Second Incremental Release, but a small portion of
area was in the 2MASS Working Database because of large
photometric uncertainties at the time of the Incremental
Release. The photometry is typically better than 5% (Cutri
et al. 2000Èsee fn. 2).
We used the 2MASS point-source catalog to extract
sources within an 8@ radius centered on R.A. 18h02m30s and
decl. [23¡02@00A. We have selected sources with the follow-
ing criteria. First, we selected the sources that were detected
in all three J, H, and K bands. We then selected sources
s
with a signal-to-noise ratio greater than 10 (i.e., the J, H,
and K magnitudes are brighter than 15.8, 15.1, and 14.3
s
mag, respectively). These selections produced D1100 such
sources. We then accepted sources with photometric uncer-
tainties p 0.25 mag, for which the Ðt to the point-spread
function produced reduced s2 2. This last criterion
l
excluded blended sources that caused higher uncertainties
in the photometry. This is important in the Galactic plane
where NIR sources are crowded and the 2MASS has a
limited spatial resolution (3A5). This criterion removed inac-
.
curate blue points that appeared in the JHK color-color
s
diagram (as described below). The criteria we have used are
conservative for the magnitude limit and photometric
uncertainties of the 2MASS survey.
We plotted the sources in the JHK color-color diagram,
s
as shown in Figure 3a, in order to identify YSOs with infra-
FIG. 2.ÈPSPC X-ray contours superimposed on an Ha image of the red color excess. Figure 3b shows H[K versus K magni-
s s
TriÐd Nebula (courtesy of Frank Winkler). The optical image was tude for the selected sample. The interstellar reddening
obtained on 1994 July 4 (UT) from the Burrell Schmidt telescope of Case
Ž
Western Reserve University through a 25 A bandpass Ha Ðlter. Total
exposure time is 1800 s, and the scale is 2A0 pixel~1. The strongest X-ray
. 2 See R. M. Cutri et al. 2000, at http ://www.ipac.caltech.edu/2mass/
peak is at the O star, HD 164492. releases/ Ðrst/doc/explsup.html.
4. No. 1, 2001 X-RAYS AND PROTOSTARS IN THE TRIFID NEBULA 449
FIG. 3b
FIG. 3a
FIG. 3c
FIG. 3.È(a) Near-infrared JHK color-color diagram : location in color-color diagram is used to determine T Tauri stars and massive YSOs. Normal stars
(dots), T Tauri stars (Ðlled circles), s
and massive YSOs (diamonds) are shown with di†erent symbols. The 2MASS counterparts of X-ray sources are marked
with crosses ; the sources above the extinction curve have high photometric uncertainties. They are 2MASS-red stars in Table 3 (see text for details).
Extinction vector is shown for 5 mag as the thick line labeled A . Thick curves are intrinsic colors of giant and dwarf stars. (b) Diagram of H [ K vs. K . T
v s s
Tauri stars and young massive protostars fall below (younger age) the PMS stars in this diagram. Symbols are the same as in (a). (c) T Tauri stars (circles) and
massive YSOs (diamonds), X-ray sources (crosses), and known embedded YSOs (triangles : from Cernicharo et al. 1998) are marked on optical image. (d)
2MASS three-color image (blue, green, and red for J, H, and K , respectively). Symbols are the same as in (c). The di†use, blue emission is probably Pab (in
s
the J band) from the H II region.
vector from Rieke & Lebofsky (1985) is also plotted. Adopt- the extinction curve (dashed line in Fig. 3a) and above the T
ing the intrinsic colors of giant and dwarf stars from Bessell Tauri star lines (solid line in Fig. 3a) are massive YSOs
& Brett (1988), we Ðnd the visual extinction toward this (Lada & Adams 1992) ; these stars are plotted as diamonds
direction is as high as A 30 mag for stars on the back in Figure 3a. In total, we found 41 T Tauri star candidates
V
side of the TriÐd Nebula. The observed JHK colors and 44 massive YSO candidates from the 2MASS sources
of YSOs can be explained by circumstellar disks models that are listed in Table 2. The T Tauri stars and YSOs are
(Lada & Adams 1992). We identiÐed the T Tauri stars with generally located along the ionization front. Figure 3c
(J[H) 0.58 ^ 0.11 ] (H[K ) ] 0.52 ^ 0.06 shows optical images, and T Tauri stars, massive YSOs, and
s and
(Meyer, Calvet, & Hillenbrand 1997) CTTS H[K [ 0.6 mag,
CTTS
X-ray sources are marked. Figure 3d shows a color compos-
where CTTS is classical T Tauri stars. These Ts Tauri stars ite of the J, H, and K images, with the J image in blue, H
fall between the two solid lines in Figure 3a. The stars below image in green, and Ks image in red. T Tauri stars, massive
s
5. 450 RHO ET AL. Vol. 562
FIG. 3d
YSOs, and X-ray sources are marked. The image also shows tive criteria as they are not detected in one or both of the J
a number of protostars at the ionization front along the and H bands. Therefore, we have relaxed the selection cri-
dust lane. teria and extracted 2MASS sources from the same area,
These protostar candidates were cross-correlated with excluding only sources with an artifact Ñag. We made a list
the X-ray sources. Taking into account the resolution of the of the 2MASS sources that are within 15A from X-ray
PSPC, we identify a possible coincidence if the separation sources. Each X-ray source has D10 2MASS counterpart
between a 2MASS source and an X-ray source is less than candidates ; only the red stars are identiÐed as possible
15A. Three X-ray sources (RXT1, RXT6, and RXT7) are counterparts to the X-ray sources. Seven red 2MASS star
coincident with either T Tauri stars or YSOs ; they are counterparts of X-ray sources are identiÐed and listed in
noted in Table 3. Figure 3d shows that many red 2MASS Table 3, with J, H, and K magnitudes and reasons that
s
stars within the X-ray source error boxes could be con- they were not selected in the earlier list of T Tauri star or
sidered coincidences, but they are not included in the list of massive YSO candidates (either J ““ Ðll ÏÏ or high reduced
sources selected according to the aforementioned conserva- s2, indicating multiple or extended sources with large
6. No. 1, 2001 X-RAYS AND PROTOSTARS IN THE TRIFID NEBULA 451
TABLE 2
2MASS YOUNG STELLAR OBJECT AND T TAURI STAR CANDIDATES IN THE TRIFID NEBULAa
YSO Candidates TTS Candidates
Number Designation Number Designation Number Designation Number Designation
1 2MASSI 23 2MASSW 1 2MASSI 23 2MASSW
J1802121[230439 J1802379[230211 J1802158[230555 J1802331[230135
2 2MASSI 24 2MASSW 2 2MASSI 24 2MASSW
J1802211[230437 J1802211[230234 J1802102[230403 J1802197[230136
3 2MASSI 25 2MASSI 3 2MASSI 25 2MASSW
J1801592[230406 J1802441[230245 J1802129[230348 J1802281[230142
4 2MASSW 26 2MASSI 4 2MASSW 26 2MASSW
J1802139[230213 J1802367[230302 J1802197[230136 J1802336[230154
5 2MASSW 27 2MASSI 5 2MASSI 27 2MASSI
J1802142[230144 J1802450[230332 J1801575[230121 J1802199[230305
6 2MASSI 28 2MASSI 6 2MASSI 28 2MASSI
J1802168[230110 J1802500[230334 J1802124[225856 J1802395[230343
7 2MASSI 29 2MASSI 7 2MASSI 29 2MASSI
J1801561[230009 J1802361[230428 J1802173[225614 J1802211[230437
8 2MASSI 30 2MASSW 8 2MASSI 30 2MASSI
J1802044[225829 J1802319[230440 J1802108[225532 J1802409[230459
9 2MASSI 31 2MASSI 9 2MASSI 31 2MASSI
J1802122[225825 J1802372[230503 J1802205[225458 J1802349[230505
10 2MASSW 32 2MASSI 10 2MASSI 32 2MASSI
J1802202[225807 J1802369[230656 J1802205[225458 J1802263[230730
11 2MASSI 33 2MASSI 11 2MASSI 33 2MASSW
J1802401[225721 J1802470[230702 J1802162[225530 J1802242[230910
12 2MASSI 34 2MASSI 12 2MASSI 34 2MASSI
J1802377[225850 J1802290[230704 J1802464[225546 J1802403[230913
13 2MASSI 35 2MASSW 13 2MASSI 35 2MASSI
J1802463[225912 J1802247[230729 J1802473[225729 J1802384[230934
14 2MASSI 36 2MASSI 14 2MASSI 36 2MASSI
J1802433[225931 J1802344[230806 J1802367[225804 J1803003[230134
15 2MASSI 37 2MASSI 15 2MASSW 37 2MASSI
J1802491[225945 J1802339[230924 J1802312[225911 J1802467[230130
16 2MASSI 38 2MASSI 16 2MASSW 38 2MASSI
J1802503[225949 J1802518[230810 J1802305[225929 J1802538[230033
17 2MASSI 39 2MASSI 17 2MASSW 39 2MASSI
J1802438[225959 J1802499[230740 J1802228[225935 J1802566[230026
18 2MASSI 40 2MASSI 18 2MASSI 40 2MASSI
J1802441[230020 J1802541[230736 J1802175[225938 J1803023[230022
19 2MASSI 41 2MASSI 19 2MASSI 41 2MASSI
J1802266[230036 J1802473[230428 J1802409[225941 J1802490[225656
20 2MASSW 42 2MASSI 20 2MASSI
J1802226[230101 J1802482[230309 J1802344[230102
21 2MASSI 43 2MASSI 21 2MASSI
J1802467[230130 J1802524[230227 J1802284[230115
22 2MASSW 44 2MASSI 22 2MASSW
J1802271[230201 J1802548[225901 J1802408[230131
a 2MASSI and 2MASSW indicate the Incremental Release and Working Database catalogs, respectively.
photometric uncertainties). These seven sources are likely expect there are large numbers of such embedded protostars
protostars because their infrared colors are red and they in the TriÐd Nebula not detected in the NIR observations.
also emit X-rays. By itself, an infrared color excess indicates This population is likely correlated with highly extincted
either the presence of a YSO or a heavily extincted main- dust lanes (see Fig. 3d) and molecular clouds.
sequence star. The 2MASS counterparts of the X-ray
sources are marked in the JHK color-color diagram (Fig. 4. X-RAY SPECTRAL ANALYSIS
s The ASCA SIS image is shown in Figure 4 with the PSPC
3a) and on the 2MASS composite image (Fig. 3d). A few
X-ray sources do not have obvious optical or 2MASS contours superposed. The X-ray emission is dominated by
counterparts. the emission from the O star. We extracted ASCA and
There are Ðve known massive YSOs in the TriÐd with ROSAT spectra from the entire region of the TriÐd Nebula.
mid-infrared emission detected using ISO (CLC98). These The spectrum (Fig. 5a) shows clear Fe K line emission,
protostars were not identiÐed as protostellar candidates along with weak Si and S lines, and a hard continuum tail
from the 2MASS data, probably because they are too up to 10 keV, the highest energy observable by ASCA. We
deeply embedded to be detected in the NIR. A 2MASS red extracted a background-corrected spectrum from a smaller
star is the counterpart of the protostar TC2 in CLC98 ; we region centered on HD 164492. HD 164492 is the brightest
7. 452 RHO ET AL. Vol. 562
TABLE 3
INFRARED COUNTERPARTS OF THE X-RAY SOURCES DETECTED IN PSPC IMAGES
2MASSa db Jd Hd Kd
s
RXT Counterparts (arcsec) R.A. (2000)c Decl. (2000)c (mag) (mag) (mag) Commentse
RXT1 . . . . . . . . YSO 10 18 02 52.4 [23 02 27.2 15.17 13.93 13.18 ...
RXT2 . . . . . . . . red 8 18 02 39.7 [22 58 29.0 17.72 15.06 13.50 J ““ Ðll ÏÏ
RXT3 . . . . . . . . red 5 18 02 41.4 [23 03 48.2 17.83 14.24 12.42 J ““ Ðll ÏÏ
red 13 18 02 40.4 [23 03 58.9 15.58 12.37 10.90 High psf *s2
RXT4 . . . . . . . . red 12.8 18 02 36.8 [23 01 43.9 15.85 12.78 11.34 High psf *s2
RXT5 . . . . . . . . NONE ... ... ... ... ... ... ...
RXT6 . . . . . . . . TTS 13 18 02 30.5 [22 59 28.7 12.71 11.65 10.91 ...
RXT7 . . . . . . . . YSO 12 18 02 26.6 [23 00 36.0 15.21 12.90 11.34 ...
RXT8f . . . . . . . Multiple ... ... ... ... ... ... ...
RXT9 . . . . . . . . red 6 18 02 21.5 [23 03 19.0 15.04 13.58 11.87 J ““ Ðll ÏÏ
RXT10 . . . . . . NONE ... ... ... ... ... ... ...
RXT11f . . . . . . red 4 18 02 34.7 [22 59 52.1 16.52 12.42 10.58 J ““ Ðll ÏÏ
RXT12 . . . . . . red 9 18 02 31.3 [23 02 18.2 15.12 13.17 11.36 J ““ Ðll ÏÏ
NOTE.ÈUnits of right ascension are hours, minutes, and seconds, and units of declination are degrees, arcminutes, and
arcseconds.
a Notes for the 2MASS sources : TTS T Tauri star ; YSO massive young stellar object ; red red 2MASS star.
b Projected distance between the X-ray and 2MASS sources.
c Coordinates of the 2MASS counterparts.
d J, H and K magnitudes of the 2MASS sources.
s
e J ““ Ðll ÏÏ means the J-band photometry is measured in band-Ðlled within the aperture, indicating their photometric
uncertainties are large. ““ High psf *s2 ÏÏ means the goodness of the Ðt of a point-spread function is high, indicating the sources are
either extended or unresolved double sources.
f RXT8 is HD 164492 (O7 star) and/or YSO (TC1 in CLC98), and RXT11 also coincides with HD 313596 (B8 star).
X-ray source in the TriÐd, and the shape of the spectrum of showed that the observed o†-source emission is dominated
the entire region in the ASCA data is not signiÐcantly di†er- by scattered emission from sources within the TriÐd
ent from the spectrum of this star alone because of the Nebula. The detection of hard emission from the TriÐd is
broad ASCA point-spread function. We made hard ([3 unusual because most single O stars have very little emis-
keV) and soft (3 keV) maps using the ASCA data, but no sion at energies above 2 keV and rarely show Fe K emission
obvious di†erence was noticeable at the spatial resolution (Corcoran et al. 1993). The only massive stars to show such
(1@) of ASCA. We also extracted an o†-source ASCA spec- hard X-ray spectra are binaries, either high-mass X-ray
trum in this direction, suspecting a contribution from the binaries (HMXBs) with collapsed companions or colliding
Galactic ridge emission. However, the o†-source spectrum wind binaries with noncollapsed (O or W-R star) compan-
ions that have strong stellar winds and signiÐcant colliding
wind X-ray emission.
We simultaneously Ðt the set of Ðve spectraÈthe
ROSAT /PSPC, ASCA/SIS0, SIS1, GIS2, and GIS3
spectraÈusing single- or two-temperature thermal models
(Mewe-Kaastra plasma model ; Kaastra 1992) with a single
absorbing column density N . The Ðts were unacceptable
H
(reduced s2 of 3). We next attempted a two-temperature
model. Following Corcoran et al.Ïs (1994) models of d Ori
and j Ori, we also included an additional ionized (““ warm ÏÏ)
absorbing medium, as representative of the photoionized
stellar wind material (Waldron 1984 ; Corcoran et al. 1994),
and allowed di†erent amounts of absorption for the hot and
cold components. The line-of-sight extinction value is
known toward this direction ; A 1.3È1.5 mag, i.e.,
V
E(B[V ) D 0.3È0.4 mag (Kohoutek, Mayer, & Lorenz 1999 ;
Lynds & OÏNeil 1985). Using E(B[V ) of 0.4 mag, we expect
an ISM N of D3 ] 1021 cm~2, with which we have Ðxed
H
the N value in our Ðt (also note that when we allow N to
H ] 1021 cm~2 falls within the errors). The model H
vary, 3
yielded an acceptable Ðt with kT D 0.14 keV (1.2 ] 106 K)
1
and N 5.9 ] 1021 cm~2, and a hotter component with
H,1 keV (3.9 ] 107 K) and N 2.7 ] 1021 cm~2,
kT D 3.3
with a line-of-sight ISM N 3 ] H,2 cm~2. The abun-
2
1021
H
dances are Ðxed at solar abundances. The Ðt results are
summarized in Table 4, along with the Fe K line character-
FIG. 4.ÈASCA SIS image (gray scale ranges 0.7È4.5 counts (6A4
. istics. The cold component arises from the O star atmo-
pixel~1) superposed on ROSAT contours. sphere, but the hot component might arise from a number
8. No. 1, 2001 X-RAYS AND PROTOSTARS IN THE TRIFID NEBULA 453
of di†erent sources, such as unresolved interacting binaries,
active low-mass stars, or PMS stars.
5. THE NATURE OF THE HARD X-RAY COMPONENT
Our simultaneous ASCA/PSPC Ðts yield a total X-ray
luminosity of 1.9È2.5 ] 1034 ergs s~1 (0.3È10 keV) using the
two-temperature model shown in Table 4. If attributed to
HD 164492, then the ratio of X-ray and bolometric lumi-
nosities ( log L /L ) is between [5.0 and [4.5, which is
X bol
much higher than the typical ratios of log L /L D [7 for
X bol
a single O-type star (Chlebowski & Harnden 1989 ;
Ž
Berghofer, Schmitt, & Cassinelli 1996). The 3 keV X-ray
component is somewhat of a mystery since winds from
single O-type stars are not known to produce such high-
temperature emission. Typically the highest temperature
emission observed in O star X-ray spectra has kT 1 keV
(e.g., Corcoran et al. 1994).
FIG. 5a We discuss a few possibilities to explain the hot com-
ponent in the TriÐd Nebula. It may be that the hot com-
ponent arises in the interaction of the wind from the O7.5
star with another object (either a companion star or a dense
region of the nebula) outside the O star atmosphere. Collid-
ing winds between an early-type star and an early-type
companion (another O star or a Wolf-Rayet star) can
produce shock-heated material in the wind interaction
regions (Stevens, Blondin, & Pollock 1992), reaching tem-
peratures of 107[108 K, and emit X-rays. However, recent
photometric and spectroscopic studies of this region found
no evidence of a companion for HD 164492 (Kohoutek,
Mayer, & Lorenz 1999). Unless the collision occurs far from
the star (d [ 25@@), it will be unresolved to the ROSAT
PSPC. However, recent radio and NIR observations
toward the central region of the TriÐd detected three
sources close to the O star (Yusef-Zadeh et al. 2000), which
may be either stars or nebular knots photoionized by the
UV Ðeld of HD 164492.
FIG. 5b Hard emission could also arise in single O stars from
nonthermal emission produced by Fermi acceleration by
shocks in the O star wind (Chen & White 1991). The hard
component is suggested as a nonthermal tail produced by
inverse Comptonization of the photospheric UV Ðeld by a
population of fast particles accelerated by a distribution of
shocks. Although it is not possible to determine if the hard
emission is from a nonthermal tail or the two thermal tem-
perature components from goodness of the Ðt to the spectra,
the presence of the Fe K line suggests that the second com-
ponent is thermal. The sources of the two spectral com-
ponents need to be resolved spatially in order to determine
their origins. Enhanced hard X-ray emission might also be
produced by an oblique magnetic rotator, as is suspected in
another O7 star, h1 Orionis C, the central star of the Orion
Nebula (Gagne et al. 1997).
The X-ray properties of the core of the H II region W3
share a number of similarities to the TriÐd emission. For
FIG. 5c W3, the luminosity is a few 1033 ergs s~1 with a similarly
high temperature (Hofner & Churchwell 1997). In W3 (and
FIG. 5.È(a) GIS1 and GIS2 spectra of the TriÐd Nebula with its best Ðt possibly in the TriÐd), the high-temperature component
of a two-temperature thermal model with additional warm absorbing
media. Hard emission and Fe XXV line appear in the spectra. (b) SIS0 and may be produced by a hot, wind-shocked cavity that results
SIS1 and PSPC spectra with the best Ðts. (c) Each of two temperature when strong stellar winds interact with a surrounding dense
components (D1.2 ] 106 K and 3.9 ] 107 K) is marked on the SIS0 molecular cloud (e.g., Churchwell 1990). The presence of a
spectrum. known YSO (TC1 in CLC98) is consistent with the presence
of a molecular cloud in the TriÐd. In addition, IRAS obser-
vations of HD 164492 (van Buren, Noriega-Crespo, &
Dgani 1995) show a bow-shock structure around the star,
9. 454 RHO ET AL. Vol. 562
TABLE 4
SPECTRAL FIT RESULTS FROM SIMULTANEOUS FIT USING ASCA/PSPC
Parameters TriÐd
ISM N (1021 cm~2) . . . . . . . . . . . . . . . . . . . . . . . . . . 43
H
T ................................................ 3.3 ^ 0.6 keV ( 3.9 ] 107 K)
2
log EM (cm~3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55.8
2
Wind N , hot component (1021 cm~2) . . . . . . 2.7`2.3
H ~2.0
T ................................................ 0.14`0.06 keV ( 1.2 ] 106 K)
1 ~0.04
log EM (cm~3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57.4
1
Wind N , 1 component (1021 cm~2) . . . . . . . . 5.9`1.1
H ~0.9
Flux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 ^ 0.5 ] 10~12
Unabsorbed Ñux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 ^ 2 ] 10~11
Luminosity (ergs s~1) . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 ] 1034 [d(kpc)/(1.67 kpc)]2
Fe K Line central energy (keV) . . . . . . . . . . . . . . 6.65`0.1
~0.2
Fe K equivalent width (keV) . . . . . . . . . . . . . . . . . 1.7 ^ 0.3
Fe K Ñux (photons s~1 cm~2) . . . . . . . . . . . . . . . 6( ^ 0.4) ] 10~4
perhaps indicative of a wind-cloud collision that might from unresolved emission from active PMS stars. With our
produce the high-temperature X-ray emission. The stellar current data, we cannot determine if one is more favored
wind outÑow at a speed of 1600 km s~1 should produce a than the other. To conclusively identify the hot component,
postshock temperature of D30 million degrees, though the a high-resolution image is needed to locate the emitting
observed temperature may be lower since radiative cooling object to determine whether the observed emission is pro-
is rapid. CLC98 suggested that the HCO` molecular clouds duced near the O star or whether a distributed group of
(likely the dust lanes) are fragmented shell around the active PMS stars dominates the observed emission. Along
nebula. In other words, the clouds and dust lanes we see in with the images, time-resolved spectra could allow us to
the optical image are located at the surface of the ionized distinguish whether the hard emission is Ñarelike (time
sphere. If this is the case, the 1600 km s~1 wind will be variable).
interacting with the lower density, ionized medium, and the
6. IDENTIFICATION OF X-RAY AND INFRARED SOURCES
shocked stellar wind can emit at high temperatures while
the photoionized materials of the edge of clouds could WITHIN THE TRIFID
supply sufficient density to emit strong X-rays. The detected X-ray sources and their counterparts are
The other possibility is that the hot component arises listed in Table 3. Most of X-ray sources are likely protostars
from deeply embedded young stars, especially since at least or PMS stars ; one source is a T Tauri star, two are massive
one embedded T Tauri star (TC1 in CLC98, which is protostars, and the others are unclassiÐed protostars. The
marked in Fig. 1) exists near the O star. The TC1 source in JHK color-color diagram using the 2MASS data suggests
s
CLC98 shows a large shift in the spectral energy distribu- that there are D80 protostars present in this nebula. It has
tion and violent ejections of high-velocity material (CLC98). been shown already (CLC98 ; LeÑoch & Cernicharo 2000)
Other ASCA observations showed bright X-ray sources that massive protostars (17È60 M ) are forming in the
_
with temperatures of 2È5 keV caused by Ñares of protostars TriÐd ; they are associated with molecular gas conden-
in the o Ophiuchi dark cloud (Koyama et al. 1992), the sations at the edges of clouds and their dynamical ages are
Orion Nebula (Yamauchi & Koyama 1993), and the R less than 104 yr. Whether low-mass protostars and T Tauri
Coronae Australis molecular cloud (Koyama et al. 1996). stars can be formed in a young (3 ] 105 yr) region such as
The hard emission was attributed to Ñares from individual the TriÐd is still an open question. Low-mass PMS stars of
PMS stars with typical X-ray luminosities in the range similarly young age were found in the Orion Nebula using
1030È1032 ergs s~1, and the peak luminosity of Ñares is new Chandra observations (Hillenbrand et al. 1998 ;
shown to be as large as 1033È1035 ergs s~1 and a tem- Garmire et al. 2000). The Chandra observation also showed
perature as high as 108 K (Feigelson & Montmerle 1999 ; the presence of young, low-mass (0.1È3 M ) PMS stars as
Grosso et al. 1997). The hard emission from W3 may be of a X-ray sources (Garmire et al. 2000). The_populations of
similar origin. Signs of active star formation in the TriÐd low-mass and massive protostars are similar in the TriÐd,
have been reported recently (LeÑoch et al. 2001) : there is a while we expect higher populations of low-mass protostars
dust cocoon or circumstellar disk around several members based on the initial mass function. This is consistent with
in the center of the TriÐd, and one young stellar source the fact that the TriÐd is a very young H II region ; T Tauri
shows a silicate feature in the circumstellar disk. Neither the stars have yet to form there. The distribution of T Tauri
o Ophiuchi dark cloud nor the R Coronae Australis molec- stars and massive YSOs is not obviously correlated with the
ular cloud is as bright in hard X-rays as the TriÐd Nebula, molecular cloud distribution. It is possible that they are
which may imply there are a higher number of protostars highly embedded in the molecular clouds, and their NIR
present in the TriÐd. A large number of protostars unre- colors cannot be fully obtained to identify protostars
solved to ASCA would dilute any Ñux variability produced because either J and/or H Ñux is unavailable. This is consis-
by Ñares. tent with the fact that 2MASS images show a higher popu-
In summary, one of two scenarios is likely responsible for lation of red stars in the southern part of the TriÐd. The
the hard emission : The emission may arise from HD 169942 HST images covering the southern part suggested the pres-
by the interaction of the wind from the O star with another ence of embedded stars at the head of the evaporating
object (a companion star or a dense region of the nebula) or globules (Hester et al. 1999). Deep NIR images and spec-
10. No. 1, 2001 X-RAYS AND PROTOSTARS IN THE TRIFID NEBULA 455
troscopy will likely reveal hundreds of young protostars in similarly to 30 Dor, we would expect D1035 ergs s~1 di†use
the TriÐd as suggested by 2MASS and HST data. X-ray emission from the TriÐd. This is higher than the total
Whether di†use X-ray emission exists within the TriÐd X-ray luminosity of the TriÐd. It is likely that supernova
Nebula is currently unknown because of the limited spatial heating contributes signiÐcantly to the bright X-ray emis-
resolution of the PSPC images. For the unidentiÐed X-ray sion from 30 Dor. The TriÐd Nebula is too young to have
sources 5 and 10, we cannot determine whether they are a hosted supernova explosions, so its di†use X-ray emission
part of di†use emission or real point sources. They are very should be much fainter than that of 30 Dor.
likely normal stars, but the possibility that they are knots of Future high-resolution X-ray observations by new tele-
di†use emission cannot be ruled out. Di†use X-ray emission scopes such as Chandra and XMM should be able to
from H II regions has been detected, although it is rare. A resolve the O star from its immediate environment and dis-
few examples have been found, such as in the Carina crete X-ray sources, such as T Tauri stars, numerous pro-
Nebula (Seward & Chlebowski 1982), RCW 49 (Goldwurm, tostars, young and old normal stars, and to resolve the
Caraveo, & Bignami 1987 ; Belloni & Mereghetti 1994), and source of the high-temperature emission. A deep NIR image
the Cygnus Superbubble (Bochkarev & Sitnik 1985), and with other wavelength observations can identify the PMS
recently Wang (1999) reported di†use X-ray emission from stars and protostars and their mass populations. The TriÐd
the giant H II region 30 Dor in the Large Magellanic Cloud. Nebula is an exciting laboratory to understand the early
ROSAT and Broadband X-Ray T elescope observations of stage of star-forming activities in H II region.
the Carina Nebula show large-scale di†use emission over at
least 40@, as well as discrete X-ray sources and hot gas sur-
rounding g Car (Corcoran et al. 1995). The nature of di†use We thank Lynne Hillenbrand for helpful discussion on
emission is unclear in H II regions. Seward & Chlebowski near-infrared colors of protostars and protostar disk
(1982) suggested that stellar winds from the OB association models and for useful comments on the manuscript and
adequately heat the plasma. Wang (1999) suggested that the John Carpenter for helpful discussion on 2MASS data. We
X-ray thermal di†use emission arises in blister-shaped thank Frank Winkler for allowing us to reproduce his
region by loops of ionized gas and the structure is explained optical image. For J. R., this work is partially supported by
by the mass loading of the hot gas produced by the central NASA/ADP grant, NASA-1407. This publication makes
OB association. use of data products from the Two-Micron All-Sky Survey,
We compare the TriÐd Nebula with 30 Dor to determine which is a joint project of the University of Massachusetts
whether stellar winds in the TriÐd may produce observable and the Infrared Processing and Analysis Center, funded by
di†use X-rays. The stellar wind luminosity in 30 Dor is a the National Aeronautics and Space Administration and
few ] 1039 ergs s~1, and the X-ray luminosity of 30 Dor is the National Science Foundation. J. R. and W. T. R.
D1038 ergs s~1 (Wang 1999). The stellar wind luminosity of acknowledge the support of the Jet Propulsion Laboratory,
HD 146692 is L 1.7 ] 1036(M/2 ] 10~6 M yr~1)(V /
0 California Institute of Technology, which is operated under
w _
1580 km s~1)2 ergs s~1. If the TriÐd emits di†use X-rays contract with NASA.
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