This document reports the detection of a compact CO outflow from L1148-IRS, confirming that this Spitzer source is physically associated with the nearby L1148 dense core. Radiative transfer modeling suggests the internal luminosity of L1148-IRS is between 0.08 and 0.13 solar luminosities, validating it as a Very Low Luminosity Object (VeLLO). The L1148 dense core has unusually low densities and column densities for a star-forming core, making it difficult to understand how L1148-IRS might have formed under these conditions.
A young protoplanet_candidate_embedded_in_the_circumstellar_disk_of_hd100546Sérgio Sacani
This document summarizes observations of HD100546 using high-contrast imaging techniques. A faint emission source was detected near the star at a projected separation of about 47 AU. The position of the source coincides with a deficit in polarization observed from the circumstellar disk. This suggests a physical link between the source and the disk. Considering various scenarios, the authors favor interpreting the source as a young protoplanet currently forming within the disk. Follow-up observations could distinguish between different possible explanations for the observed features. If confirmed, it would be a unique opportunity to study giant planet formation within an optically thick disk.
A LUMINOUS Be+WHITE DWARF SUPERSOFT SOURCE IN THE WING OF THE SMC: MAXI J0158...Carlos Bella
This document summarizes a study of the X-ray source MAXI J0158-744, which was detected by the MAXI instrument in November 2011. It exhibited an unusually bright and brief X-ray flare with a luminosity exceeding 10^39 erg/s, approaching ultraluminous X-ray source levels. Follow-up observations with Swift and other instruments over subsequent months found the source had a very soft X-ray spectrum characteristic of a supersoft source. Optical spectra of the counterpart revealed emission and absorption features consistent with a B1/2IIIe spectral type star in the Small Magellanic Cloud. The authors propose MAXI J0158-744 is a luminous supersoft source associated with
Type iax supernovae_a_new_class_of_stellar_explosionSérgio Sacani
Type Iax supernovae are a new class of stellar explosions that are spectroscopically similar to Type Ia supernovae but have lower maximum light velocities and peak magnitudes. They typically have lower ejecta masses and hotter photospheres than Type Ia. The progenitor system is likely a carbon-oxygen white dwarf that accretes matter from a helium star companion, resulting in a deflagration explosion that does not fully disrupt the white dwarf. Type Iax events occur about 31 times as frequently as Type Ia supernovae.
The document summarizes new Chandra and HST observations of the X-ray source IC 10 X-1 located in the nearby galaxy IC 10. The observations confirm that IC 10 X-1 has an average X-ray luminosity of 1.5 × 1038 erg s-1 and is strongly variable. The position of IC 10 X-1, within 0.23 arcseconds, matches the location of the Wolf-Rayet star [MAC92] 17A in IC 10. The observations suggest IC 10 X-1 may be a rare Wolf-Rayet black hole binary system, based on its luminosity, variability, and association with the Wolf-Rayet star.
A herschel and_apex_census_of_the_reddest_sources_in_orion_searching_for_the_...Sérgio Sacani
This document summarizes a study that uses Herschel and APEX data to identify the reddest, youngest protostar candidates in the Orion molecular clouds. 55 new protostar candidates are detected at 70 and 160 microns that were too faint or undetected at 24 microns in previous Spitzer data. The 11 reddest candidates with log(70 micron flux / 24 micron flux) > 1.65 are considered reliable protostars, while the remaining 44 have less extreme colors and higher contamination potential. Combining these with previously known protostars yields 18 sources called PACS Bright Red sources (PBRs) with the reddest colors. Analysis finds the PBRs have properties of very young Class 0 sources like
This document presents aluminum abundances for about 100 red giant stars in each of the Galactic globular clusters 47 Tuc and M 4. The abundances were derived from intermediate-resolution FLAMES/GIRAFFE spectra, focusing on the Al I doublet at 8772-8773 Å. Previous homogeneous abundances of O, Na, Mg, and Si were also analyzed to study multiple stellar populations in these clusters. The data confirm two stellar populations are visible in M 4, while 47 Tuc shows evidence of at least three distinct stellar groups based on the abundances of O, Na, Mg, Al, and N.
Analysis of most_light_curves_of_five_young_stars_in_taurus_auriga_and_lupus_3...Sérgio Sacani
This document analyzes light curves from the MOST satellite of five young stars in star-forming regions. Light curves of three spotted weak-line T Tauri stars (V410 Tau, V987 Tau, and Lupus 3-14) show small values of the solar-type differential rotation parameter, indicating slightly non-rigid rotation. Light curves of another spotted weak-line T Tauri star (Lupus 3-48) are consistent with rigid rotation. Three similar flares were detected in the light curve of Lupus 3-14. The light curve of the classical T Tauri star RY Tau showed continuous decreasing brightness over three weeks of observation with variable modulation and no obvious periodic signal.
G306.3-0.9 is a newly discovered young Galactic supernova remnant. Chandra X-ray observations reveal a complex morphology dominated by a bright shock, with the spectrum consistent with a young remnant in the Sedov phase implying an age of around 2,500 years. Radio observations with ATCA detect a prominent ridge of emission that correlates with the X-ray emission, with a flux density of around 160 mJy at 1 GHz. The remnant is also detected at 24μm, indicating the presence of irradiated warm dust. No compelling evidence is found for a compact stellar remnant within the remnant.
A young protoplanet_candidate_embedded_in_the_circumstellar_disk_of_hd100546Sérgio Sacani
This document summarizes observations of HD100546 using high-contrast imaging techniques. A faint emission source was detected near the star at a projected separation of about 47 AU. The position of the source coincides with a deficit in polarization observed from the circumstellar disk. This suggests a physical link between the source and the disk. Considering various scenarios, the authors favor interpreting the source as a young protoplanet currently forming within the disk. Follow-up observations could distinguish between different possible explanations for the observed features. If confirmed, it would be a unique opportunity to study giant planet formation within an optically thick disk.
A LUMINOUS Be+WHITE DWARF SUPERSOFT SOURCE IN THE WING OF THE SMC: MAXI J0158...Carlos Bella
This document summarizes a study of the X-ray source MAXI J0158-744, which was detected by the MAXI instrument in November 2011. It exhibited an unusually bright and brief X-ray flare with a luminosity exceeding 10^39 erg/s, approaching ultraluminous X-ray source levels. Follow-up observations with Swift and other instruments over subsequent months found the source had a very soft X-ray spectrum characteristic of a supersoft source. Optical spectra of the counterpart revealed emission and absorption features consistent with a B1/2IIIe spectral type star in the Small Magellanic Cloud. The authors propose MAXI J0158-744 is a luminous supersoft source associated with
Type iax supernovae_a_new_class_of_stellar_explosionSérgio Sacani
Type Iax supernovae are a new class of stellar explosions that are spectroscopically similar to Type Ia supernovae but have lower maximum light velocities and peak magnitudes. They typically have lower ejecta masses and hotter photospheres than Type Ia. The progenitor system is likely a carbon-oxygen white dwarf that accretes matter from a helium star companion, resulting in a deflagration explosion that does not fully disrupt the white dwarf. Type Iax events occur about 31 times as frequently as Type Ia supernovae.
The document summarizes new Chandra and HST observations of the X-ray source IC 10 X-1 located in the nearby galaxy IC 10. The observations confirm that IC 10 X-1 has an average X-ray luminosity of 1.5 × 1038 erg s-1 and is strongly variable. The position of IC 10 X-1, within 0.23 arcseconds, matches the location of the Wolf-Rayet star [MAC92] 17A in IC 10. The observations suggest IC 10 X-1 may be a rare Wolf-Rayet black hole binary system, based on its luminosity, variability, and association with the Wolf-Rayet star.
A herschel and_apex_census_of_the_reddest_sources_in_orion_searching_for_the_...Sérgio Sacani
This document summarizes a study that uses Herschel and APEX data to identify the reddest, youngest protostar candidates in the Orion molecular clouds. 55 new protostar candidates are detected at 70 and 160 microns that were too faint or undetected at 24 microns in previous Spitzer data. The 11 reddest candidates with log(70 micron flux / 24 micron flux) > 1.65 are considered reliable protostars, while the remaining 44 have less extreme colors and higher contamination potential. Combining these with previously known protostars yields 18 sources called PACS Bright Red sources (PBRs) with the reddest colors. Analysis finds the PBRs have properties of very young Class 0 sources like
This document presents aluminum abundances for about 100 red giant stars in each of the Galactic globular clusters 47 Tuc and M 4. The abundances were derived from intermediate-resolution FLAMES/GIRAFFE spectra, focusing on the Al I doublet at 8772-8773 Å. Previous homogeneous abundances of O, Na, Mg, and Si were also analyzed to study multiple stellar populations in these clusters. The data confirm two stellar populations are visible in M 4, while 47 Tuc shows evidence of at least three distinct stellar groups based on the abundances of O, Na, Mg, Al, and N.
Analysis of most_light_curves_of_five_young_stars_in_taurus_auriga_and_lupus_3...Sérgio Sacani
This document analyzes light curves from the MOST satellite of five young stars in star-forming regions. Light curves of three spotted weak-line T Tauri stars (V410 Tau, V987 Tau, and Lupus 3-14) show small values of the solar-type differential rotation parameter, indicating slightly non-rigid rotation. Light curves of another spotted weak-line T Tauri star (Lupus 3-48) are consistent with rigid rotation. Three similar flares were detected in the light curve of Lupus 3-14. The light curve of the classical T Tauri star RY Tau showed continuous decreasing brightness over three weeks of observation with variable modulation and no obvious periodic signal.
G306.3-0.9 is a newly discovered young Galactic supernova remnant. Chandra X-ray observations reveal a complex morphology dominated by a bright shock, with the spectrum consistent with a young remnant in the Sedov phase implying an age of around 2,500 years. Radio observations with ATCA detect a prominent ridge of emission that correlates with the X-ray emission, with a flux density of around 160 mJy at 1 GHz. The remnant is also detected at 24μm, indicating the presence of irradiated warm dust. No compelling evidence is found for a compact stellar remnant within the remnant.
1) The document analyzes the correlation function of the 6dF Galaxy Survey (6dFGS) and detects a Baryon Acoustic Oscillation (BAO) signal.
2) This BAO detection allows constraining the distance-redshift relation at an effective redshift of zeff = 0.106, achieving a distance measure of DV(zeff) = 456 ± 27 Mpc.
3) The low effective redshift of 6dFGS makes it competitive with Cepheids and low-z supernovae in constraining the Hubble constant, yielding a value of H0 = 67 ± 3.2 km s−1 Mpc−1.
This paper analyzes Spitzer observations of the Eagle Nebula to study the energetics and evolution of dust. The observations show a shell of emission within the nebula at mid-IR wavelengths that is distinct from the morphology at longer wavelengths. Spectral energy distributions are measured across the nebula and modeled to constrain dust properties and heating sources. Two possible interpretations are proposed for the nature of the mid-IR shell: 1) dust processing in shocks driven by stellar winds, or 2) emission from a hot plasma where dust is collisionally heated. The goal is to better understand dust evolution in massive star forming regions.
A multiband study_of_hercules_a_ii_multifrequency_vlaSérgio Sacani
This document summarizes a multi-frequency study of the radio galaxy Hercules A using the VLA radio telescope. The observations revealed that the bright jets and prominent rings have a flatter spectrum than the surrounding lobes and bridge, suggesting they represent a recent outburst from the active nucleus. The magnetic field closely follows the edges of the lobes, jets, and rings. There is also an asymmetry in the spectral properties between the two lobes that can be explained by relativistic beaming and light travel delays.
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 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.
This document summarizes star forming regions in the constellation of Cepheus. It describes several giant molecular cloud complexes located at various distances from the Sun, ranging from clouds within 500 pc to regions associated with the Perseus spiral arm at 2-3 kpc. Key regions discussed include the Cepheus Flare clouds below 500 pc, three OB associations (Cep OB2, Cep OB3, Cep OB4) located 600-900 pc away, and the well-known high mass star forming region S 140 located at 900 pc. Tables list molecular clouds and young stars identified in the Cepheus region. Maps show the distribution of clouds, extinction, and pre-main sequence stars across Cepheus.
The document summarizes two Chandra X-ray observations of the Type IIn supernova SN 2010jl taken around two months and one year after explosion. The first observation revealed a high temperature (10 keV) and very high absorption column density (1024 cm-2) from circumstellar matter. The second observation, one year later, showed the absorption column had decreased by a factor of three as expected from shock propagation. Both observations detected an unabsorbed luminosity of 7×1041 erg s-1. The Fe line detected in the first observation was not present in the second.
Rings in the_haloes_of_planetary_nebulaeSérgio Sacani
This document presents the discovery of ring structures in the haloes of eight planetary nebulae, tripling the number known to have such rings. The rings are analyzed using image processing techniques to enhance their visibility. They find ring spacings range from less than 0.01 pc to 0.06 pc. This suggests ring spacing increases with time after the asymptotic giant branch phase. The properties of the rings support predictions of dust-driven wind instability models of mass loss but do not rule out other models. Analyzing the new detections provides insights into mass modulation processes late in stellar evolution.
Modulations in the_radio_light_curve_of_the_typeiib_supernova_2001igSérgio Sacani
This document summarizes radio observations of the Type IIb supernova SN 2001ig made with the Australia Telescope Compact Array and Very Large Array over 700 days. The observations found periodic deviations from the standard model of radio light curves that are consistent with recurring density modulations in the circumstellar medium with a period of around 150 days. This provides evidence that the progenitor was a Wolf-Rayet star in a binary system with an eccentric 100 day orbit, causing regular build-up of circumstellar material. Such binary systems are thought to produce Type Ib/c supernovae through envelope stripping, linking these events to Type IIb supernovae.
This document summarizes a study analyzing far-infrared spectra of Saturn's rings obtained by the Cassini spacecraft. The authors modeled the spectra to estimate the size distribution of regolith grains on ring particles. They found that the spectra were best fit by a broad size distribution ranging from 1 micron to 1-10 cm, with a power law index of around 3. This suggests that the largest regolith grains are comparable in size to the smallest visible ring particles. The abundance of smaller grains was found to increase with decreasing solar phase angle, likely due to cooling effects in Saturn's shadow.
An infrared proper_motion_study_of_bullets_of_orion_nebulaSérgio Sacani
This study measured the proper motions of infrared-emitting bullets in the Orion Nebula using images taken with a four-year time baseline. The [Fe II]-emitting bullets were found to be moving at around 170 km/s, while H2 bullets had smaller motions. Differential motion was not observed between [Fe II] bullets and trailing H2 wakes, suggesting they have reached a steady configuration over at least 100 years. The proper motions provide constraints on the origin and dynamics of the bullet systems, with an impulsive origin appearing likely.
Detection of visible light from the darkest worldSérgio Sacani
This document reports the detection of visible light from the exoplanet TrES-2b using Kepler photometry data. The analysis finds a day-night contrast amplitude of 6.5 ± 1.9 parts per million, representing the lowest amplitude orbital phase variation discovered. This signal is detected at a confidence level of 99.98% and persists across different models of the data, appearing robust. If interpreted as scattering, it corresponds to a geometric albedo of 0.0253±0.0072 for TrES-2b, making it the darkest exoplanet detected so far. However, models indicate significant day-side emission, implying an even lower true albedo.
The galactic supernova_remnant_w49_b_likely_originates_from_a_jet_drivenSérgio Sacani
This Chandra observation of supernova remnant W49B finds:
1) Variable electron temperature and absorbing column across the remnant.
2) Mean metal abundances consistent with bipolar/jet-driven core-collapse supernova models.
3) Strict upper limits set on any undetected point sources, excluding the presence of a neutron star associated with W49B.
4) Morphological, spectral, and environmental characteristics indicate W49B originated from a bipolar Type Ib/Ic supernova explosion.
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.
Star formation history_in_the_smc_the_case_of_ngc602Sérgio Sacani
This document summarizes a study of the star formation history in the NGC 602 region of the Small Magellanic Cloud based on Hubble Space Telescope observations. Deep photometry reveals numerous pre-main sequence stars as well as young stars on the main sequence, allowing the study of star formation into recent times. New pre-main sequence stellar evolutionary tracks are presented. A stellar population synthesis code is used to derive the best estimate of the star formation history by comparing observed and synthetic color-magnitude diagrams. The star formation rate in the region has increased over the past tens of Myr, reaching 0.3-0.7×10−3 M☉ yr−1 in the last 2.5 Myr, comparable to
An atlas of_predicted_exotic_gravitational_lensesSérgio Sacani
This document discusses an atlas of predicted exotic gravitational lenses. It begins by noting that upcoming wide-field surveys will discover thousands of new strong gravitational lenses, some of which may have unusual image configurations. It then describes using a ray-tracing code to model exotic lenses produced by multi-component galaxy potentials, including lenses with misaligned disks and bulges that produce "broken" Einstein rings, and binary or merging galaxies that produce a Y-shaped image configuration. The document estimates the abundance of these exotic galaxy-scale lenses to be approximately one per all-sky survey. It also discusses how cluster lenses can produce a wide range of caustic structures, and interprets the central ring and counter-image in Abell 1703 as
Non xrays from_the_very_nearby_typeia_sn_2014j_constraints_on_its_environmentSérgio Sacani
Deep X-ray observations of SN 2014J reveal no X-ray emission down to a luminosity limit of Lx < 7 × 1036 ergs−1, constraining the mass-loss rate of the progenitor system to be < 10−9 M☉/yr. Alternatively, the SN shock could be expanding into a uniform medium with density < 3 cm−3. These results rule out single-degenerate systems with steady mass transfer until explosion and constrain unstable hydrogen burning systems to have recurrence times < 300 years. Allowed progenitors include double white dwarf systems or systems where mass transfer ceased before explosion.
This document summarizes a study of the young star cluster IC 5146. Optical and near-infrared photometry were obtained for over 700 stars in the region, including around the illuminating stars BD +46°3474 and the embedded variable star BD +46°3471. Around 100 emission-line stars brighter than R=20.5 were found, most in IC 5146. Spectroscopy of 38 stars found an average extinction of AV=3.0 mag. The age distribution of the emission-line stars was estimated from theoretical isochrones to have a median age of around 1 Myr.
The close circumstellar environment of betelgeuseSérgio Sacani
This document summarizes observations of the red supergiant star Betelgeuse and its circumstellar environment using the VLT/VISIR instrument. Diffraction-limited images were obtained in 6 filters between 7.76-12.81 μm and 2 filters between 17.65-19.50 μm. The images reveal a bright, extended, and complex circumstellar envelope at all wavelengths, pointing to the presence of oxygen-rich dust like silicates. A partial circular shell is observed between 0.5-1.0" from the star, which may correspond to the inner radius of the dust envelope. Several knots and filamentary structures are also identified within the nebula.
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
Direct detection of the enceladus water torus with herschelSérgio Sacani
The Herschel Space Observatory directly detected the water vapor torus around Saturn's moon Enceladus by observing absorption lines of water vapor against Saturn. Spectroscopic observations with Herschel's HIFI instrument detected water vapor lines at 557, 987, 1113, and 1670 GHz. Modeling of the spectra determined the water vapor has a column density of ~4 × 1013 cm-2 near the equatorial plane and a vertical scale height of ~50,000 km. The water torus appears rotationally cold at 16 K but is dynamically excited with non-Keplerian velocities of ~2 km/s, shaped largely by molecular collisions. Estimates of the influx of torus material into
The Voyager flights to Jupiter and Saturn were NASA missions launched in 1977 that took advantage of a rare planetary alignment to visit multiple outer planets using gravitational assists. Voyager 1 and 2 were each complex, long-lived spacecraft carrying instruments to study the planets, rings, moons, and environments. Voyager 1's encounter with Jupiter in 1979 revealed active volcanoes on Io and details of Jupiter's atmosphere, while both probes provided the first close images of Jupiter's moons."
1) The document analyzes the correlation function of the 6dF Galaxy Survey (6dFGS) and detects a Baryon Acoustic Oscillation (BAO) signal.
2) This BAO detection allows constraining the distance-redshift relation at an effective redshift of zeff = 0.106, achieving a distance measure of DV(zeff) = 456 ± 27 Mpc.
3) The low effective redshift of 6dFGS makes it competitive with Cepheids and low-z supernovae in constraining the Hubble constant, yielding a value of H0 = 67 ± 3.2 km s−1 Mpc−1.
This paper analyzes Spitzer observations of the Eagle Nebula to study the energetics and evolution of dust. The observations show a shell of emission within the nebula at mid-IR wavelengths that is distinct from the morphology at longer wavelengths. Spectral energy distributions are measured across the nebula and modeled to constrain dust properties and heating sources. Two possible interpretations are proposed for the nature of the mid-IR shell: 1) dust processing in shocks driven by stellar winds, or 2) emission from a hot plasma where dust is collisionally heated. The goal is to better understand dust evolution in massive star forming regions.
A multiband study_of_hercules_a_ii_multifrequency_vlaSérgio Sacani
This document summarizes a multi-frequency study of the radio galaxy Hercules A using the VLA radio telescope. The observations revealed that the bright jets and prominent rings have a flatter spectrum than the surrounding lobes and bridge, suggesting they represent a recent outburst from the active nucleus. The magnetic field closely follows the edges of the lobes, jets, and rings. There is also an asymmetry in the spectral properties between the two lobes that can be explained by relativistic beaming and light travel delays.
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 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.
This document summarizes star forming regions in the constellation of Cepheus. It describes several giant molecular cloud complexes located at various distances from the Sun, ranging from clouds within 500 pc to regions associated with the Perseus spiral arm at 2-3 kpc. Key regions discussed include the Cepheus Flare clouds below 500 pc, three OB associations (Cep OB2, Cep OB3, Cep OB4) located 600-900 pc away, and the well-known high mass star forming region S 140 located at 900 pc. Tables list molecular clouds and young stars identified in the Cepheus region. Maps show the distribution of clouds, extinction, and pre-main sequence stars across Cepheus.
The document summarizes two Chandra X-ray observations of the Type IIn supernova SN 2010jl taken around two months and one year after explosion. The first observation revealed a high temperature (10 keV) and very high absorption column density (1024 cm-2) from circumstellar matter. The second observation, one year later, showed the absorption column had decreased by a factor of three as expected from shock propagation. Both observations detected an unabsorbed luminosity of 7×1041 erg s-1. The Fe line detected in the first observation was not present in the second.
Rings in the_haloes_of_planetary_nebulaeSérgio Sacani
This document presents the discovery of ring structures in the haloes of eight planetary nebulae, tripling the number known to have such rings. The rings are analyzed using image processing techniques to enhance their visibility. They find ring spacings range from less than 0.01 pc to 0.06 pc. This suggests ring spacing increases with time after the asymptotic giant branch phase. The properties of the rings support predictions of dust-driven wind instability models of mass loss but do not rule out other models. Analyzing the new detections provides insights into mass modulation processes late in stellar evolution.
Modulations in the_radio_light_curve_of_the_typeiib_supernova_2001igSérgio Sacani
This document summarizes radio observations of the Type IIb supernova SN 2001ig made with the Australia Telescope Compact Array and Very Large Array over 700 days. The observations found periodic deviations from the standard model of radio light curves that are consistent with recurring density modulations in the circumstellar medium with a period of around 150 days. This provides evidence that the progenitor was a Wolf-Rayet star in a binary system with an eccentric 100 day orbit, causing regular build-up of circumstellar material. Such binary systems are thought to produce Type Ib/c supernovae through envelope stripping, linking these events to Type IIb supernovae.
This document summarizes a study analyzing far-infrared spectra of Saturn's rings obtained by the Cassini spacecraft. The authors modeled the spectra to estimate the size distribution of regolith grains on ring particles. They found that the spectra were best fit by a broad size distribution ranging from 1 micron to 1-10 cm, with a power law index of around 3. This suggests that the largest regolith grains are comparable in size to the smallest visible ring particles. The abundance of smaller grains was found to increase with decreasing solar phase angle, likely due to cooling effects in Saturn's shadow.
An infrared proper_motion_study_of_bullets_of_orion_nebulaSérgio Sacani
This study measured the proper motions of infrared-emitting bullets in the Orion Nebula using images taken with a four-year time baseline. The [Fe II]-emitting bullets were found to be moving at around 170 km/s, while H2 bullets had smaller motions. Differential motion was not observed between [Fe II] bullets and trailing H2 wakes, suggesting they have reached a steady configuration over at least 100 years. The proper motions provide constraints on the origin and dynamics of the bullet systems, with an impulsive origin appearing likely.
Detection of visible light from the darkest worldSérgio Sacani
This document reports the detection of visible light from the exoplanet TrES-2b using Kepler photometry data. The analysis finds a day-night contrast amplitude of 6.5 ± 1.9 parts per million, representing the lowest amplitude orbital phase variation discovered. This signal is detected at a confidence level of 99.98% and persists across different models of the data, appearing robust. If interpreted as scattering, it corresponds to a geometric albedo of 0.0253±0.0072 for TrES-2b, making it the darkest exoplanet detected so far. However, models indicate significant day-side emission, implying an even lower true albedo.
The galactic supernova_remnant_w49_b_likely_originates_from_a_jet_drivenSérgio Sacani
This Chandra observation of supernova remnant W49B finds:
1) Variable electron temperature and absorbing column across the remnant.
2) Mean metal abundances consistent with bipolar/jet-driven core-collapse supernova models.
3) Strict upper limits set on any undetected point sources, excluding the presence of a neutron star associated with W49B.
4) Morphological, spectral, and environmental characteristics indicate W49B originated from a bipolar Type Ib/Ic supernova explosion.
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.
Star formation history_in_the_smc_the_case_of_ngc602Sérgio Sacani
This document summarizes a study of the star formation history in the NGC 602 region of the Small Magellanic Cloud based on Hubble Space Telescope observations. Deep photometry reveals numerous pre-main sequence stars as well as young stars on the main sequence, allowing the study of star formation into recent times. New pre-main sequence stellar evolutionary tracks are presented. A stellar population synthesis code is used to derive the best estimate of the star formation history by comparing observed and synthetic color-magnitude diagrams. The star formation rate in the region has increased over the past tens of Myr, reaching 0.3-0.7×10−3 M☉ yr−1 in the last 2.5 Myr, comparable to
An atlas of_predicted_exotic_gravitational_lensesSérgio Sacani
This document discusses an atlas of predicted exotic gravitational lenses. It begins by noting that upcoming wide-field surveys will discover thousands of new strong gravitational lenses, some of which may have unusual image configurations. It then describes using a ray-tracing code to model exotic lenses produced by multi-component galaxy potentials, including lenses with misaligned disks and bulges that produce "broken" Einstein rings, and binary or merging galaxies that produce a Y-shaped image configuration. The document estimates the abundance of these exotic galaxy-scale lenses to be approximately one per all-sky survey. It also discusses how cluster lenses can produce a wide range of caustic structures, and interprets the central ring and counter-image in Abell 1703 as
Non xrays from_the_very_nearby_typeia_sn_2014j_constraints_on_its_environmentSérgio Sacani
Deep X-ray observations of SN 2014J reveal no X-ray emission down to a luminosity limit of Lx < 7 × 1036 ergs−1, constraining the mass-loss rate of the progenitor system to be < 10−9 M☉/yr. Alternatively, the SN shock could be expanding into a uniform medium with density < 3 cm−3. These results rule out single-degenerate systems with steady mass transfer until explosion and constrain unstable hydrogen burning systems to have recurrence times < 300 years. Allowed progenitors include double white dwarf systems or systems where mass transfer ceased before explosion.
This document summarizes a study of the young star cluster IC 5146. Optical and near-infrared photometry were obtained for over 700 stars in the region, including around the illuminating stars BD +46°3474 and the embedded variable star BD +46°3471. Around 100 emission-line stars brighter than R=20.5 were found, most in IC 5146. Spectroscopy of 38 stars found an average extinction of AV=3.0 mag. The age distribution of the emission-line stars was estimated from theoretical isochrones to have a median age of around 1 Myr.
The close circumstellar environment of betelgeuseSérgio Sacani
This document summarizes observations of the red supergiant star Betelgeuse and its circumstellar environment using the VLT/VISIR instrument. Diffraction-limited images were obtained in 6 filters between 7.76-12.81 μm and 2 filters between 17.65-19.50 μm. The images reveal a bright, extended, and complex circumstellar envelope at all wavelengths, pointing to the presence of oxygen-rich dust like silicates. A partial circular shell is observed between 0.5-1.0" from the star, which may correspond to the inner radius of the dust envelope. Several knots and filamentary structures are also identified within the nebula.
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
Direct detection of the enceladus water torus with herschelSérgio Sacani
The Herschel Space Observatory directly detected the water vapor torus around Saturn's moon Enceladus by observing absorption lines of water vapor against Saturn. Spectroscopic observations with Herschel's HIFI instrument detected water vapor lines at 557, 987, 1113, and 1670 GHz. Modeling of the spectra determined the water vapor has a column density of ~4 × 1013 cm-2 near the equatorial plane and a vertical scale height of ~50,000 km. The water torus appears rotationally cold at 16 K but is dynamically excited with non-Keplerian velocities of ~2 km/s, shaped largely by molecular collisions. Estimates of the influx of torus material into
The Voyager flights to Jupiter and Saturn were NASA missions launched in 1977 that took advantage of a rare planetary alignment to visit multiple outer planets using gravitational assists. Voyager 1 and 2 were each complex, long-lived spacecraft carrying instruments to study the planets, rings, moons, and environments. Voyager 1's encounter with Jupiter in 1979 revealed active volcanoes on Io and details of Jupiter's atmosphere, while both probes provided the first close images of Jupiter's moons."
This document provides guidelines for news organizations on using social media effectively and appropriately. It summarizes 10 best practices for social media use based on a review of existing social media policies at various news outlets. The best practices are: 1) Traditional journalism ethics still apply online; 2) Assume anything written online could become public; 3) Engage readers professionally on social media; 4) Break news on your own website, not social media; 5) Be aware of perceptions; 6) Independently verify information found on social media; 7) Identify yourself as a journalist; 8) Treat social media as a tool, not just for personal use; 9) Be transparent and admit mistakes; 10) Keep internal deliberations confidential.
1. INTEGRAL observations of the SNR IC443 region detected several sources, including the pulsar wind nebula (Src #5) and the enigmatic hard X-ray source Src #11.
2. JEM-X images in the 6-10 and 10-20 keV bands tentatively identified counterparts for Src #5 and Src #11. Measured fluxes from JEM-X were consistent with XMM spectra but did not provide strong constraints.
3. Optical and infrared images showed possible counterparts for Src #11, including point sources and diffuse 2MASS-Ks emission thought to originate from shocked molecular hydrogen, suggesting a correlation between X-ray and infrared emission.
Teachable moment the japan earthquake and tsunamiSérgio Sacani
On March 11, 2011, a 9.0 magnitude earthquake struck off the coast of Honshu, Japan, generating a powerful tsunami. This was one of the largest earthquakes in Japanese history and caused widespread damage. The earthquake and tsunami highlighted Japan's vulnerability to natural disasters due to its location at the boundary of four tectonic plates.
This document presents a new preon model with three fundamental spin-1/2 preons (α, β, δ) that can combine to form nine leptons, nine quarks, and nine heavy vector bosons. The preons have charges of +e/3, -2e/3, and +e/3. Quarks and leptons are composed of combinations of one spin-1/2 preon and one spin-0 "dipreon" made of two spin-1/2 preons. This model aims to address shortcomings of the standard model such as the large number of fundamental particles and mixings between particles, through a more fundamental layer of preons with an underlying symmetry.
This document summarizes a study that uses distance measurements in the nearby universe to test theories of modified gravity. The study compares distance measurements from cepheid variable stars, tip of the red giant branch stars, and water masers in different galaxies. These distance indicators operate in gravitational fields of different strengths, enabling tests of scalar-tensor gravity theories where fifth forces are screened to different extents depending on the local gravitational potential. The study finds no evidence for the enhanced gravitational forces predicted by chameleon and symmetron screening scenarios, constraining the parameter space of these theories.
Stefano Sposetti and Marco Iten detected a probable lunar impact event on February 11, 2011 while monitoring the moon from two separate observatories in Switzerland. Their videos showed a flash of light on the lunar surface at 20:36:58 UTC. Analysis of the light curves and location of the flash place the impact in a region of craters near 86°W, 16°N. The editorial board of Selenology Today notes that images from the Lunar Reconnaissance Orbiter before and after the reported event can be searched to look for an impact crater at the reported coordinates.
1) The Fermi bubbles are giant gamma-ray emitting structures extending above and below the galactic center.
2) The bubbles may have been formed by periodic capture of stars by the supermassive black hole at the galactic center, releasing energy of around 3x10^52 ergs per capture.
3) This energy injection could produce very hot plasma, accelerating electrons that produce radio and gamma-ray emission through synchrotron radiation and inverse Compton scattering.
1. This paper presents results from a 600 ks XMM-Newton observation of Mrk 509 as part of a large multiwavelength campaign.
2. The high quality spectrum allows an unprecedented investigation of the ionized outflow through the detection of multiple absorption lines.
3. The outflow is found to consist of at least two velocity components that have been observed previously, as well as a tentative high velocity component. Discrete ionization components are detected spanning four orders of magnitude in ionization parameter.
Vegetti et al. discovered a satellite galaxy located around a more distant elliptical galaxy acting as a gravitational lens. They were able to detect the satellite galaxy through its effect on distorting light from a background source, causing detectable "dents and blobs" in the ring of light formed by the main lens galaxy. This satellite galaxy has a mass of about 113 million solar masses, making it one of the lowest-mass satellite galaxies detected so far. The discovery provides evidence that gravitational lensing techniques can be used to find satellite galaxies beyond the Local Group and help test theories of galaxy formation and evolution.
The document summarizes research on the concentric crater located in Humboldt on the Moon. It finds that the concentric crater is typical in size and ratio of inner to outer ring diameters compared to other known concentric craters. Spectral analysis indicates the interior of the concentric crater is composed of highland material, supporting the hypothesis that it formed through igneous intrusion rather than volcanic extrusion. The proximity of two younger, non-concentric craters of similar size suggests conditions for concentric crater formation no longer existed at the time of their impacts. Together, this provides evidence that the concentric crater in Humboldt formed through igneous intrusion rather than volcanic activity.
This study presents a comprehensive digital mosaic of ice motion across Antarctica assembled from satellite radar data. The data reveal widespread, patterned, enhanced flow of tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent. This emphasizes the importance of basal-slip dominated tributary flow over deformation-dominated ice sheet flow, redefining our understanding of ice sheet dynamics. The extensive network of fast-flowing tributaries challenges prior views of ice sheet flow and implies a tighter connection between coastal and interior ice flow than previously thought.
The OPERA experiment measures the velocity of neutrinos produced at CERN and detected 730 km away at the Gran Sasso laboratory to high precision. To do so it must accurately measure the time of flight of neutrinos between the two sites by precisely synchronizing clocks at CERN and Gran Sasso, determining the baseline distance through geodesy, and calibrating the timing of the proton beam and neutrino detection. This allows OPERA to search for small deviations from the speed of light in the measurement of the neutrino velocity.
Observational evidence from supernovae for an accelerating universe and a cos...Sérgio Sacani
The document presents observations of 10 type Ia supernovae (SNe Ia) with redshifts between 0.16 and 0.62. Combined with previous data from the team and others, the distances to the 16 high-redshift SNe Ia are on average 10-15% farther than expected in a low-mass density universe without a cosmological constant. Different analysis methods find evidence favoring an expanding universe with a positive cosmological constant and acceleration of the expansion. The data are consistent with an accelerating universe and cosmological constant at a statistical significance of 2.8-9 sigma depending on the method and assumptions.
This document describes a model of crater formation on the Moon and terrestrial planets based on the current understanding of the impactor population in the inner Solar System. The model calculates impact rates spatially across planetary surfaces to account for nonuniform cratering. It finds that the lunar cratering rate varies with latitude and longitude, being about 25% lower in some regions and higher in others. The model reconciles measured lunar crater size-frequency distributions with observations of near-Earth objects, assuming the presence of a porous lunar megaregolith affects the size of small craters. It provides revised estimates of the ages of some lunar and planetary geological features based on crater counts and the derived crater chronology.
1) The document describes small-scale graben (extensional faults) discovered on the Moon using images from the Lunar Reconnaissance Orbiter Camera.
2) Some graben are located near lobate scarps (contractional faults), while others are found in mare basalts and in the highlands.
3) The graben crosscut small impact craters, suggesting they formed recently, within the last 50 million years. This indicates the Moon has experienced recent extensional tectonic activity.
Characterizing interstellar filaments with herschel in ic5146Sérgio Sacani
This document summarizes early results from the Herschel Gould Belt survey of the IC5146 molecular cloud. It reveals a complex network of filaments identified in the cloud, which are shown to be the main sites of prestellar core formation. Analysis of 27 filaments finds that their radial column density profiles fall off with radii as r^-1.5 to r^-2.5. Remarkably, the filaments seem to have a narrow distribution of widths centered around 0.1 pc, in contrast to a broader distribution of central Jeans lengths. This characteristic width corresponds to the sonic scale below which turbulence becomes subsonic, supporting the argument that filaments may form from dissipating large-scale turbulence.
This document describes the discovery and characterization of CFBDSIR2149, a late T dwarf found to have an unusually red J-K color and enhanced K-band flux. Spectroscopy with X-Shooter revealed it has a T7 spectral type with low surface gravity features, indicating it is a young substellar object. Comparison to atmospheric models suggests it has a temperature of 650-750K, surface gravity of logg=3.75-4.0, and a mass in the planetary regime of 4-7 Jupiter masses. An analysis of its proper motion finds an 87% probability it is a member of the young AB Doradus moving group, which would make it a free-floating planet with an
An exceptional xray_view_of_the_young_open_cluster_ngc6231Sérgio Sacani
The XMM-Newton satellite observed the young open star cluster NGC 6231 for a total of 180 kiloseconds, providing an unprecedented X-ray view. Around 600 point-like X-ray sources were detected, including many early-type O stars. The data helped refine the relationship between X-ray and bolometric luminosities for O stars, finding less scatter than previously thought, with the main exception being X-ray emission from wind interactions in binary systems. The data also provided insight into the low-mass pre-main sequence star population and star formation history of the cluster.
The first hyper_luminous_infrared_galaxy_discovered_by_wiseSérgio Sacani
This document summarizes the discovery of WISE J181417.29+341224.9 (WISE 1814+3412), the first hyper-luminous infrared galaxy (LIR > 1013 L⊙) discovered by the Wide-field Infrared Survey Explorer (WISE). Follow-up images of WISE 1814+3412 revealed four nearby sources - a QSO, two Lyman Break Galaxies at z = 2.45, and an M dwarf star. The brighter LBG dominates the bolometric emission and has a star formation rate of ~300M⊙ yr−1, accounting for <10% of the bolometric luminosity. An obscured AGN combined with starburst and
The first hyper_luminous_infrared_galaxy_discovered_by_wiseSérgio Sacani
This document summarizes the discovery of WISE J181417.29+341224.9 (WISE 1814+3412), the first hyper-luminous infrared galaxy (LIR > 1013 L⊙) discovered by the Wide-field Infrared Survey Explorer (WISE). Follow-up images of WISE 1814+3412 revealed four nearby sources - a QSO, two Lyman Break Galaxies at z=2.45, and an M dwarf star. The brighter LBG dominates the bolometric emission of WISE 1814+3412 and has a star formation rate of ~300M⊙ yr−1, accounting for <10% of the total luminosity. An obscured
The document discusses modeling of helium line formation in solar prominences using radiative transfer modeling. It describes how the models account for the prominence-corona transition region and influence of radial plasma motions on line profiles and intensities. The modeling helps interpret observations from instruments like SOHO, Hinode, STEREO, and SDO to better understand the thermal structure and magnetic fields of prominences.
Fluorescence and resonant ionization in astrophysical plasmas, with emphasis ...AstroAtom
The document discusses fluorescence and resonant ionization processes in Eta Carinae, an astrophysical laboratory. It describes how fluorescence produces emission lines in spectra of the Weigelt blobs near Eta Carinae. Resonance enhanced two-photon ionization (RETPI) can explain the formation of strongly varying emission lines through a process involving hydrogen Lyman lines. RETPI can control the ionization equilibrium of ions during periods of high radiation from the central star. These fluorescence and RETPI processes must be considered when using emission line ratios to determine physical conditions in astrophysical plasmas.
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
Extended x ray emission in the h i cavity of ngc 4151- galaxy-scale active ga...Sérgio Sacani
The document summarizes the discovery of diffuse soft X-ray emission extending about 2 kpc from the active nucleus of NGC 4151, filling the cavity of H i material. The X-ray emission has a luminosity of about 1039 erg s-1 and can be fit with either a thermal plasma model with a temperature of around 0.25 keV, or a photoionized model. This interaction between the AGN and interstellar medium implies the last episode of high nuclear activity occurred relatively recently, around 104 years ago.
The Large APEX Bolometer Camera (LABOCA) is a new 295-bolometer submillimeter camera operating at 870 μm that has been commissioned for use on the 12 m Atacama Pathfinder Experiment (APEX) telescope. LABOCA offers unprecedented mapping capabilities for submillimeter continuum emission due to APEX's efficiency and the excellent atmospheric transmission at the site. LABOCA is designed to map large areas of the sky rapidly without the need for a chopping secondary mirror by using fast scanning techniques and correlating signals across the array to remove atmospheric contributions.
This document provides an overview and context for a study of the symbiotic star SS Leporis using interferometric imaging with the PIONIER instrument on the VLTI. Key points:
- SS Leporis is a long-period interacting binary system composed of an A star accreting material from an evolved M giant companion, presenting an "Algol paradox" where the more evolved star is less massive.
- Previous studies have not fully constrained the system morphology and characteristics. New interferometric observations with PIONIER were obtained to directly probe the inner parts of the system.
- The observations were used to perform aperture synthesis imaging and model the system as a binary surrounded by a circumbinary disc. This provides the
This document discusses observations of the massive star cluster Pismis 24 using Hubble Space Telescope and ground-based data. It finds that Pismis 24-1, previously thought to have a mass over 200 solar masses, is actually a close binary system composed of at least two stars, Pismis 24-1NE and Pismis 24-1SW, resolved with HST. Photometry of the two components finds them each have an estimated mass of around 100 solar masses, within the proposed stellar upper mass limit of around 150 solar masses. High-resolution spectroscopy of Pismis 24-1 also finds evidence it is a spectroscopic binary.
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.
This document summarizes observations of IGR J12580+0134, a newly discovered hard X-ray source associated with the Seyfert 2 galaxy NGC 4845, which underwent an unusual X-ray flare. Follow-up observations with XMM-Newton, Swift, MAXI, and INTEGRAL are presented and analyzed. The spectrum is well described by an absorbed power law plus soft excess. The hard X-ray flux increased over weeks and decreased over a year as expected for a tidal disruption event. Fast variations near peak allowed estimating the black hole mass as ∼3×105 M⊙, indicating disruption of ∼10% of a 14-30 Jupiter mass object. Hard X-ray emission is from a corona forming
This document reports the discovery of the central star of the planetary nebula IC 4663, which exhibits spectral properties that mimic a nitrogen-rich Wolf-Rayet star of spectral type [WN3]. This makes it the first unambiguous case of a planetary nebula central star taking on the properties of a Wolf-Rayet star. The central star is dominated by broad helium and nitrogen emission lines. The surrounding nebula is definitively a planetary nebula based on its morphology and chemical abundances. The discovery provides evidence for an alternative evolutionary pathway for some hydrogen-deficient, helium-rich post-asymptotic giant branch stars.
Creation of cosmic structure in the complex galaxy cluster merger abell 2744Sérgio Sacani
Abell 2744 is one of the most actively merging galaxy clusters known, appearing to have "dark", "ghost", "bullet", and "stripped" substructures of around 1014 solar masses each. The cluster shows a complex phenomenology that will challenge simulations to reproduce. The authors present a detailed strong lensing, weak lensing, and X-ray analysis of Abell 2744, identifying 34 strongly lensed images around the massive Southern core and producing the most detailed mass map to date. They find evidence that the Southern core and Northwestern substructure are post-merger systems similar to the Bullet Cluster viewed from an angle, and derive a new constraint on the self-interaction cross section of dark matter particles. They
Measurements of a_massive_galaxy_clusterSérgio Sacani
This document reports on observations of IDCS J1426.5+3508, a galaxy cluster located at a redshift of 1.75. A Sunyaev-Zeldovich decrement was detected towards this cluster, indicating a total mass of 4.3×1014 solar masses. This makes it the most distant cluster detected via the Sunyaev-Zeldovich effect to date and the most massive cluster found at a redshift greater than 1.4. Despite its rarity, the cluster is not unexpected given cosmological models and the large area surveyed. However, it remains one of the rarest and most extreme clusters discovered and provides insight into the early formation of the most massive clusters.
This document summarizes a study that used optical, infrared, and submillimeter data to examine star formation in the region surrounding the IC 348 star cluster and the nearby Flying Ghost Nebula. The study identified 13 protostars driving protostellar outflows in the region, including HH 211 which had not previously been detected at visible wavelengths. The region surrounding the Flying Ghost Nebula shows ongoing star formation with outflows similar to other areas of moderate star formation in Perseus. A candidate bent jet was also found, which may have been ejected from a multiple star system near IC 348.
1. Remote sensing utilizes electromagnetic radiation reflected or emitted from objects to gather information without direct contact.
2. The wavelength of reflected or emitted radiation provides information on an object's chemical composition and temperature.
3. Different materials have unique spectral signatures across the electromagnetic spectrum that can be used for identification.
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
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∼
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) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
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2
,
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km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
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Ca-rich population. Although such an object is too red for any low-
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cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
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CDM. Therefore unlike low-
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Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
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truly diverge from their low-
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counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Climate extremes likely to drive land mammal extinction during next supercont...
1106.2545v1
1. Mon. Not. R. Astron. Soc. 000, 1–19 (2010) Printed 15 June 2011 (MN L TEX style file v2.2)
A
Confirmation of the VeLLO L1148–IRS: Star Formation at very low
(Column) Density
arXiv:1106.2545v1 [astro-ph.SR] 13 Jun 2011
J. Kauffmann1⋆ , F. Bertoldi2 , T.L. Bourke3, P.C. Myers3, C.W. Lee4, T.L. Huard5
1 NPP Fellow, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
2 Argelander Institut f¨ r Astronomie, Universit¨ t Bonn, Auf dem H¨ gel 71, 53121 Bonn, Germany
u a u
3 Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
4 Korea Astronomy and Space Science Institute, 61–1 Hwaam–dong, Yusung–gu, Daejeon 305–348, Korea
5 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
Accepted XXX. Received YYY; in original form ZZZ
ABSTRACT
We report the detection of a compact (∼ 5′′ ; about 1800 AU projected size) CO outflow from
L1148–IRS. This confirms that this Spitzer source is physically associated with the nearby
(≈ 325 pc) L1148 dense core. Radiative transfer modeling suggests an internal luminosity
of 0.08 to 0.13 L⊙ . This validates L1148–IRS as a Very Low Luminosity Object (VeLLO;
L 0.1 L⊙ ). The L1148 dense core has unusually low densities and column densities for a
star–forming core. It is difficult to understand how L1148–IRS might have formed under these
conditions. Independent of the exact final mass of this VeLLO (which is likely < 0.24 M⊙),
L1148–IRS and similar VeLLOs might hold some clues about the isolated formation of brown
dwarfs.
Key words: stars: formation; stars: low-mass, brown dwarfs; ISM: globules; ISM: individual:
L1148; ISM: jets and outflows; infrared: stars
1 INTRODUCTION for L1521F–IRS (Bourke et al. 2006) and L328–IRS (Lee et al.
2009). These papers established the initial VeLLO sample and the
The sensitivity of the Spitzer Space Telescope allows for searches
first overviews of their properties. Other well–studied VeLLO can-
and studies of young stellar objects that are much less lumi-
didates are Cha–MMS1 (Belloche et al. 2006) and L673–7–IRS
nous than those studied before. While surveys of star–forming re-
(Dunham et al. 2010a). See Table 2 for an up–to–date list. The
gions using data from the Infrared Astronomical Satellite (IRAS)
combined c2d survey data for cores and clouds reveals 15 candi-
were sensitive to sources with luminosities 0.1 L⊙ (d/140 pc)2
date VeLLOs (Dunham et al. 2008). Not all of them are well stud-
(where d is the distance; Myers et al. 1987), Spitzer can detect ob-
ied, though. The first VeLLO ever discovered was IRAM04191. It
jects with luminosities as low as 4×10−3 L⊙ (d/140 pc)2 , i.e. has
was identified by Andr´ et al. (1999) on the basis of millimeter ra-
e
a sentitivity better by a factor 25 (Dunham et al. 2008). Spitzer has
dio observations (see Dunham et al. 2006 for Spitzer results).
imaged a large number of isolated dense cores thought to be star-
less. About 60 of them were observed as part of the Spitzer Legacy The evolutionary status and fate of VeLLOs is presently unclear
Project “From Molecular Cores to Planet Forming Disks”, or c2d and likely to be diverse. There is probably general consent that
(Evans et al. 2003). VeLLOs have a present–day mass < 0.1 M⊙ (Young et al. 2004;
These observations led to a series of discoveries of Very Low also see Section 6.1). However, some VeLLOs drive prominent
Luminosity Objects (VeLLOs; for definitions see Kauffmann et al. outflows, and thus seem to accrete significantly. These objects
2005, di Francesco et al. 2007, Dunham et al. 2008), infrared stars have been interpreted as very young (∼ 104 yr) protostars of
of luminosity 0.1 L⊙ which are embedded in dense cores. stellar final mass (e.g., IRAM04191, which has a prominent
VeLLO colors and envelope properties are consistent with those of outflow; Andr´ et al. 1999; Belloche et al. 2002). In contrast,
e
class 0 or class I protostars (Lada 1987; Andre et al. 1993), young VeLLOs devoid of such outflows might not accrete at a high
stars in their main accretion phase that are deeply embedded in the rate. Some were proposed to be proto brown dwarfs forming
dense core from which they form. in isolation (i.e., not as low–mass components of clusters and
Young et al. (2004) presented the first Spitzer–identified binaries; e.g., L1014–IRS, which has a ∼ 3′′ [∼ 750 AU] outflow
VeLLO, L1014–IRS (also see: Crapsi et al. 2005b; Huard et al. only detected with interferometers; Young et al. 2004; Crapsi et al.
2006; Bourke et al. 2005). Further detailed studies were presented 2005b; Bourke et al. 2005; Huard et al. 2006). This concept has
been bolstered by recent discoveries of binary brown dwarfs
which are too loosely bound to have been expelled by multiple
⋆ E-mail: jens.kauffmann@jpl.nasa.gov stellar systems (e.g., Radigan et al. 2009 and Luhman et al.
2. 2 J. Kauffmann et al.
means that L1148–IRS does not meet all of the Dunham et al.
(2008) criteria for confirmed VeLLOs. Confirmation would require
an outflow detection towards L1148–IRS at the systemic velocity
of the dense core. This would prove that L1148–IRS (i) is a YSO
which is (ii) physically associated with the L1148 region. Here, we
present an outflow meeting these criteria.
Our study is organized as follows. Section 2 introduces the data on
which our study is based. We discuss the discovery and character-
ization of the outflow in Section 3. The physical properties of the
embedded YSO are derived in Section 4. Information on various
VeLLO natal cores are summarized in Section 5. This provides a
catalogue against which L1148 can be compared. In Section 6 we
turn to a discussion of L1148–IRS in the context of other VeLLOs.
Section 7 summarizes our study.
In order to improve the readability of this paper, some com-
plementary material is removed to two appendices. Appendix A
provides details on the photometric data used in this study. Ap-
pendix B comprehensively presents data for which a cursory anal-
ysis was executed in previous studies (i.e., Kauffmann et al. 2005),
and describes new data indirectly supporting the outflow analysis
executed here.
2 DATA & OBSERVATIONS
2.1 Distance & Previous Studies
Straizys et al. (1992) derive a distance of (325 ± 25) pc for the
L1148 region. This is smaller than the 450 pc estimated by Kun
Figure 1. The discovery of L1148–IRS. The L1148 region contains two (1998). We adopt the result by Straizys et al. (1992), since they fo-
dark dust features evident at optical wavelength (top panel). These are cus on a 1◦ × 1◦ field centered on L1148, while Kun (1998)
also detected in maps of dust continuum emission (bottom right panel). At
study an ≈ 2◦ × 10◦ region in which L1148 lies only at the edge.
24 µm wavelength, the source L1148–IRS (framed by a box in all panels)
This is consistent with a preliminary 2MASS–based distance esti-
manifests as an unusually bright point source (bottom left panel). It resides
near a relatively faint (9 mJy per 11′′ beam at 1.2 mm wavelength after mate of (301 ± 55) pc (G. Maheswar & C.W. Lee, in prep.; based
smoothing to 20′′ resolution) dust continuum emission peak (bottom right on Maheswar et al. 2010).
panel). Solid and dotted lines indicate the relative orientation of the differ- The L1148 dense core was included in the Lee et al. (1999,
ent maps. See Figure 2 for further information. Coordinates are given for 2001, 2004) surveys for inward motions. No signs of such mo-
J2000. tions were found, but the observed lines were weak and the po-
sition of L1148–IRS was not probed. Kirk et al. (2005) observed
L1148 with SCUBA at 450 µm and 850 µm wavelength, but
2009; also see protectvrule width0ptprotect their small target field (≈ 2′ diameter) did not include the VeLLO
href{http://www.vlmbinaries.org/}{http:// candidate considered here. The L1148–IRS source was then pre-
www.vlmbinaries.org/}). sented by Kauffmann et al. (2005). Wu et al. (2007) did observe
The second Spitzer VeLLO to be discovered — the source dis- this source with SHARC–II at 350 µm wavelength, but failed
cussed in the present paper, L1148–IRS (Kauffmann et al. 2005; to detect it. These data, combined with the characteristics of the
first noticed by Kun 1998) — always maintained a peculiar status. Spitzer–detected source, led Dunham et al. (2008) to the conclu-
As shown in Figure 1, this object was discovered as an unusually sion that L1148–IRS “has a high likelihood of being an embed-
bright Spitzer MIPS source (compared to the field stars), SSTc2d ded low-luminosity protostar” (their ‘group 3’). The source is also
J204056.66+672304.9, which is closely associated with a 1.2 mm included in the 1.8 cm radio continuum surveys by Scaife et al.
wavelength dust emission peak revealed by the c2d MAMBO (2010). L1148–IRS is detected at a signal–to–noise ratio ∼ 3. As
survey (Kauffmann et al. 2008). It differs from other VeLLOs in shown by Scaife et al., and repeated in Table 2, the implied intrinsic
that no other such object is as inconspicuous in dust emission luminosity at 1.8 cm wavelength is comparable to what is found for
(Kauffmann et al. 2005, 2008; Wu et al. 2007). This implies that other VeLLOs (i.e. F1.8cm d2 , the product of observed flux density
L1148–IRS resides in a natal dense core of unusually low mass and distance squared).
and average density (∼ 0.15 M⊙ , few 104 cm−3 ; Kauffmann et al. Most recently, Kirk et al. (2009) used data from the Spitzer
2008). Gould Belt Legacy survey to search the entire L1148 region for
Unfortunately, initial single–dish searches by young stellar objects (YSOs). Just a single candidate YSO, i.e.
Kauffmann et al. (2005) did not reveal any molecular out- our L1148–IRS, is found. This dearth of YSOs is confirmed by
flow. Thus, Kauffmann et al. (2005) could not entirely rule out that Dunham et al. (2008), though they find one further candidate with
L1148–IRS is just a galaxy (probability ∼ 10−4 , using 24 µm rather low YSO probability (i.e., in their ‘group 6’). Like neighbor-
source counts by Papovich et al. 2004) or background protostar ing clouds, L1148 does thus form stars only at a very small rate
accidentally aligned with the L1148 dense core. Formally, this or efficiency (Kirk et al. 2009). Nutter et al. (2009) took Akari data
3. The VeLLO L1148–IRS 3
◦ ◦
at wavelength of 65 to 160µm towards a ∼ 0. 5 × 0. 5 field con- between the VeLLO and dust emission peak position, even if such
taining L1148–IRS. They detect and confirm L1148–IRS; they do, offsets do not exist.
however, focus on the extended matter in this region and uncover
evidence for external heating of the clouds.
Detailed assessments of the properties of the natal dense core of 2.2 Spitzer Space Telescope
VeLLOs were first presented by Kauffmann et al. (2005). Based on
L1148 was observed by the Spitzer Space Telescope with the In-
maps in lines of CCS (from the the Effelsberg 100m–telescope)
frared Array Camera (IRAC; AORKEYs 5158144) and the Multi-
and N2 H+ (from the IRAM 30m–telescope), the dense core has
band Imaging Photometer for Spitzer (MIPS; AORKEY 9440768)
line widths at half intensity 0.25 km s−1 . Non–thermal motions
as part of the c2d Legacy program (Evans et al. 2003, PID 139).
are thus sub–sonic, since H2 at 10 K temperature has a line width
Further Spitzer observations (AORKEYs 14608128, 14615808,
of 0.44 km s−1 . Towards L1148–IRS, N2 H+ lines yield a systemic
18160384) were acquired by the “cores2deeper” (deep IRAC and
velocity of 2.60 km s−1 . Significant velocity gradients and jumps,
MIPS integrations; PID 20386) and “Going Long” (first MIPS
as well as multiple velocity components in C18 O, are observed
160 µm images of the region; PID 30384) programs. Initial ver-
near the YSO. The letter by Kauffmann et al. (2005) unfortunately
sions of these maps were used in Kauffmann et al. (2005). The im-
lacked the space to present the data in detail. These are therefore
ages presented here are derived from new mosaics combining all
for the first time provided in Appendix B.
of the aforementioned data. Independent imaging by the Spitzer
Based data from the IRAM 30m–telescope, Kauffmann et al. Gould Belt Legacy Survey (Allen et al., PID 30574) is discussed
(2005) found no indications for significant chemical evolution.
by Kirk et al. (2009). Spectra of L1148–IRS have been acquired
Specifically, CO is depleted by a factor less than 10, and N2 D+ too (PID 30563; AORKEY 18401280), but are not discussed here.
is not detected. See Appendix B4 for more details. However, there Details of the observations, post–processing and source extraction
is evidence for contraction motions within L1148: line asymmetries
are presented by Evans et al. (2007).
indicative of such motions are observed towards all three positions
highlighted in Fig. 2. These new data are presented in Appendix
B5.
The Kauffmann et al. (2008) dust emission maps (obtained us- 2.3 IRAM 30m–telescope
ing MAMBO at the IRAM 30m–telescope) reveal an unusually
small mass reservoir for a star–forming core. Division of the peak The IRAM 30m–telecope near Granada (Spain) was used to search
H2 column density of 6 × 1021 cm−2 by the filament minor and for an extended outflow from L1148–IRS in the (J = 2–1) tran-
major axis of the parental core (1′ × 5′ angular size; Figs. 1 and 2, sition of 12 CO. Data were taken on 2004 December 19 (single
Appendix B2) suggest mean H2 densities of (0.4–2.0)×104 cm−3 . pixel facility receiver; system temperature ∼ 380 K in Tmb –scale,
Comparison with model density distributions with central den- mapped area ∼ 2′ × 2′ ) and 2005 July 19 to 21 (HERA multi–
sity plateau and d ln(̺)/d ln(r) = −2 for large radii (Fig. 5 of beam array; ∼ 900 K, ∼ 4′ × 4′ ). The single–pixel maps were
Kauffmann et al. 2008) give a central density < 3 × 104 cm−3 . already used in Kauffmann et al. (2005). The pointing corrections
For a source–centered aperture of 4200 AU radius, a mass of only in azimuth and elevation were below 3′′ , and the focus corrections
(0.14 ± 0.02) M⊙ is derived1 . Division of this aperture mass by below 0.45 mm, as checked by regular pointing and focus checks
the aperture area gives an aperture–averaged column density of at least once every 3 hours. The intensity scale was converted to the
N (H2 ) 4200 AU = 4.8 × 1021 cm−2 . main beam brightness temperature scale according to the efficien-
cies reported on the IRAM website2 . Figure 2 gives an overview
These values are unusually low, even for starless cores
(Kauffmann et al. 2008). L1148–IRS thus resides in a natal core of of the layout of these observations. The data were calibrated and
unusually low density and column density. In this respect, L1148 is analyzed using IRAM’s CLASS software package3 .
similar to the VeLLO core L1014, which was deemed to be “star- In parallel to these outflow searches, we used a variety of other
less” previous to Spitzer observations. This makes it so interesting. tracers to probe the physical and chemical conditions in the dense
The mass concentration appears to be centrally peaked: as ex- gas. This includes lines of N2 H+ (1–0) and N2 D+ (1–0), CS (2–
1) and (3–2), C18 O (2–1), HCO+ and H13 CO+ (1–0), and HCN
plained in Appendix B2, cuts through the emission suggest density
′′ (1–0). All observations were obtained in frequency–switched mode
profiles d ln(̺)/d ln(r) ∼ − 2. L1148–IRS actually resides 7. 6
(i.e., 2500 AU) offset from the dust emission peak. While this off- using the single–pixel receivers and the autocorrelator backends.
The N2 H+ and C18 O lines were mapped on 2004 December 19
set is potentially interesting, Kauffmann et al. (2008) use Monte–
in the same ∼ 2′ × 2′ field for which 12 CO data were obtained.
Carlo experiments to show that this dislocation is only marginally
significant given the uncertainties of their data: the beam of 11′′ Our N2 H+ and C18 O maps were already used in Kauffmann et al.
(2005). The remaining lines were observed on 2005 July 19 to 21 in
size, the low signal–to–noise ratio, possible anomalous refraction,
relatively deep integrations towards the three positions near L1148–
and potential pointing errors of order 3′′ have to be taken into ac-
count. In combination, these effects can lead to apparent offsets IRS sketched in Figure 2 (chosen to probe L1148–IRS, its immedi-
ate environment, and the neighboring dust core). Focus and point-
ing uncertainties are as previously quoted for the outflow search.
More details are given in Table B1. CLASS was used to calibrate
1 The aperture radius of 4200 AU was defined by Motte & Andr´ (2001).e and exploit the data. We removed low–order baselines and partially
In Taurus, this size conveniently corresponds to a radius of 30′′ . Also, used Fourier (FFT) filtering to further improve the baseline quality.
Motte & Andr´ argue that this radius roughly contains the mass that can
e
be accreted in about 105 yr of free–fall collapse of an initially hydrostatic
sphere of ∼ 0.2 km s−1 sound speed. However, except for these general
considerations, the radius is somewhat arbitrary. We adopt this size to com- 2 http://www.iram.es/IRAMES/
pare with previous observations. 3 http://www.iram.fr/IRAMFR/GILDAS/
4. 4 J. Kauffmann et al.
of 12 CO, respectively (115.271202 GHz and 230.538000 GHz;
Winnewisser et al. 1997). All 8 units of the correlator took data;
for each receiver, 2 units were centered on the line to acquire spec-
tra at 0.1 km s−1 and 0.2 km s−1 resolution, and 2 further units
were symmetrically displaced from the line to collect continuum
data with a bandwidth of 320 MHz. The primary beam sizes were
20′′ and 40′′ . The minimum projected baseline in D configuration
is ∼ 20 m, and so structures larger ∼ 16′′ , respectively ∼ 33′′ , are
not at all probed by the maps. L1148–IRS was in the phase center
of the array.
3C454.3 was typically used for bandpass calibration, while
1928+738 and 2037+511 served as phase calibrators. As usual for
the PdBI, MWC349 data yielded the initial flux calibration (as-
sumed to have flux densities of 1.12 Jy and 1.7 Jy in the 3 mm
and 1 mm bands, respectively). Based on this, the fluxes of the
other calibrators were fixed and iterated to obtain an optimum cal-
ibration across all epochs. The flux calibration can be checked by
imaging the phase calibrator 2037+511 in those epochs where it
is not used to derive this calibration (i.e., is not held ‘fixed’ in
the calibration routines). We find that the observations reproduce
the epoch–averaged mean flux density with maximum deviations
of 7% and 20% in the 3 mm and 1 mm band, respectively.
The data were calibrated and imaged (including cleaning) us-
ing the GILDAS software suite. Here, we use all epochs to con-
struct maps in the 3 mm band, but only the best 4 periods (i.e.,
excluding July 22 and August 2) are taken in the 1 mm band. This
yields beam sizes of 4. 5 × 3. 4 (position angle east of north of 82◦ )
′′ ′′
′′ ′′ ◦
and 2. 5×1. 7 (p.a. of 65 ) at 3 mm and 1 mm wavelength, respec-
tively. To improve the signal–to–noise ratio, the spectra are sampled
into bins of 0.3 km s−1 width. The continuum data are clipped in
Figure 2. Overview of observing strategy and results. As shown by the the spectral range to exclude CO emission from our target source.
grey shading in the bottom main panel, the region contains two parallel fil- This yields noise levels in the 3 mm and 1 mm band spectral line
aments detected in dust continuum emission. They have masses of 8.6 M⊙ data of 23 mJy beam−1 and 46 mJy beam−1 , respectively, while
and 3.1 M⊙ , respectively (a black solid line marks the adopted boundary we find 0.39 mJy beam−1 and 1.0 mJy beam−1 for the contin-
between the filaments). The position of L1148–IRS and its outflow are in-
uum data.
dicated by dots and lines, respectively. Boxes centered on L1148–IRS in-
dicate the regions searched for outflows. Circles mark positions probed for
dense core contraction motions (Section 2.1, Appendix B5). The top zoom
panel presents details of the MAMBO dust emission map in greyscale and 3 AN OUTFLOW FROM L1148–IRS
contours (starting at, and spaced by, 2 mJy per 11′′ beam after smooth-
ing to the 20′′ beam marked by a circle). Markers indicate the position of Previous analysis failed to establish that L1148–IRS (i) is a YSO
L1148–IRS, its outflow, and of two of the positions searched for contraction and (ii) is physically associated with the L1148 region. Here, we
motions. Note that L1148–IRS is offset from the nearby dust emission peak show that the source drives a weak small–scale CO outflow ( 5′′ ,
(by a marginally significant amount). Coordinates are given for J2000. about 1800 AU in projection). This confirms the hypotheses (i) and
(ii).
2.4 KPNO 4m–telescope
As part of a larger program to survey the c2d cores in the near– 3.1 A Compact CO Outflow
infrared, deep J, H, and Ks observations of L1148 were ob- 3.1.1 Single–dish Observations
tained during September of 2004 using FLAMINGOS (Florida
Multi–object Imaging Near–IR Grism Observational Spectrometer; We initially used the IRAM 30m–telescope to search for an outflow
Elston 1998) on the 4m–telescope at Kitt Peak National Observa- in the 12 CO (2–1) line. This search failed (Kauffmann et al. 2005).
tory (KPNO). We use the data acquisition and reduction strategies It is briefly summarized below.
that have been described in Huard et al. (2006). The single–pixel facility receiver was used to map an area of
2′ × 2′ size with 30′′ spacing in frequency–switched mode (layout
indicated in Figure 2). The top panels of Figure 3 show an example
2.5 Plateau de Bure Interferometer spectrum from this search: emission from the dense core (as well
as “telluric” emission4 from Earth’s atmosphere) are detected, but
The Plateau de Bure Interferometer (PdBI) observed L1148–IRS
on 6 occasions during the summer of 2006 (project P057; observed
on May 13, June 5 and 15, July 22, August 2, and September 4 The LSR velocity of the telescope can, e.g., be found from
1). Between 4 and 5 antennas of the array were used in the ‘D’ the calculator provided on the homepage of the Far Ultravio-
configuration (i.e., the most compact one). The 3 mm and 1 mm let Spectroscopic Explorer (switched to topocentric coordinates),
band receivers were tuned to the (J = 1–0) and (2–1) transitions http://fuse.pha.jhu.edu/support/tools/vlsr.html,
5. The VeLLO L1148–IRS 5
no obvious outflow signal was found (neither in the form of line
wings, nor in terms of clear spatial trends in emission). However,
Fourier components, as well as baselines of 2nd order, had to be
removed during data reduction. Thus, these observations were not
sensitive to outflows manifesting in wide and faint emission lines.
Therefore, we later raster–mapped a field of about 4′ × 4′ size
with 24′′ spacing using the HERA multi–beam array in position–
switched mode (indicated in Figure 2). These data have very flat
baselines. Unfortunately, the reference position was not free of
emission. Therefore, the data are severely contaminated within
about ±2 km s−1 from systemic velocity. After smoothing to
0.5 km s−1 velocity resolution, these spectra have a noise level of
0.8 Jy beam−1 in the main beam brightness scale. Still, no outflow
emission was found. Also the mean spectrum averaged over all map
pixels does not reveal any CO emission beyond ±2 km s−1 veloc-
ity offset (at a noise level of 54 mJy beam−1 ).
Figure 3 compares the single–dish observations with the
interferometer–detected outflow described below. For this compar-
ison, the PdBI spectra in the 12 CO (2–1) and (1–0) transitions are
integrated over source–centered apertures of 3′′ and 10′′ radius,
respectively. The data show that the single–dish observations are
sensitive enough to detect the outflow. The outflow emission is,
however, massively confused with the dense core emission. This is
similar to the situation in L1014 (Bourke et al. 2005).
3.1.2 Interferometric Observations
The non–detection with single–dish telescopes did not rule out the
existence of a compact outflow from L1148–IRS, such as the one
seen in L1014 (Bourke et al. 2005). We therefore also used IRAM’s
Figure 3. CO spectra towards L1148–IRS. The panels show 12 CO (J = 2–
Plateau de Bure Interferometer (PdBI) to observe the (1–0) and (2–
1) data (top) and (J = 1–0) spectra (bottom). For the (2–1) transition, the
1) transitions of 12 CO. These observations reveal an outflow from solid line presents the frequency–switched IRAM 30m–telescope spectrum
L1148–IRS. As we detail below, it manifests in two symmetric ve- (11′′ beam) taken towards L1148–IRS. The signal near 7 km s−1 velocity
locity components (Figures 3 and 5) that form a bipolar outflow is of telluric origin and thus not relevant here. The shaded histograms por-
system (Figure 4). tray the data acquired with the Plateau de Bure Interferometer. These spec-
In the PdBI–derived data cubes, significant 12 CO emission is tra are averaged over source–centered apertures of 3′′ and 10′′ radius for
detected in the 1.2 to 4.2 km s−1 velocity range. (“Significant” the (2–1) and (1–0) lines, respectively. The systemic velocity derived from
means that, in a given position–position–velocity cell, the emission N2 H+ observations (Section 2.1, Appendix B3) is marked by a dashed line.
of both 12 CO transitions exceeds the noise level by a factor 4.
The velocity channels are spaced by 0.3 km s−1 .) The N2 H+ –
derived systemic velocity is 2.60 km s−1 (Section 2.1, Appendix fitting of the bright and elongated outflow emission with a straight
B3). Relative to this we obtain maximum projected velocity offsets line (Figure 4) gives a most likely position angle of 107◦ ± 22◦ .
of −1.4 to + 1.6 km s−1 for the 12 CO outflow emission. We ap- (To calculate the uncertainty, we derive the position angles when
′′
proximate this as ±1.5 km s−1 in the following. Correspondingly, displacing the fitted line by half a beam at 5. 5 offset from L1148–
we use velocity ranges of 0.9 to 2.4 km s−1 (blue–shifted lobe) and IRS.) This fit is guided by the fact that L1148–IRS resides right
3.0 to 4.5 km s−1 (red–shifted lobe; we exclude the central chan- between the respective intensity peaks of the two lobes; this sug-
nel at 2.7 km s−1 for clarity) to calculate the velocity–integrated gests an outflow direction similar to the position angle of the line
emission of the lobes. connecting the peaks. Unfortunately, though, the emission farther
Figure 4 presents integrated intensities in order to explore away from the star ( 5′′ ) shows no clear structure. This leaves the
the structure of the lobes. These are more apparent in the 12 CO option of a wide–angle outflow propagating in a direction signifi-
(1–0) data. In this line, the blue–shifted lobe is shorter than the cantly different from the one obtained above.
′′ ′′
red–shifted one. The extent of the latter lobe is 5. 5 ± 0. 3, or Figure 3 shows spectra of the outflow emission. Gaussian fits
(1800 ± 100) AU in projection; to measure this, we find the most to the spectra, and comparison to the N2 H+ systemic velocity,
elongated contour (at a signal–to–noise level of 9.5 ± 1.0), drop yield projected velocity offsets of −1.0 and +1.2 km s−1 for the
12
to 50% of this intensity, measure this contour’s maximum offset CO (1–0) line, respectively −0.9 and +1.2 km s−1 for the (2–1)
from L1148–IRS, and subtract the beam radius linearly. Manual line. We approximate this as ±1.0 km s−1 in the following. Gaus-
sian line fitting of the PdBI spectra gives velocity–integrated flux
densities of 21.0 Jy km s−1 and 8.9 Jy km s−1 (15% of the single-
and using the “source” command within the AS- dish flux density) for the (1–0) and (2–1) lines, respectively.
TRO program of the GILDAS software package The position–velocity diagrams presented in Figure 5 show
(http://www.iram.fr/IRAMFR/GILDAS/). The LSR velocity that the lobes are kinematically well–separated along the entire out-
of telluric lines is the negative of the telescope’s LSR velocity. flow axis. Some faint outflow features can possibly be traced to
6. 6 J. Kauffmann et al.
Figure 5. Position–velocity diagrams along the trajectory indicated in Fig-
ure 4. The spatial origin coincides with L1148–IRS, and the offset increases
in the direction of the arrow drawn in Figure 4. Contours start at, and are
spaced by, the noise level times a factor ±2. Dashed lines are drawn for neg-
ative signal, and solid contours are used otherwise. The horizontal dashed
line marks the systemic velocity derived from N2 H+ observations (Section
2.1, Appendix B3).
Figure 4. The outflow lobes for both 12 CO transitions. The greyscale
map presents the emission integrated over the 0.9 to 4.5 km s−1 veloc-
ity interval. Solid contours outline the emission of the blue-shifted lobe at
0.9 to 2.4 km s−1 velocity, while dotted contours delineate the red-shifted 3.2 Outflow Mass and Kinematics
lobe at 3.0 to 4.5 km s−1 . These contours start at, and are spaced by, the
To derive the outflow mass, we assume the 12 CO emission to be
noise level times a factor ±3; they are dashed for areas with negative emis-
optically thin, adopt an H2 –to–12 CO abundance ratio of 104 , a
sion. The central cross marks the position of L1148–IRS. Ellipses give the
beam sizes at half sensitivity. The arrow marks the location and orientation mean mass per H2 molecule of 2.4 H–masses, and use Eq. (A4) of
of the position–velocity cut presented in Figure 5. Bourke et al. (1997) to calculate the column densities (for 12 CO,
we use a permanent dipole moment of 0.11 D and a rotational con-
stant of 57.636 GHz). We adopt an excitation temperature of 20 K.
This is a bit more than canonical dense core temperatures ∼ 10 K,
but less than the few 102 K observed in outflows of much higher ve-
locity (see, e.g., Santiago-Garc´a et al. 2009 for a summary). This
ı
velocity offsets as large as ±2.5 km s−1 . The 12 CO (2–1) panel temperature uncertainty introduces a moderate mass uncertainty:
reveals that the knot at +5′′ offset is detected in several velocity temperatures in the range 10 to 50 K would give masses different
channels, and is therefore probably real. The elongated lobe seen by less than a factor 2. We obtain outflow mass estimates, mout , of
in the (1–0) maps appears to form a counterpart of this knot. 1.3 × 10−3 M⊙ and 3.9 × 10−4 M⊙ for the 12 CO (1–0) and (2–
The CO emission cannot come from a circumstellar disk. Kep- 1) observations, respectively. Correction for typical 12 CO outflow
lerian motion at 1 km s−1 speed and 1800 AU radius would require optical depths of 2 to 5 (Levreault 1988) would increase the masses
a central mass of 2 M⊙ . This significantly exceeds the estimated by similar factors. For the (2–1) line, comparison with single–dish
mass of the central star (Section 6.1) and of the dense core mate- data implies a total flux loss of a factor 7 (Figure 3). This could lead
rial immediately surrounding the YSO (Section 2.1). The emission to underestimation of the outflow mass by similar factors.
must thus come from an outflow. We adopt a characteristic outflow velocity of vout =
There is a remote chance that the compact CO emission is ± 1 km s−1 , and a radial size of r = 1800 AU. These are, of
not from an outflow, but is just an artifact of the interferometer– course, projected properties, which in principle must be corrected
induced spatial filtering of the dense core emission. We cannot rule for the inclination angle. This angle is, unfortunately, not known,
this option out. However, as we will show in Section 3.5, the close which introduces systematic uncertainties into our analysis. Using
association of CO emission and L1148–IRS alone is sufficient to the formalism of Cabrit & Bertout (1990) and Bourke et al. (1997),
reliably demonstrate the protostellar nature of L1148–IRS. we derive the properties listed in Table 1. The quoted uncertain-
7. The VeLLO L1148–IRS 7
Table 1. Outflow properties. The quoted uncertainties refer to the range in 3.3 Absence of Compact Dust Emission
outflow masses derived from the different 12 CO transitions.
Compact dust emission, such as emitted by circumstellar disks,
is not detected towards L1148–IRS. At 1 mm and 3 mm
Property Definition Value
wavelength, we observe intensities of 0.23 mJy beam−1 and
r 0.56 mJy beam−1 , respectively. This is insignificant compared to
size (radius) 1800
AU the noise levels reported in Section 2.5. If we add the noise level
vout times a factor 3, we obtain upper flux density limits of < 3.2 mJy
velocity | ± 1|
km s−1 and < 1.7 mJy, where we assume that the dust emission should be
mout more compact than the beam.
mass 0.4 to 1.3
10−3 M⊙ These upper limits are in line with, e.g., interferometric con-
mout · vout tinuum observations of L1014–IRS (Bourke et al. 2005). To derive
momentum 0.4 to 1.3
10−3 M⊙ km s−1 mass limits from these flux densities, we adopt the framework laid
mout · 2
vout /2 out by Kauffmann et al. (2008). Assuming dust with temperatures
energy 2 −2
0.2 to 0.6
10−4 M ⊙ km s 10 K, this yields mass limits < 0.02 M⊙ and < 0.13 M⊙ ,
3
mout · vout /[2 r] respectively.
mechanical luminosity 0.4 to 1.3
10−5 L⊙
2
mout · vout /r
force 0.5 to 1.5 3.4 Near–Infrared Nebulosity
10−7 M⊙ km s−1 yr−1
r/vout The near–infrared (NIR) FLAMINGOS imaging observations pre-
dynamical age 8.5 sented in Figure 6 reveal elongated nebulosity towards L1148–IRS.
103 yr
mout · vout /r This nebulosity is likely related to outflows from the star.
rate 0.5 to 1.5 L1148-IRS is detected in all bands, but we only use the two
10−7 M⊙ yr−1
bands with the best data (i.e., H and Ks ) for our analysis. Fits of
elongated Gaussians to the H–band image (which has the higher
SNR) give a position angle (east of north) of 133◦ for the major
axis. Along this axis, H–band emission from L1148–IRS above
′′ ′′
10% of the peak intensity has a width of 4. 1 (3. 7 in the Ks band),
′′ ′′
while nearby stars in the image have a width of only 2. 5 (2. 7 for
ties refer to the range in outflow masses derived from the different the Ks band) for this position angle. Repetition of this procedure
12
CO transitions. Given their linear dependence on mout , the out- for the minor axis, and removal of the instrument–induced source
flow properties also suffer from the systematic uncertainties affect- width at 10% peak intensity, suggests an intrinsic extension of order
ing mass estimates. 3. 2 × 2. 4 or 1040 × 780 AU2 . Both bands reveal an arc–like
′′ ′′
feature about 5′′ to the west of L1148–IRS. This could be related
The properties of L1148–IRS and its outflow are unusual, but not to the aforementioned western blob in the red–shifted 12 CO (2–1)
extreme for an embedded YSO. L1148–IRS is less luminous than outflow lobe.
any source in the comprehensive Wu et al. (2004) outflow compila- The CO–detected lobes and the NIR nebulosity are well
tion. It also has an outflow mass, mechanical luminosity, and force aligned (133◦ vs. 107◦ ± 22◦ ). The nebulosity thus seems to trace
smaller than observed for all (but 4, allowing for uncertainties) of structures such as an outflow–blown cavity.
the 292 outflow systems with known luminosity in the Wu et al.
study. These trends do not merely reflect the low luminosity of
3.5 L1148–IRS as a Confirmed VeLLO
L1148–IRS; for L1148–IRS, the above properties are still 1 to 2
magnitudes below what is derived when extrapolating typical out- As pointed out by Dunham et al. (2008), confirmation of a VeLLO
flow properties from Wu et al. (2004) to the internal luminosity candidate requires (i) that the internal luminosity is below 0.1 L⊙ ,
of L1148–IRS. These deviations are, however, marginally within and (ii) proof of embeddedness in a dense core. In the character-
the scatter observed for other YSOs, and the L1148–IRS outflow ization framework of Dunham et al. (2008), the ouflow discovery
is thus not extreme. The outflow survey of embedded YSOs by furnishes the latter. Following the terminology of Dunham et al.,
Bontemps et al. (1996) can be used for another comparison. Based L1148–IRS is thus a “confirmed embedded low–luminosity proto-
on this study, the force of the L1148–IRS outflow is consistent with star” (their ‘group 1’).
what is expected for class I sources of comparable internal luminos- However, given the relatively weak emission, low velocity,
ity. The YSO envelope mass of L1148–IRS does, however, exceed and small lobe separation in L1148–IRS, one may doubt that the
the typical one expected for the observed outflow force by a factor compact CO emission is really coming from an outflow. As we
∼ 10. show here, though, the proximity of compact CO emission and IR
Andr´ et al. (1999,
e IRAM04191), Bourke et al. (2005, source independently demonstrates that L1148–IRS is physically
L1014–IRS) and Phan-Bao et al. (2008, ISO–Oph 102) report out- associated to the dense core. Then, L1148–IRS must still be deeply
flow properties for other VeLLOs and brown dwarfs. The outflow of embedded, since there is no other way to produce the Spitzer MIPS
L1148–IRS is similar to those of L1014–IRS and ISO–Oph 102 in emission at the observed intensities (Section 4).
terms of velocity (all have ∼ 1 km s−1 ), but its mass (∼ 10−3 M⊙ We establish the association by computing the chance align-
vs. ∼ 10−5 M⊙ , without mass corrections) and size (1800 AU vs. ment probability between background sources (i.e., galaxies) and
1000 AU) appear to be larger. This is small, though, compared the 12 CO emission. A background source density ∼ 2000 sr−1 is
to the ∼ 10 km s−1 velocity range and ∼ 15000 AU extent of to be expected for 24 µm sources brighter 70 mJy (Papovich et al.
IRAM04191. 2004). L1148–IRS and the 12 CO (2–1) emission peaks are aligned
8. 8 J. Kauffmann et al.
Figure 7. The spectral energy distribution of L1148–IRS. Bars represent
flux density measurements with their associated uncertainty and filter width,
while arrows indicate upper limits. Solid and dashed lines describe a dense
core model containing a point source with 0.1 L⊙ internal luminosity and
3500 K effective temperature; the solid line holds for an aperture of 2′′
radius, which is used to model the observations at 10 µm wavelength,
while the dashed line refers to an aperture of 4200 AU radius, as applied to
the observations at larger wavelengths. This is detailed in Section 4.2.
4.1 Observations
Figure 7 presents the spectral energy distribution (SED) of L1148–
IRS. These data are assembled from the 2MASS point source cat-
alogue (Skrutskie et al. 2006), our FLAMINGOS observations, the
IRAS faint source catalogue (Moshir & al. 1990), the final release
of the c2d source catalogue (Evans et al. 2007), our cores2deeper
Spitzer project (PID 20386), our deep MIPS 160 µm survey of
cores (PID 30384), SHARC–II imaging by Wu et al. (2007), the
SCUBA legacy source catalogue (Francesco et al. 2008), and our
Figure 6. Images of L1148–IRS in the H (bottom panel) and Ks bands c2d MAMBO survey (Kauffmann et al. 2008). Appendix A dis-
(top panel) as seen by FLAMINGOS, shown as their negative. Contours cusses how we consolidate these data from different origins. Table
delineate the 12 CO (1–0) outflow lobes for signals exceeding the noise by A1 lists the flux densities in detail.
a factor 6 (see Figure 4). The arrows indicate positions and directions of Integration of the SED yields bolometric luminosities and
the cuts through the intensity distribution that are discussed in the text. The
temperatures of 0.12 L⊙ and 110 K, respectively. We derive these
images reveal that L1148–IRS is elongated, with the major axis at position
parameters using power–laws to interpolate between the detected
angle ≈ 133◦ . In addition there is an arc–like extended feature about 5′′ to
the west of L1148–IRS. To facilitate comparison between both images, the flux densities. We further assume flux densities scaling with wave-
arc is indicated by a solid tracer line. length as λ4 for λ > 350 µm (Kauffmann et al. 2008). Propagation
of the flux–weighted observational uncertainties gives uncertainties
< 20% in luminosity, and ±15 K in temperature. This is in agree-
to within 1′′ distance (Figure 4). For an individual cloud, the prob- ment with the L1148–IRS characterization by Kauffmann et al.
ability for chance alignment is thus π (1′′ )2 · 2000 sr−1 = 1.5 × (2005, 2008), but a bit warmer and fainter than what is found by
10−8 . For the entire c2d MAMBO survey, with ∼ 110 dust emis- Kirk et al. (2009; probably because they use MAMBO fluxes for
sion peaks, the probability of one chance alignment is 1.6 × 10−6 larger apertures).
(assuming that every dust emission peak contains interferometer–
detected CO structures like those presented here). There is no re-
4.2 Modeling
alistic option that dense core and L1148–IRS are not physically
associated. We model the SED of L1148–IRS as a spherical dense core that
contains a point source and is externally illuminated by the inter-
stellar radiation field (ISRF). The point source is assumed to emit
like a black body of luminosity Lint and temperature Teff ; we refer
4 THE SPECTRAL ENERGY DISTRIBUTION OF
to these as the internal luminosity and the stellar effective tempera-
L1148–IRS
ture. The ISRF is taken from P´ rault (1987). We reduce its intensity
e
The outflow observations establish the protostellar nature of at the core surface by a factor 4. This reflects shielding by extended
L1148–IRS. However, we still need to characterize the embedded material of a total (surface to surface) extinction of 3 mag, and is
infrared source. Here, we gather photometry of this object, sketch necessary to simultaneously match the MAMBO and MIPS3 obser-
a model for the analysis of the observations, and discuss the prop- vations. We adopt dust opacities as Weingartner & Draine (2001)
erties derived using this model. predict for their “case B” and a total–to–selective extinction ratio
9. The VeLLO L1148–IRS 9
of RV = 5.5 (since this model provides a good fit to observed dust
opacities at wavelengths 10 µm; e.g., Indebetouw et al. 2005).
Model flux densities are calculated using a code kindly provided by
E. Kr¨ gel (e.g., Appendix A of Pillai et al. 2006).
u
The dense core’s density profile, ̺(r), is modeled as a con-
tinuous step–wise power law. We truncate the sphere at an outer
radius of 32500 AU ≈ 0.16 pc, corresponding to ≈ 100′′ . The
density is assumed to be negligible within the inner truncation ra-
dius, rin . For most radii, the slope of the density profile is set to
d ln(̺)/d ln(r) = −2. However, good matches of the SED re-
quire a flatter density law in some inner part of the sphere. We
do this by introducing a constant density between the inner and
in out out
outer transition radii, rtrans and rtrans . Our fits use rtrans =
14 ′′
2 × 10 m ≈ 1340 AU (i.e., 8. 25 diameter), since this is large
enough to provide good SED fits (as demonstrated by the results
below) but is compact enough to be consistent with the steep dust Figure 8. Quality of SED fits in dependence on the model effective temper-
ature and internal luminosity. Only cells with shading or crosses have been
emission intensity profile that rules out extended regions of con-
examined. Grey shading gives χ2 , the mean squared relative deviation be-
rel
stant density (Section 2.1). With these assumptions, the density tween SED model and observations at wavelengths < 10 µm. Crosses are
profile is fully defined once the density at the outer truncation ra- drawn if no model can fit all of the SED constraints. As explained in the
dius, ̺out , is specified. We fix the latter by requiring the model to main text, only solutions with χ2 < 0.3 are deemed acceptable. These
rel
exactly match the MAMBO flux density measurement. This even- solutions are enclosed by a black line. The modeling thus constrains the
in
tually leaves two envelope parameters (i.e., rin and rtrans ) and two internal luminosity to 0.08 Lint /L⊙ 0.13 and the effective tempera-
source parameters (i.e., Lint and Teff ) unconstrained. ture to 2500 Teff /K 5000.
At wavelengths < 10 µm, we attempt to minimize the mean
√
squared relative difference between the observed and predicted flux to a mean deviation of 0.08 = 28% between the observations
densities (i.e., the difference between model and observation, di- and the model for wavelengths < 10 µm. Here, we require that
vided by the observation; this property, χ2 , takes the role of the
rel good fits not to exceed this mean deviation by more than a fac-
classical χ2 ). We do not normalize the differences by the obser- tor 2, i.e., we require χ2 < 0.30 ≈ (2 × 0.28)2 . For certain
rel
vational flux density uncertainties (as usually done to derive χ2 ) luminosity–temperature pairs, no solution exists, since no model
because the predicted flux densities do sensitively depend on the simultaneously fits the strict J–band and MIPS constraints.
adopted geometry (e.g., Whitney et al. 2003). In this situation, the The modeling constrains the internal luminosity to
deviations between good models and observed flux densities are
not dominated by observational uncertainties. We further require Lint = 0.08 to 0.13 L⊙ .
that a valid model does strictly not exceed the J–band limits. The L1148–IRS does thus marginally fulfill the VeLLO luminosity cri-
synthetic observations are calculated for an aperture of 2′′ radius, terion of Lint 0.1 L⊙ . The luminosity is well constrained, since
and they are corrected for an intensity background determined be- it only requires a good SED match and does not sensitively de-
tween 5′′ and 10′′ radius. This is used to capture the effect of the pend on model parameters. This is different for the effective photo-
background subtraction in the 2MASS, FLAMINGOS, and IRAC spheric temperature, which we find to be Teff = 2500 to 5000 K.
observations. The temperature basically follows from the SED slopes at wave-
At wavelengths > 10 µm, we require the model to strictly lengths < 10 µm. Unfortunately, at these wavelength the spherical
match the observations within their observational uncertainties (ex- geometry of our model is probably too simplistic to capture the
cept for all IRAS and the MIPS3 bands, which are too uncertain). relevant inner envelope extinction and scattering processes. This
This appears appropriate since in this wavelength domain, devia- induces further systematic uncertainties. In any event, though, a
tions between good model and observation should be dominated central source of several 1000 K must be present to explain the
by observational uncertainties. We use an aperture of 4200 AU ra- detections in the 2MASS/FLAMINGOS bands.
dius to calculate synthetic observations. This is exactly the aperture The SED of L1148–IRS is thus consistent with the idea of
used in MAMBO observations (Section 2.1). The exact aperture L1148–IRS being embedded in the dense core. In particular, this
size does not matter for the MIPS1 and MIPS2 bands, since the model provides a quantitative explanation for the failure to detect
emission originates (in the model) at radii smaller 4200 AU. the VeLLO with SHARC–II. Initially, this lack of bright 350 µm
The PdBI–derived upper limits for dust continuum emission emission was interpreted as evidence against L1148–IRS being
are not useful for our analysis of the SED of the L1148 core on large an embedded VeLLO, since all other VeLLOs show this emis-
′′
spatial scales. Specifically, the interferometer probes radii 4. 5, sion (Wu et al. 2007; Dunham et al. 2008). Our SED model shows,
i.e. 730 AU, while the analysis above considers scales as large as though, that no emission is to be expected, even if an embedded
4200 AU. The PdBI maps are only useful to examine the (absence source is present. Slightly more sensitive 350 µm observations
of) disks around L1148–IR, as done in Sec. 3.3. should be able to detect emission, though.
4.3 Results
5 VELLO NATAL CORES AND OUTFLOWS
Figure 8 presents the smallest mean squared relative deviation
in
found (by varying rin and rtrans ) for a given pair of luminosity and Comprehensive understanding of L1148–IRS and other VeLLOs
temperature. We find a minimum value of 0.08. This corresponds requires a good knowledge of the environment in which these ob-
10. 10 J. Kauffmann et al.
jects form. Therefore, we launched an investigation of the proper- 5.3 Properties of VeLLO Natal Cores
ties of the L1148 dense core. These results, as well as those for
The VeLLOs in Table 2 can roughly be divided into two
other VeLLOs, are collected here to support our further discussion.
groups. The first group is composed of L1521F, Cha–MMS1, and
We also include additional data on outflows. Sections 5.3 and 5.4
IRAM04191. These cores fail in none of the Crapsi et al. (2005a)
summarize this information.
criteria for “evolved” dense cores (if we stick only to criteria that
can be tested with existing data). For instance, these cores are
very dense (in terms of volume and column density), they have
5.1 Data for L1148–IRS strongly peaked density profile (as indicated by small values of
r70% , i.e.,the radius of the dust emission contour at 70% peak in-
Section 2.1 summarizes the data situation for L1148. The informa-
tensity; Crapsi et al. 2005a), and the inner regions of the dense core
tion is collected from Kauffmann et al. (2005) and Kauffmann et al.
are in an advanced stage of chemical evolution (i.e., CO depletion,
(2008). As described in this summary, some of the data are also pre-
and production of deuterated N2 H+ ). Crapsi et al. (2005a) argued
sented in Appendix B. Please refer to those sections for details.
that their criteria select dense cores relatively close to the onset of
protostellar collapse. It is thus not surprising to find that collapse
has indeed started in some of these objects.
5.2 Data for other VeLLOs The second group is composed of “unevolved” dense cores,
that fail in at least one of the Crapsi et al. criteria; these cores have
Here, we review the properties of known and proposed VeLLOs. relatively low (column) densities, and there are often no signs of
First, we assess the quality of VeLLO candidates. Specifically, we advanced chemistry. Following Crapsi et al. (2005a), these dense
consider objects that have previously been discussed to be similar cores are not expected to collapse and form stars. Section 6.3 ex-
to L1014–IRS, have indications for luminosities 0.1 L⊙ , or were plores how stars might still have formed in these cores. The most
discussed in the context of Brown Dwarf formation. prominent member of this group is L1014; the discovery of a
Visual inspection of Spitzer images of Oph B–11 Spitzer source in this core of low density, which was believed to
(Greaves et al. 2003) does not show any far–infrared counterpart. be “starless”, was a big surprise (Young et al. 2004). Also L1148
The core may actually be starless and is not considered further belongs to this group.
here. We also tentatively remove Lupus 3 MMS (Tachihara et al. The terminology used above is not meant to indicate that “un-
2007) and L1415–IRS (Stecklum et al. 2007) from the VeLLO evolved” cores mature and eventually become “evolved” ones! It
category. In these cases, estimation of the internal luminosity on is only used to indicate the relation to the Crapsi et al. criteria.
basis of the flux density at 70 µm wavelength (Dunham et al.
2008) suggests luminosities significantly exceeding the VeLLO In summary, some VeLLOs fulfil the Crapsi et al. (2005a) criteria
limit of 0.1 L⊙ . We rate IC1396A:γb (Reach et al. 2009) as a for evolved cores, while others do not. Since star formation is on-
source of unclear type, since the above luminosity estimate is going in all cores listed in Table 2, the initial conditions for stars to
not possible for this source. Preliminary photometry of the VLA form appear to be very diverse.
source J025616+192703 in the L1457 dense core implies a low L1148–IRS different from the other VeLLOs in that this
luminosity (Heithausen & B¨ ttner 2010), but data are too limited to
o source appears to have the lowest aperture mass of all VeLLOs. It
judge the probability that this really is a YSO and not a background also features the lowest N2 H+ line width ([0.232±0.048] km s−1 ;
object. Barrado et al. (2009) present SSTB213 J041757, a possible the next higher value for VeLLOs is 0.3 km s−1 for L1521F). Fi-
VeLLO candidate in Taurus. Luhman & Mamajek (2010) show nally, L1148 is the only “unevolved” VeLLO core in which inward
that this is unlikely to be a Taurus YSO, though, and SSTB213 motions have been detected. Since line asymmetries are easier de-
J041757 is thus excluded here. tected for narrow lines (Eq. B2), this might be a consequence of the
Chen et al. (2010) and Enoch et al. (2010) have recently pre- low N2 H+ line width.
sented good candidates for “first hydrostatic cores” (Larson 1969)
with internal luminosities 0.01 L⊙ . These could be dense cores
5.4 Properties of VeLLO Outflows
which have just become optically thick to their own radiation, be-
fore eventually collapsing into a more compact YSO. Such ob- VeLLOs differ vastly in their outflow properties. For example, only
jects have a low age and luminosity, and they are embedded in a 2 out of the 7 VeLLOs discussed in Table 2 (i.e., IRAM04191 and
dense core. This qualifies first hydrostatic cores as VeLLOs. The L673–7–IRS) drive a “prominent” extended outflow that can easily
Chen et al. and Enoch et al. sources will be included in our compar- be detected using single–dish telescopes. The remaining VeLLOs
ison once their nature has been established by decisive evidence. all appear to drive outflows (based on Spitzer image morphology
Table 2 lists 7 well–studied VeLLOs in order of decreasing and interferometer observations), but sensitive high–resolution ob-
aperture mass, M4200AU . It evaluates some criteria for dense core servations are needed to detect these (like those presented in Sec-
evolution forwarded by Crapsi et al. (2005a). By comparing prop- tion 3).
erties like column densities of dense gas tracers to characteristic As seen in Table 2, the presence of prominent outflow activ-
thresholds, these criteria essentially test whether a dense core con- ity does not appear to correlate with any other dense core property.
tains a significant mass of high density gas. Where appropriate (i.e., In the present sample, to be specific, an extended outflow is driven
not when evaluating the CO depletion factor: Appendix B4), we by a VeLLO in one of the most “evolved” cores, i.e. IRAM04191,
convert published values to match the dust properties adopted by which also has a large aperture mass. But also the VeLLO in L673–
Kauffmann et al. (2008; their Appendix A). We also list internal lu- 7 has a prominent outflow, despite a very moderate aperture mass
minosities and results of outflow searches, as reported in the respec- and failure in some of the Crapsi et al. criteria. In addition, cores
tive discovery paper. Distance–normalized flux densities at 1.8 cm more evolved than IRAM04191 (e.g., L1521F), as well as cores
wavelength, as reported by Scaife et al. (2010), characterize the ra- very similar to L673–7 (e.g., L1014), do not drive such flow. This
dio emission properties of the VeLLOs. diversity could be a consequence of VeLLO evolution; VeLLOs
11. The VeLLO L1148–IRS 11
Table 2. VeLLOs and their Natal Cores
Evolved Cores Unevolved Cores
Property L1521F Cha–MMS1 IRAM04191 L673–7 L1014 L328 L1148
protostar properties:
outflow Y ? Y Y Y ? Y
extended outflow n n Y Y n n n
Lint /L⊙ ≈ 0.04 [≈ 0.01] ≈ 0.07 ≈ 0.04 ≈ 0.09 ≈ 0.05 ≈ 0.10
F1.8cm d2 /10−2 mJy kpc2 0.3 ? 0.3 0.5 1.9 ? 0.7
dense core properties:
M4200 AU /M⊙ 0.87 [0.8] 0.60 0.39 0.36 [> 0.13/0.31] 0.14
N (H2 ) 4200 AU /1022 × cm−2 3.0 [2.7] 2.0 1.3 1.2 [> 0.4/1.1] 0.5
N (N2 D+ ) > 1.0 × 1012 cm−2 Y [Y] ? ? n n n
N (N2 H+ ) > 8.5 × 1012 cm−2 Y [Y] Y ? n Y n
N (N2 D+ )/N (N2 H+ ) 0.1 Y Y ? ? Y n ?
fd (CO) > 10 Y ? ? ? n n n
nc (H2 ) > 2.5 × 105 cm−3 Y Y Y n n n n
∆v(N2 H+ ) > 0.25 km s−1 Y Y Y Y Y Y n
inward motions Y ? Y n n n Y
r70% < 4 800 AU Y Y Y Y Y Y Y
References. Data are from Lee et al. (1999, 2009); Andr´ et al. (1999); Motte & Andr´ (2001); Belloche et al. (2002, 2006); Young et al. (2004); Crapsi et al.
e e
(2005a,b); Bourke et al. (2005, 2006); Dunham et al. (2006, 2010a); Kauffmann et al. (2005, 2008, and this work); and Scaife et al. (2010)
Notes. The dense core properties are compared to the criteria for “evolved” cores by Crapsi et al. (2005a) after conversion of the limiting density to our choice
of dust emission properties. A ‘Y’ marker indicates that a criterion is met, a ‘n’ marker that it is not, a question mark that the data are insufficient to decide.
Properties marked by square brackets ([. . . ]) are not readily available from the relevant publications and must be gleaned from the other published properties.
For Cha–MMS1, the N2 H+ and N2 D+ column densities have to be derived from the abundances and dust column densities reported by Belloche et al.
(2006). The aperture mass is derived from models for the density structure presented in the same publication. For L328–IRS, the envelope masses are from
lower limits of the 1.2 mm wavelength dust emission (Lee et al. 2009; 70 mJy within 2000 AU radius) and integration of the Lee et al. envelope density
model to 4200 AU radius. We deviate from the Crapsi et al. practice to infer inward motions from asymmetries in the N2 H+ lines; instead, inward motions
are either inferred from the analysis of line shifts (L1521F, L673–7, L1014, L328, and L1148), or from detailed modeling of line shapes (IRAM04191). For
all sources the uncertainty in the internal luminosity is of order ±0.03 L⊙ .
without outflows might be in a stage preceding or following an 6 DISCUSSION: L1148–IRS IN CONTEXT
accretion phase, in which prominent outflows are produced. It is
not clear whether other options — i.e., VeLLO formation without 6.1 Evolutionary Stage & Mass of L1148–IRS
prominent outflows in any evolutionary stage — provide credible L1148–IRS has a bolometric temperature (110 ± 15) K (Section
models. 4.1). This implies that L11148–IRS belongs to the protostellar class
It is also not clear how the presence of prominent outflows re- I, and suggests an age < 7 × 105 yr (Evans et al. 2009). We use
lates to the concept of “episodic accretion”, i.e., accretion (and thus this limit in the following.
outflow generation) occurring only during short episodes of the
protostellar lifetime (Kenyon et al. 1990). In this picture, VeLLOs As shown by Young et al. (2004), the internal luminosity of
would quasi–periodically create and gradually loose their promi- 0.1 L⊙ limits the present mass of all VeLLOs to a most likely value
nent outflows. Dynamical ages for the outflows of IRAM04191 0.1 M⊙ , if the luminosity is dominated by accretion power. This
and L673–7–IRS suggest that individual outflow periods5 last is probably the case for L1148–IRS, since it appears to drive an
a few 104 yr in VeLLOs. If VeLLOs without prominent out- (supposedly accretion–powered) outflow. Further, the young brown
flows are indeed in a dormant stage, this stage should prevail dwarf FU Tau (a class II object of 106 yr) has a luminosity of
for an even longer timescale (> 104 yr), as indicated by the 0.2 L⊙ (Luhman et al. 2009; 0.1 L⊙ for the brightest compo-
large fraction of VeLLOs without such outflows. Combination of nent, if FU Tau is an unresolved binary). This object might be un-
Spitzer source counts (Evans et al. 2009) with evolutionary models usually luminous (Luhman et al. 2009), but its properties support
(Dunham et al. 2010b) indeed shows that YSOs might accrete most the notion that YSO luminosities 0.1 L⊙ imply a mass in the
of their mass in 10 bursts occurring over a period ∼ 2 × 105 yr. brown dwarf domain. Thus, we find that the most likely present–
These models do thus imply dormant periods of several 104 yr, just day mass is 0.1 M⊙ .
as suggested by VeLLO outflow statistics. Comparison with evolutionary tracks by Baraffe et al. (1998)
and Chabrier et al. (2000) suggest a very conservative mass limit
≪ 0.35 M⊙ (when reducing the model luminosities by a factor
3: Reiners et al. 2005). Models by Wuchterl & Tscharnuter (2003)
suggest < 0.1 M⊙ , if one only considers early stages with sig-
nificant accretion. Unfortunately, their models are not well tested
against observations.
5 Prominent outflows are detectable during this period. This does, however, To understand the collapse conditions in L1148, consider the col-
not require that they are continuously driven during this time. lapse of a hydrostatic isothermal sphere of radius R that is subject
12. 12 J. Kauffmann et al.
to an environmental pressure, Penv . To be unstable, the sphere must the expected mass of the collapsing natal dense core, M : in most
have a mass cases M ≫ MBD . L1148–IRS can be used to study this problem,
Tg
2
R even in case this VeLLO has a final mass exceeding the BD mass
M > 2.0 M⊙ , (1) limit.
10 K 0.1 pc
and the pressure must obey Consider once again pressure–bound hydrostatic isothermal
4 −2
spheres. Combination of Eqs. (1, 2) yields the condition
Pext Tg R
> 3.3 × 104 cm−3 (2) Tg
4
Penv /kB
−1/2
kB 10 K 0.1 pc M > 1.2 M⊙ (3)
10 K 105 K cm−3
(Bonnor 1956 and Ebert 1955; kB is Boltzmann’s constant). Star
formation requires that the inner parts of the protostellar en- for unstable spheres. This system will form a star (or BD) of mass
velope are unstable6 . We can use the aforementioned aperture M⋆ = η M , where η 1 is the star formation efficiency. For
mass, M4200AU , to test this condition. For R = 4200 AU and typical temperatures (≈ 10 K) and pressures (a few 105 K cm−3 ;
Tg = 10 K, Eq. (1) yields the condition M > 0.41 M⊙ . Thus, e.g. Bertoldi & McKee 1992), one obtains the collapse condition
M4200AU fails the condition for gravitational instability. The reser- M 1 M⊙ . Typical values of η are believed to be ∼ 1/3 (e.g.,
voir actively forming the VeLLO must therefore have a radius Alves et al. 2007), yielding typical stellar masses ∼ 0.3 M⊙ .
< 4200 AU. This implies an unstable mass smaller M4200AU , i.e. In this framework, to achieve lower stellar masses, BD for-
< 0.14 M⊙ (Section 2.1). Radii < 4200 AU also imply a pressure mation requires unusually small temperature (Tg ≪ 10 K), large
Pext /kB > 8 × 105 cm−2 . As we discuss in Section 6.3, this pres- pressure (Penv /kB ≫ 105 K cm−3 ), low efficiency (η ≪ 1/3),
sure is relatively high. This has implications on VeLLO formation or a combination of these. L1148–IRS provides a test case for such
models. reasoning: Eq. (1) suggests M < 0.14 M⊙ for the collapsing core
Combined with the present–day mass of L1148–IRS, < in this region.
0.1 M⊙ , this estimate of the collapsing mass suggests a final mass The structure of the L1148 core thus appears to require pecu-
< 0.24 M⊙ . If this VeLLO has a present–day mass < 0.05 M⊙ , liar environmental conditions. We have no satisfying explanation
and the immediate envelope of < 0.14 M⊙ is accreted with an ef- why and in which sense (temperature, pressure, etc.) these should
ficiency ∼ 1/3 (as deemed typical; e.g., Alves et al. 2007), then prevail in L1148. One can, however, speculate that the unusual
L1148–IRS could have a final mass even below the brown dwarf kinematic conditions in this region might have played a role: mul-
limit. After L328–IRS (Lee et al. 2009), this is the second VeLLO tiple velocity components (in C18 O), velocity jumps near L1148–
for which such a small final mass is derived. IRS (in CCS) and contraction motions on spatial scales 0.3 pc
are not commonly observed in dense cores (see Section 2.1 and
Appendix B3).
6.2 The Nature and Evolution of VeLLOs The environmental conditions in L1148 have actually been
There is probably general consent that VeLLOs have a most likely explored by Nutter et al. (2009). Spatial offsets between intensity
present–day mass < 0.1 M⊙ (Section 6.1). The final mass at the peaks at different wavelengths are consistent with external heat-
end of the accretion phase might, however, be much larger. ing of the L1148 core. One could imagine that the core is sculpted
VeLLO natal cores differ significantly in the mass of gas at by such a radiation field. Kirk et al. (2009) suggests indeed that
high density they contain (Section 5). Since VeLLOs form from this the entire Cepheus Flare Complex is shaped by external triggering.
gas, these differences may suggest that different VeLLOs take dif- Related externally triggered compression events would be suited to
ferent evolutionary paths (Bourke et al. 2006). Some may have sig- produce low critical masses via an increase in Penv .
nificant future accretion and attain a stellar final mass (Andr´ et al.
e It might, of course, also be that the initial unstable mass of the
1999), while lack of accretion in others could render these ob- dense core was ∼ 1 M⊙ , as suggested by Eq. (3), but that we now
jects young brown dwarfs (Young et al. 2004; Huard et al. 2006). observe a much more evolved phase, where the initial mass is no
Table 2 thus presents a first attempt to systematically characterize longer relevant. Lee et al. (2009), for instance, suggest that L328–
the likeliness of these different evolutionary paths for several VeL- IRS might have moved out of its natal core. This would leave this
LOs. The number of positive indicators for significant amounts of VeLLO with a small mass reservoir to accrete from. Huard et al.
high density gas near the VeLLO increase towards the left of Ta- (2006) present a similar argument for L1014–IRS. The complex
ble 2. The VeLLO final mass is therefore likely to increase in this kinematics in L1148 might suggest such a scenario also for L1148–
direction too. L328–IRS and L1148–IRS hold a peculiar position IRS. In fact, Section 2.1 shows that there is a possible — though not
among VeLLOs, given that their most likely final mass is very low ′′
significant — 7. 6 spatial offset (i.e., 2500 AU) between L1148–
(< 0.15 M⊙ and < 0.24 M⊙ , respectively; see Lee et al. 2009 IRS and the core’s column density peak. The growth of L1148–IRS
and Section 6.1). might thus be stinted, because it has detached from the dense core
from which it cannot accrete from it any longer.
6.3 Formation of Brown Dwarfs: Lessons from L1148 Similarly, L1148–IRS could be in a very advanced stage of
evolution where most of the envelope has been dispersed. In prin-
One unsolved aspect of isolated brown dwarf (BD) formation is the ciple, strong VeLLO outflows (e.g., as those from IRAM04191;
large difference between the final BD mass, MBD 0.08 M⊙ , and Andr´ et al. 1999) might be able to do this.
e
The credibility of these scenarios is unclear, though. Consider
6 To be specific, this is a requirement only for models with inside–out col- L1148–IRS as an example. Section 6.1 suggests that the present–
lapse. The evolution of these collapsing spheres is similar to those stud- day mass of this VeLLO is 0.1 M⊙ . The immediate environment
ied by Shu (1977). One major difference, though, is that Shu considers — of L1148–IRS contains ∼ 0.14 M⊙ (from the 4200 AU aperture
strictly speaking — infinite spheres with singular density profiles. His struc- mass). If outflows have dispersed the gas, they must thus have dis-
tures are unstable to perturbations at all radii, just as required here. rupted a core of about 0.75 M⊙ . It is not known whether dispersal