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Thomas P Robitaille - One of the best experts on this subject based on the ideXlab platform.
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a modular set of synthetic spectral energy distributions for Young Stellar Objects
Astronomy and Astrophysics, 2017Co-Authors: Thomas P RobitailleAbstract:In this paper, I present a new set of synthetic spectral energy distributions (SEDs) for Young Stellar Objects (YSOs) spanning a wide range of evolutionary stages, from the Youngest deeply embedded protostars to pre-main-sequence stars with few or no disks. These models include significant improvements on the previous generation of published models: in particular, the new models cover a much wider and more uniform region of parameter space, do not include highly model-dependent parameters, and include a number of improvements that make them more suited to modeling far-infrared and sub-mm observations of forming stars. Rather than all being part of a single monolithic set of models, the new models are split up into sets of varying complexity. The aim of the new set of models is not to provide the most physically realistic models for Young stars, but rather to provide deliberately simplified models for initial modeling, which allows a wide range of parameter space to be explored. I present the design of the model set, and show examples of fitting these models to real observations to show how the new grid design can help us better understand what can be determined from limited unresolved observations. The models, as well as a Python-based fitting tool are publicly available to the community.
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surveying the agents of galaxy evolution in the tidally stripped low metallicity small magellanic cloud sage smc iii Young Stellar Objects
The Astrophysical Journal, 2013Co-Authors: Barbara A Whitney, Thomas P Robitaille, L. R. Carlson, Remy Indebetouw, Marta Sewilo, J Seale, Margaret Meixner, J. M. OliveiraAbstract:The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved Stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK s ) and optical (UBVI) data, we identified a population of ~1000 intermediate- to high-mass Young Stellar Objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.
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three dimensional radiation transfer in Young Stellar Objects
Astrophysical Journal Supplement Series, 2013Co-Authors: Barbara A Whitney, Thomas P Robitaille, J E Bjorkman, Ruobing Dong, Michael J Wolff, Kenneth Wood, J HonorAbstract:We have updated our publicly available dust radiative transfer code (HOCHUNK3D) to include new emission processes and various three-dimensional (3D) geometries appropriate for forming stars. The 3D geometries include warps and spirals in disks, accretion hotspots on the central star, fractal clumping density enhancements, and misaligned inner disks. Additional axisymmetric (2D) features include gaps in disks and envelopes, "puffed-up inner rims" in disks, multiple bipolar cavity walls, and iteration of disk vertical structure assuming hydrostatic equilibrium (HSEQ). We include the option for simple power-law envelope geometry, which, combined with fractal clumping and bipolar cavities, can be used to model evolved stars as well as protostars. We include non-thermal emission from polycyclic aromatic hydrocarbons (PAHs) and very small grains, and external illumination from the interStellar radiation field. The grid structure was modified to allow multiple dust species in each cell; based on this, a simple prescription is implemented to model dust stratification. We describe these features in detail, and show example calculations of each. Some of the more interesting results include the following: (1) outflow cavities may be more clumpy than infalling envelopes. (2) PAH emission in high-mass stars may be a better indicator of evolutionary stage than the broadband spectral energy distribution slope; and related to this, (3) externally illuminated clumps and high-mass stars in optically thin clouds can masquerade as Young Stellar Objects. (4) Our HSEQ models suggest that dust settling is likely ubiquitous in T Tauri disks, in agreement with previous observations.
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three dimensional radiation transfer in Young Stellar Objects
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Barbara A Whitney, Thomas P Robitaille, J E Bjorkman, Ruobing Dong, Michael J Wolff, Kenneth Wood, J HonorAbstract:We have updated our publicly available dust radiative transfer code (HOCHUNK3D) to include new emission processes and various 3-D geometries appropriate for forming stars. The 3-D geometries include warps and spirals in disks, accretion hotspots on the central star, fractal clumping density enhancements, and misaligned inner disks. Additional axisymmetric (2-D) features include gaps in disks and envelopes, "puffed-up inner rims" in disks, multiple bipolar cavity walls, and iteration of disk vertical structure assuming hydrostatic equilibrium. We include the option for simple power-law envelope geometry, which combined with fractal clumping, and bipolar cavities, can be used to model evolved stars as well as protostars. We include non-thermal emission from PAHs and very small grains, and external illumination from the interStellar radiation field. The grid structure was modified to allow multiple dust species in each cell; based on this, a simple prescription is implemented to model dust stratification. We describe these features in detail, and show example calculations of each. Some of the more interesting results include the following: 1) Outflow cavities may be more clumpy than infalling envelopes. 2) PAH emission in high-mass stars may be a better indicator of evolutionary stage than the broadband SED slope; and related to this, 3) externally illuminated clumps and high-mass stars in optically thin clouds can masquerade as YSOs. 4) Our hydrostatic equilibrium models suggest that dust settling is likely ubiquitous in T Tauri disks, in agreement with previous observations.
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a pan carina Young Stellar object catalog intermediate mass Young Stellar Objects in the carina nebula identified via mid infrared excess emission
Astrophysical Journal Supplement Series, 2011Co-Authors: Matthew S Povich, Nathan Smith, Steven R Majewski, Konstantin V Getman, Leisa K Townsley, B L Babler, Patrick S Broos, Remy Indebetouw, M R Meade, Thomas P RobitailleAbstract:We present a catalog of 1439 Young Stellar Objects (YSOs) spanning the 1.42 deg2 field surveyed by the Chandra Carina Complex Project (CCCP), which includes the major ionizing clusters and the most active sites of ongoing star formation within the Great Nebula in Carina. Candidate YSOs were identified via infrared (IR) excess emission from dusty circumStellar disks and envelopes, using data from the Spitzer Space Telescope (the Vela-Carina survey) and the Two-Micron All Sky Survey. We model the 1-24 μm IR spectral energy distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO Catalog (PCYC) is dominated by intermediate-mass (2 M ☉ 2 × 104 YSOs and a present-day star formation rate (SFR) of >0.008 M ☉ yr–1. The global SFR in the Carina Nebula, averaged over the past ~5 Myr, has been approximately constant.
Barbara A Whitney - One of the best experts on this subject based on the ideXlab platform.
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surveying the agents of galaxy evolution in the tidally stripped low metallicity small magellanic cloud sage smc iii Young Stellar Objects
The Astrophysical Journal, 2013Co-Authors: Barbara A Whitney, Thomas P Robitaille, L. R. Carlson, Remy Indebetouw, Marta Sewilo, J Seale, Margaret Meixner, J. M. OliveiraAbstract:The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved Stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK s ) and optical (UBVI) data, we identified a population of ~1000 intermediate- to high-mass Young Stellar Objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.
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three dimensional radiation transfer in Young Stellar Objects
Astrophysical Journal Supplement Series, 2013Co-Authors: Barbara A Whitney, Thomas P Robitaille, J E Bjorkman, Ruobing Dong, Michael J Wolff, Kenneth Wood, J HonorAbstract:We have updated our publicly available dust radiative transfer code (HOCHUNK3D) to include new emission processes and various three-dimensional (3D) geometries appropriate for forming stars. The 3D geometries include warps and spirals in disks, accretion hotspots on the central star, fractal clumping density enhancements, and misaligned inner disks. Additional axisymmetric (2D) features include gaps in disks and envelopes, "puffed-up inner rims" in disks, multiple bipolar cavity walls, and iteration of disk vertical structure assuming hydrostatic equilibrium (HSEQ). We include the option for simple power-law envelope geometry, which, combined with fractal clumping and bipolar cavities, can be used to model evolved stars as well as protostars. We include non-thermal emission from polycyclic aromatic hydrocarbons (PAHs) and very small grains, and external illumination from the interStellar radiation field. The grid structure was modified to allow multiple dust species in each cell; based on this, a simple prescription is implemented to model dust stratification. We describe these features in detail, and show example calculations of each. Some of the more interesting results include the following: (1) outflow cavities may be more clumpy than infalling envelopes. (2) PAH emission in high-mass stars may be a better indicator of evolutionary stage than the broadband spectral energy distribution slope; and related to this, (3) externally illuminated clumps and high-mass stars in optically thin clouds can masquerade as Young Stellar Objects. (4) Our HSEQ models suggest that dust settling is likely ubiquitous in T Tauri disks, in agreement with previous observations.
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three dimensional radiation transfer in Young Stellar Objects
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: Barbara A Whitney, Thomas P Robitaille, J E Bjorkman, Ruobing Dong, Michael J Wolff, Kenneth Wood, J HonorAbstract:We have updated our publicly available dust radiative transfer code (HOCHUNK3D) to include new emission processes and various 3-D geometries appropriate for forming stars. The 3-D geometries include warps and spirals in disks, accretion hotspots on the central star, fractal clumping density enhancements, and misaligned inner disks. Additional axisymmetric (2-D) features include gaps in disks and envelopes, "puffed-up inner rims" in disks, multiple bipolar cavity walls, and iteration of disk vertical structure assuming hydrostatic equilibrium. We include the option for simple power-law envelope geometry, which combined with fractal clumping, and bipolar cavities, can be used to model evolved stars as well as protostars. We include non-thermal emission from PAHs and very small grains, and external illumination from the interStellar radiation field. The grid structure was modified to allow multiple dust species in each cell; based on this, a simple prescription is implemented to model dust stratification. We describe these features in detail, and show example calculations of each. Some of the more interesting results include the following: 1) Outflow cavities may be more clumpy than infalling envelopes. 2) PAH emission in high-mass stars may be a better indicator of evolutionary stage than the broadband SED slope; and related to this, 3) externally illuminated clumps and high-mass stars in optically thin clouds can masquerade as YSOs. 4) Our hydrostatic equilibrium models suggest that dust settling is likely ubiquitous in T Tauri disks, in agreement with previous observations.
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the present day star formation rate of the milky way determined from spitzer detected Young Stellar Objects
The Astrophysical Journal, 2010Co-Authors: Thomas P Robitaille, Barbara A WhitneyAbstract:We present initial results from a population synthesis model aimed at determining the star formation rate (SFR) of the Milky Way. We find that a total SFR of 0.68-1.45 M ? yr?1 is able to reproduce the observed number of Young Stellar Objects (YSOs) in the Spitzer/IRAC GLIMPSE survey of the Galactic plane, assuming simple prescriptions for the three-dimensional Galactic distributions of YSOs and interStellar dust, and using model spectral energy distributions to predict the brightness and color of the synthetic YSOs at different wavelengths. This is the first Galaxy-wide measurement derived from pre-main-sequence Objects themselves, rather than global observables such as the total radio continuum, H?, or FIR flux. The value obtained is slightly lower than, but generally consistent with previously determined values. We will extend this method in the future to fit the brightness, color, and angular distribution of YSOs, and simultaneously make use of multiple surveys, to place constraints on the input assumptions, and reduce uncertainties in the SFR estimate. Ultimately, this will be one of the most accurate methods for determining the Galactic SFR, as it makes use of stars of all masses (limited only by sensitivity) rather than solely massive stars or indirect tracers of massive stars.
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the present day star formation rate of the milky way determined from spitzer detected Young Stellar Objects
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Thomas P Robitaille, Barbara A WhitneyAbstract:We present initial results from a population synthesis model aimed at determining the star formation rate of the Milky-Way. We find that a total star formation rate of 0.68 to 1.45 Msun/yr is able to reproduce the observed number of Young Stellar Objects in the Spitzer/IRAC GLIMPSE survey of the Galactic plane, assuming simple prescriptions for the 3D Galactic distributions of YSOs and interStellar dust, and using model SEDs to predict the brightness and color of the synthetic YSOs at different wavelengths. This is the first Galaxy-wide measurement derived from pre-main-sequence Objects themselves, rather than global observables such as the total radio continuum, Halpha, or FIR flux. The value obtained is slightly lower than, but generally consistent with previously determined values. We will extend this method in the future to fit the brightness, color, and angular distribution of YSOs, and simultaneously make use of multiple surveys, to place constraints on the input assumptions, and reduce uncertainties in the star formation rate estimate. Ultimately, this will be one of the most accurate methods for determining the Galactic star formation rate, as it makes use of stars of all masses (limited only by sensitivity) rather than solely massive stars or indirect tracers of massive stars.
Ewine F Van Dishoeck - One of the best experts on this subject based on the ideXlab platform.
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complex organic molecules in organic poor massive Young Stellar Objects
Astronomy and Astrophysics, 2015Co-Authors: Karin I Oberg, Ewine F Van Dishoeck, Edith C Fayolle, Robin T Garrod, Suzanne E BisschopAbstract:Context. Massive Young Stellar Objects (MYSOs) with hot cores are classic sources of complex organic molecules. The origins of these molecules in such sources, as well as the smalland large-scale differentiation between nitrogenand oxygen-bearing complex species, are poorly understood. Aims. We aim to use complex molecule abundances toward a chemically less explored class of MYSOs with weak hot organic emission lines to constrain the impact of hot molecular cores and initial ice conditions on the chemical composition toward MYSOs. Methods. We use the IRAM 30m and the Submillimeter Array to search for complex organic molecules over 8-16 GHz in the 1 mm atmospheric window toward three MYSOs with known ice abundances, but without luminous molecular hot cores. Results. Complex molecules are detected toward all three sources at comparable abundances with respect to CH3OH to classical hot core sources. The relative importance of CH3CHO, CH3CCH, CH3OCH3, CH3CN, and HNCO differ between the organic-poor MYSOs and hot cores, however. Furthermore, the N-bearing molecules are generally concentrated toward the source centers, while most Oand C-bearing molecules are present both in the center and in the colder envelope. Gas-phase HNCO/CH3OH ratios Article number, page 1 of 28 ar X iv :1 50 1. 03 16 8v 1 [ as tr oph .S R ] 1 3 Ja n 20 15 Edith C. Fayolle et al.: New constraints on the origins of organics are tentatively correlated with the ratios of NH3 ice over CH3OH ice in the same lines of sight, which is consistent with new gas-grain model predictions. Conclusions. Hot cores are not required to form complex organic molecules, and source temperature and initial ice composition both seem to affect complex organic distributions toward MYSOs. To quantify the relative impact of temperature and initial conditions requires, however, a larger spatially resolved survey of MYSOs with ice detections.
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complex organic molecules in organic poor massive Young Stellar Objects
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Karin I Oberg, Ewine F Van Dishoeck, Edith C Fayolle, Robin T Garrod, Suzanne E BisschopAbstract:Massive Young Stellar Objects (MYSOs) with hot cores are classic sources of complex organic molecules. The origins of these molecules in such sources, as well as the small- and large-scale differentiation between nitrogen- and oxygen-bearing complex species, are poorly understood. We aim to use complex molecule abundances toward a chemically less explored class of MYSOs with weak hot organic emission lines to constrain the impact of hot molecular cores and initial ice conditions on the chemical composition toward MYSOs. We use the IRAM 30m and the Submillimeter Array to search for complex organic molecules over 8-16 GHz in the 1~mm atmospheric window toward three MYSOs with known ice abundances, but without luminous molecular hot cores. Complex molecules are detected toward all three sources at comparable abundances with respect to CH$_3$OH to classical hot core sources. The relative importance of CH$_3$CHO, CH$_3$CCH, CH$_3$OCH$_3$, CH$_3$CN, and HNCO differ between the organic-poor MYSOs and hot cores, however. Furthermore, the N-bearing molecules are generally concentrated toward the source centers, while most O- and C-bearing molecules are present both in the center and in the colder envelope. Gas-phase HNCO/CH$_3$OH ratios are tentatively correlated with the ratios of NH$_3$ ice over CH$_3$OH ice in the same lines of sight, which is consistent with new gas-grain model predictions. Hot cores are not required to form complex organic molecules, and source temperature and initial ice composition both seem to affect complex organic distributions toward MYSOs. To quantify the relative impact of temperature and initial conditions requires, however, a larger spatially resolved survey of MYSOs with ice detections.
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the c2d spitzer spectroscopic survey of ices around low mass Young Stellar Objects iv nh3 and ch3oh
The Astrophysical Journal, 2010Co-Authors: S Bottinelli, Karin I Oberg, A C A Boogert, K M Pontoppidan, Geoffrey A Blake, Ewine F Van Dishoeck, J Bouwman, Martha Beckwith, H Linnartz, Neal J EvansAbstract:NH_3 and CH_3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and CH3OCH3. Despite a number of recent studies, little is known about their abundances in the solid state. This is particularly the case for low-mass protostars, for which only the launch of the Spitzer Space Telescope has permitted high-sensitivity observations of the ices around these Objects. In this work, we investigate the ~8–10μm region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass Young Stellar Objects (YSOs). These data are part of a survey of interStellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10μm silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH_(3-) and CH_3OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ~9μm in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH_3 ν_2 umbrella mode and derive abundances with respect to water between ~2% and 15%. Simultaneously, we also revisited the case of CH_3OH ice by studying the ν_4 C–O stretch mode of this molecule at ~9.7μm in 16 Objects, yielding abundances consistent with those derived by Boogert et al. based on a simultaneous 9.75 and 3.53μm data analysis. Our study indicates that NH_3 is present primarily in H_2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH_3OH being in an almost pure methanol ice, or mixed mainly with CO or CO_2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH_3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10%–20% of nitrogen is locked up in known ices.
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the c2d spitzer spectroscopic survey of ices around low mass Young Stellar Objects iv nh3 and ch3oh
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Karin I Oberg, A C A Boogert, Ewine F Van Dishoeck, S Bottinelli, J Bouwman, Martha BeckwithAbstract:NH3 and CH3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and HCOOCH3. Despite a number of recent studies, little is known about their abundances in the solid state. (...) In this work, we investigate the ~ 8-10 micron region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass Young Stellar Objects (YSOs). These data are part of a survey of interStellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10 micron silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH3- and CH3OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ~9 micron in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH3 nu_2 umbrella mode, and derive abundances with respect to water between ~2 and 15%. Simultaneously, we also revisited the case of CH3OH ice by studying the nu_4 C-O stretch mode of this molecule at ~9.7 micron in 16 Objects, yielding abundances consistent with those derived by Boogert et al. 2008 (hereafter paper I) based on a simultaneous 9.75 and 3.53 micron data analysis. Our study indicates that NH3 is present primarily in H2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH3OH being in an almost pure methanol ice, or mixed mainly with CO or CO2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10-20 % of nitrogen is locked up in known ices.
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the c2d spitzer spectroscopic survey of ices around low mass Young Stellar Objects iii ch4
The Astrophysical Journal, 2008Co-Authors: Karin I Oberg, Neal J Evans, A C A Boogert, K M Pontoppidan, Geoffrey A Blake, F Lahuis, Ewine F Van DishoeckAbstract:CH4 is proposed to be the starting point of a rich organic chemistry. Solid CH4 abundances have previously been determined mostly toward high-mass star-forming regions. Spitzer IRS now provides a unique opportunity to probe solid CH4 toward low-mass star-forming regions as well. Infrared spectra from the Spitzer Space Telescope are presented to determine the solid CH4 abundance toward a large sample of low-mass Young Stellar Objects. A total of 25 out of 52 ice sources in the “Cores to Disks” (c2d) Legacy program have an absorption feature at 7.7 μm, attributed to the bending mode of solid CH4. The solid CH4/H2O abundances are 2%–8%, except for three sources with abundances as high as 11%–13%. The latter sources have relatively large uncertainties due to small total ice column densities. Toward sources with H2O column densities above cm−2, the CH4 abundances (20 out of 25) are nearly constant at . Correlation plots with solid H2O, CH3OH, CO2, and CO column densities and abundances relative to H2O reveal a closer relationship of solid CH4 with CO2 and H2O than with solid CO and CH3OH. The inferred solid CH4 abundances are consistent with models where CH4 is formed through sequential hydrogenation of C on grain surfaces. Finally, the equal or higher abundances toward low-mass Young Stellar Objects compared with high-mass Objects and the correlation studies support this formation pathway as well, but not the two competing theories: formation from CH3OH and formation in gas phase with subsequent freezeout.
Karin I Oberg - One of the best experts on this subject based on the ideXlab platform.
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complex organic molecules in organic poor massive Young Stellar Objects
Astronomy and Astrophysics, 2015Co-Authors: Karin I Oberg, Ewine F Van Dishoeck, Edith C Fayolle, Robin T Garrod, Suzanne E BisschopAbstract:Context. Massive Young Stellar Objects (MYSOs) with hot cores are classic sources of complex organic molecules. The origins of these molecules in such sources, as well as the smalland large-scale differentiation between nitrogenand oxygen-bearing complex species, are poorly understood. Aims. We aim to use complex molecule abundances toward a chemically less explored class of MYSOs with weak hot organic emission lines to constrain the impact of hot molecular cores and initial ice conditions on the chemical composition toward MYSOs. Methods. We use the IRAM 30m and the Submillimeter Array to search for complex organic molecules over 8-16 GHz in the 1 mm atmospheric window toward three MYSOs with known ice abundances, but without luminous molecular hot cores. Results. Complex molecules are detected toward all three sources at comparable abundances with respect to CH3OH to classical hot core sources. The relative importance of CH3CHO, CH3CCH, CH3OCH3, CH3CN, and HNCO differ between the organic-poor MYSOs and hot cores, however. Furthermore, the N-bearing molecules are generally concentrated toward the source centers, while most Oand C-bearing molecules are present both in the center and in the colder envelope. Gas-phase HNCO/CH3OH ratios Article number, page 1 of 28 ar X iv :1 50 1. 03 16 8v 1 [ as tr oph .S R ] 1 3 Ja n 20 15 Edith C. Fayolle et al.: New constraints on the origins of organics are tentatively correlated with the ratios of NH3 ice over CH3OH ice in the same lines of sight, which is consistent with new gas-grain model predictions. Conclusions. Hot cores are not required to form complex organic molecules, and source temperature and initial ice composition both seem to affect complex organic distributions toward MYSOs. To quantify the relative impact of temperature and initial conditions requires, however, a larger spatially resolved survey of MYSOs with ice detections.
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complex organic molecules in organic poor massive Young Stellar Objects
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Karin I Oberg, Ewine F Van Dishoeck, Edith C Fayolle, Robin T Garrod, Suzanne E BisschopAbstract:Massive Young Stellar Objects (MYSOs) with hot cores are classic sources of complex organic molecules. The origins of these molecules in such sources, as well as the small- and large-scale differentiation between nitrogen- and oxygen-bearing complex species, are poorly understood. We aim to use complex molecule abundances toward a chemically less explored class of MYSOs with weak hot organic emission lines to constrain the impact of hot molecular cores and initial ice conditions on the chemical composition toward MYSOs. We use the IRAM 30m and the Submillimeter Array to search for complex organic molecules over 8-16 GHz in the 1~mm atmospheric window toward three MYSOs with known ice abundances, but without luminous molecular hot cores. Complex molecules are detected toward all three sources at comparable abundances with respect to CH$_3$OH to classical hot core sources. The relative importance of CH$_3$CHO, CH$_3$CCH, CH$_3$OCH$_3$, CH$_3$CN, and HNCO differ between the organic-poor MYSOs and hot cores, however. Furthermore, the N-bearing molecules are generally concentrated toward the source centers, while most O- and C-bearing molecules are present both in the center and in the colder envelope. Gas-phase HNCO/CH$_3$OH ratios are tentatively correlated with the ratios of NH$_3$ ice over CH$_3$OH ice in the same lines of sight, which is consistent with new gas-grain model predictions. Hot cores are not required to form complex organic molecules, and source temperature and initial ice composition both seem to affect complex organic distributions toward MYSOs. To quantify the relative impact of temperature and initial conditions requires, however, a larger spatially resolved survey of MYSOs with ice detections.
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the c2d spitzer spectroscopic survey of ices around low mass Young Stellar Objects iv nh3 and ch3oh
The Astrophysical Journal, 2010Co-Authors: S Bottinelli, Karin I Oberg, A C A Boogert, K M Pontoppidan, Geoffrey A Blake, Ewine F Van Dishoeck, J Bouwman, Martha Beckwith, H Linnartz, Neal J EvansAbstract:NH_3 and CH_3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and CH3OCH3. Despite a number of recent studies, little is known about their abundances in the solid state. This is particularly the case for low-mass protostars, for which only the launch of the Spitzer Space Telescope has permitted high-sensitivity observations of the ices around these Objects. In this work, we investigate the ~8–10μm region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass Young Stellar Objects (YSOs). These data are part of a survey of interStellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10μm silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH_(3-) and CH_3OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ~9μm in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH_3 ν_2 umbrella mode and derive abundances with respect to water between ~2% and 15%. Simultaneously, we also revisited the case of CH_3OH ice by studying the ν_4 C–O stretch mode of this molecule at ~9.7μm in 16 Objects, yielding abundances consistent with those derived by Boogert et al. based on a simultaneous 9.75 and 3.53μm data analysis. Our study indicates that NH_3 is present primarily in H_2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH_3OH being in an almost pure methanol ice, or mixed mainly with CO or CO_2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH_3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10%–20% of nitrogen is locked up in known ices.
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the c2d spitzer spectroscopic survey of ices around low mass Young Stellar Objects iv nh3 and ch3oh
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Karin I Oberg, A C A Boogert, Ewine F Van Dishoeck, S Bottinelli, J Bouwman, Martha BeckwithAbstract:NH3 and CH3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and HCOOCH3. Despite a number of recent studies, little is known about their abundances in the solid state. (...) In this work, we investigate the ~ 8-10 micron region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass Young Stellar Objects (YSOs). These data are part of a survey of interStellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10 micron silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH3- and CH3OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ~9 micron in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH3 nu_2 umbrella mode, and derive abundances with respect to water between ~2 and 15%. Simultaneously, we also revisited the case of CH3OH ice by studying the nu_4 C-O stretch mode of this molecule at ~9.7 micron in 16 Objects, yielding abundances consistent with those derived by Boogert et al. 2008 (hereafter paper I) based on a simultaneous 9.75 and 3.53 micron data analysis. Our study indicates that NH3 is present primarily in H2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH3OH being in an almost pure methanol ice, or mixed mainly with CO or CO2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10-20 % of nitrogen is locked up in known ices.
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the c2d spitzer spectroscopic survey of ices around low mass Young Stellar Objects iii ch4
The Astrophysical Journal, 2008Co-Authors: Karin I Oberg, Neal J Evans, A C A Boogert, K M Pontoppidan, Geoffrey A Blake, F Lahuis, Ewine F Van DishoeckAbstract:CH4 is proposed to be the starting point of a rich organic chemistry. Solid CH4 abundances have previously been determined mostly toward high-mass star-forming regions. Spitzer IRS now provides a unique opportunity to probe solid CH4 toward low-mass star-forming regions as well. Infrared spectra from the Spitzer Space Telescope are presented to determine the solid CH4 abundance toward a large sample of low-mass Young Stellar Objects. A total of 25 out of 52 ice sources in the “Cores to Disks” (c2d) Legacy program have an absorption feature at 7.7 μm, attributed to the bending mode of solid CH4. The solid CH4/H2O abundances are 2%–8%, except for three sources with abundances as high as 11%–13%. The latter sources have relatively large uncertainties due to small total ice column densities. Toward sources with H2O column densities above cm−2, the CH4 abundances (20 out of 25) are nearly constant at . Correlation plots with solid H2O, CH3OH, CO2, and CO column densities and abundances relative to H2O reveal a closer relationship of solid CH4 with CO2 and H2O than with solid CO and CH3OH. The inferred solid CH4 abundances are consistent with models where CH4 is formed through sequential hydrogenation of C on grain surfaces. Finally, the equal or higher abundances toward low-mass Young Stellar Objects compared with high-mass Objects and the correlation studies support this formation pathway as well, but not the two competing theories: formation from CH3OH and formation in gas phase with subsequent freezeout.
R A Gutermuth - One of the best experts on this subject based on the ideXlab platform.
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spitzer observations of long term infrared variability among Young Stellar Objects in chamaeleon i
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: Kevin Flaherty, J Muzerolle, Thomas S Megeath, Lindsay Demarchi, Z Balog, William Herbst, Elise Furlan, R A GutermuthAbstract:Infrared variability is common among Young Stellar Objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited to total baselines of about a month due to the orientation of the spacecraft. Here we present observations of the Chameleon I cluster whose low declination makes it observable by the Spitzer space telescope over a 200 day period. We observe 30 Young Stellar Objects with a daily cadence to better sample variability on timescales of months. We find such variability is common, occurring in ~80% of the detected cluster members. The change in [3.6]-[4.5] color over 200 days for many of the sources falls between that expected for extinction and fluctuations in disk emission. With our high cadence and long baseline we can derive power spectral density curves covering two orders of magnitude in frequency and find significant power at low frequencies, up to the boundaries of our 200 day survey. Such long timescales are difficult to explain with variations driven by the interaction between the disk and Stellar magnetic field, which has a dynamical timescale of days to weeks. The most likely explanation is either structural or temperature fluctuations spread throughout the inner ~0.5 au of the disk, suggesting that the intrinsic dust structure is highly dynamic.
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the spitzer space telescope survey of the orion a and b molecular clouds ii the spatial distribution and demographics of dusty Young Stellar Objects
The Astronomical Journal, 2015Co-Authors: S T Megeath, R A Gutermuth, J Muzerolle, E Kryukova, J L Hora, L E Allen, K M Flaherty, Lee Hartmann, Philip C MyersAbstract:We analyze the spatial distribution of dusty Young Stellar Objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc^(−2) to over 10,000 pc^(−2), with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities ≥10 pc^(−2), we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ~2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the Young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions.
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the spitzer space telescope survey of the orion a and b molecular clouds ii the spatial distribution and demographics of dusty Young Stellar Objects
arXiv: Astrophysics of Galaxies, 2015Co-Authors: S T Megeath, R A Gutermuth, J Muzerolle, E Kryukova, J L Hora, L E Allen, K M Flaherty, Lee Hartmann, Philip C MyersAbstract:We analyze the spatial distribution of dusty Young Stellar Objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities $\ge10$ pc$^{-2}$, we find that 59% of the YSOs are in the largest cluster, the Orion Nebular Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups show that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only $\sim 2$ Myr in age. We find the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the Young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or by dynamical interactions in dense, clustered regions.
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Young Stellar Objects in the massive star forming region w49
The Astrophysical Journal, 2015Co-Authors: G Saral, R A Gutermuth, J L Hora, Sarah Willis, X Koenig, A T SaygacAbstract:We present the initial results of our investigation of the star-forming complex W49, one of the Youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of Young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the Young Stellar Objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate Objects using color-color and color-magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ⩾7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I Objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.
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Young Stellar Objects in the gould belt
Astrophysical Journal Supplement Series, 2015Co-Authors: Michael M Dunham, R A Gutermuth, Lori Allen, Neal J Evans, H Broekhovenfiene, Lucas A Cieza, James Di Francesco, Paul M Harvey, J Hatchell, Amanda HeidermanAbstract:We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks" (c2d) and "Gould Belt" (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the Gould Belt. We compile extinction corrected SEDs for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0+I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background AGB stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40-0.78 Myr for Class 0+I YSOs and 0.26-0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0+I sample is classified as Class 0, leading to durations of 0.13-0.26 Myr (Class 0) and 0.27-0.52 Myr (Class I). We revisit infrared color-color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.
