The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Karin I Oberg - One of the best experts on this subject based on the ideXlab platform.
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constraining gas phase carbon oxygen and nitrogen in the im lup Protoplanetary Disk
The Astrophysical Journal, 2018Co-Authors: Ryan A Loomis, Karin I Oberg, Sean M. Andrews, David J. Wilner, Jane Huang, Ilsedore L Cleeves, Viviana V GuzmanAbstract:We present new constraints on gas-phase C, N, and O abundances in the molecular layer of the IM Lup Protoplanetary Disk. Building on previous physical and chemical modeling of this Disk, we use new ALMA observations of C$_2$H to constrain the C/O ratio in the molecular layer to be $\sim0.8$, i.e., higher than the solar value of $\sim0.54$. We use archival ALMA observations of HCN and H$^{13}$CN to show that no depletion of N is required (assuming an interstellar abundance of $7.5\times10^{-5}$ per H). These results suggest that an appreciable fraction of O is sequestered in water ice in large grains settled to the Disk mid-plane. Similarly, a fraction of the available C is locked up in less volatile molecules. By contrast, N remains largely unprocessed, likely as N$_2$. This pattern of depletion suggests the presence of true abundance variations in this Disk, and not a simple overall depletion of gas mass. If these results hold more generally, then combined CO, C$_2$H, and HCN observations of Disks may provide a promising path for constraining gas-phase C/O and N/O during planet-formation. Together, these tracers offer the opportunity to link the volatile compositions of Disks to the atmospheres of planets formed from them.
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h2co ortho to para ratio in the Protoplanetary Disk hd 163296
The Astrophysical Journal, 2018Co-Authors: Viviana V Guzman, Karin I Oberg, John M Carpenter, Le R Gal, J PaguesAbstract:Ortho-to-para (o/p) ratios of species like water, ammonia, and formaldehyde () are believed to encode information about the formation history of the molecule. Measurements of o/p ratios in Protoplanetary Disks could thus be used to constrain their physical and chemical histories. We present the first measurement of the o/p ratio in a Protoplanetary Disk, using three ortho and two para lines observed with the Submillimeter Array (SMA) combined with one highly resolved measurement of a single line with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Disk around Herbig Ae star HD 163296. We find a Disk-averaged o/p ratio of 1.8–2.8 (depending on the assumed Disk structure), corresponding to a spin temperature of 11–22 K. We also derive a rotational temperature of 24 K from the flux ratio of the three ortho lines. The observed spatial distribution, as seen by ALMA, as well as the rotational temperature and the o/p ratio, at the large scales the SMA is most sensitive to, are consistent with a low-temperature formation pathway, most likely grain surface chemistry, of in this Disk.
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h2co ortho to para ratio in the Protoplanetary Disk hd 163296
arXiv: Astrophysics of Galaxies, 2018Co-Authors: Viviana V Guzman, Karin I Oberg, John M Carpenter, Le R Gal, J PaguesAbstract:Ortho-to-para (o/p) ratios of species like water, ammonia and formaldehyde (H2CO) are believed to encode information about the formation history of the molecule. Measurements of o/p ratios in Protoplanetary Disks could thus be used to constrain their physical and chemical histories. We present the first measurement of the H2CO o/p ratio in a Protoplanetary Disk, using three ortho and two para lines observed with the Sub-millimeter Array (SMA) combined with one highly resolved measurement of a single H2CO line with ALMA toward the Disk around Herbig Ae star HD 163296. We find a Disk-averaged H2CO o/p ratio of 1.8-2.8 (depending on the assumed Disk structure), corresponding to a spin temperature of 11-22 K. We also derive a rotational temperature of 24 K from the flux ratio of the three ortho lines. The observed spatial distribution, as seen by ALMA, as well as the rotational temperature and the o/p ratio, at the large scales the SMA is most sensitive to, are consistent with a low-temperature formation pathway, most likely grain surface chemistry, of H2CO in this Disk.
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a subarcsecond alma molecular line imaging survey of the circumbinary Protoplanetary Disk orbiting v4046 sgr
The Astrophysical Journal, 2018Co-Authors: Joel H Kastner, Sean M. Andrews, D A Dicksonvandervelde, P Hilyblant, T Forveille, Uma Gorti, Karin I ObergAbstract:We present a suite of ALMA interferometric molecular line and continuum images that elucidate, on linear size scales of $\sim$30--40 AU, the chemical structure of the nearby, evolved, Protoplanetary Disk orbiting the close binary system V4046 Sgr. The observations were undertaken in the 1.1--1.4 mm wavelength range (ALMA Bands 6 and 7) with antenna configurations involving maximum baselines of several hundred meters, yielding subarcsecond-resolution images in more than a dozen molecular species and isotopologues. Isotopologues of CO and HCN display centrally peaked morphologies of integrated emission line intensity, whereas the line emission from complex nitrile group molecules (HC$_3$N, CH$_3$CN), deuterated molecules (DCN, DCO$^+$), hydrocarbons (as traced by C$_2$H), and potential CO ice line tracers (N$_2$H$^+$, and H$_2$CO) appears as a sequence of sharp and diffuse rings. The dimensions and morphologies of HC$_3$N and CH$_3$CN emission are suggestive of photodesorption of organic ices from the surfaces of dust grains, while the sequence of increasing radius of peak intensity represented by DCN (smallest), DCO$^+$, N$_2$H$^+$, and H$_2$CO (largest) is qualitatively consistent with the expected decline of midplane gas temperature with increasing Disk radius. Empirical modeling indicates that the sharp-edged C$_2$H emission ring lies at relatively deep Disk layers, leaving open the question of the origin of C$_2$H abundance enhancements in evolved Disks. This study of the "molecular anatomy" of V4046 Sgr should serve as motivation for additional subarcsecond ALMA molecular line imaging surveys of nearby, evolved Protoplanetary Disks aimed at addressing major uncertainties in Protoplanetary Disk physical and chemical structure and molecular production pathways.
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the coupled physical structure of gas and dust in the im lup Protoplanetary Disk
The Astrophysical Journal, 2016Co-Authors: Ilsedore L Cleeves, Ryan A Loomis, Karin I Oberg, Sean M. Andrews, David J. Wilner, Jane Huang, Ian CzekalaAbstract:The spatial distribution of gas and solids in Protoplanetary Disks determines the composition and formation efficiency of planetary systems. A number of Disks show starkly different distributions for the gas and small grains compared to millimeter-centimeter sized dust. We present new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of the dust continuum, CO, $^{13}$CO, and C$^{18}$O in the IM Lup Protoplanetary Disk, one of the first systems where this dust-gas dichotomy was clearly seen. The $^{12}$CO is detected out to a radius of 970 AU, while the millimeter continuum emission is truncated at just 313 AU. Based upon this data, we have built a comprehensive physical and chemical model for the Disk structure, which takes into account the complex, coupled nature of the gas and dust and the interplay between the local and external environment. We constrain the distributions of gas and dust, the gas temperatures, the CO abundances, the CO optical depths, and the incident external radiation field. We find that the reduction/removal of dust from the outer Disk exposes this region to higher stellar and external radiation and decreases the rate of freeze-out, allowing CO to remain in the gas out to large radial distances. We estimate a gas-phase CO abundance of $5\%$ of the ISM value and a low external radiation field ($G_0\lesssim4$). The latter is consistent with that expected from the local stellar population. We additionally find tentative evidence for ring-like continuum substructure, suggestions of isotope-selective photodissociation, and a diffuse gas halo.
E Chapillon - One of the best experts on this subject based on the ideXlab platform.
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first detection of the simplest organic acid in a Protoplanetary Disk
The Astrophysical Journal, 2018Co-Authors: C Favre, D Fedele, Dmitry Semenov, Sergey Parfenov, Claudio Codella, C Ceccarelli, Edwin A Bergin, E ChapillonAbstract:The formation of asteroids, comets, and planets occurs in the interior of Protoplanetary Disks during the early phase of star formation. Consequently, the chemical composition of the Disk might shape the properties of the emerging planetary system. In this context, it is crucial to understand whether and what organic molecules are synthesized in the Disk. In this Letter, we report the first detection of formic acid (HCOOH) toward the TW Hydrae Protoplanetary Disk. The observations of the trans-HCOOH 6_((1,6)–5(1,5)) transition were carried out at 129 GHz with Atacama Large Millimeter/Submillimeter Array (ALMA). We measured a Disk-averaged gas-phase t-HCOOH column density of ~(2–4) × 10^(12) cm^(−2), namely as large as that of methanol. HCOOH is the first organic molecule containing two oxygen atoms detected in a Protoplanetary Disk, a proof that organic chemistry is very active, albeit difficult to observe, in these objects. Specifically, this simplest acid stands as the basis for synthesis of more complex carboxylic acids used by life on Earth.
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first detection of the simplest organic acid in a Protoplanetary Disk
arXiv: Solar and Stellar Astrophysics, 2018Co-Authors: C Favre, D Fedele, Dmitry Semenov, Sergey Parfenov, Claudio Codella, C Ceccarelli, Edwin A Bergin, E ChapillonAbstract:The formation of asteroids, comets and planets occurs in the interior of Protoplanetary Disks during the early phase of star formation. Consequently, the chemical composition of the Disk might shape the properties of the emerging planetary system. In this context, it is crucial to understand whether and what organic molecules are synthesized in the Disk. In this Letter, we report the first detection of formic acid (HCOOH) towards the TW Hydrae Protoplanetary Disk. The observations of the trans-HCOOH 6$_{(1,6)-5(1,5)}$ transition were carried out at 129~GHz with ALMA. We measured a Disk-averaged gas-phase t-HCOOH column density of $\sim$ (2-4)$\times$10$^{12}$~cm$^{-2}$, namely as large as that of methanol. HCOOH is the first organic molecules containing two oxygen atoms detected in a Protoplanetary Disk, a proof that organic chemistry is very active even though difficult to observe in these objects. Specifically, this simplest acid stands as the basis for synthesis of more complex carboxylic acids used by life on Earth.
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chemistry in Disks xi sulfur bearing species as tracers of Protoplanetary Disk physics and chemistry the dm tau case
Astronomy and Astrophysics, 2018Co-Authors: D Semenov, C Favre, D Fedele, E Chapillon, Th Henning, S. Guilloteau, R. Teague, Anne Dutrey, F. Hersant, V. PietuAbstract:Context. Several sulfur-bearing molecules are observed in the interstellar medium and in comets, in strong contrast to Protoplanetary Disks where only CS, H2CS, and SO have been detected so far. Aims. We combine observations and chemical models to constrain the sulfur abundances and their sensitivity to physical and chemical conditions in the DM Tau Protoplanetary Disk. Methods. We obtained 0.5'' Atacama Large Millimeter Array observations of DM Tau in Bands 4 and 6 in lines of CS, SO, SO2, OCS, CCS, H2CS, and H2S, achieving a similar to 5 mJy sensitivity. Using the non-Local Thermodynamical Equilibrium radiative transfer code RADEX and the forward-modeling tool DiskFit, Disk-averaged CS column densities and upper limits for the other species were derived. Results. Only CS was detected with a derived column density of similar to 2-6 x 10(12) cm(-2). We report a first tentative detection of SO2 in DM Tau. The upper limits range between similar to 10(11) and 10(14) cm(2) for the other S-bearing species. The best-fit chemical model matching these values requires a gas-phase C/O ratio of greater than or similar to 1 at r greater than or similar to 50-100 au. With chemical modeling we demonstrate that sulfur-bearing species could be robust tracers of the gas-phase C/O ratio, surface reaction rates, grain size and UV intensities. Conclusions. The lack of detections of a variety of sulfur-bearing molecules in DM Tau other than CS implies a dearth of reactive sulfur in the gas phase, either through efficient freeze-out or because most of the elemental sulfur is in other large species, as found in comets. The inferred high CS/SO and CS/SO2 ratios require a non-solar C/O gas-phase ratio of greater than or similar to 1, consistent with the recent observations of hydrocarbon rings in DM Tau. The stronger depletion of oxygen-bearing S-species compared to CS is likely linked to the low observed abundances of gaseous water in DM Tau and points to a removal mechanism of oxygen from the gas.
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Chemistry in Disks. XI. Sulfur-bearing species as tracers of Protoplanetary Disk physics and chemistry: the DM Tau case
Astronomy and Astrophysics - A&A, 2018Co-Authors: D Semenov, C Favre, D Fedele, E Chapillon, Th Henning, S. Guilloteau, R. Teague, Anne Dutrey, F. Hersant, V. PietuAbstract:Context. Several sulfur-bearing molecules are observed in the interstellar medium and in comets, in strong contrast to Protoplanetary Disks where only CS, H$_2$CS and SO have been detected so far. Aims. We combine observations and chemical models to constrain the sulfur abundances and their sensitivity to physical and chemical conditions in the DM Tau Protoplanetary Disk. Methods. We obtained $0.5^{''}$ ALMA observations of DM Tau in Bands 4 and 6 in lines of CS, SO, SO$_2$, OCS, CCS, H$_2$CS and H$_2$S, achieving a $\sim 5$ mJy sensitivity. Using the non-LTE radiative transfer code RADEX and the forward-modeling tool DiskFit, Disk-averaged CS column densities and upper limits for the other species were derived. Results. Only CS was detected with a derived column density of $\sim 2-6 \times 10^{12}$ cm$^{-2}$. We report a first tentative detection of SO$_2$ in DM Tau. The upper limits range between $\sim 10^{11}$ and $10^{14}$ cm$^{-2}$ for the other S-bearing species. The best-fit chemical model matching these values requires a gas-phase C/O ratio of > 1 at $r \sim 50-100$ au. With chemical modeling we demonstrate that sulfur-bearing species could be robust tracers of the gas-phase C/O ratio, surface reaction rates, grain size and UV intensities. Conclusions. The lack of detections of a variety of sulfur-bearing molecules in DM Tau other than CS implies a dearth of reactive sulfur in the gas phase, either through efficient freeze-out or because most of the elemental sulfur is in other large species, as found in comets. The inferred high CS/SO and CS/SO$_2$ ratios require a non-solar C/O gas-phase ratio of > 1, consistent with the recent observations of hydrocarbon rings in DM Tau. The stronger depletion of oxygen-bearing S-species compared to CS is likely linked to the low observed abundances of gaseous water in DM Tau and points to a removal mechanism of oxygen from the gas.
Daiki Ishimoto - One of the best experts on this subject based on the ideXlab platform.
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a gap with a deficit of large grains in the Protoplanetary Disk around tw hya
The Astrophysical Journal, 2016Co-Authors: Takashi Tsukagoshi, Satoshi Okuzumi, Takayuki Muto, Kazuhiro D. Kanagawa, Hideko Nomura, Ryohei Kawabe, Daiki Ishimoto, Shigeru IdaAbstract:We report ∼3 au resolution imaging observations of the Protoplanetary Disk around TW Hya at 145 and 233 GHz with the Atacama Large Millimeter/submillimeter Array. Our observations revealed two deep gaps (∼25%-50%) at 22 and 37 au and shallower gaps (a few percent) at 6, 28, and 44 au, as recently reported by Andrews et al. The central hole with a radius of ∼3 au was also marginally resolved. The most remarkable finding is that the spectral index α(R) between bands 4 and 6 peaks at the 22 au gap. The derived power-law index of the dust opacity β(R) is ∼1.7 at the 22 au gap and decreases toward the Disk center to ∼0. The most prominent gap at 22 au could be caused by the gravitational interaction between the Disk and an unseen planet with a mass of ≲1.5 M Neptune, although other origins may be possible. The planet-induced gap is supported by the fact that β(R) is enhanced at the 22 au gap, indicating a deficit of ∼millimeter-sized grains within the gap due to dust filtration by a planet.
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a gap with a deficit of large grains in the Protoplanetary Disk around tw hya
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: Takashi Tsukagoshi, Satoshi Okuzumi, Takayuki Muto, Kazuhiro D. Kanagawa, Hideko Nomura, Ryohei Kawabe, Daiki Ishimoto, Shigeru IdaAbstract:We report $\sim$3 au resolution imaging observations of the Protoplanetary Disk around TW Hya at 145 and 233 GHz with the Atacama Large Millimeter/Submillimeter Array. Our observations revealed two deep gaps ($\sim$25--50 \%) at 22 and 37~au and shallower gaps (a few \%) at 6, 28, and 44~au, as recently reported by Andrews et al. (2016). The central hole with a radius of $\sim3$~au was also marginally resolved. The most remarkable finding is that the spectral index $\alpha (R)$ between bands 4 and 6 peaks at the 22~au gap. The derived power-law index of the dust opacity $\beta (R)$ is $\sim1.7$ at the 22~au gap and decreases toward the Disk center to $\sim0$. The most prominent gap at 22~au could be caused by the gravitational interaction between the Disk and an unseen planet with a mass of $\lesssim$1.5 $M_\mathrm{Neptune}$ although other origins may be possible. The planet-induced gap is supported by the fact that $\beta (R)$ is enhanced at the 22~au gap, indicating a deficit of $\sim$mm-sized grains within the gap due to dust filtration by a planet.
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alma observations of a gap and a ring in the Protoplanetary Disk around tw hya
The Astrophysical Journal, 2016Co-Authors: Hideko Nomura, Satoshi Okuzumi, Takayuki Muto, Kazuhiro D. Kanagawa, Takashi Tsukagoshi, Ryohei Kawabe, Daiki Ishimoto, Shigeru Ida, Catherine WalshAbstract:We report the first detection of a gap and a ring in 336 GHz dust continuum emission from the Protoplanetary Disk around TW Hya, using the Atacama Large Millimeter/Submillimeter Array (ALMA). The gap and ring are located at around 25 and 41 au from the central star, respectively, and are associated with the CO snow line at ∼30 au. The gap has a radial width of less than 15 au and a mass deficit of more than 23%, taking into account that the observations are limited to an angular resolution of ∼15 au. In addition, the 13 CO and C 18 O J 3 2 =- lines show a decrement in CO line emission throughout the Disk, down to ∼10 au, indicating a freeze-out of gas-phase CO onto grain surfaces and possible subsequent surface reactions to form larger molecules. The observed gap could be caused by gravitational interaction between the Disk gas and a planet with a mass less than super-Neptune (2MNeptune), or could be the result of the destruction of large dust aggregates due to the sintering of CO ice.
Hideko Nomura - One of the best experts on this subject based on the ideXlab platform.
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modeling nitrogen fractionation in the Protoplanetary Disk around tw hya model constraints on grain population and carbon to oxygen elemental abundance ratio
The Astrophysical Journal, 2021Co-Authors: Seokho Lee, Hideko Nomura, Kenji Furuya, Jeongeun LeeAbstract:Observations conducted using the Atacama Large Millimeter/submillimeter Array on the Protoplanetary Disk around TW Hya show the nitrogen fractionation of HCN molecules in HC$^{14}$N/HC$^{15}$N $\sim$120 at a radius of $\sim$20 AU. In this study, we investigated the physical and chemical conditions that control this nitrogen fractionation process. To this end, a new Disk model was developed, in which the isotope-selective photodissociation of N$_2$ and isotope-exchange chemical reactions have been incorporated. Our model can successfully reproduce the observed HCN column density when the elemental abundances of the gas-phase carbon and oxygen are depleted by two orders of magnitude relative to those in the interstellar medium and carbon is more abundant than oxygen ([C/O]$_{\rm elem}>$ 1). The isotope-selective photodissociation of N$_2$ is the dominant nitrogen fractionation process in our models. The observed HC$^{14}$N/HC$^{15}$N ratio, which increases outwards, can also be reproduced by the model by assuming that the small dust grains in the atmosphere of the outer Disk are depleted more than those in the inner Disk. This is consistent with grain evolution models, according to which small dust grains are continuously replenished in the inner Disk due to fragmentation of the large dust grains that radially drift from the outer Disk.
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the first detection of 13c17o in a Protoplanetary Disk a robust tracer of Disk gas mass
The Astrophysical Journal, 2019Co-Authors: Alice S Booth, Hideko Nomura, Catherine Walsh, J D Ilee, Shota Notsu, Eiji AkiyamaAbstract:Measurements of the gas mass are necessary to determine the planet formation potential of Protoplanetary Disks. Observations of rare CO isotopologues are typically used to determine Disk gas masses; however, if the line emission is optically thick this will result in an underestimated Disk mass. With the Atacama Large Millimeter/submillimeter Array we have detected the rarest stable CO isotopologue, , in a Protoplanetary Disk for the first time. We compare our observations with the existing detections of , , , and in the HD 163296 Disk. Radiative transfer modeling using a previously benchmarked model, and assuming interstellar isotopic abundances, significantly underestimates the integrated intensity of the J = 3–2 line. Reconciliation between the observations and the model requires a global increase in CO gas mass by a factor of 3.5. This is a factor of 2–6 larger than previous gas mass estimates using . We find that emission is optically thick within the snow line, while the emission is optically thin and is thus a robust tracer of the bulk Disk CO gas mass.
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the first detection of 13c 17o in a Protoplanetary Disk a robust tracer of Disk gas mass
The Astrophysical Journal, 2019Co-Authors: Hideko Nomura, Catherine Walsh, Alice S Booth, J D Ilee, Shota Notsu, Eiji AkiyamaAbstract:Measurements of the gas mass are necessary to determine the planet formation potential of Protoplanetary Disks. Observations of rare CO isotopologues are typically used to determine Disk gas masses; however, if the line emission is optically thick this will result in an underestimated Disk mass. With the Atacama Large Millimeter/submillimeter Array we have detected the rarest stable CO isotopologue, , in a Protoplanetary Disk for the first time. We compare our observations with the existing detections of , , , and in the HD 163296 Disk. Radiative transfer modeling using a previously benchmarked model, and assuming interstellar isotopic abundances, significantly underestimates the integrated intensity of the J = 3–2 line. Reconciliation between the observations and the model requires a global increase in CO gas mass by a factor of 3.5. This is a factor of 2–6 larger than previous gas mass estimates using . We find that emission is optically thick within the snow line, while the emission is optically thin and is thus a robust tracer of the bulk Disk CO gas mass.
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the first detection of 13c17o in a Protoplanetary Disk a robust tracer of Disk gas mass
arXiv: Earth and Planetary Astrophysics, 2019Co-Authors: Hideko Nomura, Catherine Walsh, Alice S Booth, J D Ilee, Shota Notsu, Eiji AkiyamaAbstract:Measurements of the gas mass are necessary to determine the planet formation potential of Protoplanetary Disks. Observations of rare CO isotopologues are typically used to determine Disk gas masses; however, if the line emission is optically thick this will result in an underestimated Disk mass. With ALMA we have detected the rarest stable CO isotopologue, 13C17O, in a Protoplanetary Disk for the first time. We compare our observations with the existing detections of 12CO, 13CO, C18O and C17O in the HD163296 Disk. Radiative transfer modelling using a previously benchmarked model, and assuming interstellar isotopic abundances, significantly underestimates the integrated intensity of the 13C17O J=3-2 line. Reconciliation between the observations and the model requires a global increase in CO gas mass by a factor of 3.5. This is a factor of 2-6 larger than previous gas mass estimates using C18O. We find that C18O emission is optically thick within the CO snow line, while the 13C17O emission is optically thin and is thus a robust tracer of the bulk Disk CO gas mass.
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a gap with a deficit of large grains in the Protoplanetary Disk around tw hya
The Astrophysical Journal, 2016Co-Authors: Takashi Tsukagoshi, Satoshi Okuzumi, Takayuki Muto, Kazuhiro D. Kanagawa, Hideko Nomura, Ryohei Kawabe, Daiki Ishimoto, Shigeru IdaAbstract:We report ∼3 au resolution imaging observations of the Protoplanetary Disk around TW Hya at 145 and 233 GHz with the Atacama Large Millimeter/submillimeter Array. Our observations revealed two deep gaps (∼25%-50%) at 22 and 37 au and shallower gaps (a few percent) at 6, 28, and 44 au, as recently reported by Andrews et al. The central hole with a radius of ∼3 au was also marginally resolved. The most remarkable finding is that the spectral index α(R) between bands 4 and 6 peaks at the 22 au gap. The derived power-law index of the dust opacity β(R) is ∼1.7 at the 22 au gap and decreases toward the Disk center to ∼0. The most prominent gap at 22 au could be caused by the gravitational interaction between the Disk and an unseen planet with a mass of ≲1.5 M Neptune, although other origins may be possible. The planet-induced gap is supported by the fact that β(R) is enhanced at the 22 au gap, indicating a deficit of ∼millimeter-sized grains within the gap due to dust filtration by a planet.
Catherine Walsh - One of the best experts on this subject based on the ideXlab platform.
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the first detection of 13c17o in a Protoplanetary Disk a robust tracer of Disk gas mass
The Astrophysical Journal, 2019Co-Authors: Alice S Booth, Hideko Nomura, Catherine Walsh, J D Ilee, Shota Notsu, Eiji AkiyamaAbstract:Measurements of the gas mass are necessary to determine the planet formation potential of Protoplanetary Disks. Observations of rare CO isotopologues are typically used to determine Disk gas masses; however, if the line emission is optically thick this will result in an underestimated Disk mass. With the Atacama Large Millimeter/submillimeter Array we have detected the rarest stable CO isotopologue, , in a Protoplanetary Disk for the first time. We compare our observations with the existing detections of , , , and in the HD 163296 Disk. Radiative transfer modeling using a previously benchmarked model, and assuming interstellar isotopic abundances, significantly underestimates the integrated intensity of the J = 3–2 line. Reconciliation between the observations and the model requires a global increase in CO gas mass by a factor of 3.5. This is a factor of 2–6 larger than previous gas mass estimates using . We find that emission is optically thick within the snow line, while the emission is optically thin and is thus a robust tracer of the bulk Disk CO gas mass.
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the first detection of 13c 17o in a Protoplanetary Disk a robust tracer of Disk gas mass
The Astrophysical Journal, 2019Co-Authors: Hideko Nomura, Catherine Walsh, Alice S Booth, J D Ilee, Shota Notsu, Eiji AkiyamaAbstract:Measurements of the gas mass are necessary to determine the planet formation potential of Protoplanetary Disks. Observations of rare CO isotopologues are typically used to determine Disk gas masses; however, if the line emission is optically thick this will result in an underestimated Disk mass. With the Atacama Large Millimeter/submillimeter Array we have detected the rarest stable CO isotopologue, , in a Protoplanetary Disk for the first time. We compare our observations with the existing detections of , , , and in the HD 163296 Disk. Radiative transfer modeling using a previously benchmarked model, and assuming interstellar isotopic abundances, significantly underestimates the integrated intensity of the J = 3–2 line. Reconciliation between the observations and the model requires a global increase in CO gas mass by a factor of 3.5. This is a factor of 2–6 larger than previous gas mass estimates using . We find that emission is optically thick within the snow line, while the emission is optically thin and is thus a robust tracer of the bulk Disk CO gas mass.
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cometary compositions compared with Protoplanetary Disk midplane chemical evolution an emerging chemical evolution taxonomy for comets
Astronomy and Astrophysics, 2019Co-Authors: Christian Eistrup, Catherine Walsh, Ewine F Van DishoeckAbstract:[Abridged] With a growing number of molecules observed in many comets, and an improved understanding of chemical evolution in Protoplanetary Disk midplanes, comparisons can be made between models and observations that could potentially constrain the formation histories of comets. A $\chi^{2}$-method was used to determine maximum likelihood surfaces for 14 different comets that formed at a given time (up to 8 Myr) and place (out to beyond the CO iceline) in the pre-solar nebula midplane. This was done using observed volatile abundances for the 14 comets and the evolution of volatile abundances from chemical modelling of Disk midplanes. Considering all parent species (ten molecules) in a scenario that assumed reset initial chemistry, the $\chi^{2}$ likelihood surfaces show a characteristic trail in the parameter space with high likelihood of formation around 30 AU at early times and 12 AU at later times for ten comets. This trail roughly traces the vicinity of the CO iceline in time. The formation histories for all comets were thereby constrained to the vicinity of the CO iceline, assuming that the chemistry was partially reset early in the pre-solar nebula. This is found, both when considering carbon-, oxygen-, and sulphur-bearing molecules (ten in total), and when only considering carbon- and oxygen-bearing molecules (seven in total). Since these 14 comets did not previously fall into the same taxonomical categories together, this chemical constraint may be proposed as an alternative taxonomy for comets. Based on the most likely time for each of these comets to have formed during the Disk chemical evolution, a formation time classification for the 14 comets is suggested.
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the first detection of 13c17o in a Protoplanetary Disk a robust tracer of Disk gas mass
arXiv: Earth and Planetary Astrophysics, 2019Co-Authors: Hideko Nomura, Catherine Walsh, Alice S Booth, J D Ilee, Shota Notsu, Eiji AkiyamaAbstract:Measurements of the gas mass are necessary to determine the planet formation potential of Protoplanetary Disks. Observations of rare CO isotopologues are typically used to determine Disk gas masses; however, if the line emission is optically thick this will result in an underestimated Disk mass. With ALMA we have detected the rarest stable CO isotopologue, 13C17O, in a Protoplanetary Disk for the first time. We compare our observations with the existing detections of 12CO, 13CO, C18O and C17O in the HD163296 Disk. Radiative transfer modelling using a previously benchmarked model, and assuming interstellar isotopic abundances, significantly underestimates the integrated intensity of the 13C17O J=3-2 line. Reconciliation between the observations and the model requires a global increase in CO gas mass by a factor of 3.5. This is a factor of 2-6 larger than previous gas mass estimates using C18O. We find that C18O emission is optically thick within the CO snow line, while the 13C17O emission is optically thin and is thus a robust tracer of the bulk Disk CO gas mass.
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co emission tracing a warp or radial flow within 100 au in the hd 100546 Protoplanetary Disk
Astronomy and Astrophysics, 2017Co-Authors: Catherine Walsh, Cail Daley, Stefano Facchini, A JuhaszAbstract:We present spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) images of 12 CO J = 3−2 emission from the Protoplanetary Disk around the Herbig Ae star, HD 100546. We expand upon earlier analyses of this data and model the spatially-resolved kinematic structure of the CO emission. Assuming a velocity profile which prescribes a flat or flared emitting surface in Keplerian rotation, we uncover significant residuals with a peak of ≈7 δv , where δv = 0.21 km s -1 is the width of a single spectral resolution element. The shape and extent of the residuals reveal the possible presence of a severely warped and twisted inner Disk extending to at most 100 au. Adapting the model to include a misaligned inner gas Disk with (i) an inclination almost edge-on to the line of sight, and (ii) a position angle almost orthogonal to that of the outer Disk reduces the residuals to δv . However, these findings are contrasted by recent VLT/SPHERE, MagAO/GPI, and VLTI/PIONIER observations of HD 100546 that show no evidence of a severely misaligned inner dust Disk down to spatial scales of ~ 1 au. An alternative explanation for the observed kinematics are fast radial flows mediated by (proto)planets. Inclusion of a radial velocity component at close to free-fall speeds and inwards of ≈50 au results in residuals of ≈4 δv . Hence, the model including a radial velocity component only does not reproduce the data as well as that including a twisted and misaligned inner gas Disk. Molecular emission data at a higher spatial resolution (of order 10 au) are required to further constrain the kinematics within ≲100 au. HD 100546 joins several other Protoplanetary Disks for which high spectral resolution molecular emission shows that the gas velocity structure cannot be described by a purely Keplerian velocity profile with a universal inclination and position angle. Regardless of the process, the most likely cause is the presence of an unseen planetary companion.
