The TW Hya Rosetta Stone Project. III. Resolving the Gaseous Thermal Profile of the Disk

Calahan, Jenny K.; Bergin, Edwin A.; Zhang, Ke; Cleeves, L. Ilsedore; Bergner, Jennifer B.; Blake, Geoffrey A.; Cazzoletti, P.; Guzmán, Viviana V.; Hogerheijde, M. R.; Huang, Jane; Kama, M.; Loomis, Ryan A.; Öberg, Karin I.; Qi, Charlie; Dishoeck, E. F. van; Scheltinga, Jeroen Terwisscha van; Walsh, Catherine; Wilner, David J.

doi:10.3847/1538-4357/abd255

Cited by 60 publications

(62 citation statements)

References 90 publications

(157 reference statements)

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“…We conclude that the c-C 3 H 2 appears to be reasonably well approximated by LTE. The critical density for the transitions observed is typically around 10 6 cm −3 , and our results suggest there remains a substantial amount of H 2 gas, >10 6 cm −3 , at high (z/r > 0.25) altitudes and moderately far out radii (25-110 au), consistent with disk mass estimates provided by HD for this source (Bergin et al 2013;Favre et al 2013;Cleeves et al 2015;Trapman et al 2019;Calahan et al 2021). How this relatively old disk maintains such a large amount of gas, however, is still unclear.…”

Section: The Rotational Emission Of C-c 3 H 2 Appears To Be Thermalizedsupporting

confidence: 87%

The TW Hya Rosetta Stone Project IV: A Hydrocarbon-rich Disk Atmosphere

Cleeves

Loomis

Bergin

et al. 2021

ApJ

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Connecting the composition of planet-forming disks with that of gas giant exoplanet atmospheres, in particular through C/O ratios, is one of the key goals of disk chemistry. Small hydrocarbons like C 2 H and C 3 H 2 have been identified as tracers of C/O, as they form abundantly under high C/O conditions. We present resolved c-C 3 H 2 observations from the TW Hya Rosetta Stone Project, a program designed to map the chemistry of common molecules at 15-20 au resolution in the TW Hya disk. Augmented by archival data, these observations comprise the most extensive multi-line set for disks of both ortho and para spin isomers spanning a wide range of energies, E u = 29-97 K. We find the ortho-to-para ratio of c-C 3 H 2 is consistent with 3 throughout extent of the emission, and the total abundance of both c-C 3 H 2 isomers is (7.5-10) × 10 −11 per H atom, or 1%-10% of the previously published C 2 H abundance in the same source. We find c-C 3 H 2 comes from a layer near the surface that extends no deeper than z/r = 0.25. Our observations are consistent with substantial radial variation in gas-phase C/O in TW Hya, with a sharp increase outside ∼30 au. Even if we are not directly tracing the midplane, if planets accrete from the surface via, e.g., meridional flows, then such a change should be imprinted on forming planets. Perhaps interestingly, the HR 8799 planetary system also shows an increasing gradient in its giant planets' atmospheric C/O ratios. While these stars are quite different, hydrocarbon rings in disks are common, and therefore our results are consistent with the young planets of HR 8799 still bearing the imprint of their parent disk's volatile chemistry.

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Section: The Rotational Emission Of C-c 3 H 2 Appears To Be Thermalizedsupporting

confidence: 87%

The TW Hya Rosetta Stone Project IV: A Hydrocarbon-rich Disk Atmosphere

Cleeves

Loomis

Bergin

et al. 2021

ApJ

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“…The amount of volatile depletion observed cannot be explained solely by freeze-out, photodissociation or chemical processing in the warm molecular layer (van Zadel-hoff et al 2001;Williams & Best 2014;Miotello et al 2017;Schwarz et al 2018;Bosman et al 2018;Zhang et al 2019). Detailed analysis of the TW Hya disk, using [C I], HD, CO and C 2 H emission, shows that the depletion in CO is related to elemental carbon depletion (Bergin et al 2013;Kama et al 2016b;Calahan et al 2021) and cannot be due to high dust-to-gas ratios only.…”

Section: Introductionmentioning

confidence: 98%

Tracing pebble drift and trapping using radial carbon depletion profiles in protoplanetary disks

Sturm,

McClure,

Harsono

et al. 2022

Preprint

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Context. The composition of planets may be largely determined by the chemical processing and accretion of icy pebbles in protoplanetary disks. Recent observations of protoplanetary disks hint at wide-spread depletion of gaseous carbon. The missing volatile carbon is likely frozen in CO and/or CO 2 ice on grains and locked into the disk through pebble trapping in pressure bumps or planetesimals. Aims. We aim to measure the total elemental C/H ratio in the outer region of seven disks, four of which have been previously shown to be depleted of carbon gas interior to 0.1 AU, through near-infrared spectroscopy. Methods. We present the results of the first successful ACA (Atacama Compact Array) [C I] J = 1-0 mini-survey of seven protoplanetary disks. Using tailored azimuthally symmetric DALI (Dust And LInes) thermo-chemical disk models, supported by the [C I] J = 1-0 and resolved CO isotopologue data, we determine the system-averaged elemental volatile carbon abundance in the outer disk of three sources. Results. Six out of seven sources are detected in [C I] J = 1-0 with ACA, four of which show a distinct disk component. Based on the modeling we find severe cold gaseous carbon depletion by a factor of 157 +17 −15 in the outer disk of DL Tau and moderate depletion in the outer disks of DR Tau and DO Tau, by factors of 5 +2 −1 and 17 +3 −2 , respectively. The carbon abundance is in general expected to be higher in the inner disk if carbon-rich ices drift on large grains towards the star. Combining the outer and inner disk carbon abundances, we demonstrate definitive evidence for radial drift in the disk of DL Tau, where the existence of multiple dust rings points to either short lived or leaky dust traps. We find dust locking in the compact and smooth disks of DO Tau and DR Tau, hinting at unresolved dust substructure. Comparing our results with inner/outer disk carbon depletion around stars of different ages and luminosities, we identify an observational evolutionary trend in gaseous carbon depletion that is consistent with dynamical models of CO depletion processes. Conclusions. Transport efficiency of solids in protoplanetary disks can significantly differ from what we expect based on the current resolved substructure in the continuum observations. This has important implications for our understanding of the impact of radial drift and pebble accretion on planetary compositions.

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“…The gas and dust density structures used in this work fit the observations, but they are not unique in doing so (see, e.g. Calahan et al 2021). The assumed disk structure could thus affect our results.…”

Section: Caveatsmentioning

confidence: 69%

“…As HD predominantly emits from warm gas, it should be noted that the accuracy of HD as a gas mass tracer depends on how well the temperature structure of the disk is known (see e.g. Trapman et al 2017;Calahan et al 2021). If the disks are significantly warmer than our models we would overestimate their gas mass.…”

Section: Resultsmentioning

confidence: 92%

“…When compared to gas masses derived independently from HD, the CO-based gas masses are found to be 5 − 100 × lower, even after including the effects of photo-dissociation and freeze-out (see, e.g. Favre et al 2013;Schwarz et al 2016;Kama et al 2016;Mc-Clure et al 2016;Trapman et al 2017;Calahan et al 2021). This could imply that the low CO-based gas masses found in disk surveys carried out with the Atacama Large Millimiter/submillimeter Array (ALMA) are severely underestimating the gas masses of protoplanetary disks (see, e.g.…”

Section: Introductionmentioning

confidence: 99%

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A novel way of measuring the gas disk mass of protoplanetary disks using N2H+ and C18O

Trapman,

Zhang,

Hoff

et al. 2022

Preprint

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Measuring the gas mass of protoplanetary disks, the reservoir available for giant planet formation, has proven to be difficult. We currently lack a far-infrared observatory capable of observing HD, and the most common gas mass tracer, CO, suffers from a poorly constrained CO-to-H 2 ratio. Expanding on previous work, we investigate if N 2 H + , a chemical tracer of CO poor gas, can be used to observationally measure the CO-to-H 2 ratio and correct CO-based gas masses. Using disk structures obtained from the literature, we set up thermochemical models for three disks, TW Hya, DM Tau and GM Aur, to examine how well the CO-to-H 2 ratio and gas mass can be measured from N 2 H + and C 18 O line fluxes. Furthermore, we compare these gas masses to independently gas masses measured from archival HD observations. The N 2 H + (3-2)/C 18 O (2-1) line ratio scales with the disk CO-to-H 2 ratio. Using these two lines, we measure 4.6 × 10 −3 M ≤ M disk ≤ 1.1 × 10 −1 M for TW Hya, 1.5 × 10 −2 M ≤ M disk ≤ 9.6 × 10 −2 M for GM Aur and 3.1 × 10 −2 M ≤ M disk ≤ 9.6 × 10 −2 M for DM Tau. These gas masses agree with values obtained from HD within their respective uncertainties. The uncertainty on the N 2 H + + C 18 O gas mass can be reduced by observationally constraining the cosmic ray ionization rate in disks. These results demonstrate the potential of using the combination of N 2 H + and C 18 O to measure gas masses of protoplanetary disks.

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The TW Hya Rosetta Stone Project. III. Resolving the Gaseous Thermal Profile of the Disk

Cited by 60 publications

References 90 publications

The TW Hya Rosetta Stone Project IV: A Hydrocarbon-rich Disk Atmosphere

The TW Hya Rosetta Stone Project IV: A Hydrocarbon-rich Disk Atmosphere

Tracing pebble drift and trapping using radial carbon depletion profiles in protoplanetary disks

A novel way of measuring the gas disk mass of protoplanetary disks using N2H+ and C18O

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