An Evolutionary Study of Volatile Chemistry in Protoplanetary Disks

Bergner, Jennifer B.; Öberg, Karin I.; Bergin, Edwin A.; Andrews, Sean M.; Blake, Geoffrey A.; Carpenter, John M.; Cleeves, L. Ilsedore; Guzmán, Viviana V.; Huang, Jane; Jørgensen, J. K.; Qi, Chunhua; Schwarz, Kamber R.; Williams, Jonathan P.; Wilner, David J.

doi:10.3847/1538-4357/ab9e71

Cited by 53 publications

(69 citation statements)

References 116 publications

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“…The derived C 17 O abundances are thus within a factor of 5 of the ISM abundance, suggesting that no substantial processing has happened, as observed for Class II disks where the CO abundance can be 2 orders of magnitude below the ISM value (e.g., Favre et al 2013). These results are consistent with the results from Zhang et al (2020) for three Class I disks in Taurus (including TMC1A) but not with the order-of-magnitude depletion found by Bergner et al (2020) for two Class I disks in Serpens. For H 2 CO, the abundance ranges between ∼3×10 −10 and ∼8×10 −9 in the different sources, except for TMC1A, where the abundance is ∼5×10 −11 , probably due to the absence of emission in the inner region.…”

Section: O and H 2 Co Column Densities And Abundancessupporting

confidence: 87%

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Temperature Structures of Embedded Disks: Young Disks in Taurus Are Warm

Hoff

Harsono

Tobin

et al. 2020

ApJ

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The chemical composition of gas and ice in disks around young stars sets the bulk composition of planets. In contrast to protoplanetary disks (Class II), young disks that are still embedded in their natal envelope (Class 0 and I) are predicted to be too warm for CO to freeze out, as has been confirmed observationally for L1527 IRS. To establish whether young disks are generally warmer than their more evolved counterparts, we observed five young (Class 0/I and I) disks in Taurus with the Atacama Large Millimeter/submillimeter Array, targeting2,1 , and CH 3 OH 5 K −4 K transitions at 0 48×0 31 resolution. The different freeze-out temperatures of these species allow us to derive a global temperature structure. C 17 O and H 2 CO are detected in all disks, with no signs of CO freeze-out in the inner ∼100 au and a CO abundance close to ∼10 −4 . The H 2 CO emission originates in the surface layers of the two edge-on disks, as witnessed by the especially beautiful V-shaped emission pattern in IRAS04302+2247. HDO and CH 3 OH are not detected, with column density upper limits more than 100 times lower than for hot cores. Young disks are thus found to be warmer than more evolved protoplanetary disks around solar analogs, with no CO freeze-out (or only in the outermost part of 100 au disks) or processing. However, they are not as warm as hot cores or disks around outbursting sources and therefore do not have a large gas-phase reservoir of complex molecules.

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Section: O and H 2 Co Column Densities And Abundancessupporting

confidence: 87%

“…Since the 2-3 Myr old disks in Lupus and Cha I show CO depletion by a factor of 10-100 (Ansdell et al 2016), these results suggest that the CO abundance decreases by a factor of 10 within 1 Myr. On the other hand, Bergner et al (2020) found C 18 O abundances a factor of 10 below the ISM value in two Class I sources in Serpens.…”

Section: Introductionmentioning

confidence: 83%

Temperature Structures of Embedded Disks: Young Disks in Taurus Are Warm

Hoff

Harsono

Tobin

et al. 2020

ApJ

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“…9 summarizes our results of the carbon abundance in the outer disk compared to the inner disk. We added TW Hya (Zhang et al 2019;Kama et al 2016b;McClure et al 2020), HD 163296 (Kama et al 2015Zhang et al 2019) and HD 100546 (Kama et al 2015(Kama et al , 2016b) and a combined point for ten Class 0/I sources (Harsono et al 2014;Zhang et al 2020b;Bergner et al 2020) to the figure for reference. These three sources are the only other sources for which the carbon abundance is determined in both the inner disk and outer disk.…”

Section: Discussionmentioning

confidence: 99%

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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“…Interestingly, changes in the C/O ratio as a result of pebble transport may also reflect changes in the CO/H 2 , which is approximately a few times 10 −4 in the interstellar medium (ISM). In models that include pebble transport (Öberg & Bergin 2016;Krijt et al 2020), molecular CO is depleted by one to two orders of magnitude in the outer disk, which is indeed seen in spatially resolved CO isotopolog observations (Schwarz et al 2016(Schwarz et al , 2019Zhang et al 2019) and is shown to happen in the transition between the protostellar and the protoplanetary disk phase (Zhang et al 2020;Bergner et al 2020). As the mixture of ices that are most affected by this depletion process (e.g., H 2 O, CO 2 , CO) is overall oxygen-rich, this process can result in outer disk surface layers with C/O > 1 in the gas phase (Krijt et al 2020;Bosman et al 2021).…”

Section: Introductionmentioning

confidence: 70%

If you like C/O variations, you should have put a ring on it

Marel

Bosman

Krijt

et al. 2021

A&A

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Context. The C/O ratio as traced with C2H emission in protoplanetary disks is fundamental for constraining the formation mechanisms of exoplanets and for our understanding of volatile depletion in disks, but current C2H observations show an apparent bimodal distribution that is not well understood, indicating that the C/O distribution is not described by a simple radial dependence. Aims. The transport of icy pebbles has been suggested to alter the local elemental abundances in protoplanetary disks through settling, drift, and trapping in pressure bumps, resulting in a depletion of volatiles in the surface layer and an increase in the elemental C/O. Methods. We combine all disks with spatially resolved ALMA C2H observations with high-resolution continuum images and constraints on the CO snow line to determine if the C2H emission is indeed related to the location of the icy pebbles. Results. We report a possible correlation between the presence of a significant CO-ice dust reservoir and high C2H emission, which is only found in disks with dust rings outside the CO snow line. In contrast, compact dust disks (without pressure bumps) and warm transition disks (with their dust ring inside the CO snow line) are not detected in C2H, suggesting that such disks may have never contained a significant CO ice reservoir. Conclusions. This correlation provides evidence for the regulation of the C/O profile by the complex interplay of CO snow line and pressure bump locations in the disk. These results demonstrate the importance of including dust transport in chemical disk models for a proper interpretation of exoplanet atmospheric compositions and a better understanding of volatile depletion in disks, in particular the use of CO isotopologs to determine gas surface densities.

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An Evolutionary Study of Volatile Chemistry in Protoplanetary Disks

Cited by 53 publications

References 116 publications

Temperature Structures of Embedded Disks: Young Disks in Taurus Are Warm

Temperature Structures of Embedded Disks: Young Disks in Taurus Are Warm

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

If you like C/O variations, you should have put a ring on it

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