Cleeves, LI, Loomis, RA, Teague, R et al. (15 more authors) (2021) The TW Hya Rosetta Stone Project IV: A Hydrocarbon-rich Disk Atmosphere. The Astrophysical Journal, 911 (1). 29. p. 29. ISSN 0004-637X
Abstract
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 C2H and C3H2 have been identified as tracers of C/O, as they form abundantly under high C/O conditions. We present resolved c–C3H2 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, Eu = 29–97 K. We find the ortho-to-para ratio of c–C3H2 is consistent with 3 throughout extent of the emission, and the total abundance of both c–C3H2 isomers is (7.5–10) × 10^−11 per H atom, or 1%–10% of the previously published C2H abundance in the same source. We find c–C3H2 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.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2021. The American Astronomical Society. This is an author produced version of a journal article published in The Astrophysical Journal. Uploaded in accordance with the publisher's self-archiving policy. |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Physics and Astronomy (Leeds) > Astrophysics (Leeds) |
Funding Information: | Funder Grant number STFC (Science and Technology Facilities Council) ST/R000549/1 STFC (Science and Technology Facilities Council) Not Known MRC (Medical Research Council) MR/T040726/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 22 Apr 2021 15:54 |
Last Modified: | 13 Apr 2022 00:38 |
Published Version: | https://iopscience.iop.org/article/10.3847/1538-43... |
Status: | Published |
Publisher: | American Astronomical Society |
Identification Number: | 10.3847/1538-4357/abe862 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:173284 |