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A Significantly Low CO Abundance toward the TW Hya Protoplanetary Disk: A Path to Active Carbon Chemistry?

Favre, Cécile and Cleeves, L. Ilsedore and Bergin, Edwin A. and Qi, Chunhua and Blake, Geoffrey A. (2013) A Significantly Low CO Abundance toward the TW Hya Protoplanetary Disk: A Path to Active Carbon Chemistry? Astrophysical Journal Letters, 776 (2). Art. No. L38. ISSN 2041-8205.

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In this Letter we report the CO abundance relative to H_2 derived toward the circumstellar disk of the T-Tauri star TW Hya from the HD (1–0) and C^(18)O (2–1) emission lines. The HD (1–0) line was observed by the Herschel Space Observatory Photodetector Array Camera and Spectrometer whereas C^(18)O (2–1) observations were carried out with the Submillimeter Array at a spatial resolution of 2."8 × 1."9 (corresponding to ~151 × 103 AU). In the disk's warm molecular layer (T > 20 K) we measure a disk-averaged gas-phase CO abundance relative to H_2 of _χ(CO) = (0.1-3) × 10^(–5), substantially lower than the canonical value of _χ(CO) = 10^(–4). We infer that the best explanation of this low _χ(CO) is the chemical destruction of CO followed by rapid formation of carbon chains, or perhaps CO_2, that can subsequently freeze-out, resulting in the bulk mass of carbon locked up in ice grain mantles and oxygen in water. As a consequence of this likely time-dependent carbon sink mechanism, CO may be an unreliable tracer of H_2 gas mass.

Item Type:Article
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URLURL TypeDescription Paper
Favre, Cécile0000-0002-5789-6931
Cleeves, L. Ilsedore0000-0003-2076-8001
Bergin, Edwin A.0000-0003-4179-6394
Qi, Chunhua0000-0001-8642-1786
Blake, Geoffrey A.0000-0003-0787-1610
Additional Information:© 2013 American Astronomical Society. Received 2013 July 28; accepted 2013 September 20; published 2013 October 7. We thank the anonymous referee for raising interesting issues. This work was supported by the National Science Foundation under grant 1008800. This Letter makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00001.SV and SMA data. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The Submillimeter Array is a joint project between the Smithsonian Astrophysical. Facilities: SMA, Herschel, ALMA Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica.
Funding AgencyGrant Number
Smithsonian InstitutionUNSPECIFIED
Academia SinicaUNSPECIFIED
Subject Keywords: astrochemistry; ISM: abundances; protoplanetary disks; stars: formation
Issue or Number:2
Record Number:CaltechAUTHORS:20131104-134256791
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Official Citation:A Significantly Low CO Abundance toward the TW Hya Protoplanetary Disk: A Path to Active Carbon Chemistry? Cécile Favre et al. 2013 ApJ 776 L38
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42226
Deposited By: Ruth Sustaita
Deposited On:04 Nov 2013 21:59
Last Modified:09 Mar 2020 13:19

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