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The Radial Distribution of H_2 and CO in TW Hya as Revealed by Resolved ALMA Observations of CO Isotopologues

Schwarz, Kamber R. and Bergin, Edwin A. and Cleeves, L. Ilsedore and Blake, Geoffrey A. and Zhang, Ke and Öberg, Karin I. and van Dishoeck, Ewine F. and Qi, Chunhua (2016) The Radial Distribution of H_2 and CO in TW Hya as Revealed by Resolved ALMA Observations of CO Isotopologues. Astrophysical Journal, 823 (2). Art. No. 91. ISSN 0004-637X.

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CO is widely used as a tracer of molecular gas. However, there is now mounting evidence that gas phase carbon is depleted in the disk around TW Hya. Previous efforts to quantify this depletion have been hampered by uncertainties regarding the radial thermal structure in the disk. Here we present resolved ALMA observations of ^(13)CO 3-2, C^(18)O 3-2, ^(13)CO 6-5, and C^(18)O 6-5 emission in TW Hya, which allow us to derive radial gas temperature and gas surface density profiles, as well as map the CO abundance as a function of radius. These observations provide a measurement of the surface CO snowline at ~30 AU and show evidence for an outer ring of CO emission centered at 53 AU, a feature previously seen only in less abundant species. Further, the derived CO gas temperature profile constrains the freeze out temperature of CO in the warm molecular layer to <21K. Combined with the previous detection of HD 1-0, these data constrain the surface density of the warm H_2 gas in the inner ~30 AU such that Σwarm gas = 4.7^(+3.0)_(-2.9) g cm^(-2)(R/10 au)^(-1/2). We find that CO is depleted by two orders of magnitude from R = 10-60 AU, with the small amount of CO returning to the gas phase inside the surface CO snowline insufficient to explain the overall depletion. Finally, this new data is used in conjunction with previous modeling of the TW Hya disk to constrain the midplane CO snowline to 17–23 AU.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper DOIArticle
Schwarz, Kamber R.0000-0002-6429-9457
Bergin, Edwin A.0000-0003-4179-6394
Cleeves, L. Ilsedore0000-0003-2076-8001
Blake, Geoffrey A.0000-0003-0787-1610
Zhang, Ke0000-0002-0661-7517
Öberg, Karin I.0000-0001-8798-1347
van Dishoeck, Ewine F.0000-0001-7591-1907
Qi, Chunhua0000-0001-8642-1786
Additional Information:© 2016 The American Astronomical Society. Received 2015 December 31; accepted 2016 March 25; published 2016 May 25. This paper makes use of the following ALMA data: ADS/ JAO.ALMA#2012.1.00422.s. ALMA is a partnership of ESO (representing its member states), NSF (U.S.) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan) and KASI (Republic of Korea), in cooperation with the Republic of Chile. The joint ALMA observatory is operated by ESO, AUI/NRAO, and NAOJ. This work was supported by funding from the national science foundation grant AST- 1514670 and AST-1344133 (INSPIRE).
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Subject Keywords:astrochemistry – circumstellar matter – ISM: abundances – molecular data – protoplanetary disks – radio lines: ISM
Issue or Number:2
Record Number:CaltechAUTHORS:20160405-120201278
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65932
Deposited By: Joy Painter
Deposited On:06 Apr 2016 18:46
Last Modified:09 Mar 2020 13:19

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