A SIGNIFICANTLY LOW CO ABUNDANCE TOWARD THE TW Hya PROTOPLANETARY DISK: A PATH TO ACTIVE CARBON CHEMISTRY?
- Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
In this Letter we report the CO abundance relative to H{sub 2} derived toward the circumstellar disk of the T-Tauri star TW Hya from the HD (1 – 0) and C{sup 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{sup 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{sub 2} of χ(CO) = (0.1-3) × 10{sup –5}, substantially lower than the canonical value of χ(CO) = 10{sup –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{sub 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{sub 2} gas mass.
- OSTI ID:
- 22215432
- Journal Information:
- Astrophysical Journal Letters, Vol. 776, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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