Qi, Chunhua and Wilner, David J. and Aikawa, Yuri and Blake, Geoffrey A. and Hogerhejde, Michiel R. (2008) Resolving the Chemistry in the Disk of TW Hydrae. I. Deuterated Species. Astrophysical Journal, 24 (3). pp. 459-471. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:QICapj08
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We present Submillimeter Array observations of several deuterated species in the disk around the classical T Tauri star TW Hydrae at arcsecond scales, including detections of the DCN J = 3–2 and DCO+ J = 3–2 lines and upper limits to the HDO 31,2–22,1, ortho-H2D+ 11,0–11,1, and para-D2H+ 11,0–10,1 transitions. We also present observations of the HCN J = 3–2, HCO+ J = 3–2, and H13CO+ J = 4–3 lines for comparison with their deuterated isotopologues. We constrain the radial and vertical distributions of various species in the disk by fitting the data using a model where the molecular emission from an irradiated accretion disk is sampled with a two-dimensional Monte Carlo radiative transfer code. We find that the distribution of DCO+ differs markedly from that of HCO+. The D/H ratios inferred change by at least 1 order of magnitude (0.01-0.1) for radii <30 to ≥70 AU, and there is a rapid falloff of the abundance of DCO+ at radii larger than 90 AU. Using a simple analytical chemical model, we constrain the degree of ionization, x(e−) = n(e−)/n(H2), to be ~10^−7 in the disk layer(s) where these molecules are present. Provided the distribution of DCN follows that of HCN, the ratio of DCN to HCN is determined to be (1.7 ± 0.5) × 10^−2; however, this ratio is very sensitive to the poorly constrained vertical distribution of HCN. The resolved radial distribution of DCO+ indicates that in situ deuterium fractionation remains active within the TW Hydrae disk and must be considered in the molecular evolution of circumstellar accretion disks.
|Additional Information:||© 2008. The American Astronomical Society. Received 2007 October 5; accepted 2008 March 18; published 2008 July 10. Print publication: Issue 2 (2008 July 10). Partial support for this work comes from NASA Origins of Solar Systems Grant NNG05GI81G. M.R.H. is supported by a VIDI grant from the Netherlands Organization for Scientific Research. C.Q. acknowledges Paola Caselli for her help and useful suggestions. We thank the referee for very useful comments. Online-only material: Color figures|
|Subject Keywords:||circumstellar matter; comets: general; ISM: molecules; planetary systems: protoplanetary disks; stars: individual (TW Hydrae); stars: pre-main sequence|
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|Deposited On:||12 Jan 2009 23:45|
|Last Modified:||26 Dec 2012 10:41|
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