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Issue A&A Volume 400, Number 1, March II 2003 Page(s) L1 - L4 Section Letters DOI 10.1051/0004-6361:20030091

A&A 400, L1-L4 (2003)
DOI: 10.1051/0004-6361:20030091

Letter

Detection of DCO ⁺ in a circumstellar disk

E. F. van Dishoeck¹, W.-F. Thi^{1, 2} and G.-J. van Zadelhoff<sup>1

1</sup>  Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
²  Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK

(Received 9 December 2002 / Accepted 21 January 2003 )

Abstract
We report the first detection of DCO ⁺ in a circumstellar disk. The DCO ⁺ J=5-4 line at 360.169 GHz is observed with the 15 m James Clerk Maxwell Telescope in the disk around the pre-main sequence star TW Hya. Together with measurements of the HCO ⁺ and H ¹³CO ⁺ J=4-3 lines, this allows an accurate determination of the DCO ⁺/HCO ⁺ ratio in this disk. The inferred value of is close to that found in cold pre-stellar cores and is somewhat higher than that measured in the envelope around the low-mass protostar IRAS 16293-2422. It is also close to the DCN/HCN ratio obtained for pristine cometary material in the jet of comet Hale-Bopp. The observed DCO ⁺/HCO ⁺ ratio for TW Hya is consistent with theoretical models of disks which consider gas-phase fractionation processes within a realistic 2-D temperature distribution and which include the effects of freeze-out onto grains.

Offprint request: E. F. van Dishoeck ewine@strw.leidenuniv.nl

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