Astron. Astrophys. 347, L19-L22 (1999)

Letter to the Editor

Discovery of solid HDO in grain mantles ^*

T.C. Teixeira ¹, J.P. Devlin ², V. Buch ³ and J.P. Emerson <sup>4

1</sup> Institute of Physics and Astronomy, University of Å rhus, Ny Munkegade, DK-8000 Å rhus C, Denmark (tct@obs.aau.dk)
² Department of Chemistry, Oklahoma State University, USA (devlin@osuunx.ucc.okstate.edu)
³ Department of Physical Chemistry, Hebrew University of Jerusalem, Israel (viki@fh.huji.ac.il)
⁴ Department of Physics, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK (j.p.emerson@qmw.ac.uk)

Received 5 May 1999 / Accepted 10 June 1999

Abstract

The observation of deuterium fractionation in the molecular gas in hot cores is currently interpreted as evaporation of deuterium-rich molecules from the icy grain mantles where they accumulated during the cold, dense cloud core stage. The predicted enrichment in deuterium of the ices has never been observed. This work provides the first detections of solid HDO in grain mantles. We find column densities in the solid state of cm^-2 for W33A, and cm^-2 for NGC7538 IRS9. The estimated [HDO]/[H₂O] ratios range from in W33A to in NGC7538 IRS9. These values are comparable to the predictions by chemical models, and provide support for the assumption that the origin of the deuterium enhancement in "hot cores" is evaporation from grain mantles.

Key words: line: identification ISM: dust, extinction ISM: molecules infrared: ISM: lines and bands

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

Send offprint requests to: T.C. Teixeira

© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999

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