Astronomy & Astrophysics

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Issue		A&A Volume 454, Number 2, August I 2006 APEX Special Booklet
Page(s)		L55 - L58
Section		Letters
DOI		10.1051/0004-6361:20065337

A&A 454, L55-L58 (2006)
DOI: 10.1051/0004-6361:20065337

Letter

Detection of H $\mathsf$ D $\mathsf$ in a massive prestellar core in Orion B

J. Harju¹, L. K. Haikala¹, K. Lehtinen¹, M. Juvela¹, K. Mattila¹, O. Miettinen¹, M. Dumke², R. Güsten³ and L.-Å. Nyman²

¹ Observatory, PO Box 14, 00014 University of Helsinki, Finland
e-mail: jorma.harju@helsinki.fi
² European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

(Received 31 March 2006 / Accepted 23 May 2006)

Abstract
Aims.The purpose of this study is to examine the prediction that the deuterated H₃⁺ ion, H₂D⁺, can be found exclusively in the coldest regions of molecular cloud cores. This is also a feasibility study for the detection of the ground-state line of ortho-H₂D⁺ at 372 GHz with APEX.
Methods.The $(1_ \rightarrow 1_)$ transition of H₂D⁺ at 372 GHz was searched towards selected positions in the massive star forming cloud OriB9 , in the dark cloud L183 , and in the low- to intermediate mass star-forming cloud R CrA.
Results.The line was detected in cold, prestellar cores in the regions of OriB9 and L183 , but only upper limits were obtained towards other locations which either have elevated temperatures or contain a newly born star. The H₂D⁺ detection towards OriB9 is the first one in a massive star-forming region. The fractional ortho-H₂D⁺ abundances (relative to H₂) are estimated to be ~1 $\times$ 10^-10 in two cold cores in OriB9 , and 3 $\times$ 10^-10 in the cold core of L183 .
Conclusions.The H₂D⁺ detection in OriB9 shows that also massive star forming regions contain very cold prestellar cores which probably have reached matured chemical composition characterized, e.g., by a high degree of deuterium fractionation. Besides as a tracer of the interior parts of prestellar cores, H₂D⁺ may therefore be used to put contraints on the timescales related to massive star formation.

Key words: ISM: clouds -- ISM: molecules -- ISM: individual objects: IRAS 05405-0117 -- stars: formation -- radio lines: ISM -- telescopes

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Letter

Detection of H D in a massive prestellar core in Orion B

Detection of H $\mathsf$ D $\mathsf$ in a massive prestellar core in Orion B