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Issue A&A Volume 454, Number 2, August I 2006 APEX Special Booklet Page(s) L59 - L62 Section Letters DOI 10.1051/0004-6361:20065104

A&A 454, L59-L62 (2006)
DOI: 10.1051/0004-6361:20065104

Letter

Probable detection of H D in the starless core Barnard 68

M. R. Hogerheijde¹, P. Caselli^{2, 3}, M. Emprechtinger⁴, F. F. S. van der Tak^{5, 6}, J. Alves^{7, 8}, A. Belloche⁶, R. Güsten⁶, A. A. Lundgren⁹, L.-Å. Nyman⁹, N. Volgenau⁴ and M. C. Wiedner<sup>4

1</sup>  Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
    e-mail: michiel@strw.leidenuniv.nl
²  INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
³  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁴  I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
⁵  Netherlands Institute for Space Research (SRON), PO Box 800, 9700 AV Groningen, The Netherlands
⁶  Max-Planck-Institut für Radioastromie, Auf dem Hügel 69, 53121 Bonn, Germany
⁷  European Southern Observatory, Karl Schwarzschild-Straße 2, 85748 Garching bei München, Germany
⁸  Present address: Centro Astronómico Hispano Alemán, Apt. 511, 04080 Almería, Spain
⁹  European Southern Observatory, Casilla 19001, Santiago 19, Chile

(Received 27 February 2006 / Accepted 4 May 2006)

Abstract
Context. The presence of H₂D⁺ in dense cloud cores underlies ion-molecule reactions that strongly enhance the deuterium fractionation of many molecular species.
Aims.We determine the H₂D⁺ abundance in one starless core, Barnard 68, that has a particularly well established physical, chemical, and dynamical structure.
Methods.We observed the ortho-H₂D⁺ ground-state line 1₁₀-1₁₁, the N₂H⁺ J=4-3 line, and the H¹³CO⁺ 4-3 line with the APEX telescope.
Results.We report the probable detection of the o-H₂D⁺ line at an intensity  K and exclusively thermal line width, and find only upper limits to the N₂H⁺ 4-3 and H¹³CO⁺ 4-3 intensities.
Conclusions.Within the uncertainties in the chemical reaction rates and the collisional excitation rates, chemical model calculations and excitation simulations reproduce the observed intensities and that of o-H₂D⁺ in particular.

Key words: ISM: abundances -- ISM: individual objects: Barnard 68 -- ISM: molecules -- submillimeter

© ESO 2006

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