Journal Article

A search for absorption of Mg and Ca compounds in molecular clouds towards Galactic continuum sources

Seiichi Sakamoto, Glenn J. White, Kentarou Kawaguchi, Masatoshi Ohishi, Kumiko S. Usuda and Tetsuo Hasegawa

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 301, issue 3, pages 872-880
Published in print December 1998 | ISSN: 0035-8711
Published online December 1998 | e-ISSN: 1365-2966 | DOI: https://dx.doi.org/10.1111/j.1365-8711.1998.02080.x
A search for absorption of Mg and Ca compounds in molecular clouds towards Galactic continuum sources

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Abstract

Absorption lines of MgH and CaH N = 1 - 0 transitions were searched for in foreground molecular clouds towards the continuum sources associated with Sgr B2 (M) and W49A (N). None of these lines was detected with our sensitivity level of ∼20 mK. Millimetric absorption lines of MgO, MgOH, CaO and CaOH were also searched for towards Sgr B2 (M) without success. The fractional abundances relative to molecular hydrogen are ≲ 1.0 × 10−11 for MgH, ≲ 7.9 × 10−13 for MgO, ≲ 1.6 × 10−10 for MgOH, ≲ 1.6 × 10−9 for CaH, ≲ 2.0 × 10−12 for CaO, and ≲ 2.5 × 10−10 for CaOH, respectively. The low abundances measured in absorption indicate that a significant fraction of interstellar magnesium and calcium cannot be tied up in their monohydrides, monoxides and monohydroxides. The low abundance of MgH also implies that grain-surface chemistry involving magnesium is not efficient and that magnesium is depleted on to grains to a factor of ≳ 102.5 in well-shielded molecular clouds.

Keywords: ISM: abundances; ISM: clouds; ISM: individual: Sgr B2; ISM: individual: W49A; ISM: molecules; radio lines: ISM

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

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