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

Sakamoto, Seiichi; White, Glenn J.; Kawaguchi, Kentarou; Ohishi, Masatoshi; Usuda, Kumiko S. and Hasegawa, Tetsuo (1998). A search for absorption of Mg and Ca compounds in molecular clouds towards Galactic continuum sources. Monthly Notices of the Royal Astronomical Society, 301(3) pp. 872–880.

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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.

Item Type: Journal Article
Copyright Holders: 1998 RAS
ISSN: 1365-2966
Keywords: abundances; clouds; Sgr B2; W49A; molecules; radio lines
Academic Unit/Department: Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 31823
Depositing User: G. J. White
Date Deposited: 10 Feb 2012 15:59
Last Modified: 18 Jan 2016 12:04
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