Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998mnras.301..872s&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 301, Issue 3, pp. 872-880.
Astronomy and Astrophysics
Astronomy
6
Ism: Abundances, Ism: Clouds, Ism: Individual: Sgr B2, Ism: Individual: W49A, Ism: Molecules, Radio Lines: Ism
Scientific paper
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 <~1.0x10^-11 for MgH, <~7.9x10^-13 for MgO, <~1.6x10^-10 for MgOH, <~1.6x10^-9 for CaH, <~2.0x10^-12 for CaO, and <~2.5x10^-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 >~10^2.5 in well-shielded molecular clouds.
Hasegawa Tetsuo
Kawaguchi Kentarou
Ohishi Masatoshi
Sakamoto Seiichi
Usuda Kumiko S.
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