Chemical inhomogeneities in interstellar clouds: the high latitude cloud MCLD 123.5+24.9.

Details Chemical inhomogeneities in interstellar clouds: the high latitude cloud MCLD 123.5+24.9. Chemical inhomogeneities in interstellar clouds: the high latitude cloud MCLD 123.5+24.9.

Feb 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...318..579g&link_type=abstract

Astronomy and Astrophysics, v.318, p.579-594

Astronomy and Astrophysics

Astrophysics

27

Molecular Processes, Ism: Mcld 123.5+24.9 (Gal 123.5+24.9), Abundances, Clouds, Molecules, Radio Lines: Molecules

Scientific paper

We report on observations designed to disclose the presence of the High Ionization Phase predicted to exist in dark clouds by chemical models (Le Bourlot et al. 1993A&A...267..233L and 1993ApJ...416L..87L). In addition to a high neutral carbon abundance, a high CS/SO abundance ratio and a low abundance of molecular ions, such a phase might be characterized by a low D/H fractionation ratio. In this paper, we present both observational and model results on the sulfur bearing molecules CS and SO, and their most abundant isotopomers, on the molecular ions HCO^+^, H^13^CO^+^, HC^18^O^+^ and DCO^+^. We have also taken new ^13^CO and C^18^O data to improve the determination of the physical conditions at the observed positions. One of the two dark clouds investigated, a core in the high latitude cloud MCLD 123.5+24.9, presents surprinsingly strong CS and ^34^CS lines relative to its column density, together with weak DCO^+^ lines. It has also a cold temperature and rather strong CCH and C_3_H_2_ lines. These observed features are characteristic of the presence of the High Ionization Phase along the line of sight. This cloud core might therefore be a good candidate for further investigation of this new phase of dark interstellar clouds.

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