The Physics and Chemistry of Small Translucent Molecular Clouds. V. SO and SO 2

Details The Physics and Chemistry of Small Translucent Molecular Clouds. V. SO and SO 2 The Physics and Chemistry of Small Translucent Molecular Clouds. V. SO and SO 2

Dec 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...455..556t&link_type=abstract

Astrophysical Journal v.455, p.556

Astronomy and Astrophysics

Astronomy

27

Ism: Abundances, Ism: Clouds, Ism: Molecules

Scientific paper

A survey of SO and SO2 has been conducted in nine cirrus cores and 21 Clemens-Barvainis translucent objects whose structures and chemistry have been studied earlier in this series. SO 32-21 emission is seen quite strongly in all objects, SO 23-12 in nine objects, and SO2(313-202) emission in 14 objects. SO appears quite spatially confined and has narrow line widths like C18O. Observations are modeled in terms of our previous hydrostatic equilibrium and n ˜r-α structures together with other chemical and physical properties derived earlier. We find high SO abundances, 10-8 to 10-7, and abundance ratios SO/SO2 from 1 to 15. Both abundances increase sharply with extinction Aν0, characteristic of a transition between diffuse and dense cloud chemistry. A simple ion-molecule reaction network is presented, which includes all processes relevant to S+, S, SO+, SO, and SO2. When solved analytically, this scheme predicts all observed aspects of SO and SO2 quantitatively, namely, the Aν0 dependence of their abundances, the SO/SO2 abundance ratio, and the dependence of individual source abundances upon core density and ambient radiation field. SO and SO2 are particularly sensitive to photodissociation. The key formation reactions are driven by OH, and the required OH abundance is found to be large (˜10-5) though not inconsistent with current observations of OH. Other sulfur chemistries (grain catalysis, shock processes) are entirely inconsistent with the observed SO and SO2 characteristics in these translucent objects.

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