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The Surprising Constancy of Relative Chemical Abundances in Different Regions of Interstellar Space – Particularly for Formaldehyde

Published online by Cambridge University Press:  14 August 2015

Carl Heiles  and
M. A. Gordon
Carl Heiles
Affiliation:
Astronomy Dept., University of California, Berkeley, Calif., U.S.A.
M. A. Gordon
Affiliation:
NRAO, Charlottesville, Va., U.S.A.

Abstract

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Many of the places in which radio astronomers search for molecules are located in exotic regions lying near the galactic center, near H II regions or other continuum sources, or in high density regions. Such regions have wide variations in their physical environment. Here we wish to compare two types of region whose environments are thought to be well-understood. One of these is dust clouds; the other is unshielded (from UV) cold clouds in front of bright radio sources. For the sake of interest, we include without comment results for molecular regions near the Galactic center and near Orion A.

Comparison of dust clouds and unshielded clouds is of interest because the volume density differs by a factor of 104 or more and the extinction differs by 8 mag. or more. Neither type of cloud lies near H II regions or other sources of intense radiation. Even though their properties differ widely, we will see that the abundances of OH and H2CO relative to hydrogen are approximately the same in the two. Although this is understandable for OH, no current theory would predict this situation for H2CO.

Type
Part VII Molecules, Theory and Observations
Information
Symposium - International Astronomical Union , Volume 52: Interstellar Dust and Related Topics , 1973 , pp. 375 - 379
Copyright
Copyright © Reidel 1973 

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