Interstellar CH in southern OB associations
Received 6 June 1996 / Accepted 1 October 1996
Optical absorption line observations of interstellar CH and CH are presented towards the southern OB associations CMa OB1, NGC 2439, Vela OB1, NGC 4755, and Cen OB1. A total of 5-11 stars per association were observed, with visual extinctions ranging from = 0.5-4.5 mag. The derived CH and CH velocities agree within the measurement errors. Towards a particular association, the CH column density N (CH ) is correlated to the visual extinction of the background star. These findings weaken the possibility that magnetic shocks are the general mechanism that is required to produce interstellar CH . It is found that N (CH ) is correlated to N (CH), which indicates that N (CH ) is correlated to the optical depth of a cloud. The correlations are difficult to reconcile with scenarios where the sites of CH formation are constrained to the surface of molecular clouds. The observations support ideas which involve turbulence as a major CH production mechanism. In particular, the results are in agreement with expectations from a scenario where the CH formation proceeds in cool gas via a fraction of fast, non-Maxwellian H2 or C , created by the dissipation of interstellar turbulence.
Key words: ISM: abundances ISM: clouds ISM: molecules open clusters and associations
Send offprint requests to: R. Gredel
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998