Volume 421, Number 3, July III 2004
|Page(s)||1087 - 1099|
|Section||Interstellar and circumstellar matter|
|Published online||29 June 2004|
Observations of globules and the dependence on star formation activity
Institute of Astronomy, ETH Zentrum, 8092 Zürich, Switzerland
2 Observatory, PO Box 14, 00014 University of Helsinki, Finland
3 Swedish-ESO Submillimetre Telescope, European Southern Observatory, Casilla 19001, Santiago, Chile
Corresponding author: P. Harjunpää, email@example.com
Accepted: 6 April 2004
We have studied the ratio of 13CO and C18O column densities to the extinction AJ of background field stars in the direction of three globules: B 133, B 335, L 466. Selected positions in the globules were observed in the 12CO() line and in and transitions of 13CO and C18O using the 15-m Swedish-ESO Submillimetre Telescope (SEST) in Chile. One of the clouds, L 466, was also mapped in the C18O() line. In addition to the N(13CO)/AJ and N(C18O)/AJ ratios also the ratios of N(13CO) and N(C18O) to AV and N(H2) are given. These ratios were found to vary from cloud to cloud so that they are larger in B 335 than in B 133 and L 466. These variations are thought to primarily arise from variations of the column density ratio of CO and its isotopes to H2. The alternative explanation in terms of the N(H2)/AJ ratio being larger in starforming regions (B 335) than in more quiescent regions lacking star formation (B 133 and L 466) appears less likely. We also discuss the evidence for N(CO)/AJ variations on the basis of previous observations in star forming and non-star forming dark clouds.
Key words: ISM: general / ISM: abundances / ISM: molecules
© ESO, 2004
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