Issue |
A&A
Volume 421, Number 3, July III 2004
|
|
---|---|---|
Page(s) | 1087 - 1099 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20035752 | |
Published online | 29 June 2004 |
The relationship of CO abundance to extinction and
N(H
):*,**
Observations of globules and the dependence on star formation activity
1
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, paivi.harjunpaa@helsinki.fi
Received:
26
November
2003
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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