EDP Sciences
Free Access
Volume 395, Number 1, November III 2002
Page(s) 233 - 242
Section Diffuse matter in space
DOI https://doi.org/10.1051/0004-6361:20021280
Published online 29 October 2002

A&A 395, 233-242 (2002)
DOI: 10.1051/0004-6361:20021280

The abundance of gaseous H $_{\mathsf 2}$O and O $_{\mathsf 2}$ in cores of dense interstellar clouds

H. Roberts1 and E. Herbst2

1  Department of Physics, The Ohio State University, Columbus, OH 43210, USA
2  Departments of Physics and Astronomy, The Ohio State University, Columbus, OH 43210, USA

(Received 21 May 2002 / Accepted 30 August 2002 )

We have used chemical models that include both gas-phase and grain-surface processes to try to understand the low water and molecular oxygen abundances inferred from SWAS observations towards dense molecular clouds. The models represent an improvement over pure gas-phase chemistries in that they are more realistic, and they are largely successful at reproducing the low O 2 abundances. For cold clouds, such as TMC-1 and L134N, the limits on the H 2O abundance are met by the models only after relatively long periods of accretion (10 6-10 7 yr), but we show that ground-based observations of these clouds do not necessarily contradict these ages, especially for L134N. If the upper limits on the H 2O abundance were to be revised downwards, however, or if water were to be observed in the cold clouds at the same level as in some star-forming regions, then even heavier depletions would be required. For this reason, the low H 2O abundance observed by SWAS in $\rho$ Oph cannot be reproduced by the models without calculating unphysically low abundances of CO.

Key words: ISM: abundances -- ISM: molecules -- molecular processes

Offprint request: E. Herbst, herbst@mps.ohio-state.edu

SIMBAD Objects

© ESO 2002

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.