The Abundance and Emission of H2O and O2 in Clumpy Molecular Clouds
| Autor: | Spaans, M, van Dishoeck, EF |
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| Přispěvatelé: | Kapteyn Astronomical Institute |
| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | None Astrophysical Journal, 548(2), L217-L220. IOP PUBLISHING LTD |
| ISSN: | 0004-637X |
| DOI: | 10.48550/arxiv.astro-ph/0011427 |
| Popis: | Recent observations with the Submillimeter Wave Astronomy Satellite indicate abundances of gaseous H2O and O2 in dense molecular clouds which are significantly lower than found in standard homogeneous chemistry models. We present here results for the thermal and chemical balance of inhomogeneous molecular clouds exposed to ultraviolet radiation in which the abundances of H2O and O2 are computed for various density distributions, radiation field strengths and geometries. It is found that an inhomogeneous density distribution lowers the column densities of H2O and O2 compared to the homogeneous case by more than an order of magnitude at the same A_V. O2 is particularly sensitive to the penetrating ultraviolet radiation, more so than H2O. The S140 and rho Oph clouds are studied as relevant test cases of star-forming and quiescent regions. The SWAS results of S140 can be accommodated naturally in a clumpy model with mean density of 2x10^3 cm-3 and enhancement I_UV=140 compared with the average interstellar radiation field, in agreement with observations of [CI] and 13CO of this cloud. Additional radiative transfer computations suggest that this diffuse H2O component is warm, ~60-90 K, and can account for the bulk of the 1_10-1_01 line emission observed by SWAS. The rho Oph model yields consistent O2 abundances but too much H2O, even for [C]/[O]=0.94, if I_UV To be published in ApJL |
| Databáze: | OpenAIRE |
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