Physics
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000esasp.456...67b&link_type=abstract
ISO beyond the peaks: The 2nd ISO workshop on analytical spectroscopy. Eds. A. Salama, M.F.Kessler, K. Leech & B. Schulz. ESA-SP
Physics
9
Star-Formation, Gas-Phase Molecules, Abundances
Scientific paper
We present a study of gas-phase H2O and CO2 towards a sample of 14 massive protostars with the ISO-SWS. Modeling of the H2O spectra using a homogeneous model with a constant excitation temperature Tex shows that the H2O abundances increase with temperature, up to a few times 10-5 with respect to H2 for the hottest sources (Tex~ 500 K). This is still a factor of 10 lower than the H2O ice abundances observed towards cold sources in which evaporation is not significant (Keane et al. 2000). Gas-phase CO2 is not abundant in our sources. The abundances are nearly constant for Tex >~ 100 K at a value of a few times 10-7, much lower than the solid-state abundances of ~1-3× 10-6 (Gerakines et al. 1999). Gas/solid ratios have been determined, using the solid-state features of H2O (Keane et al. 2000) and CO2 (Gerakines et al. 1999) as observed with ISO-SWS towards the same objects. For both H2O and CO2 the gas/solid ratio increases with temperature, but the increase is much stronger for H2O than for CO2, suggesting a different type of chemistry. In addition to the homogeneous models, a power law model has been developed for one of our sources, based on the physical structure of this region as determined from submillimeter data by van der Tak et al. (1999). The resulting H2O model spectrum gives a good fit to the data.
Boonman M. S. A.
Doty Steven D.
Lahuis Fred
van Dishoeck Ewine F.
Wright Chris M.
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