Other
Scientific paper
Mar 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999esasp.427..325g&link_type=abstract
The Universe as Seen by ISO. Eds. P. Cox & M. F. Kessler. ESA-SP 427., p. 325
Other
8
Key Words: Stars:Agb, Circumstellar Matter, Molecules
Scientific paper
We present radiative transfer models of the pumping of H2O, HCN and CO2 in the innermost regions of envelopes around AGB stars. Our main goal is to predict/explain what infrared lines/bands will be observed in emission and what lines/bands in absorption against the continuum, as well as their relative strengths, covering the ISO-SWS wavelength range. Our models are non-local and include the effect of excitation and absorption of line photons by dust. The abundance of the three molecules is maintained constant through the region of the envelope considered in the calculations, and collisional excitation between vibrational levels is neglected. Our main results can be summarized as follows: 1) If the density, H2O abundance, and gas velocity dispersion in the proximity of the stellar photosphere are not very high, the 6 μm H2O band is expected to present a combination of absorption and emission lines, qualitatively similar to what has been found in the star forming region Orion BN/KL (González-Alfonso et al. 1998). The intensities of the absorption lines will increase over those of the emission lines in stars with high mass loss rates. If high densities are found in the innermost regions of circumstellar envelopes (hereafter CSEs), blocking by the star will produce that most lines will be observed in absorption against the continuum. 2) HCN bands around 14 μm are in emission, whereas most of the other bands are expected to be in absorption. We successfully explain the band intensities observed in IRC+10216 (Cernicharo et al. 1999), where a similar pattern of absorption/emission bands is observed. 3) In stars with low mass loss rates the CO2 bands at around 15 and 10 μm are expected to be in emission, whereas those around 4-5 μm are in absorption. However, for very high mass loss rates (hereafter dot{M}) the 15 μm bands can be observed also in absorption, as observed by Justannont et al. (1997) for the 0110(1)-0000(1) band.
Cernicharo Jose
Gonzalez-Alfonso Eduardo
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