Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997mnras.291..296l&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 291, Issue 2, pp. 296-304.
Astronomy and Astrophysics
Astronomy
12
Radiative Transfer, Stars: Agb And Post-Agb, Circumstellar Matter, Infrared: Stars
Scientific paper
OH/IR star dust envelopes are modelled, using a Monte Carlo type numerical method. Some characteristics of the circumstellar shell (such as extinction opacity at a given wavelength, its size and the exponent of the power-law density distribution rho~r^m) are estimated by fitting the spectral energy distribution. IRAS LRS data are used for the silicate feature at 9.7 mum. Near-infrared and IRAS fluxes at 12, 25, 60 and 100 μm are also considered. A tendency for the optical thickness to increase with the colour index [K-L'], suggested by previous work, is confirmed. The silicate feature changes from emission to absorption when the optical thickness at this band (tau_9.7) is around 3-6. In addition, the density exponent found for absorption feature stars is m=2.5. This result is compatible with two possible scenarios: a mass-loss increasing in time (if the outflow velocity is constant), or a more or less constant mass-loss rate and an accelerated expansion.
de Araújo Francisco Xavier
Lorenz-Martins Silvia
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