Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...314..896l&link_type=abstract
Astronomy and Astrophysics, v.314, p.896-908
Astronomy and Astrophysics
Astrophysics
65
Radiative Transfer, Stars: Circumstellar Matter, Stars: Mass Loss, Stars: Agb And Post-Agb, Infrared: Stars, Radio Continuum: Stars
Scientific paper
We present mid-infrared (10-20μm) photometry obtained on 27 variable oxygen-rich late-type stars, at different epochs during the period 1984-1990. The sample includes representative objects of miras with optical counterparts, as well as type II OH/IR sources; there are also at least 2 supergiants. These measurements are merged with near-infrared ones, already reported and obtained quasi-simultaneously, to derive 72 (1-20μm) broad band energy distributions. These results are complemented also with IRAS data and flux measurements obtained in the sub-millimeter range. The resulting spectra are interpreted in terms of a circumstellar dust shell radiative transfer model applied for each object at different phases of their lightcurves. The modelling appears to be consistent for a large variety of oxygen-rich sources with optical depth at 10μm ranging from ~0.01 to 10. The temperature of formation of the grains is taken to range from 800 to 950K depending on the pressure at the site of dust formation (P~10^-7^-10^-4^dyn.cm^-2^). Physical parameters such as inner radius of the circumstellar dust shell, bolometric luminosity and mass-loss rate are evaluated. For the objects in the sample, the mass-loss rate ranges from 2x10^-8^ to 10^-4^Msun_/yr. In the context of the planned and underway near-infrared surveys we discuss the relations between color indices and optical depth for oxygen-rich sources. Circumstellar shell optical depths and mass-loss rates are shown to be correlated to the [K-12μm] color. Unfortunately, near-infrared data alone seem to be insufficient to determine physical parameters reliably.
Bertre Th. Le
Le Sidaner Pierre
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