Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...278..167l&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 278, no. 1, p. 167-178
Astronomy and Astrophysics
Astronomy
28
Asymptotic Giant Branch Stars, Infrared Astronomy, Interstellar Matter, Mira Variables, Stellar Envelopes, Stellar Spectrophotometry, Visible Spectrum, Binary Stars, Light Curve, Radiative Transfer, Stellar Models, Stellar Temperature
Scientific paper
Photometric and spectroscopic data obtained on two sources representative of mass-losing oxygen-rich miras, IRC -30023 and IRC -20197, are presented. The latter is shown to have an early-type companion, probably a main sequence star of type A or F. (This binarity is noteworthy as IRC -20197 shows a typical type-II OH-maser emission.) The bolometric luminosities are changing by a factor approximately 2.5 from minimum to maximum. The data are interpreted in terms of a radiative transfer model of the circumstellar dust shells. The hottest grains are found to have temperatures in the range 750-950 K, with 850 K as the most likely value. Pressures on the order of 10-6 to 10-5 dyn/sq cm are inferred for the zone of grain formation. Grains which are condensing out at the minima of the variable stars and which are dynamically coupled with the gas do not survive the variations of luminosity, and the circumstellar shells are filled in mainly with grains formed around the maxima. Mass-loss rates of 4 10-7 and 10-5 solar mass/yr are derived. The surrounding interstellar medium is heated dominantly by these miras up to distances of 1 to 2 pc. In this domain, the interstellar dust is reaching temperatures approximately 30-50 K and might contribute significantly to the source fluxes in the submillimeter range. This effect starts to be significant at lambda approximately 60 micrometers for a source like IRC -30023, and at lambda approximately 100 micrometers, for a source like IRC -20197. In this wavelength range, the contribution of the circumstellar dust to the source fluxes can be separated from that of the interstellar dust through imaging. We caution that the excesses which have been observed in the far-infrared range with a low spatial resolution (approximately 1) do not imply necessarily that the central stars have undergone in the past an episode of enhanced mass loss.
Bertre Th. Le
Le Sidaner Pierre
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