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Astron. Astrophys. 351, 559-572 (1999)


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Mass-loss rates and luminosity functions of dust-enshrouded AGB stars and red supergiants in the LMC

J.Th. van Loon 1, M.A.T. Groenewegen 3, A. de Koter 2, N.R. Trams 4, L.B.F.M. Waters 2,5, A.A. Zijlstra 6, P.A. Whitelock 7 and C. Loup 8

1 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
2 Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85740 Garching bei München, Germany
4 Astrophysics Division of ESA, ESTEC, P.O.Box 299, 2200 AG Noordwijk, The Netherlands
5 Space Research Organization Netherlands, Landleven 12, 9700 AV Groningen, The Netherlands
6 University of Manchester Institute of Science and Technology, P.O.Box 88, Manchester M60 1QD, UK
7 South African Astronomical Observatory, P.O.Box 9, 7935 Observatory, Republic of South Africa
8 Institut d'Astrophysique de Paris, 98bis Boulevard Arago, 75014 Paris, France

Received 28 June 1999 / Accepted 17 September 1999

Abstract

A radiative transfer code is used to model the spectral energy distributions of 57 mass-losing Asymptotic Giant Branch (AGB) stars and red supergiants (RSGs) in the Large Magellanic Cloud (LMC) for which ISO spectroscopic and photometric data are available. As a result we derive mass-loss rates and bolometric luminosities.

A gap in the luminosity distribution around [FORMULA] mag separates AGB stars from RSGs. The luminosity distributions of optically bright carbon stars, dust-enshrouded carbon stars and dust-enshrouded M-type stars have only little overlap, suggesting that the dust-enshrouded AGB stars are at the very tip of the AGB and will not evolve significantly in luminosity before mass loss ends their AGB evolution.

Derived mass-loss rates span a range from [FORMULA] to [FORMULA] [FORMULA] yr-1. More luminous and cooler stars are found to reach higher mass-loss rates. The highest mass-loss rates exceed the classical limit set by the momentum of the stellar radiation field, [FORMULA], by a factor of a few due to multiple scattering of photons in the circumstellar dust envelope. Mass-loss rates are lower than the mass consumption rate by nuclear burning, [FORMULA], for most of the RSGs. Two RSGs have [FORMULA], however, suggesting that RSGs shed most of their stellar mantles in short phases of intense mass loss. Stars on the thermal pulsing AGB may also experience episodes of intensified mass loss, but their quiescent mass-loss rates are usually already higher than [FORMULA].

Key words: stars: carbon – stars: circumstellar matter – stars: mass-loss – stars: AGB and post-AGB – galaxies: Magellanic Clouds – infrared: stars

Send offprint requests to: Jacco van Loon (jacco@ast.cam.ac.uk)

© European Southern Observatory (ESO) 1999

Online publication: November 3, 1999

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