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

A radiative transfer code is used to model the spectral energy distribution s 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 an available. As a result we derive mass-loss rates and b olometric luminosities. A gap in the luminosity distribution around M-bol = -7.5 mag separates AGE scars from RSGs. The luminosity distributions of optically bright carbon st ars, dust-enshrouded carbon stars and dust-enshrouded M-type stars have onl y little overlap, suggesting that the dust-enshrouded AGE stars are at the very tip of the AGE and will not evolve significantly in luminosity before mass loss ends their AGE evolution. Derived mass-loss rates span a range from (M) over dot similar to 10(-7) to 10(-3) M. yr(-1). More luminous and cooler stars are found to reach higher mass-loss rates. The highest mass-loss rates exceed the classical limit se t by the momentum of the stellar radiation field, Lie, 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 , (M) over dot (nuc), for most of the RSGs. Two RSGs have (M) over dot much greater than (M) over dot (nuc), however, suggesting that RSGs shed most o f their stellar mantles in short phases of intense mass loss. Stars on the thermal pulsing AGE may also experience episodes of intensified mass loss, but their quiescent mass-loss rates are usually already higher than (M) ove r dot (nuc).