The VMC survey

III. Mass-loss rates and luminosities of LMC AGB stars^{⋆,⋆⋆,⋆⋆⋆}

¹ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussel, Belgium
e-mail: marco.gullieuszik@oapd.inaf.it
² University of Hertforshire, Physics Astronomy and Mathematics, Hatfield AL10 9AB, UK
³ University Observatory Munich, Scheinerstrasse 1, 81679 München, Germany
⁴ Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, 100871 Beijing, PR China
⁵ Department of Astronomy and Space Science, Kyung Hee University, Yongin-shi, 449-701 Kyungki-do, Republic of Korea
⁶ Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG, UK
⁷ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁸ European Southern Observatory, Av. Alonso de Cordoba 3107, Casilla 19, Santiago, Chile
⁹ Astronomy Unit, School of Physics & Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, UK

Received: 16 June 2011
Accepted: 18 October 2011

Abstract

Context. Asymptotic giant branch (AGB) stars are major contributors to both the chemical enrichment of the interstellar medium and the integrated light of galaxies. Despite its importance, the AGB is one of the least understood phases of stellar evolution. The main difficulties associated with detailed modelling of the AGB are related to the mass-loss process and the 3rd dredge-up efficiency

Aims. We provide direct measures of mass-loss rates and luminosities for a complete sample of AGB stars in the Large Magellanic Cloud, disentangling the C- and O-rich stellar populations.

Methods. Dust radiative transfer models are presented for all 374 AGB stars candidates in one of the fields observed by the new VISTA survey of the Magellanic Clouds (VMC). Mass-loss rates, luminosities and a classification of C- and O-rich stars are derived by fitting the models to the spectral energy distribution (SED) obtained by combining VMC data with existing optical, near-, and mid-infrared photometry.

Results. The classification technique is reliable at a level of – at worst – 75% and significantly better for the reddest dusty stars. We classified none of the stars with a relevant mass-loss rate as O-rich, and we can exclude the presence of more than one dusty O-rich star at a  ~ 94% level. The bolometric luminosity function we obtained is fully consistent with most of the literature data on the LMC and with the prediction of theoretical models, with a peak of the C-star distribution at M_bol ≃  −4.8 mag and no stars brighter than the classical AGB tip, at M_bol =  −7.1 mag.

Conclusions. This exploratory study shows that our method provides reliable mass-loss rates, luminosities and chemical classifications for all AGB stars. These results offer already important constraints to AGB evolutionary models. Most of our conclusions, especially for the rarer dust-enshrouded extreme AGB stars, are however strongly limited by the relatively small area covered by our study. Forthcoming VMC observations will easily remove this limitation.