Luminous AGB stars in nearby galaxies

A study using virtual observatory tools

¹ Department of Astrophysics Astronomy & Mechanics, Faculty of Physics, University of Athens, 15783 Athens, Greece e-mail: vivitsal@phys.uoa.gr
² Institute for Astronomy and Astrophysics, National Observatory of Athens, PO Box 20048, 11810 Athens, Greece
³ Observatoire Astronomique de Strasbourg, 67000 Strasbourg, France

Received: 28 March 2005
Accepted: 20 September 2005

Abstract

Context.

Aims.This study focuses on very luminous ( mag) AGB stars with  mag and  mag in the LMC, SMC, M 31, and M 33 from 2MASS data.

Methods.The data were taken from the 2MASS All-Sky Point Source catalogue archive. We used Virtual Observatory tools and took advantage of its capabilities at various stages in the analysis.

Results.It is well known that stars with the colors we selected correspond mainly to carbon stars. Although the most luminous AGBs detected here contain a large number of carbon stars, they are not included in existing catalogues produced from data in the optical domain, where they are not visible since they are dust-enshrouded. A comparison of the AGB stars detected with combined near and mid–infrared data from MSX and 2MASS in the LMC shows that 10% of the bright AGB stars are bright carbon stars never detected before and that the other 50% are OH/IR oxygen rich stars, whereas the 40% that remain were not cross–matched.

Conclusions.The catalogues of the most luminous AGB stars compiled here are an important complement to existing data. In the LMC, these bright AGB stars are centrally located, whereas they are concentrated in an active star-formation ring in M 31. In the SMC and M 33, there are not enough of them to draw definite conclusions, although they tend to be centrally located. Their luminosity functions are similar for the four galaxies we studied.