EDP Sciences
Free access
Volume 427, Number 3, December I 2004
Page(s) 945 - 958
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20041454

A&A 427, 945-958 (2004)
DOI: 10.1051/0004-6361:20041454

Late-type giant variables in NGC 6522, LMC and SMC. How do they differ?

M. Schultheis1, 2, I. S. Glass3 and M.-R. Cioni4

1  CNRS UMR 6091, Observatoire de Besançon, BP 1615, 25010 Besançon Cedex, France
    e-mail: mathias@obs-besancon.fr
2  CNRS UMR 7095, Institut d'Astrophysique de Paris, 98bis Bld. Arago, 75014 Paris, France
3  South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
4  European Southern Observatory, Karl-Schwarschild-Str. 2, 85748 Garching bei München, Germany

(Received 11 June 2004 / Accepted 3 August 2004 )

Complete samples of 2MASS stars in three fields of differing metallicities (and possibly differing age distributions) have been extracted and cross-correlated with MACHO and ISO data to determine their variability and mass-loss properties. In each MK histogram a fall-off in numbers is seen above the tip of the RGB. The luminosity of the tip increases with metallicity as does the average  (J-K)0 at a given MK0. These quantities have been compared with the data for galactic globular clusters obtained by Ferraro et al. (2000). In the J-H, H-K colour-colour diagrams, the increasing proportion of stars with high H-K values is conspicuous at lower metallicities. This is well-known to result from the increasing proportion of carbon stars.

All three fields contain similar types of variables, mainly short-period (usually tens of days), Mira like (long-period, large amplitude) and double-period (having both long and short periods). The proportion of stars that vary decreases at lower metallicities and the minimum period associated with a given amplitude gets longer. Various trends are seen in the  K, log P diagrams of each field. The Magellanic Cloud fields largely resemble each other but the Bulge field is noticeably different. The stars that follow the "A" K, log  P relation in the Bulge hardly extend beyond $M_{K,0}^{\rm Tip}$ and the other groups also appear truncated in MK relative to their Magellanic Cloud counterparts. In the Clouds there are many stars with periods around 200-300 d that follow the "C" or Mira relation but have relatively small amplitudes.

The mid-IR sample detected by ISOCAM during the Magellanic Cloud Mini-Survey (MCMS) appears to be reliable and complete for sources with MK more luminous than -7 mag, i.e., for those close to the top of the AGB. The various colour-colour and colour-magnitude diagrams reflect the increasing dominance of carbon stars at low metallicity. Mira magnitude vs. log  P relations exist at least up to 7  $\mu$m. Mass-loss from longer-period and double-period SRVs occurs at similar rates in each field, in spite of the metallicity differences.

Key words: stars: AGB and post-AGB -- galaxies: Magellanic Clouds -- Galaxy: bulge

SIMBAD Objects

© ESO 2004