Late-type giant variables in NGC 6522, LMC and SMC. How do they differ?
CNRS UMR 6091, Observatoire de Besançon, BP 1615, 25010 Besançon Cedex, France e-mail: email@example.com
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
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 at a given . These quantities have been compared with the data for galactic globular clusters obtained by Ferraro et al. ([CITE]). In the , colour–colour diagrams, the increasing proportion of stars with high 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 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 μm. 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
© ESO, 2004