T. Tanabe 1, S. Nishida 1, Y. Nakada 1, T. Onaka 2, I. S. Glass 3, & M. Sauvage 4
1 Institute of Astronomy, The University of Tokyo, Japan
2 Department of Astronomy, University of Tokyo, Japan
3 South African Astronomical Observatory, South Africa
4 CEA/DSM/DAPNIA/Service d'Astrophys. C. E. Saclay, France
Globular clusters (GCs) associated with the Magellanic Clouds (MCs) have advantage over GCs in our Galaxy that they span a wide range of age, which enables us to study the evolution of stars with various masses. We have performed systematic observations of AGB stars in GCs in the MCs with ISO in the MIR and with a ground-based telescope in the NIR. ISO observations consist of CAM broad band (LW1, LW2, LW10) imagings of 17 GCs, CAM CVF observations of 4 intermediate-age GCs and PHOT 25 and 60 micron photometries of 7 bright AGB stars belonging to 3 intermediate-age GCs.
ISOCAM (LW1, LW2, LW10) observations have revealed previously unknown extremely red objects in the intermediate-age GCs. Among them, two stars (hereafter MIR stars) are very bright in the mid-infrared and have bolometric luminosities comparable to other AGB stars. We thus conclude that they are in the final stage of their AGB evolution, experiencing heavy mass-loss. CAM CVF observations of these stars suggest they are carbon-rich. One of the MIR stars does not show any 60 excess. The other MIR star may have such excess but we cannot conclude it because there is one AGB carbon star within the PHOT aperture. Five other stars observed with ISOPHOT all of which are carbon stars show 60 micron excesses. The MIR star which does not show any FIR excess have the luminosity well below the tip AGB luminosity. This may be also the for the other MIR one. All these may give us observational constraints on the evolution of AGB stars and we will discuss it more detail.