Near-IR spectra of ISOGAL sources in the inner Galactic Bulge ^*,**

¹ Institut d'Astrophysique de Paris, CNRS, 98bis Bd Arago, 75014 Paris, France
² Observatoire de Strasbourg, UMR 7550, 11 rue de l'Université, 6700 Strasbourg, France
³ Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India

Corresponding author: M. Schultheis, schulthe@iap.fr

Received: 26 June 2002
Accepted: 20 March 2003

Abstract

We present near-IR spectra (HK-band) of a sample of 107 sources with mid-IR excesses at 7 and 15m detected during the ISOGAL survey. Making use of the DENIS interstellar extinction map from Schultheis et al. (1999) we derive luminosities and find that the M_bol vs.  and diagrams are powerful tools for identifying supergiants, AGB stars, giants and young stellar objects. The majority of our sample are AGB stars (~80%) while we find four good supergiant candidates, nine young stellar objects and 12 RGB candidates. We have used the most recent relation by Jeong et al. ([CITE]) based on recent theoretical modeling of dust formation of AGB stars to determine mass-loss rates. The mass-loss rates of the supergiants are comparable with those in the solar neighbourhood while the long-period variables cover a mass-loss range from . The red giant candidates lie at the lower end of the mass-loss rate range between . We used the equivalent width of the CO bandhead at 2.3 , the NaI doublet and the CaI triplet to estimate metallicities using the relation by Ramírez et al. ([CITE]). The metallicity distribution of the ISOGAL objects shows a mean  dex with a dispersion of which is in agreement with the values of Ramírez et al. ([CITE]) for Galactic Bulge fields between and . A comparison with the solar neighbourhood sample of Lançon & Wood ([CITE]) shows that our sample is ~0.5 dex more metal-rich on average.