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

We present near-IR spectra (HK-band) of a sample of 107 sources with mid-IR excesses at 7 and 15 mum 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. (CO)-C-12 and M-bol vs. H2O diagrams are powerful tools for identifying supergiants, AGB stars, giants and young stellar objects. The majority of our sample are AGB stars (similar to80%) while we find four good supergiant candidates, nine young stellar objects and 12 RGB candidates. We have used the most recent K-0 - [15] relation by Jeong et al. (2002) 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 - 5 < log (M) over dot < -7. The red giant candidates lie at the lower end of the mass-loss rate range between -6.5 < log (M) over dot < - 9. We used the equivalent width of the CO bandhead at 2.3 mum, the NaI doublet and the CaI triplet to estimate metallicities using the relation by Ramirez et al. (2000b). The metallicity distribution of the ISOGAL objects shows a mean [Fe/H] similar to -0.25 dex with a dispersion of +/-0.40 dex which is in agreement with the values of Ramirez et al. (2000b) for Galactic Bulge fields between b = -4degrees and b = -1.3degrees. A comparison with the solar neighbourhood sample of Lanc, on & Wood (2000) shows that our sample is similar to0.5 dex more metal-rich on average.