Stellar population in the galactic Bulge with ISOGAL and Near-IR data

Erwin Schrödinger Fellowship J 1971 Stellar populations in the galactic Bulge Mathias SCHULTHEIS 09.10.2000 The ISOGAL survey used the still unique capabilities of ISOCAM to observe at 7 and 15m m, - 20 deg^2 of selected fields of the inner Galaxy, with a sensitivity and pixel surface two orders of magnitude better than IRAS. Combined with the Near-IR data of DENIS, the ISOGAL provides an excellent tool to study the stellar populations in the highest extincted regions of the Inner Galaxy. A number of ambiguities remain about ISOGAL source identification for various reasons: similar colours for some classes of AGB and post-AGB stars and YSOs, absence of velocity information allowing to distinguish stellar populations of different origin. Near-IR and optical spectroscopy will complement ISOGAL to better characterise these objects. Besides AGB stars and YSO`s, we expect to find also objects such as post-AGB stars, Herbig Ae/Be stars, T-Tauri stars and even b -Pic type objects. Kinematical information will be used to determine the gradient of velocity dispersion as a function of the distance to the galactic Centre. These studies offer a starting point for the upcoming multi-object spectrographs on 8-m class telescopes (e.g. NIRMOS on the VLT). In most parts of the galactic Bulge, the study of stellar populations is hampered by its high interstellar absorption. Using additional H-band data, we will map the highest extincted region. A detailed comparison with CO data, will give us a better understanding of the relation between dust/gas in the Bulge with the aim to build a 3-D extinction map. This can be used to make star counts in order to determine the fundamental parameters for the in-plane bar. Semiregular Variables are long-period Variables stars with a quasi-periodic behaviour in their light curve. Up to now the status of Semiregular Variables is nearly unknown in the Inner Galaxy. High quality long-term monitoring programs such as the EROS project will give us a better understanding of the nature of Bulge Semiregular Variables. Besides a classification of their pulsational type and a study of the number density, near and mid-IR properties, a link to their spectral type and the spectral features will be done. Finally, stellar atmosphere models of AGB stars will be used to determine the metallicity by using CO bands and metal lines, such as Na and Ca, in the near Infrared. As the AGB phase dominate the integrated light in the Near- IR, synthetic spectra of AGB stars as a function of metallicity provide a main ingredient for population synthesis models