STELLAR POPULATIONS AND INHOMOGENEITIES OF THE GALACTIC PLANE FROM DENIS STAR COUNTS

This paper reports on the analysis of 3-colour (IJK(s)) near infrared star counts obtained during the commissioning phase of the Deep Near I nfrared Southern Sky Survey (DENIS) project. Observing methods, data p rocessing, source: extraction and calibration are briefly outlined. Ni ne strips of 12' of RA x 30 degrees in declination crossing the galact ic plane at different longitudes ranging from 217 degrees to 385 degre es, covering approximately 50 square degrees are analyzed. One strip h as been measured in 3 colours, the others in J and K-s only. More than 250 000 objects are detected and calibrated. The completeness limits are 17.5, 15.5 and 13.5 in the I, J and K-s bands, respectively. Colou r-colour diagrams are shown to be efficient tool for breaking out dwar f and giant star populations especially at low latitude, where the int erstellar extinction strongly affects the far away red giants. Source counts are compared to the SKY model developed by Wainscoat et al. (19 92). This small sample of DENIS data is tentatively used to investigat e the existence and the spatial distribution of the stellar population s associated with the molecular ring at R-G.C. = 4 kpc.