Spatial Distribution of Evolved Giant Stars in the Galactic Disc Using DENIS Data

Abstract

I will present the analysis of 3-colour (IJK _s ) near infrared star counts obtained during the commissioning phase of the Deep Near Infrared Southern Sky Survey (DENIS) project. Nine strips of 12’ of RA ×30° in declination crossing the galactic plane at different longitudes ranging from 217 °to 385 °, covering approximately 50 square degrees are analyzed. One strip has been measured in 3 colours, the others in J and K 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_sbands, respectively. Colour-colour diagrams are shown to be efficient tool for breaking out dwarf and giant star populations especiall y at low latitude, where the interstellar extinction strongly affects the far away red giants. Source counts are compared to the SKY model developed by Cohen (1997). This small sample of DENIS data is tentatively used to investigate the existence and the spatial distribution of the stellar populations associated with the molecular ring at R = 4 kpc. The detail of my work has been published in Ruphy et al., (1996), Ruphy, (1996) and Ruphy et al., (1997).