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Astron. Astrophys. 326, 597-607

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Stellar populations and inhomogeneities
of the galactic plane from DENIS star counts*

S. Ruphy1, N. Epchtein1, M. Cohen2, E. Copet1, B. de Batz1, J. Borsenberger3, P. Fouqué1,5, S. Kimeswenger4, F. Lacombe1, T. Le Bertre1, D. Rouan1, and D. Tiphène1

1Observatoire de Paris, F-92195 Meudon, France
2Radio Astronomy Laboratory, University of California, Berkeley, CA 94720, USA
3Institut d'Astrophysique de Paris, 98 bis Bd. Arago, F-75014 Paris, France
4Institut für Astronomie der Leopold-Franzens Universität, Technikerstraße 25, A-6020 Innsbruck, Austria
5European Southern Observatory, Casilla 19001, Santiago 19, Chile

Received 17 April 1997 / Accepted 23 May 1997


This paper reports on the analysis of 3-colour (IJKs) near infrared star counts obtained during the commissioning phase of the Deep Near Infrared Southern Sky Survey (DENIS) project. Observing methods, data processing, source extraction and calibration are briefly outlined. Nine strips of 12' of RA x 30FORMULA in declination crossing the galactic plane at different longitudes ranging from 217FORMULA to 385FORMULA , covering approximately 50 square degrees are analyzed. One strip has been measured in 3 colours, the others in J and Ks 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 Ks bands, respectively. Colour-colour diagrams are shown to be efficient tool for breaking out dwarf and giant star populations especially at low latitude, where the interstellar extinction strongly affects the far away red giants. Source counts are compared to the SKY model developed by Wainscoat et al. (1992). 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 RG.C. = 4 kpc.

Key words: galaxy: structure - galaxy: stellar content - infrared: stars

*Based on observations collected at the European Southern Observatory, La Silla, Chile

Send offprint requests to: epchtein@obspm.fr

© European Southern Observatory (ESO) 1997

Online publication: September 18, 1997
Last change: October 15, 1997