Stellar populations in a standard ISOGAL field in the Galactic disc^*

¹ Institut d'Astrophysique de Paris, CNRS and Université Paris 6, 98bis boulevard Arago, 75014 Paris, France e-mail: shashi@iap.fr
² Physical Research Laboratory, Navrangpura, Ahmedabad-380 009, India e-mail: shashi@prl.res.in
³ Observatoire de Besançon, Besançon, France
⁴ Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany
⁵ GEPI, UMS-CNRS 2201, Observatoire de Paris, France

Received: 28 February 2008
Accepted: 3 September 2008

Abstract

Aims. We identify the stellar populations (mostly red giants and young stars) detected in the ISOGAL survey at 7 and 15 μm towards a field (LN45) in the direction , .

Methods. The sources detected in the survey of the Galactic plane by the Infrared Space Observatory were characterised based on colour-colour and colour-magnitude diagrams. We combine the ISOGAL catalogue with the data from surveys such as 2MASS and GLIMPSE. Interstellar extinction and distance were estimated using the red clump stars detected by 2MASS in combination with the isochrones for the AGB/RGB branch. Absolute magnitudes were thus derived and the stellar populations identified from their absolute magnitudes and their infrared excess.

Results. A standard approach to analysing the ISOGAL disc observations has been established. We identify several hundred RGB/AGB stars and 22 candidate young stellar objects in the direction of this field in an area of 0.16 deg². An overdensity of stellar sources is found at distances corresponding to the distance of the Scutum-Crux spiral arm. In addition, we determined mass-loss rates of AGB-stars using dust radiative transfer models from the literature.