The ISOGAL field FC–01863+00035: Mid-IR interstellar extinction and stellar populations ^*,**,***

¹ Department of Astronomy, Beijing Normal University, Beijing 100875, PR China
² Institut d'Astrophysique de Paris, CNRS, 98 bis Bd Arago, 75014 Paris, France
³ National Astronomical Observatories, Chinese Academy of Sciences, Datun Rd. No.20(A), Beijing 100012, PR China (on leave)
⁴ Physical Research Laboratory, Navarangpura, Ahmedabad 380009, India
⁵ GEPI, Observatoire de Paris, 21 avenue de l'Observatoire, 75014 Paris, France

Corresponding author: B. W. Jiang, bjiang@bnu.edu.cn

Received: 18 July 2002
Accepted: 23 December 2002

Abstract

A 0.35° 0.29°field centered at °, ° was observed during the ISOGAL survey by ISOCAM imaging at 7 μm and 15 μm. 648 objects were detected and their brightness are measured.
By combining with the DENIS data in the near-infrared J and K_S bands, one derives the extinction at 7 μm through which yields from the near-IR extinction values of van de Hulst–Glass (Glass 1999). The extinction structure along the line of sight is then determined from the values of or K_S–[7] of the ISOGAL sources identified as RGB or early AGB stars with mild mass-loss. The distribution of A_V ranges from 0 to ~45 and it reflects the concentration of the extinction in the spiral arms. Based on their locations in color-magnitude diagrams and a few cross-identifications with IRAS and MSX sources, the nature of objects is discussed in comparison with the case of a low extinction field in Baade's Window. Most of the objects are either AGB stars with moderate mass loss rate or luminous RGB stars. Some of them may be AGB stars with high mass loss rate. In addition, a few young stellar objects (YSOs) are present.