EDP Sciences
Free access
Volume 386, Number 3, May II 2002
Page(s) 899 - 909
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20020282

A&A 386, 899-909 (2002)
DOI: 10.1051/0004-6361:20020282

Low resolution spectroscopy of ISOGAL sources: Search for early-type stars with infrared excess

M. Schultheis1, M. Parthasarathy2, 3, A. Omont1, M. Cohen4, S. Ganesh5, F. Sevre1 and G. Simon6

1  Institut d'Astrophysique de Paris, CNRS, 98bis Bld. Arago, 75014 Paris, France
2  Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
3  National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
4  Radio Astronomy Laboratory, University of California, Berkeley, CA 94720, USA
5  Physical Research Laboratory, Navarangpura, Ahmedabad 380009, India
6  DASGAL CNRS UMR 8633, Observatoire de Paris, France

(Received 8 August 2001 / Accepted 22 February 2002 )

An analysis of low resolution spectra and infrared data of 29 ISOGAL-DENIS sources with mid-IR excess is presented. Eight ISOGAL sources from our sample with 7-15 $\mu$m excesses are found to be B and A-type stars, some of them with emission lines. Two ISOGAL sources, J175614.4-240831 (B3-4IIIe) and J173845.3-312403 (B7IIIe), show a bump between 5000 and 6000 Å  which may be attributed to extended red emission (ERE). Some of the B, A and F-type giants with a large infrared excess might be in the post-AGB phase. For about 50% of the sources in this preliminary study, a nearby second (or even multiple) component was found. Such sources, in particular two B-stars, are not discussed when the probability of the optical spectrum being associated with the ISOGAL source is low. These results confirm that the DENIS-ISOGAL I-J/K-[15] diagram is the most suitable diagram to distinguish between early (AB) and late spectral types (KM). It provides the most useful tool to systematically search for nearby early-type stars with an infrared excess among the background of distant AGB stars in ISOGAL fields of the Galactic disk.

Key words: stars: AGB and post-AGB -- stars: early-type -- Galaxy: solar neighbourhood -- ISM: reflection nebulae -- ISM: dust, extinction

Offprint request: M. Schultheis, schulthe@iap.fr

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