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

M. Schultheis·M. Parthasarathy·A. Omont·M. Cohen·S. Ganesh·F. Sevre·G. Simon
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Abstract

An analysis of low resolution spectra and infared data of 29 ISOGAL-DENIS sources with mid-IR excess is presented. Eight ISOGAL sources from our sample with 7-15 micron excess 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 (B7III), show a bump between 5000 and 6000 Angstroem which maybe 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.

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M. Schultheis, M. Parthasarathy, A. Omont, M. Cohen, S. Ganesh, F. Sevre, G. Simon. 2002-02-22. Low resolution spectroscopy of ISOGAL sources: Search for early-type stars with infrared excess. https://doi.org/10.1051/0004-6361%3A20020282

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