DENIS and ISOGAL properties of variable star candidates in the Galactic Bulge
Résumé
Repeated DENIS observations (summer 1996 & 1998) in the J (1.25 mu m) and the KS (2.15 mu m) bands are used to look for variable stars. We present two catalogues of ~ 1000 probable variables in an area of ~ 4 deg2 of the inner galactic bulge. The first one contains ~ 720 variable star candidates which show variability in J and KS while the second consists of sources only observed to be variable in KS (~ 270 sources), mainly in regions with high interstellar extinction. Using the extinction map by Schultheis et al. (\cite{Schultheis99a}), most of the variable stars are found to be above the RGB tip and thus belong to the AGB while there is a small fraction of candidates which could be below the RGB tip with rather small ``amplitudes'' of ~ 0.3-0.4 mag in KS. Our catalogue has been cross-correlated with five ISOGAL fields (total area ~ 0.5 deg2) in order to study the mid-IR properties of the LPVs. The AGB variables can be distinguished from other M-type giants by their high 7 mu m luminosities and redder K0-[7] colours. Based on a few repeated ISOCAM observations a good correlation is found between near- and mid-IR variability. This is paper no.~7 in a refereed journal based on data from the ISOGAL project. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA. Based on observations collected at the European Southern Observatory, La Silla Chile
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