HE 1015–2050: DISCOVERY OF A HYDROGEN-DEFICIENT CARBON STAR AT HIGH GALACTIC LATITUDE

Abstract

Medium resolution spectral analysis of candidate Faint High Latitude Carbon (FHLC) stars from Hamburg/ESO survey has given us the potential to discover objects of rare types. Two primary spectral characteristics of R Coroanae Borealis (RCB) stars are hydrogen deficiency and weaker CN bands relative to C_{2} bands. They are also characterized by their characteristic location in the J-H, H-K plane with respect to cool carbon stars. From a spectral analysis of a sample of 243 candidate FHLC stars, we have discovered a hydrogen-deficient carbon (HdC) star HE 1015-2050, at high Galactic latitude. A differential analysis of its spectrum with that of the spectrum of U Aquarii (U Aqr), a well-known cool HdC star of RCB type, provides sufficient evidence to put this object in a group same as that of U Aqr. Further, it is shown that HE 1015-2050 does not belong to any of the C-star groups CH, C-R, C-N or C-J. Cool RCB stars form a group of relatively rare astrophysical objects; approximately 51 are known in the Galaxy and some 18 in the Large Magellanic Clouds (LMC) and five in Small Magellanic Cloud (SMC). The present discovery adds a new member to this rare group. Although its spectral characteristics and its location in the J-H vs H-K plane places HE 1015-2050 in the same group to which U Aqr belongs, extended photometric observations would be useful to learn if there is any sudden decline in brightness, this being a characteristic property of HdC stars of RCB type.