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 the Hamburg/ESO survey has given us the potential to discover objects of rare types. Two primary spectral characteristics of R Coronae Borealis (RCB) stars are hydrogen deficiency and weaker CN bands relative to C2 bands. They are also characterized by their characteristic location in the J – H and H – K planes 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 same group as that of U Aqr. Furthermore, 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 Cloud and five in the Small Magellanic Cloud. The present discovery adds a new member to this rare group. Although its spectral characteristics and its location in the J – H versus H – K plane place 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.