ON THE HYDROGEN-DEFICIENT NATURE OF Z-URSAE-INORIS

Z Ursae Minoris was classified by Benson et al, (1994, AJ, 108, 247) a s an R Coronae Borealis (RCB) variable star from its light variations. Hydrogen deficiency, which is a defining feature of RCB stars, was no t established. To investigate this aspect we have obtained high-resolu tion spectra in both blue (4200-4630 Angstrom) and red (5050-7950 Angs trom) regions. Lines of the CH molecule (G band) at about 4300 Angstro m, which are present in spectra of N-type carbon stars are weak or abs ent in the spectrum of Z UMi indicating its hydrogen-deficient nature and membership of the rare class of RCB variables.