1997PASP..109..796G

Z Ursa Minoris was classified by Benson et al. (1994) a a R Coronae Borealis (RCB) variable star from its light variations. Hydrogen deficiency, which is a defining feature of RCB stars, was not established. To investigate this aspect we have obtained high resolution spectra in both blue (4200-4630Å) and red (5050-7950Å) regions. Lines of the CH molecule (G band) at about 4300Å, which are present in spectra of N-type carbon stars are weak or absent in the spectrum of Z UMi indicating its hydrogen deficient nature and membership of the rare class of RCB variables.