Z Ursa Minoris - A new R coronae borealis variable

Priscilla J. Benson, Wellesley College
Geoffrey C. Clayton, University of Colorado Boulder
Peter Garnavich, National Research Council Canada
Paula Szkody, University of Washington


We have monitored Z Ursa Minoris using a V filter beginning 1992 April. It suddenly dimmed by almost 6 mag in late summer 1993. We obtained a spectrum 1993 November 20.54 UT which confirms that Z UMi is probably an R Coronae Borealis (RCB) star. The spectrum of Z UMi shows the strong carbon bands and weak hydrogen lines of an RCB star. It also shows the typical late decline emission in the Na I D lines. The light curve shows evidence for stellar pulsations as well as the large and rapid fading which characterizes the RCB stars.