R Coronae Borealis stars at minimum light - UW Cen

Abstract

Two high-resolution optical spectra of the R Coronae Borealis (R CrB) star UW Cen in decline are discussed. A spectrum from mid-1992 when the star had faded by 3 mag shows just a few differences with the spectrum at maximum light. The ubiquitous sharp emission lines seen in R CrB at a similar drop below maximum light are absent. In contrast, a spectrum from mid-2002 when the star was 5 mag below maximum light shows an array of sharp emission lines and a collection of broad emission lines. Comparisons are made with spectra of R CrB obtained during the deep 1995–1996 minimum. The many common features are discussed in terms of a torus-jet geometry.