Optical Spectroscopy at Deep Light Minimum of R Coronae Borealis

Abstract

ABSTRACTWe present optical spectroscopy late in a deep minimum for the quintessential hydrogen-deficient carbon star R Coronae Borealis. Starting 3.5 years into the current deep and long minimum, we have secured observations that reveal some of the oddest optical spectra ever obtained for any astronomical object. Helium emission lines from triplet transitions, strong Ca II H and K emission, and forbidden lines of oxygen and nitrogen are the only spectral features observed. The spectra can be interpreted as coming from a chromospheric-like region lying above a carbon shell ejection front combined with a large-scale nebular-like region surrounding the star.“The variable star R Coronae Borealis is a jewel worthy of a place in any crown. It is one of the most interesting and most peculiar of all variables, and is often called the ideal irregular variable. Its times of minimum are distributed at random, according to the laws of pure chance”—Margaret Mayall (1962)