The R Coronae Borealis stars
This year marks the bicentennial of the discovery of the variability of R Coronae Borealis. The R Coronae Borealis (RCB) stars are distinguished from other hydrogen-deficient objects by their spectacular dust-formation episodes. They may decline by up to 8 magnitudes in a few weeks, revealing a rich emission-line spectrum. Their atmospheres have unusual abundances with very little hydrogen and an overabundance of carbon and nitrogen. The RCB stars are thought to be the product of a final helium shell flash or the coalescence of a binary white-dwarf system. Dust may form in non-equilibrium conditions created behind shocks caused by pulsations in the atmospheres of these stars. The RCB stars are interesting and important, first because they represent a rare, or short-lived stage of stellar evolution, and second because these stars regularly produce large amounts of dust so they are laboratories for the study of dust formation and evolution.
Publication Source (Journal or Book title)
Publications of the Astronomical Society of the Pacific
Clayton, G. (1996). The R Coronae Borealis stars. Publications of the Astronomical Society of the Pacific, 108 (721), 225-241. https://doi.org/10.1086/133715