R Coronae Borealis stars and their dust
R Coronae Borealis (RCB) stars are the more prominent group of high luminosity hydrogen deficient stars that are rich in carbon and helium. They also show characteristic irregular light drops of several magnitudes (between 3 and 8 magnitudes) at unpredictable times, caused by expulsion of self-made clouds of dust. They range in
surface temperatures from 4500 K to 20000 K. Some of them seem to have made even such complex molecules like fullerenes (C60) in their circumstellar regions. Neither their evolutionary history nor the dust
formation mechanism are well understood. Two scenarios that have been suggested are that the present stars are a result of merger of two white dwarfs (CO+He) or a post born-again (AGB) giant that is surviving after a final helium shell flash. The talk would describe the RCB properties and highlight the problems and challenges they pose
in understanding their origins and dust production.