R Coronae Borealis stars

摘要

In the last ten years a significant step forward has been made toward a better understanding of the evolutionary status and unusual nature of the R Coronae Borealis (RCB) stars, a rare class of hydrogen-poor and carbon-rich variable stars. More detailed abundance analyses of the majority of RCB stars, and objects related to them, have become available in the last couple of years. In addition to this, recent theoretical studies of the most popular evolutionary models ("Double Degenerate" and "Final Flash") provide a new insight into the origin of these stars. Regarding the nature of the RCB declines, more observations from the light maxima and the decline phase are now available, including more data from space. However, the characteristics of the various emission lines appearing during the RCB declines, and the nature of their emitting regions, are still not entirely understood.