The Hydrogen-deficient Carbon Stars: Advances in Formation and Dust Production - Courtney Crawford

Courtney Crawford - Sydney Uinversity
The Hydrogen-deficient Carbon Stars: Advances in Formation and Dust Production
The Hydrogen-deficient Carbon (HdC) stars are a class of exotic variable supergiants with distinct abundances. There are two types: the famously dust-producing R Coronae Borealis (RCB) variables and their dustless counterparts the dustless HdC (dLHdC) stars. The RCB stars have been known for nearly 2 centuries, and yet our understanding of these stars is only recently becoming clear. The study of these stars has a rich history though many questions remain unanswered. In this review, I will present a summary of what we know about these stars, which includes new research on their formation via double-white-dwarf (DWD) merger, and the first large scale study of their dust formation properties. I will show that the dLHdC stars are likely formed by a different DWD merger population than the dusty RCB stars. I will also show evidence that the dust production frequency increases as the stellar temperature decreases and show the first evidence that the dust production may be intrinsically tied to the stellar pulsations.