RCrB and HdC Stars

HdC stars are hydrogen-deficeint carbon (HdC) stars. They likely formed from giants that have shed ALL of their hydrogen in the AGB stage, or were possibly created from the merger of white dwarfs. Typical HdC stars are not variable. RCrB stars are variable due to pulsations, and/or to circumstellar clouds of sooty carbon grains. These stars recently experienced a final He-shell flash.

Examples include RCrB, RYSgr, XXCam, and MVSgr.

Carbon features also make an appearance in the carbon stars, the DQ class of white dwarfs, and in comets.