The evolutionary considerations of R CR B stars - Observational approach

Abstract

The properties of the hydrogen-deficient stars called extreme helium stars, R Cr B stars, and hydrogen-deficient carbon stars are briefly examined, emphasizing the R Cr B stars. Luminosities and temperatures, distribution and kinematics, abundances, pulsations, circumstellar environment, and structure and origin are addressed. The stage of stellar evolution at which a medium-mass star of normal composition could become hydrogen-deficient is considered.