Hydrogen­deficient stars and stellar systems C. Simon Jeffery Dept of Physics and Astronomy, University of St Andrews, Fife KY16 9SS, Scotland (email: csj @ st­and.ac.uk). ... 1986). ... The former are well known as RCrB stars, the latter have become generally known as `hydrogen­deficient carbon stars' (HdC), although Warner's (1967) original use of the term was intended to apply to all H­def objects with excess carbon. ... 1991: ApJ 378, 326 C.S.Jeffery: Hydrogen­deficient stars Figure 1. ...