O-18 and the origins of HdC and R CrB stars

We have detected enormously enhanced O-18 and correspondingly small values of O-16/O-18 in many hydrogen-deficient carbon (HdC) stars and R Coronae Borealis (R CrB) stars. The similar ratios suggest a common origin for the two types of stars. Of the two leading candidates for the origin of R. CrB stars, white dwarf mergers and final helium flashes., the former appears more likely to produce this and other observed isotopic anomalies.