next up previous
Next: Physical Characteristics Up: Basic Properties Previous: Galactic distribution and absolute

Numbers and distances

The absolute magnitude of the RCBs in the LMC and the small number of Galactic RCBs implies that they are very rare stars. Together with statistics for related stars, the total number of hydrogen-deficient stars in the Galaxy is estimated to be about 1000. Whilst the luminosity of RCBs is similar to that of other low-mass stars as they evolve rapidly from the asymptotic RED GIANT branch to become WHITE DWARFS, their frequency is much lower. They do not, it seems, represent a stage in the evolution of all normal low-mass stars.

From the preceding estimates of mass and luminosity, it is seen that RCBs have very high luminosity-to-mass ratios ( $L/M\sim10\,000$) and lie close to the Eddington limit for radiative stability. If they were any more luminous, their atmospheres would be expelled by radiation pressure.

Simon Jeffery