UNSTABLE DEGENERATES REVISITED

Chandrasekhar & Tooper (1964) found that a sequence of increasingly ma ssive helium white dwarfs suffers a general relativistic pulsational i nstability when the radius R(M) has been reduced to a value such that R/R(S) congruent-to 246, where R(S) is the Schwarzschild radius 2GM/c2 . We show that this curious dimensionless number is essentially (2M(p) /m(e))2/3 congruent-to 238, where M(p) and m(e) are the masses of the proton and electron respectively. The case of different compositions i s also covered by our analysis; in general, the corresponding result i s (mu(e)M(p)/M(e))2/3, where mu(e) is the mean molecular weight per el ectron.