Stability and Radial Vibration Periods of the Hamada-Salpeter White Dwarf Models

Abstract

The recent discovery by Hewish et al. ^1,2 of rapidly pulsing radio sources with periods of ~ 1·337, 1·274, 1·188 and 0·2531 s has already provoked a considerable amount of activity among theoretical astrophysicists. Hewish et al. sought an explanation in terms of the radial vibrations of white dwarf or neutron star models as calculated by Meltzer and Thorne³ (hereafter MT). The apparent failure of the MT white dwarfs to pulsate in the fundamental mode with a period less than ~8s led Hewish et al. to suggest tentatively that neutron stars might possibly be responsible. While several authors have proposed other, more or less bizarre theories^4–6, we shall show in this article that the white dwarf explanation may have been dismissed prematurely. We have found that the fundamental periods for the reasonably realistic white-dwarf models of Hamada and Salpeter⁷ can be as low as ~1·79 to ~ 2·05 s, the actual value being somewhat dependent on the composition.