Pulsation Periods of Rotating White Dwarfs

Abstract

The discovery by Hewish et al.^1,2 of pulsating radio sources with periods in the range of 0·25 to 1·34 s has stimulated renewed interest in the oscillation properties of highly condensed stars in the search for objects with fundamental periods of this order. Such calculations were made by Roxburgh and Durney³ in 1966 as part of an investigation into the stability of rotating white dwarfs and we recall their results in this paper. Their investigation was primarily concerned with determining at what point white dwarfs became dynamically unstable, and in particular in determining the effect of uniform rotation on the onset of instability. The calculations were done for pure helium white dwarfs with a Chandrasekhar equation of state and included the effects of general relativity and uniform rotation. Calculations with more realistic equations of state, but without the effect of rotation, have recently been undertaken by Meltzer and Thorne⁴ and corrected by Faulkner and Gribbin⁵, but these authors have not found periods as short as those observed.