Nonradial oscillations of cooling white dwarfs.
Abstract
The equations for linear adiabatic nonradial oscillations have been solved for cooling whitedwarf models. Periods and eigenfunctions are obtained for the g2, g1, P', P2 modes of nonradial quadrupole oscillations. Periods of the g1mode range from 50 to 200 seconds for typical white dwarf stars with M = 0.4 1.0M0 and L = 104L0 102L0. It is shown that there exist periodluminosity relations for gmodes along the cooling whitedwarf sequence. The damping of nonradial oscillations due to radiative heat leakage, neutrino losses, and gravitational radiation is studied in the quasiadiabatic approximation, and all models are found to be pulsationally stable. It is found that the emission of gravitational waves is the most efficient mechanism for the damping of f and pmodes while radiative heat leakage is the most efficient for gmodes. Damping times range from a few tens of years to about 10 yearstime scales much shorter than Kelvin or cooling times for white dwarfs. Results are compared with observations of ultrashortperiod variables. It is suggested that light variations of HL Tau 76 (P = 747 s) and G4432 (F = 600 s) may be associated with nonradial g1 oscillations of white dwarfs with convective envelopes. The importance of gravitational radiation from nova outbursts is also discussed. Subject headings: gravitation  interiors, stellar  pulsation  white dwarf stars
 Publication:

The Astrophysical Journal
 Pub Date:
 October 1973
 DOI:
 10.1086/152415
 Bibcode:
 1973ApJ...185..277O