Pulsation properties of DA white dwarfs: radial mode instabilities

Journal Article · Tue Feb 15 00:00:00 EST 1983 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/160740· OSTI ID:6303205

Saio, H; Winget, D E; Robinson, E L

We have solved the equations describing linear, nonadiabatic, radial pulsations for models of compositionally stratified, evolving, DA white dwarfs. We find a kappa-mechanism, radial mode, instability strip that is caused by the development of a hydrogen partial ionization zone during the evolutionary cooling of our models. Instabilities occur for radial modes with periods, product, in the range 4> or approx. =product> or approx. =0.2 s, with e-folding growth times, tau/sub e/, in the range 2 x 10/sup 9/> or approx. =tau/sub e/ > or approx. =8 x 10/sup 2/ s; the minimum growth times occur in the shortest period unstable modes. Comparison with our previous calculations for nonradial pulsations indicates that the blue edge for the radial instability strip is approx.1600 K hotter than the blue edge of the theoretical ZZ Ceti instability strip, and further, that the maximum instability occurs at temperatures approx.600 K hotter than the blue edge of the theoretical ZZ Ceti instability strip. Our results also indicate that the development of this instability strip is insensitive to the mass of the surface hydrogen layer and to uncertainties in the hydrogen opacities. We demonstrate that existing observations of the DA white dwars are insufficient to determine if such radial pulsations exist in the DA white dwarfs, and we evaluate the prospects for detecting these pulsations in the future.

• Research Organization: McDonald Observatory and Department of Astronomy, University of Texas at Austin
• OSTI ID: 6303205
• Journal Information: Astrophys. J.; (United States), Vol. 265:2
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
WHITE DWARF STARS
PULSATIONS
HELIUM
HYDROGEN
INSTABILITY
IONIZATION
NUMERICAL SOLUTION
OSCILLATION MODES
OSCILLATIONS
STAR MODELS
DWARF STARS
ELEMENTS
FLUIDS
GASES
MATHEMATICAL MODELS
NONMETALS
RARE GASES
STARS
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources