Nonradial instability strips based on carbon and oxygen partial ionization in hot, evolved stars

Journal Article · Fri Jun 15 04:00:00 EDT 1984 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/162158· OSTI ID:6409408

Starrfield, S; Cox, A N; Kidman, R B; Pesnell, W D

We have calculated periods and growth rates for a new class of nonradically pulsated variable stars in the linear, nonradial nonadiabatic theory. The best observed member of this class is PG 1159-035 which is observed to be pulsating in a number of periods around 500 s and may well have an effective temperature exceeding 10/sup 5/ K. Stellar envelopes constructed for a 0.6 M star are in the effective temperature range 7 x 10/sup 4/ K< or =T/sub e/< or =1.5 x 10/sup 5/ K following the white dwarf cooling track at radii 0.016-0.030 R. These envelopes have compositions of half carbon and half oxygen by mass. We assume that the observed periods are nonradial g-modes (l = 2 or 3) and search in the interval between approx.25 s and 1200 s, to find regions of instability for a very broad range of effective temperatures. Blue edges of our instability strips are strongly dependent upon both the thermal structure and the interior composition. Pure carbon envelopes have nonradial blue edge at T< or =10/sup 5/ K, while the half-carbon, half-oxygen envelopes have a nonradial blue edge exceeding 1.5 x 10/sup 5/ K. The pulsation excitation mechanism is the cyclical ionization of the K-shell electrons of carbon and oxygen at an interior temperature approx.10/sup 6/ K. These results imply that PG 1159-035 has a significant amount of oxygen present in its surface layers, and while current stellar evolution theory predicts that this oxygen is produced during helium shell flashes, its presence this close to the surface (M/sub s/approx. 10/sup 12/M)) implies that extremely efficient stellar mass loss mechanisms have ejected the entire hydrogen and most of the helium envelopes.

• Research Organization: Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545
• OSTI ID: 6409408
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 281:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics &amp; Cosmology-- Stars &amp; Quasi-Stellar
Radio &amp; X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ATMOSPHERES
CARBON
CONVECTION
DWARF STARS
ELEMENTS
ENERGY TRANSFER
HEAT TRANSFER
HYDROGEN
IONIZATION
LUMINOSITY
MASS TRANSFER
MATHEMATICAL MODELS
MATHEMATICS
NONMETALS
NUMERICAL ANALYSIS
OPTICAL PROPERTIES
OSCILLATION MODES
OXYGEN
PHYSICAL PROPERTIES
PULSATIONS
STAR EVOLUTION
STAR MODELS
STARS
STELLAR ATMOSPHERES
VARIABLE STARS
WHITE DWARF STARS