Linear, nonadiabatic analysis of nonradial oscillations of massive near main sequence stars
Journal Article
·
· Astrophys. J.; (United States)
The equations for linear, nonadiabatic, nonradial oscillations have been solved for models with 7 M/sub sun/, 12 M/sub sun/, and 20 M/sub sun/ in the core-hydrogen burning and hydrogen exhaustion phases. Although the nonadiabatic periods are essentially the same as those of the corresponding adiabatic ones for those models investigated, the e-folding times for the oscillation amplitude are considerably different from the results of a quasi-adiabatic analysis, in particular for f and p modes. All the modes investigated are stable. However, the opacity bump near the He/sup +/ ionization zone has a destabilizing influence on nonradial modes in the 7 M/sub sun/ models about as strong as on purely radial oscillations. The effective temperatures of the 12 M/sub sun/ and 20 M/sub sun/ models are too high for the opacity bump mehcanism to be effective as a destabilizing mechanism for nonradial modes. For the g/sup +/ modes another driving zone exists in the intermediate-to-high temperature region. This driving zone's effect on stability is larger than the destabilizing effect of the nuclear reactions of zero-age main-sequence models. The phase lag of maximum luminosity behind minimum radius is small except for relatively high order g/sup +/ modes, for which the maximum luminosity and the maximum temperature occur near the phase of maximum radius because of the dominant effect of horizontal motions. ''Avoided crossing'' of the modes in evolved models is also discussed.
- Research Organization:
- Joint Institute for Laboratory Astrophysics, University of Colorado and National Bureau of Standards
- OSTI ID:
- 5286577
- Journal Information:
- Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 236:2; ISSN ASJOA
- Country of Publication:
- United States
- Language:
- English
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