Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a...102..375d&link_type=abstract
Astronomy and Astrophysics, vol. 102, no. 3, Oct. 1981, p. 375-385.
Astronomy and Astrophysics
Astrophysics
99
Hydrogen, Stellar Gravitation, Stellar Oscillations, White Dwarf Stars, Linear Equations, Nonadiabatic Theory, Propagation Modes, Stellar Envelopes, Stellar Models, Systems Stability
Scientific paper
A linear nonadiabatic stability analysis is presented of gravity modes for chemically stratified DA white dwarf envelopes. Two slightly overlapping instability strips are found, differentiated by the amount of hydrogen in the outer envelope. For 'hydrogen poor' DAs, the instability strip is in the temperature range from 11,500 K to approximately 13,500 K. Here, the Kappa mechanism in the helium partial ionization zone is responsible for driving the pulsations. For 'hydrogen rich' DAs, the instability strip is between approximately 10,000 K and 11,500 K, and the Kappa mechanism in the hydrogen partial ionization zone drives the pulsations. Comparison with observations, especially the multichannel spectrophotometry, indicates that there is no ZZ Ceti star hotter than 12,000 K. This agrees with the theoretical results presented here so long as the DAs have enough hydrogen in their outer layers when they reach the instability strip.
Dolez Noel
Vauclair Gerard
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