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Title: Why DA and DB white dwarfs do not show coronal activity and p-mode oscillations

The problems of nonradiative heating of outer atmospheric layers and p-mode oscillations in white dwarfs caused by acoustic waves generated in convective zones are discussed. These effects have been studied by calculating the cutoff periods for adiabatic and isothermal waves propagating in atmospheres of DA and DB stars with Teff greater than or equal 20,000 K and log g = 6-9. The obtained cutoff periods are approximately bounded by 0.01 and 40 sec for high- and low-gravity white dwarfs, respectively. Expected amplitudes of p-mode oscillations corresponding to trapped acoustic waves with small angular wave numbers are estimated, indicating that the amplitudes could be observed as Doppler shifts of spectral lines which might be detectable if adequate spectral resolution were available. The luminosity variations corresponding to these amplitudes are unlikely to be observable when all damping processes are accounted for. Results also indicate that the present theory of convection predicts some irregularities in the behavior of physical parameters. 34 refs.
Authors:
;  [1]
  1. (NASA, Marshall Space Flight Center, Huntsville, AL (USA))
Publication Date:
OSTI Identifier:
7265997
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; (USA); Journal Volume: 346
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; WHITE DWARF STARS; STELLAR ACTIVITY; LUMINOSITY; OSCILLATIONS; SOUND WAVES; STELLAR ATMOSPHERES; STELLAR CORONAE; VARIATIONS; WAVE PROPAGATION; ATMOSPHERES; DWARF STARS; OPTICAL PROPERTIES; PHYSICAL PROPERTIES; STARS 640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar, Radio & X-Ray Sources