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Radial pulsations in DB white dwarfs?Theoretical models of DB white dwarfs are unstable against radial pulsation at effective temperatures near 20,000-30,000 K. Many high-overtone modes are unstable, with periods ranging from 12 s down to the acoustic cutoff period of approximately 0.1 s. The blue edge for radial instability lies at slightly higher effective temperatures than for nonradial pulsations, with the temperature of the blue edge dependent on the assumed efficiency of convection. Models with increased convective efficiency have radial blue edges that are increasingly closer to the nonradial blue edge; in all models the instability persists into the nonradial instability strip. Radial pulsations therefore may exist in the hottest DB stars that lie below the DB gap; the greatest chance for detection would be observations in the ultraviolet. These models also explain why searches for radial pulsations in DA white dwarfs have failed: the efficient convection needed to explain the blue edge for nonradial DA pulsation means that the radial instability strip is 1000 K cooler than found in previous investigations. The multiperiodic nature of the expected pulsations can be used to advantage to identify very low amplitude modes using the uniform spacing of the modes in frequency. This frequency spacing is a direct indicator of the mass of the star.
Document ID
19930041430
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Kawaler, Steven D.
(Iowa State Univ. of Science and Technology, Ames, United States)
Date Acquired
August 16, 2013
Publication Date
February 10, 1993
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 404
Issue: 1
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
93A25427
Funding Number(s)
CONTRACT_GRANT: NSF AST-91-15213
CONTRACT_GRANT: NAGW-1364
Distribution Limits
Public
Copyright
Other

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