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Excitation of Gravity-Mode Pulsations in DA & DB White Dwarfs

Published online by Cambridge University Press:  12 April 2016

Yanqin Wu
Yanqin Wu*
Affiliation:
Astronomy Unit, School of Mathematical Sciences, Queen Mary and Westfield College, Mile End Road, London E1 4NS, UK

Abstract

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Oscillations in white dwarfs of hydrogen or helium envelopes are believed to be excited close to the surface, where convective energy transport dominates the stellar luminosity. The convective motion in these stars is fast and can respond instantaneously to the pulsation state. In this limit, we find the convective envelope to be the seat of mode excitation because it acts as an insulating blanket with respect to the perturbed flux that enters it from below. This retaining of the flux leads to driving. Driving exceeds radiative damping provided ωτc ≥ 1, where ω is the radian frequency of the mode and τc ≈ 4τth with τth being the thermal time constant evaluated at the base of the convective envelope. We follow Brickhill (1991) in naming this mechanism as ‘convective driving’. We also studied the dynamical interaction between turbulent convection and pulsation. In the limit of fast convection, turbulent damping inside the convective region is negligible, while that coming from the overshoot region is more significant. I discuss the application of ‘convective driving’ in other types of pulsating stars.

Type
Part 7. Pulsating White Dwarfs and Subdwarfs
Information
International Astronomical Union Colloquium , Volume 176: The Impact of Large-Scale Surveys on Pulsating Star Research , 2000 , pp. 508 - 513
Copyright
Copyright © Astronomical Society of the Pacific 2000

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