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| Paper: |
Excitation of Gravity-Mode Pulsations in DA & DB White Dwarfs |
| Volume: |
203, The Impact of Large-Scale Surveys on Pulsating Star Research, IAU Colloquium 176 |
| Page: |
508 |
| Authors: |
Wu, Y. |
| Abstract: |
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 ω τc >= 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. |
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