The 21st European Workshop on White Dwarfs was held in Austin, TX from July 23rd to 27th of 2018The standard theory of pulsations deals with the
frequencies and growth rates of infinitesimal perturbations
in a stellar model. Modes which are calculated
to be linearly driven should increase their
amplitudes exponentially with time; the fact that
nearly constant amplitudes are usually observed
is evidence that nonlinear mechanisms inhibit the
growth of finite amplitude pulsations. Models predict
that the mass of DAV convection zones is very
sensitive to temperature (i.e., MCZ is proportional to T -90
eff ), leading
to the possibility that even “small amplitude”
pulsators may experience significant nonlinear effects.
In particular, the outer turning point of finite amplitude
g-mode pulsations can vary with the
local surface temperature, producing a reflected
wave that is slightly out of phase with that required
for a standing wave. This can lead to a lack of coherence
of the mode and a reduction in its global
amplitude. We compute the size of this effect for
specific examples and discuss the results in the context
of Kepler and K2 observations.Astronom