Abstract
We present results of realistic 21) numerical radiation hydrodynamics calculations, simulating the surface convection zones of DA white dwarfs in the range of effective temperatures from 14 200 K down to 11400 K. Comparison with mixing length theory (MLT) yields a conflicting picture: The dynamics of convection is not governed by up- and downflowing bubbles which dissolve after travelling some characteristic distance - but by the formation, advection, merging, and disruption of fast narrow downdrafts in a slowly upstreaming surrounding. MLT tremendously underestimates the depth of the region where material is mixed. Nevertheless, it turns out that a mixing length model with α = 1.5 gives a good fit of the photospheric temperature structure (T eff = 12 600 K) and that a 1D temperature stratification suffices to reproduce the mean spectrum of the 2D simulations, indicating that the photospheric temperature inhomogeneities are negligible for spectroscopic analysis. In deeper layers the temperature stratification of our hydrodynamical models corresponds to larger values of α. Introducing our envelope models into nonadiabatic pulsation calculations results in a blue edge of the ZZ Ceti instability strip near T eff = 12 400 K at log g = 8.0.
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References
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© 1995 Springer Verlag
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Freytag, B., Steffen, M., Ludwig, HG. (1995). Numerical simulations of convection and overshoot in the envelope of DA white dwarfs. In: Koester, D., Werner, K. (eds) White Dwarfs. Lecture Notes in Physics, vol 443. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-59157-5_179
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DOI: https://doi.org/10.1007/3-540-59157-5_179
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