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Time-dependent Turbulence in Stars

Published online by Cambridge University Press:  12 August 2011

W. David Arnett  and
Casey Meakin
W. David Arnett
Affiliation:
Steward Observatory, University of Arizona, Tucson AZ 85721, USA email: wdarnett@gmail.com
Casey Meakin
Affiliation:
Steward Observatory, University of Arizona, Tucson AZ 85721, USA email: wdarnett@gmail.com
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Abstract

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Three-dimensional (3D) hydrodynamic simulations of shell oxygen burning by Meakin & Arnett (2007b) exhibit bursty, recurrent fluctuations in turbulent kinetic energy. These are shown to be due to a global instability in the convective region, which has been suppressed in simulations of stellar evolution which use mixing-length theory (MLT). Quantitatively similar behavior occurs in the model of a convective roll (cell) of Lorenz (1963), which is known to have a strange attractor that gives rise to random fluctuations in time. An extension of the Lorenz model, which includes Kolmogorov damping and nuclear burning, is shown to exhibit bursty, recurrent fluctuations like those seen in the 3D simulations. A simple model of a convective layer (composed of multiple Lorenz cells) gives luminosity fluctuations which are suggestive of irregular variables (red giants and supergiants, see Schwarzschild (1975). Details and additional discussion may be found in Arnett & Meakin (2011).

Apparent inconsistencies between Arnett, Meakin, & Young (2009) and Nordlund, Stein, & Asplund (2009) on the nature of convective driving have been resolved, and are discussed.

Keywords

turbulenceirregular variablesconvection
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 6 , Symposium S271: Astrophysical Dynamics: From Stars to Galaxies , June 2010 , pp. 205 - 212
Copyright
Copyright © International Astronomical Union 2011

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