Hydrodynamic simulations of He shell flash convection

Falk Herwig, Bernd Freytag, Robert M. Hueckstaedt, Francis Timmes

Research output: Contribution to journalArticle

53 Citations (Scopus)

Abstract

We present the first hydrodynamic, multidimensional simulations of He shell flash convection. We investigate the properties of shell convection immediately before the He luminosity peak during the 15th thermal pulse of a stellar evolution track with initially 2 solar masses and metallicity Z = 0.01. This choice is a representative example of a low-mass asymptotic giant branch thermal pulse. We construct the initial vertical stratification with a set of polytropes to resemble the stellar evolution structure. Convection is driven by a constant volume heating in a thin layer at the bottom of the unstable layer. We calculate a grid of two-dimensional simulations with different resolutions and heating rates, plus one low-resolution three-dimensional run. The flow field is dominated by large convective cells that are centered in the lower half of the convection zone. It generates a rich spectrum of gravity waves in the stable layers both above and beneath the convective shell. The magnitude of the convective velocities from our one-dimensional mixing-length theory model and the rms-averaged vertical velocities from the hydrodynamic model are consistent within a factor of a few. However, the velocity profile in the hydrodynamic simulation is more asymmetric and decays exponentially inside the convection zone. Both g-modes and convective motions cross the formal convective boundaries, which leads to mixing across the boundaries. Our resolution study shows consistent flow structures among the higher resolution runs, and we see indications for convergence of the vertical velocity profile inside the convection zone for the highest resolution simulations. Many of the convective properties, in particular the exponential decay of the velocities, depend only weakly on the heating rate. However, the amplitudes of the gravity waves increase with both the heating rate and the resolution.

Original languageEnglish (US)
Pages (from-to)1057-1074
Number of pages18
JournalAstrophysical Journal
Volume642
Issue number2 I
DOIs
StatePublished - May 10 2006
Externally publishedYes

Fingerprint

flash
convection
hydrodynamics
shell
heating
simulation
stellar evolution
gravity waves
velocity profile
gravity wave
velocity distribution
high resolution
flow structure
decay
stratification
pulses
flow field
metallicity
flow distribution
indication

Keywords

  • Convection
  • Hydrodynamics
  • Nuclear reactions, nucleosynthesis, abundances stars: AGB and post-AGB

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Hydrodynamic simulations of He shell flash convection. / Herwig, Falk; Freytag, Bernd; Hueckstaedt, Robert M.; Timmes, Francis.

In: Astrophysical Journal, Vol. 642, No. 2 I, 10.05.2006, p. 1057-1074.

Research output: Contribution to journalArticle

Herwig, F, Freytag, B, Hueckstaedt, RM & Timmes, F 2006, 'Hydrodynamic simulations of He shell flash convection', Astrophysical Journal, vol. 642, no. 2 I, pp. 1057-1074. https://doi.org/10.1086/501119
Herwig, Falk ; Freytag, Bernd ; Hueckstaedt, Robert M. ; Timmes, Francis. / Hydrodynamic simulations of He shell flash convection. In: Astrophysical Journal. 2006 ; Vol. 642, No. 2 I. pp. 1057-1074.
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