NUMERICAL SIMULATIONS OF A ROTATING RED GIANT STAR. I. THREE-DIMENSIONAL MODELS OF TURBULENT CONVECTION AND ASSOCIATED MEAN FLOWS

Journal Article · Thu Sep 10 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/702/2/1078; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21336047

Brun, A S ^[1]

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1. DSM/IRFU/SAp, CEA-Saclay and UMR AIM, CEA-CNRS-Universite Paris 7, 91191 Gif-sur-Yvette (France)

With the development of one-dimensional stellar evolution codes including rotation and the increasing number of observational data for stars of various evolutionary stages, it becomes more and more possible to follow the evolution of the rotation profile and angular momentum distribution in stars. In this context, understanding the interplay between rotation and convection in the very extended envelopes of giant stars is very important considering that all low- and intermediate-mass stars become red giants after the central hydrogen burning phase. In this paper, we analyze the interplay between rotation and convection in the envelope of red giant stars using three-dimensional numerical experiments. We make use of the Anelastic Spherical Harmonics code to simulate the inner 50% of the envelope of a low-mass star on the red giant branch. We discuss the organization and dynamics of convection, and put a special emphasis on the distribution of angular momentum in such a rotating extended envelope. To do so, we explore two directions of the parameter space, namely, the bulk rotation rate and the Reynolds number with a series of four simulations. We find that turbulent convection in red giant stars is dynamically rich, and that it is particularly sensitive to the rotation rate of the star. Reynolds stresses and meridional circulation establish various differential rotation profiles (either cylindrical or shellular) depending on the convective Rossby number of the simulations, but they all agree that the radial shear is large. Temperature fluctuations are found to be large and in the slowly rotating cases, a dominant l = 1 temperature dipole influences the convective motions. Both baroclinic effects and turbulent advection are strong in all cases and mostly oppose one another.

• OSTI ID: 21336047
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 702; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ADVECTION
ANGULAR MOMENTUM
COMPUTERIZED SIMULATION
CONVECTION
CYLINDRICAL CONFIGURATION
DIPOLES
HYDRODYNAMICS
HYDROGEN BURNING
MASS
RED GIANT STARS
REYNOLDS NUMBER
ROTATION
SPHERICAL HARMONICS
STAR EVOLUTION
THREE-DIMENSIONAL CALCULATIONS