Coupled Groups of g-Modes in a Sun with a Mixed Core

Details Coupled Groups of g-Modes in a Sun with a Mixed Core Coupled Groups of g-Modes in a Sun with a Mixed Core

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007apj...661..568w&link_type=abstract

The Astrophysical Journal, Volume 661, Issue 1, pp. 568-585.

Astronomy and Astrophysics

Astronomy

7

Stars: Oscillations, Sun: Interior, Sun: Oscillations

Scientific paper

Groups of linear g-modes can sum to create nonlinear motion in small ``hot volumes'' (diameter ~10 Mm) near the solar center that help drive the modes. We explore the consequences of coupling only in the hot volumes where the time-averaged rate of 3He burning can double if temperature oscillations exceed 10%. Anticipating large local motions in the core, we impose a mixed shell r=(0.10+/-0.03) Rsolar on an otherwise standard solar model before computing g-mode solutions. Mixing is rapid (<<106 yr) in this shell, with slower mixing somewhat beyond. If l is the principal spherical harmonic index, a set of g-modes for any single l<=5 with six consecutive radial harmonics can be excited with nearly linear thermal amplitudes AT<=0.05 throughout the star. But far smaller thresholds for excitation are actually expected when sets for many values of l can be computed simultaneously. This is a new kind of stellar instability whose effectiveness rises with the number of active modes. Each set rotates rigidly and maximizes the release of nuclear energy from its hot volumes. There is some evidence for their rotation rates in the long solar activity record. The upward wave flux powered by the hot volumes has also been suggested to explain the 1.3 yr reversing flows tentatively detected below the Sun's convective envelope. An analog using uncoupled modes is also investigated based on an observation that indicates g-mode activity up to l~=20. If all modes in that range had linear amplitudes of only AT~=0.0015, their combined effect would give positive growth rates to dozens of low harmonic g-modes.

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