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Semiconvection significantly affects the evolution of massive stars, but as yet there is no consensus on how to treat this instability in stellar models. An improved understanding of the nonlinear hydrodynamics of semiconvection clearly is desirable. At its onset, semiconvection consists of self-excited internal gravity waves. In massive stars, the the fastest-growing disturbances have wavelengths of order $10^3$ km. Numerous finite-amplitude outcomes can be envisaged, including wave breaking by overturning or shear instability, the cascading of wave energy to smaller scales via resonant couplings to higher wave numbers, and the formation of overturning layers separated by thin diffusive interfaces. Each possibility leads to a different recipe for describing the transport of heat and chemical species in stellar models, some of which coincide with prescriptions that have previously been suggested in the literature (e.g., Spruit 1992, A\&A, 253 , 131, Langer, et al. 1985, A\&A, 145 , 179.) The present study aims to evaluate which (if any) of these prescriptions are correct by computing the nonlinear evolution of semiconvective oscillations in a 30M$\odot$ main-sequence star. Two-dimensional hydrodynamical simulations are employed to examine the growth and destruction of individual waves, the stability of overturning layers, and the adjustments occurring in the structure of the semiconvective zone as a whole.
This work is supported by an International Fellowship from the Natural Sciences and Engineering Research Council of Canada.
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