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Semiconvection - mixing that occurs in regions that are stable whenconsidering compositional gradients, but unstable when ignoring them - is shownto have the greatest potential impact on main sequence stars with masses in therange 1.2 - 1.7 solar masses. We present the first stellar evolutioncalculations using a prescription for semiconvection derived from extrapolationof direct numerical simulations of double-diffusive mixing down to stellarparameters. The dominant mode of semiconvection in stars is layeredsemiconvection, where the layer height is an adjustable parameter analogous tothe mixing length in convection. The rate of mixing across the semiconvectiveregion is sensitively dependent on the layer height. We find that there is acritical layer height that separates weak semiconvective mixing (whereevolution is well-approximated by using the Ledoux criterion) from strongsemiconvective mixing (where evolution is well-approximated by using theSchwarzschild criterion). This critical layer height is much smaller than theminimum layer height expected from simulations so we predict that for realisticlayer heights, the evolution is nearly the same as a model ran with theSchwarzschild criterion. We also investigate the effects of compositionalgradient smoothing, finding that it causes convective cores to artificiallyshrink in the absence of additional mixing beyond the convective boundary.Layered semiconvection with realistic layer heights provides enough such mixingthat stars will still evolve as if the Schwarzschild criterion is employed.Finally, we discuss the potential of detecting such semiconvection and itsimplication on convective core sizes in solar-like oscillators.

Main Sequence Evolution with Layered Semiconvection