= Composition shift of a convective pre-main-sequence track
{title2=$L\propto\mu^{-8}T_e^{20}$}
For <convective contraction with power-law opacity> $\kappa\propto\rho T^4$ at fixed stellar mass and opacity normalization, $T_e\propto\mu^{1/2}R^{1/8}$ and $L\propto\mu^2R^{5/2}$. Eliminating $R$ gives $L\propto\mu^{-8}T_e^{20}$. Thus a larger <mean molecular weight> moves the track to larger <effective temperature> at a given <luminosity>, with $T_e|_L\propto\mu^{2/5}$. Contraction decreases both temperature and luminosity for this particular opacity exponent.
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