The light curve slope as a function of flux as calculated in multizone models of a cooling layer (solid curves) with column depths y = 10⁸, 10⁹, and 10¹⁰  g  cm^-2. For comparison we show the one-zone model result for y = 10⁸  g  cm^-2 as the dashed curve. The gray areas show the expected range of values of α when ions dominate the heat capacity or when electrons dominate the heat capacity, taking the cooling to lie between L ∝ T⁴ and L ∝ T⁵.