gas and radiation temperatures at the photosphere position are nearly constant in time and equal to about 5600 K (Fig. \[fig:crwdnt\]b). And from $t=40$ days to $t=100$ days, the photosphere is located at the outer edge of the hydrogen recombination front (Fig.\[fig:crwlxh\]b).

After $t=100$ days the radiation flux at the inner edge of the CRW becomes comparable to the luminosity of star (Fig. \[fig:crwlxh\]a). This effect is caused by radiative diffusion from the central envelope layers where the energy of radioactive decays is being released. Later on the luminosity is entirely determined by radiative diffusion and not by the CRW.

Radiative diffusion cooling {#sec:dmd-difcln}
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A cooling by radiative diffusion starts in the optically thick expelled envelope at day 94 and ends in the semi-transparent medium at day 116 (Fig. \[fig:snphs\]). Shortly before the end of the phase of radiative diffusion cooling, the complete hydrogen recombination occurs at $t_\mathrm{H} \approx 111.3$ days. In the optimal model the radiative diffusion takes place in the inner layers with the nearly uniform density distribution and results in the characteristic shoulder of the bolometric luminosity. It should be noted that this behavior of the light curve was discussed by Falk & Arnett ([@fa77]). To 