strength and accelerates due to the effect of hydrodynamic cumulation. Only a small portion of the star undergoes this acceleration and acquires a high velocity. For example, the layers of velocities exceeding 5000 km s$^{-1}$ have a mass of $\approx 0.478 M_{\sun}$.

By day 0.8651 the shock wave reaches the stellar surface and then begins to heat the external layers, so that the color temperature jumps to $3.84 \times 10^{5}$ K at day 0.8823, the effective temperature increases up to $1.76 \times 10^{5}$ K at day 0.8943, and the bolometric luminosity rises accordingly up to $6.46 \times 10^{44}$ ergs$^{-1}$ at day 0.8943 (Fig. \[fig:swbrck\]). Note that the maximum of the color temperature coincides closely with the moment of 0.8803 days when a velocity at the stellar surface reaches the escape velocity.

A very rapid rise in the bolometric luminosity to maximum, starting at day 0.8651, instantly changes a growth of the photospheric radius into its reduction because of the intense radiative losses of energy in the outermost layers (Fig. \[fig:swbrck\]b). At day 0.8691 these layers begin to move outward, and the additional cooling by adiabatic expansion makes the reduction of the photospheric radius more noticeable. At the same time the 