the effective temperature and the corresponding brightness reduction taken from the SN 1987A observations.

The time-dependent approach with model B satisfactorily reproduces the strength of the H$\alpha$ emission component on day 26.24 with some emission deficit near the maximum in comparison to what was observed (Fig. \[fig:hmd117\]c). This deficit is not significant because model A, calculated for this phase and not plotted on Fig. \[fig:hmd117\]c for the sake of clarity, gives the emission component with a relative flux of 3.1 at the maximum, which is much higher than the observed one, so the real situation is somewhere between these two cases and is closer to model B. Note that in SN 1987A the H$\alpha$ emission component demonstrated the same behavior in the early phase (Utrobin & Chugai [@uc05]). In contrast, the H$\alpha$ absorption component calculated in model B is stronger than that observed on day 26.24 in SN 1999em. This discrepancy is presumably related to a poor description of the ultraviolet radiation at frequencies between the Balmer and Lyman edges. This radiation interacts with numerous metal lines and controls the populations of hydrogen levels. It is very important that both the emission and absorption components of the H$\alpha$ line calculated 