of 0.036 $M_{\sun}$, the bulk of the radioactive $^{56}$Ni being mixed in the velocity range $\le 660$ kms$^{-1}$ (Fig. \[fig:denicl\]) in order to reproduce the observed transition from the plateau to the tail.

H[$\alpha$]{} profile: evidence against short distance {#sec:evidis}
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It is quite clear that any well-observed SN should be described by a unique hydrodynamic model in combination with the atmosphere model based on it. The experience during the study of SN 1987A showed that such a combination of the models had to fit not only the photometric, but also the spectroscopic observations. We believe that the adequate hydrodynamic and atmosphere models of SN 1999em are able to distinguish between the short and long distances. A distance of 7.85 Mpc, the average value of the EPM distance estimates, is taken as the short distance, and the Cepheid distance of 11.7 Mpc is taken as the long distance.

[c c c @[ ]{} c @[ ]{} c c c]{} Model & $R_0$ & $M_{env}$ & $E$ & $M_{\mathrm{Ni}}$ & $X$ & $Z$\
& $(R_{\sun})$ & $(M_{\sun})$ & ($10^{51}$ erg) & $(10^{-2} M_{\sun})$ & &\
D07 & 375 & 16 & 0.686 & 1.62 & 0.735 & 0.017\
D11 & 500 