Astron. Astrophys. 328, 203-210 (1997)

6. Conclusions

The observed V light curves of different SNe Ia have been compared with models of the bolometric light curve obtained varying the values of and . The distribution of Ni was assumed to be central with the exception of the models for the bright SN 1991T, where an outer Ni shell was also used. The KE of the ejecta was rescaled according to and in all cases except SN 1991T. Both and influence the light curve, but while influences mostly the level of the curve, affects also the time of maximum and the decline rate, so that a simultaneous fit to both the maximum and the late light curve, up to when the positrons begin to dominate, can only be obtained for a single set of and values. Changes in the distribution of Ni and in the opacities between the various models would of course alter this result.

The comparison of the (late) light curves of SNe Ia with models confirms the suggestions derived from the analysis of observed spectra near maximum of the existence of a range in both the Ni and the ejecta mass.

It appears that objects which have usually been regarded as `typical' SNe Ia may actually differ by more than 0.5 mag at maximum. This difference increases with time, suggesting that both and may be significantly different in these objects (in particular, SN 1994D appears to be brighter and to have a larger than SNe 1992A and 1993L). Not surprisingly there appears to be a correlation between and for the sample of 5 objects discussed here.

In general a reasonable fit to the late light curves can be obtained by assuming that the ejecta become progressively transparent also to the positrons generated in the Co decay. However, there are indications that the positron opacity is not constant from object to object or with time: the late light curve of SN 1991bg can be fitted if the assumption of complete transparency of the ejecta to the positrons is made, while those of SNe 1992A and 1993L after 500 days seem to require complete trapping of the positrons.

© European Southern Observatory (ESO) 1997

Online publication: March 24, 1998

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