THE RATE OF (TYPE-IA) SNE IN ELLIPTIC GALAXIES

We reanalyzed the databases of the Asiago and Crimea supernova (SN) searches in order to derive a new, more accurate frequency of type Ia SNe in E galaxies and to resolve the problem of recent discordant determinations. The selection effect due to the low dynamic range of the plates used in our photographic surveys has been investigated. For the material of our surveys it does not increase with the distances of the galaxies. We estimate to have lost about 10% of SNe in ellipticals for this bias. The rate of type Ia SNe in ellipticals is found to be 0.12 +/- 0.06(H/75)2 SNu. With the extreme assumption that only faint SNIa explode in E galaxies, an upper limit 0.30 SNu is derived. In the same sample of E galaxies we find no indication that the SN rate depends on the ISM content, dust or gas. This confirms the standard scenario in which SNIa in ellipticals derive from old progenitors.