PHOTOMETRIC AND SPECTROSCOPIC OBSERVATIONS OF 4 SUPERNOVAE

We present photometric and spectroscopic observations of four SNe obtained at the Asiago Observatory during the long term ongoing program of monitoring of supernovae. Three of them, SN 1983G in NGC 4753, SN 1987N in NGC 7606 and SN 1989 A in NGC 3687 are classified of type Ia and exhibit, along with the typical uniformity of this SN subtype, also some minor spectroscopic peculiarities. In particular, while their photometric behaviour and absolute magnitudes at maximum are close to the average, the expansion velocities of the photosphere at maximum light span a range of 6000 km s-1. The light curves in different colours of the type II SN 1988 A in NGC 4579 show that this SN belongs to the Plateau subtype. While it is known that the maximum absolute luminosities of this class of SN II show a high dispersion, their V absolute magnitudes at phase later than 5 months have a dispersion, sigma = 0.6, comparable to that of SN Ia at maximum, suggesting that an analogous mass of Ni-56 is produced. The rate of decline at late phases (up to 450 days after maximum) is close to that expected from the radioactive decay of Co-56 (gamma-V = 1.08 +/- 0.05 mag/100 d).