What stars become supernovae?

This paper assembles a variety of empirical lines of evidence on the masses and stellar-population types of stars that trigger supernova (SN) explosions. The main theoretical motivations are to determine whether type I supernovae (SN I) can have massive precursors and whether there is an interval of stellar mass between the masses of precursors of pulsars and white dwarfs that is disrupted by carbon detonation. Statistics of stellar birthrates, SN, pulsars, and SN remnants in the Galaxy show that SN II (or all SN) could arise from stars with masses greater than about 12 to 49 solar masses. Several methods of estimating the masses of stars that become white dwarfs are consistent with a lower limit of about 5 solar masses, so carbon detonation may be avoided. Studies of the properties of galaxies in which SN occur, and their distributions within galaxies, support the usual views that SN I have low-mass precursors and SN II have massive precursors. The restriction of known SN II to Sc and Sb galaxies is shown to be statistically consistent with massive stars in other galaxies also dying as SN II. Possible implications of the peculiarities of some SN-producing galaxies are discussed.