The nature of the progenitors of supernovae of type I

Abstract

This paper examines the hypothesis that supernovae of type I are produced by relatively 'young' single stars. The fact that SN I are not concentrated in spiral arms implies that their progenitors have M approximately less than 8 M sun. The existence of white dwarfs in open clusters places a limit M approximately greater than 5 M sun on SN I progenitors. The similarity of the colours of ellipticals that have produced supernovae to that of E galaxies which have not implies that young stellar populations cannot contribute more than 3 per cent of the ultraviolet light of supernova-prone ellipticals. It follows that the hypothetical young stellar population in supernova-prone ellipticals must produce SN I 17 times as efficiently (per unit of ultraviolet luminosity) as do Sc galaxies. This would only be possible if the mass spectrum of star formation in ellipticals is very sharlpy peaked at M approximately equal to 5 M sun. It is also shown (see figure 1) that hydrogen-rich E galaxies are, in the mean, less luminous than those which are not observed to contain hydrogen. Observations of the Virgo cluster show no significant difference between the velocity dispersion of E galaxies that have produced supernovae and those which have not. Such a difference might have been expected on the hypothesis that SN I are associated with a relatively young stellar population. This is so because high-velocity ellipticals are most likely to have had their star producing hydrogen gas removed by ram pressure stripping. Finally it is pointed out that galactic SN I have a rather large |z|, which is contrary to expectation for objects with massive progenitors. On balance the available evidence does not appear to favour the idea that SN I are produced by single relatively-young progenitors.