Observed and physical properties of core-collapse supernovae

I use photometry and spectroscopy data for 24 Type II plateau supernovae (SNe IIP) to examine their observed and physical properties. This data set shows that these objects encompass a wide range of similar to5 mag in their plateau luminosities, their expansion velocities vary by a factor of 5, and the nickel masses produced in these explosions go from 0.0016 to 0.26 M.. From a subset of 16 objects I find that the explosion energies vary between 0.6 x 10(51) and 5.5 x 10(51) ergs, the ejected masses encompass the range 14-56 M, and the progenitors radii go from 80 to 600 R. Despite this great diversity, several regularities emerge, which reveal that there is a continuum in the properties of these objects from the faint, low-energy, nickel-poor SNe 1997D and 1999br, to the bright, high-energy, nickel-rich SN 1992am. This study provides evidence that more massive progenitors produce more energetic explosions, thus suggesting that the outcome of the core collapse is somewhat determined by the envelope mass. I also find that SNe with greater energies produce more nickel. Similar relationships appear to hold for SNe Ib/c, which suggests that both SNe II and SNe Ib/c share the same core physics. When the whole sample of core-collapse objects is considered, there is a continuous distribution of energies below 8 x 10(51) ergs. Far above in energy scale and nickel production lies the extreme hypernova 1998bw, the only SN firmly associated with a gamma-ray burst.