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The vast majority of Type II supernovae (SNe) are produced by red supergiants (RSGs), but SN 1987A revealed that blue supergiants (BSGs) can produce members of this class as well, albeit with some peculiar properties. This best studied event revolutionized our understanding of SNe, and linking it to the bulk of Type II events is essential. We present here optical photometry and spectroscopy gathered for SN 2000cb, which is clearly not a standard Type II SN and yet is not a SN 1987A analog. The light curve of SN 2000cb is reminiscent of that of SN 1987A in shape, with a slow rise to a late optical peak, but on substantially different time scales. Spectroscopically, SN 2000cb resembles a normal SN II but with ejecta velocities that far exceed those measured for SN 1987A or normal SNe II, above 18000 km/s for H-alpha at early times. The red colours, high velocities, late photometric peak, and our modeling of this object all point toward a scenario involving the high-energy explosion of a small-radius star, most likely a BSG, producing 0.1 solar masses of Ni-56. Adding a similar object to the sample, SN 2005ci, we derive a rate of about 2% of the core-collapse rate for this loosely defined class of BSG explosions., Comment: Accepted to MNRAS on March 14, 2011

The vast majority of Type II supernovae (SNe) are produced by red supergiants (RSGs), but SN 1987A revealed that blue supergiants (BSGs) can produce members of this class as well, albeit with some peculiar properties. This best studied event revolutionized our understanding of SNe, and linking it to the bulk of Type II events is essential. We present here optical photometry and spectroscopy gathered for SN 2000cb, which is clearly not a standard Type II SN and yet is not a SN 1987A analog. The light curve of SN 2000cb is reminiscent of that of SN 1987A in shape, with a slow rise to a late optical peak, but on substantially different time scales. Spectroscopically, SN 2000cb resembles a normal SN II but with ejecta velocities that far exceed those measured for SN 1987A or normal SNe II, above 18000 km/s for H-alpha at early times. The red colours, high velocities, late photometric peak, and our modeling of this object all point toward a scenario involving the high-energy explosion of a small-radius star, most likely a BSG, producing 0.1 solar masses of Ni-56. Adding a similar object to the sample, SN 2005ci, we derive a rate of about 2% of the core-collapse rate for this loosely defined class of BSG explosions., Comment: Accepted to MNRAS on March 14, 2011

By definition, a Type Ic supernova (SN Ic) does not have conspicuous lines of hydrogen or helium in its optical spectrum. SNe Ic usually are modelled in terms of the gravitational collapse of bare carbon-oxygen cores. We consider the possibility that the spectra of ordinary (SN 1994I-like) SNe Ic have been misinterpreted, and that SNe Ic eject hydrogen. An absorption feature usually attributed to a blend of Si II 6355 and C II 6580 may be produced by H-alpha. If SN 1994I-like SNe Ic eject hydrogen, the possibility that hypernova (SN 1998bw-like) SNe Ic, some of which are associated with gamma-ray bursts, also eject hydrogen should be considered. The implications of hydrogen for SN Ic progenitors and explosion models are briefly discussed., Comment: Accepted by PASP. Several significant changes including one additional figure

By definition, a Type Ic supernova (SN Ic) does not have conspicuous lines of hydrogen or helium in its optical spectrum. SNe Ic usually are modelled in terms of the gravitational collapse of bare carbon-oxygen cores. We consider the possibility that the spectra of ordinary (SN 1994I-like) SNe Ic have been misinterpreted, and that SNe Ic eject hydrogen. An absorption feature usually attributed to a blend of Si II 6355 and C II 6580 may be produced by H-alpha. If SN 1994I-like SNe Ic eject hydrogen, the possibility that hypernova (SN 1998bw-like) SNe Ic, some of which are associated with gamma-ray bursts, also eject hydrogen should be considered. The implications of hydrogen for SN Ic progenitors and explosion models are briefly discussed., Comment: Accepted by PASP. Several significant changes including one additional figure

Results of numerical calculations of Type II supernova light curves are presented. The model progenitor stars have 6 $M{_\odot}$ cores and various envelopes, originating from a numerically evolved 20 $M{_\odot}$ star. Five parameters that affect the light curves are examined: the ejected mass, the progenitor radius, the explosion energy, the $^{56}$Ni mass, and the extent of $^{56}$Ni mixing. The following affects have been found: 1) the larger the progenitor radius the brighter the early--time light curve, with little affect on the late--time light curve, 2) the larger the envelope mass the fainter the early light curve and the flatter the slope of the late light curve, 3) the larger the explosion energy the brighter the early light curve and the steeper the slope of the late light curve, 4) the larger the $^{56}$Ni mass the brighter the overall light curve after 20 to 50 days, with no affect on the early light curve, 5) the more extensive the $^{56}$Ni mixing the brighter the early light curve and the steeper the late light curve. The primary parameters affecting the light curve shape are the progenitor radius and the ejected mass. The secondary parameters are the explosion energy, $^{56}$Ni mass and $^{56}$Ni mixing. I find that while in principle the general shape and absolute magnitude of a light curve indicate a unique set of parameters, in practice it is difficult to avoid some ambiguity in the parameters. I find that the nickel--powered diffusion wave and the recombination of helium produce a prominent secondary peak in all our calculations. The feature is less prominent when compositional mixing, both $^{56}$Ni mixing and mixing between the hydrogen and helium layers, occurs. The model photospheric temperatures and velocities are presented, for comparison to observation., Comment: 39 pages, 15 figures. Astrophysical Journal (Accepted, Dec. 20, 2004)

Results of numerical calculations of Type II supernova light curves are presented. The model progenitor stars have 6 $M{_\odot}$ cores and various envelopes, originating from a numerically evolved 20 $M{_\odot}$ star. Five parameters that affect the light curves are examined: the ejected mass, the progenitor radius, the explosion energy, the $^{56}$Ni mass, and the extent of $^{56}$Ni mixing. The following affects have been found: 1) the larger the progenitor radius the brighter the early--time light curve, with little affect on the late--time light curve, 2) the larger the envelope mass the fainter the early light curve and the flatter the slope of the late light curve, 3) the larger the explosion energy the brighter the early light curve and the steeper the slope of the late light curve, 4) the larger the $^{56}$Ni mass the brighter the overall light curve after 20 to 50 days, with no affect on the early light curve, 5) the more extensive the $^{56}$Ni mixing the brighter the early light curve and the steeper the late light curve. The primary parameters affecting the light curve shape are the progenitor radius and the ejected mass. The secondary parameters are the explosion energy, $^{56}$Ni mass and $^{56}$Ni mixing. I find that while in principle the general shape and absolute magnitude of a light curve indicate a unique set of parameters, in practice it is difficult to avoid some ambiguity in the parameters. I find that the nickel--powered diffusion wave and the recombination of helium produce a prominent secondary peak in all our calculations. The feature is less prominent when compositional mixing, both $^{56}$Ni mixing and mixing between the hydrogen and helium layers, occurs. The model photospheric temperatures and velocities are presented, for comparison to observation., Comment: 39 pages, 15 figures. Astrophysical Journal (Accepted, Dec. 20, 2004)