H-alpha Spectral diversity of type II supernovae
  We present a spectroscopic analysis of the H-alpha profiles of hydrogen-rich
type II supernovae. A total of 52 type II supernovae having well sampled
optical light curves and spectral sequences were analyzed. Concentrating on the
H-alpha P-Cygni profile we measure its velocity from the FWHM of emission and
the ratio of absorption to emission (a/e) at a common epoch at the start of the
recombination phase, and search for correlations between these spectral
parameters and photometric properties of the V-band light curves. Testing the
strength of various correlations we find that a/e appears to be the dominant
spectral parameter in terms of describing the diversity in our measured
supernova properties. It is found that supernovae with smaller a/e have higher
H-alpha velocities, more rapidly declining light curves from maximum, during
the plateau and radioactive tail phase, are brighter at maximum light and have
shorter optically thick phase durations. We discuss possible explanations of
these results in terms of physical properties of type II supernovae,
speculating that the most likely parameters which influence the morphologies of
H-alpha profiles are the mass and density profile of the hydrogen envelope,
together with additional emission components due to circumstellar interaction.
