Hα Spectral Diversity of Type II Supernovae: Correlations with Photometric Properties

Abstract

We present a spectroscopic analysis of the Hα 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 Hα P-Cygni profile we measure its velocity from the FWHM of the 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 Hα 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 that influence the morphologies of Hα profiles are the mass and density profile of the hydrogen envelope, together with additional emission components due to circumstellar interaction.