H-alpha Spectral diversity of type II supernovae

TL;DR

This study analyzes the spectral diversity of type II supernovae, focusing on H-alpha profiles, and finds that the absorption-to-emission ratio correlates with various photometric and spectral properties, revealing insights into supernova physical characteristics.

Contribution

It introduces a detailed spectroscopic analysis of H-alpha profiles in type II supernovae and identifies key spectral parameters linked to supernova diversity and physical properties.

Findings

Smaller a/e ratios correlate with higher H-alpha velocities.

Supernovae with smaller a/e have faster light curve declines.

Brighter supernovae at maximum light tend to have shorter optically thick phases.

Abstract

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.