On the Early Spectroscopic Distinction of Type II Supernovae

This paper considers the possible spectroscopic differences between two subtypes of Type II supernovae (those supernovae with hydrogen in their spectra): the Linears (II-L), which show a linear decline in their light curves, and the Plateaus (II-P), which show a plateau phase in their light curve. The early phases of evolution of the two supernovae are described as well as clues from the literature that indicate, usually indirectly, the physical nature of the spectroscopic differences. A hypothesis is suggested that the early spectroscopic differences at Hα are the spectroscopic differences between these two subtypes, and that the lack of a strong P Cyg profile at Hα predicts a linear light curve.