Circumstellar Na I and Ca II lines in type IIP supernovae and SN 1998S

TL;DR

This study models the detectability of circumstellar Na I and Ca II lines in type IIP supernovae spectra, finding Ca II lines are observable under certain conditions, while Na I lines are generally not, with implications for understanding supernova environments.

Contribution

It introduces a model predicting the visibility of circumstellar Na I and Ca II lines in supernova spectra, highlighting conditions for their detection and explaining observed features in SN 1998S.

Findings

Ca II lines are detectable in type IIP supernovae with moderate wind density.

Na I lines are generally not visible in type IIP supernovae spectra.

Ultraviolet excess due to shock wave Comptonization explains line intensities in SN 1998S.

Abstract

We study a possibility of detection of circumstellar absorption lines of Na I D$_{1,2}$ and Ca II H,K in spectra of type IIP supernovae at the photospheric epoch. The modelling shows that the circumstellar lines of Na I doublet will not be seen in type IIP supernovae for moderate wind density, e.g., characteristic of SN 1999em, whereas rather pronounced Ca II lines with P Cygni profile should be detectable. A similar model is used to describe Na I and Ca II circumstellar lines seen in SN 1998S, type IIL with a dense wind. We show that line intensities in this supernova are reproduced, if one assumes an ultraviolet excess, which is caused primarily by the comptonization of supernova radiation in the shock wave.