Searching for swept-up Hydrogen and Helium in the late-time spectra of 11 nearby Type Ia supernovae

TL;DR

This study analyzes late-time spectra of 11 nearby Type Ia supernovae, finding limited evidence of hydrogen-rich material from companion stars, which challenges some progenitor models and suggests alternative explosion scenarios.

Contribution

The paper presents new late-time spectral observations of 11 SNe Ia and reports a tentative hydrogen detection in one, providing constraints on progenitor models and expanding the sample of non-detections.

Findings

Tentative H-alpha detection in SN 2013ct (~0.007 Msun)

No H-alpha detected in other 10 SNe Ia

No evidence of He emission features

Abstract

The direct detection of a stellar system that explodes as a Type Ia supernova (SN Ia) has not yet been successful. Various indirect methods have been used to investigate SN Ia progenitor systems but none have produced conclusive results. A prediction of single-degenerate models is that H- (or He-) rich material from the envelope of the companion star should be swept up by the SN ejecta in the explosion. Seven SNe Ia have been analysed to date looking for signs of H-rich material in their late-time spectra and none were detected. We present results from new late-time spectra of 11 SNe Ia obtained at the Very Large Telescope using XShooter and FORS2. We present the tentative detection of H-alpha emission for SN 2013ct, corresponding to ~0.007 Msun of stripped/ablated companion star material (under the assumptions of the spectral modelling). This mass is significantly lower than expected for single-degenerate scenarios, suggesting that >0.1 Msun of H-rich is present but not observed. We do not detect H-alpha emission in the other 10 SNe Ia. This brings the total sample of normal SNe Ia with non-detections (<0.001-0.058 Msun) of H-rich material to 17 events. The simplest explanation for these non-detections is that these objects did not result from the explosion of a CO white dwarf accreting matter from a H-rich companion star via Roche-lobe overflow or symbiotic channels. However, further spectral modelling is needed to confirm this. We also find no evidence of He-emission features, but models with He-rich companion stars are not available to place mass limits.