Near-infrared line identification in type Ia supernovae during the transitional phase

TL;DR

This study compares synthetic near-infrared spectra from a supernova model with observations of type Ia supernovae during the transitional phase, identifying key spectral features and suggesting the presence of nickel and manganese in the ejecta.

Contribution

It provides the first detailed near-infrared spectral analysis during the transition from photospheric to nebular phase in type Ia supernovae, linking spectral features to specific elements.

Findings

Fe II and Co II lines explain most features

Detection of [Ni II] indicates central 58Ni presence

Possible identification of Mn II supports high-density burning

Abstract

We present near-infrared synthetic spectra of a delayed-detonation hydrodynamical model and compare them to observed spectra of four normal type Ia supernovae ranging from day +56.5 to day +85. This is the epoch during which supernovae are believed to be undergoing the transition from the photospheric phase, where spectra are characterized by line scattering above an optically thick photosphere, to the nebular phase, where spectra consist of optically thin emission from forbidden lines. We find that most spectral features in the near-infrared can be accounted for by permitted lines of Fe II and Co II. In addition, we find that [Ni II] fits the emission feature near 1.98 {\mu}m, suggesting that a substantial mass of 58Ni exists near the center of the ejecta in these objects, arising from nuclear burning at high density. A tentative identification of Mn II at 1.15 {\mu}m may support this conclusion as well.