What sodium absorption lines tell us about type Ia supernovae

TL;DR

This paper introduces the NaDA model suggesting sodium absorption lines in some SN Ia originate from dust at 1 pc, with photon-stimulated desorption explaining variability better than previous models, challenging single-degenerate scenarios.

Contribution

The paper proposes a novel NaDA model for sodium absorption lines in SN Ia, emphasizing photon-stimulated desorption from dust at 1 pc, differing from prior recombination explanations.

Findings

NaDA model fits observed line variability better than recombination models.

Dust mass required exceeds single-degenerate scenario expectations.

Variable NaI D lines imply a non-single-degenerate origin for some SN Ia.

Abstract

We propose that the sodium responsible for the variable NaI D absorption lines in some type Ia supernovae (SN Ia) originate mainly from dust residing at ~1 pc from the supernovae. In this Na-from-dust absorption (NaDA) model the process by which the SN Ia peak luminosity releases sodium from dust at 1 pc from the SN is similar to the processes by which solar radiation releases sodium from cometary dust when comets approach a distance of 1 AU from the Sun. The dust grains are not sublimated but rather stay intact, and release sodium by photon-stimulated desorption (PSD; or photo-sputtering). Some of the Na might start in the gas phase before the explosion. Weakening in absorption strength is caused by Na-ionizing radiation of the SN. We apply the NaDA model to SN 2006X and SN 2007le, and find it to comply better with the observed time variability of the NaI D absorption lines than the Na recombination model. The mass in the dusty shell of the NaDA model is much too high to be accounted for in the single-degenerate scenario for SN Ia. Therefore, the presence of variable NaI D lines in some SN Ia further weakens the already very problematic single-degenerate scenario for SN Ia.