The helium common-envelope wind scenario for SN 2020eyj

TL;DR

This paper proposes a helium common-envelope wind model to explain the unique features of SN 2020eyj, including its massive helium-rich circumstellar material and specific explosion characteristics.

Contribution

It introduces a novel helium common-envelope wind scenario that accounts for the large CSM and observed properties of SN 2020eyj, expanding understanding of SN Ia progenitors.

Findings

Helium CE mass can exceed 0.3 solar masses before explosion.

The model explains the dim peak brightness and low ejecta velocity.

The scenario accounts for the low birth rate of such supernovae.

Abstract

SN 2020eyj is the first type Ia supernova (SN Ia) showing the signature of a compact helium-rich circumstellar material (CSM). Such a large CSM is difficult to explain in a single-degenerate scenario where the donor star is a helium star. Here we show that, under certain conditions, it is possible that the transfer of helium leads to a common envelope (CE) engulfing the system, similar to the common-envelope wind model proposed by Meng \& Podsiadlowski (2017). If in such a helium common-envelope wind (HeCEW) model the initial white dwarf (WD) mass is larger than 1.1 $M_{\rm \odot}$ and the helium star more massive than 1.8 $M_{\rm \odot}$, the mass of a helium CE can be larger than 0.3 $M_{\rm \odot}$ prior to supernova explosion. The CE mass heavily depends on the initial parameters of the binary system. A dynamical CE ejection event could occur shortly before the supernova, and then our model may naturally explain the properties of SN 2020eyj, specifically the massive He-rich CSM, its dim peak brightness, low ejecta velocity and low birth rate.