Abstract

We propose a model for the origin of the broad He II 4686 Å emission in early spectrum of SN 2020jfo (type IIP). The 4686 Å line is emitted presumably by dense fragments embedded into a hot gas of the forward shock wave. The fragments are produced as a result of a heavy braking of the dense low mass shell, at the ejecta boundary and a simultaneous Rayleigh–Taylor instability. The temperature of line-emitting fragments is \({\approx}5\times 10^{4}\) K. Calculations of ionization and excitation of helium and hydrogen accounts for the He II 4686 Å luminosity, large flux ratio of He II 4686 Å/H\(\alpha\) and a significant optical depth of 4686 Å line. We demonstrate that fragments heating by hot electrons of the forward shock compensates cooling via He II 304 Å emission.

中文翻译：

---

SNe IIP 早期光谱中 Broad He II 4686 Å 发射的起源

摘要

我们提出了一个模型，用于解释 SN 2020jfo（IIP 型）早期光谱中宽 He II 4686 Å 发射的起源。4686 Å 线可能是由嵌入前向激波热气体中的致密碎片发射的。这些碎片是由于致密的低质量壳在喷射物边界处剧烈制动以及同时发生的瑞利-泰勒不稳定性而产生的。线发射碎片的温度为\({\approx}5\times 10^{4}\) K。氦和氢的电离和激发计算说明了 He II 4686 Å 的光度，He II 的大通量比4686 Å/H \(\alpha\)和 4686 Å 线的显着光学深度。我们证明，由前向激波的热电子加热的碎片可以通过 He II 304 Å 发射来补偿冷却。