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arXiv 1811.04087astro-ph.SR
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红超巨星核塌缩时的表面丰度

The surface abundances of Red Supergiants at core-collapse

Ben Davies, Luc Dessart

摘要:

在II-P型超新星(SN)的最初几周到几个月内,光谱形成区域位于爆炸恒星的富氢包层内。在超新星爆发后的几天内,当光球层很热时,拍摄的光谱显示出电离的碳,氮和氧,以及氢和氦的特征。因此,对这个非常早期阶段的定量分析可能会限制恒星包层在核心坍缩点的化学丰度。使用现有的和新的演化计算的红超巨星(RSG),我们表明,终端表面[C/N]比的预测与祖星的初始质量。具体来说,一颗初始质量超过20 M $_{\odot}$的恒星在RSG阶段爆炸时,应该有一个明确的低[C/N]丰度信号。此外,我们表明,模型的预测是相对不敏感的不确定性对流混合的治疗。虽然有一个依赖于初始旋转,这可以处理在概率意义上的卷积模型预测与观测到的恒星自转速率分布。使用数值实验,我们提出了一种策略,使用非常早的时间光谱,以确定上限的祖先质量分布的II-P型SNe。

英文摘要:

In the first weeks-to-months of a type II-P supernova (SN), the spectrum formation region is within the hydrogen-rich envelope of the exploding star. Optical spectra taken within a few days of the SN explosion, when the photosphere is hot, show features of ionised carbon, nitrogen and oxygen, as well as hydrogen and helium. Quantitative analysis of this very early phase may therefore constrain the chemical abundances of the stellar envelope at the point of core-collapse. Using existing and new evolutionary calculations for Red Supergiants (RSGs), we show that the predictions for the terminal surface [C/N] ratio is correlated with the initial mass of the progenitor star. Specifically, a star with an initial mass above 20M$_{\odot}$ exploding in the RSG phase should have an unequivocal signal of a low [C/N] abundance. Furthermore, we show that the model predictions are relatively insensitive to uncertainties in the treatment of convective mixing. Although there is a dependence on initial rotation, this can be dealt with in a probabilistic sense by convolving the model predictions with the observed distribution of stellar rotation rates. Using numerical experiments, we present a strategy for using very early-time spectroscopy to determine the upper limit to the progenitor mass distribution for type II-P SNe.

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