超新星及其前兆风的早期光谱：SN 2013 cu的发光蓝色变星/黄色超巨星祖先
Early-time spectra of supernovae and their precursor winds: the luminous blue variable/yellow hypergiant progenitor of SN 2013cu
摘要：
我们提出了第一个定量光谱建模的早期超新星与其祖先风相互作用。使用辐射转移程序CMFGEN，我们研究了最近报道的IIb型SN 2013 cu爆炸后15.5 h的光谱。这是第一次，我们能够直接测量SN祖先的化学丰度，并发现相对富含H的风，H和He丰度（按质量计）分别为X=0.46 +- 0.2和Y=0.52 +- 0.2。相对于太阳值，风在N中增强，在C中耗尽（质量分数为8.2e-3和1 e-5）。我们得到，一个稠密的风/星周介质，质量损失率Mdot= 3e-3 Msun/yr和风速vwind=100 km/s，围绕在前SN阶段的恒星。这些值低于以前的分析估计，虽然我们发现Mdot/vinf与以前的工作一致。我们还计算了CMFGEN模型，以约束祖光谱类型，并发现高Mdot和低vwind意味着恒星有一个有效的温度约8000 K之前立即SN爆炸。我们的模型表明，它的前身要么是一颗不稳定的发光蓝变星，要么是一颗正在经历爆发阶段的黄色超巨星，并排除了WR星的可能性。我们将爆炸后15.5 h的光谱归类为XWN 5（h），并主张使用前缀“X”（eXplosion），以避免爆炸后非恒星光谱与大质量恒星光谱之间的混淆。我们发现，由于SN事件前后电离结构的巨大差异，祖先光谱类型与爆炸后早期光谱类型有显着不同。结果表明：LBV/YHG -> XWN 5（h）-> SN IIb.未来的早期紫外光谱将提供额外的光谱诊断，并进一步限制SN前体的性质，如它们的金属丰度。
英文摘要：
We present the first quantitative spectroscopic modeling of an early-time supernova that interacts with its progenitor wind. Using the radiative transfer code CMFGEN, we investigate the recently-reported 15.5 h post-explosion spectrum of the type IIb SN 2013cu. For the first time, we are able to directly measure the chemical abundances of a SN progenitor and find a relatively H-rich wind, with H and He abundances (by mass) of X=0.46 +- 0.2 and Y=0.52 +- 0.2, respectively. The wind is enhanced in N and depleted in C relative to solar values (mass fractions of 8.2e-3 and 1e-5). We obtain that a dense wind/circumstellar medium, with a mass-loss rate of Mdot= 3e-3 Msun/yr and wind velocity vwind=100 km/s, surrounds the star at the pre-SN stage. These values are lower than previous analytical estimates, although we find Mdot/vinf consistent with previous work. We also compute a CMFGEN model to constrain the progenitor spectral type and find that the high Mdot and low vwind imply that the star had an effective temperature of ~8000 K immediately before the SN explosion. Our models suggest that the progenitor was either an unstable luminous blue variable or a yellow hypergiant undergoing an eruptive phase, and rule out a WR star. We classify the post-explosion spectra at 15.5 h as XWN5(h) and advocate for the use of the prefix `X' (eXplosion) to avoid confusion between post-explosion, non-stellar spectra with those of massive stars. We show that the progenitor spectral type is significantly different than the early post-explosion spectral type owing to the huge differences in the ionization structure before and after the SN event. We find the following temporal evolution: LBV/YHG -> XWN5(h) -> SN IIb. Future early-time spectroscopy in the UV will give access to additional spectroscopic diagnostics and further constrain the properties of SN precursors, such as their metallicities.
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