Light-travel-time diagnostics in early supernova spectra: substantial mass-loss of the IIb progenitor of SN 2013cu through a superwind
Light-travel-time diagnostics in early supernova spectra: substantial mass-loss of the IIb progenitor of SN 2013cu through a superwind
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DOI：
10.1093/mnras/stv2283
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发表时间：
2015-09
影响因子：
4.8
通讯作者：
G. Gräfener;J. Vink
中科院分区：
文献类型：
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作者：
G. Gräfener;J. Vink
iib型超新星（SNe）的前身被认为在直接前sn阶段几乎完全失去了它们的富h包层。最近，SN IIb （SN2013cu）的第一个“闪光光谱”已经被提出，足够早地研究它的直接星周介质（CSM）。与Groh（2014）之前的研究类似，我们使用非lte模型大气分析了光学厚度CSM的结构和化学成分。我们首次考虑了光传播时间（LTT）对光谱形成的影响，它影响了可观测发射线的形状和强度，以及推断出的SN亮度。根据新的CSM参数，我们估计CSM质量的下限为~0.3Msun，比以前的估计高10-100倍。谱拟合表明CSM以均匀和球对称的超风的形式存在，其质量损失率超过通常预期的两个数量级。衍生的化学成分与刚刚离开或即将离开红超巨星（RSG）阶段的祖先一致，证实了sniib起源的标准图片。由于其巨大的质量损失，SN的前身可能会出现极端的RSG，发光蓝变星（LBV），或黄色超巨星（YHG）。直接探测到的超风和推断出的高CSM质量表明，恒星风质量的损失可能在SNe IIb的形成过程中发挥了重要作用。
The progenitors of type-IIb supernovae (SNe) are believed to have lost their H-rich envelopes almost completely in the direct pre-SN phase. Recently the first 'flash spectrum' of a SN IIb (SN2013cu) has been presented, taken early enough to study its immediate circumstellar medium (CSM). Similar to a previous study by Groh (2014) we analyse the structure and chemical composition of the optically-thick CSM using non-LTE model atmospheres. For the first time we take light-travel time (LTT) effects on the spectrum formation into account, which affect the shapes and strengths of the observable emission lines, as well as the inferred SN luminosity. Based on the new CSM parameters we estimate a lower limit of ~0.3Msun for the CSM mass, which is a factor 10-100 higher than previous estimates. The spectral fit implies a CSM in the form of a homogeneous and spherically symmetric superwind whose mass-loss rate exceeds common expectations by up to two orders of magnitude. The derived chemical composition is in agreement with a progenitor that has just left, or is just about to leave the Red-Supergiant (RSG) stage, confirming the standard picture for the origin of SNe IIb. Due to its extreme mass loss the SN progenitor will likely appear as extreme RSG, Luminous Blue Variable (LBV), or Yellow Hypergiant (YHG). The direct detection of a superwind, and the high inferred CSM mass suggest that stellar wind mass loss may play an important role in the formation of SNe IIb.