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arXiv 1604.01044astro-ph.HEastro-ph.SR
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Ia型超新星晚期光谱的渐进性红移

Progressive Red Shifts in the Late-Time Spectra of Type Ia Supernovae

C. S. Black, R. A. Fesen, J. T. Parrent

摘要:

我们研究了晚时间的演化,光学星云的Ia型超新星(SNe Ia)的特征,使用的样本包括160光谱的27个正常SNe Ia从文献中,以及未发表的光谱SN 2008 Q和ASASSN-14 lp。特别注意的是星云的功能之间的4000-6000 A的宽度和中心波长的时间变化。对突出的晚期4700 A特征的分析显示,对于我们的整个样品,中心波长从~4600 A逐渐向更长的波长偏移,至少到+300天。我们没有发现任何证据表明该功能的红移减缓或停止在[Fe III]混合质心4701 A已提出。特征的宽度也稳定地增加,其中FWHM在+100天时约170 A,到+350天时增长到200 A或更大。在4850和5000 A附近的两个较弱的相邻特征表现出与4700 A特征非常相似的红移,但直到非常晚的时间才显示出宽度的变化。我们讨论了可能的原因,观察到的红移这些后期的光学功能,包括贡献[钴II]发射在早期星云的时代和出现的额外功能在以后的时间。我们的结论是,无处不在的红移,这些共同的晚时间,星云超新星Ia光谱特征是不是主要是由于在禁止铁线的蓝移的减少,但结果,在一定程度上,允许铁线的速度和/或光学深度的降低。

英文摘要:

We examine the evolution of late-time, optical nebular features of Type Ia supernovae (SNe Ia) using a sample consisting of 160 spectra of 27 normal SNe Ia taken from the literature as well as unpublished spectra of SN 2008Q and ASASSN-14lp. Particular attention was given to nebular features between 4000-6000 A in terms of temporal changes in width and central wavelength. Analysis of the prominent late-time 4700 A feature shows a progressive central wavelength shift from ~4600 A to longer wavelengths out to at least day +300 for our entire sample. We find no evidence for the feature's red-ward shift slowing or halting at an [Fe III] blend centroid of 4701 A as has been proposed. The width of the feature also steadily increases with a FWHM ~170 A at day +100 growing to 200 A or more by day +350. Two weaker adjacent features around 4850 and 5000 A exhibit very similar red shifts to that of the 4700 A feature but show no change in width until very late times. We discuss possible causes for the observed red-ward shifting of these late-time optical features including contribution from [Co II] emission at early nebular epochs and the emergence of additional features at later times. We conclude that the ubiquitous red shift of these common late-time, nebular SN Ia spectral features is not mainly due to a decrease in a blueshift of forbidden Fe lines but the result, in part, of decreasing velocity and/or optical depth of permitted Fe lines.

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