SN 2008年的祖星：消失或再次自我遮蔽？
The SN 2008S Progenitor Star: Gone or Again Self-Obscured?
摘要：
我们用大双筒望远镜（LBT）获得了SN 2008 S的后期光学和近红外成像。我们发现，（1）它在光学（UBVR）波长下也是不可见的，其星等极限约为25 mag，（2）当在近红外（HK）中检测到时，它在约20 mag处迅速衰落。2010年3月和5月的近红外探测结果与黑体温度T ~ 900 K和总光度L ~ 40000 Lsun的尘埃发射一致，与被遮蔽的祖星的光度相当。如果它是一颗超新星，那么近红外辐射很可能是由于激波加热的尘埃，因为从峰值开始经过的时间太长，不足以支持近红外尘埃回波，而且光度的下降比56 Co的斜率要浅。如果它是从幸存的祖先再处理的发射，尘埃光球必须重新建立自己比瞬变前更接近恒星（~40 AU而不是150 AU），除非有第二个，更冷的尘埃成分在中红外波长占主导地位。在大致恒定的温度下持续快速衰减有利于瞬态发射，但需要中红外和未来斯皮策观测中的SED峰来关闭这种情况。
英文摘要：
We obtained late-time optical and near-IR imaging of SN 2008S with the Large Binocular Telescope (LBT). We find that (1) it is again invisible at optical (UBVR) wavelengths to magnitude limits of approximately 25 mag, and (2) while detected in the near-IR (HK) at approximately 20 mag, it is fading rapidly. The near-IR detections in March and May 2010 are consistent with dust emission at a blackbody temperature of T ~ 900 K and a total luminosity of L ~ 40000 Lsun, comparable to the luminosity of the obscured progenitor star. If it is a supernova, the near-IR emission is likely due to shock heated dust since the elapsed time from peak is too long to support a near-IR dust echo and the decline in luminosity is shallower than the 56Co slope. If it is reprocessed emission from a surviving progenitor, a dust photosphere must have reestablished itself closer to the star than before the transient (~40 AU rather than 150 AU), unless there is a second, cooler dust component that dominates at mid-IR wavelengths. The continued rapid fading at roughly constant temperature favors transient emission, but the SED peaks in the mid-IR and future Spitzer observations will be needed to close the case.
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