SN 2015bh: NGC 2770's 4th supernova or a luminous blue variable on its way to a Wolf-Rayet star?
SN 2015bh: NGC 2770's 4th supernova or a luminous blue variable on its way to a Wolf-Rayet star?
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DOI：
10.1051/0004-6361/201629968
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发表时间：
2016-06
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影响因子：
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通讯作者：
C. Thöne;A. D. U. Postigo;A. D. U. Postigo;G. Leloudas;G. Leloudas;C. Gall;C. Gall;Z. Cano
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文献类型：
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作者：
C. Thöne;A. D. U. Postigo;A. D. U. Postigo;G. Leloudas;G. Leloudas;C. Gall;C. Gall;Z. Cano
在生命的最后阶段，超大质量恒星通常会表现出不可预测的爆发，可以模仿超新星，所谓的“SN冒名顶替者”，但这种区别并不总是直截了当的。在这里，我们介绍了NGC 2770中一个亮蓝变星（LBV）在20多年的爆发中的观测结果，该变星在2015年经历了一次可能的终端爆炸，称为SN 2015 bh。这一可能的SN或“主事件”之前有一个前兆峰值$\sim $40天前最大。主事件的总能量释放为1.8\times10 $^{49}$ erg，这可以通过一个<0.5 M$_\odot$的壳层陷入致密的CSM来模拟。所有的发射线显示一个单一的狭窄的P-Cygni配置文件在LBV阶段和双P-Cygni配置文件后的最大值，这表明该第二个组件与可能的SN的关联。自1994年以来，这颗星星比典型的S-Dor爆发时更红。SN 2015 bh位于NGC 2770的旋臂内，旁边有许多小的恒星形成区，金属丰度为0.5太阳能，恒星年龄为7- 1000万年。SN 2015 bh与SN 2009 ip有许多相似之处，它们与其他例子一起可能形成一类新的天体，这些天体在“超级喷发”或最终的核心坍塌之前几十年就爆发了。如果星星在这次事件中幸存下来，它无疑会发生变化，我们认为这些“僵尸恒星”可能会在短短几年的时间内从LBV演变为沃尔夫拉叶星星。这些类型的大质量恒星的最终命运只能在可能的SN之后数年的观测中确定。
Very massive stars in the final phases of their lives often show unpredictable outbursts that can mimic supernovae, so-called, "SN impostors", but the distinction is not always straigthforward. Here we present observations of a luminous blue variable (LBV) in NGC 2770 in outburst over more than 20 years that experienced a possible terminal explosion as type IIn SN in 2015, named SN 2015bh. This possible SN or "main event" was preceded by a precursor peaking $\sim$ 40 days before maximum. The total energy release of the main event is $\sim$1.8$\times$10$^{49}$ erg, which can be modeled by a $<$ 0.5 M$_\odot$ shell plunging into a dense CSM. All emission lines show a single narrow P-Cygni profile during the LBV phase and a double P-Cygni profile post maximum suggesting an association of this second component with the possible SN. Since 1994 the star has been redder than during a typical S-Dor like outburst. SN 2015bh lies within a spiral arm of NGC 2770 next to a number of small star-forming regions with a metallicity of $\sim$ 0.5 solar and a stellar population age of 7-10 Myr. SN 2015bh shares many similarities with SN 2009ip, which, together with other examples may form a new class of objects that exhibit outbursts a few decades prior to "hyper-eruption" or final core-collapse. If the star survives this event it is undoubtedly altered, and we suggest that these "zombie stars" may evolve from an LBV to a Wolf Rayet star over a very short timescale of only a few years. The final fate of these types of massive stars can only be determined with observations years after the possible SN.