低金属量星系PHL 293 B中一颗大质量恒星的可能消失
The possible disappearance of a massive star in the low metallicity galaxy PHL 293B
摘要：
我们研究了在最贫金属的矮星系之一PHL~ 293 B中的一颗疑似超大质量恒星。令人兴奋的是，我们在2019年的光谱中发现了恒星特征的突然消失，特别是与大质量发光蓝变星（LBV）相关的具有P~Cygni轮廓的宽H线。这些特征在我们2019年使用ESO VLT的ESTO和X-shooter仪器获得的光谱中不存在。我们使用CMFGEN计算辐射转移模型，该模型与观测到的LBV光谱相吻合，并且与地面和存档的哈勃空间望远镜测光相一致。我们的模型表明，在2001- 2011年期间，LBV的光度为$L_* = 2.5-3.5 \times 10^6 ~L_{\odot}$，质量损失率为$\dot{M} = 0.005-0.020 ~M_{\odot}$ ~yr $^{-1}$，风速为1000~km~s $^{-1}$，有效温度和恒星温度分别为$T_\mathrm{eff} = 6000-6800$ ~K和$T_\mathrm{*}=9500-15000$ ~K。这些恒星的特性表明它处于爆发状态。我们考虑了两个主要的假设，从2011年以来获得的光谱中没有宽发射分量。一种可能性是，我们看到的是一颗幸存恒星的LBV爆发的结束，光度略有下降，有效温度向更高的转变，以及一些尘埃遮蔽。或者，LBV可能已经坍缩成一个巨大的黑洞，而不会产生明亮的超新星。
英文摘要：
We investigate a suspected very massive star in one of the most metal-poor dwarf galaxies, PHL~293B. Excitingly, we find the sudden disappearance of the stellar signatures from our 2019 spectra, in particular the broad H lines with P~Cygni profiles that have been associated with a massive luminous blue variable (LBV) star. Such features are absent from our spectra obtained in 2019 with the ESPRESSO and X-shooter instruments of the ESO's VLT. We compute radiative transfer models using CMFGEN that fit the observed spectrum of the LBV and are consistent with ground-based and archival Hubble Space Telescope photometry. Our models show that during 2001--2011 the LBV had a luminosity $L_* = 2.5-3.5 \times 10^6 ~L_{\odot}$, a mass-loss rate $\dot{M} = 0.005-0.020 ~M_{\odot}$~yr$^{-1}$, a wind velocity of 1000~km~s$^{-1}$, and effective and stellar temperatures of $T_\mathrm{eff} = 6000-6800$~K and $T_\mathrm{*}=9500-15000$~K. These stellar properties indicate an eruptive state. We consider two main hypotheses for the absence of the broad emission components from the spectra obtained since 2011. One possibility is that we are seeing the end of an LBV eruption of a surviving star, with a mild drop in luminosity, a shift to hotter effective temperatures, and some dust obscuration. Alternatively, the LBV could have collapsed to a massive black hole without the production of a bright supernova.
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