DISCOVERY OF THE MASSIVE OVERCONTACT BINARY VFTS 352: EVIDENCE FOR ENHANCED INTERNAL MIXING-猫眼课题宝

DOI：

10.1088/0004-637x/812/2/102

发表时间：

2015-09

期刊：

The Astrophysical Journal

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

L. Almeida;H. Sana;H. Sana;S. D. Mink;F. Tramper;I. Soszyn´ski;N. Langer;R. Barbá;M. Cantiello;A. Damineli;A. D. Koter;A. D. Koter;Miriam García;G. Gräfener;A. Herrero;A. Herrero;I. Howarth;J. M. Apell'aniz;C. Norman;O. H. Ramírez-Agudelo;J. Vink

由于缺乏观测约束，预计在两颗大质量恒星合并之前的接触阶段的特征很差。在此，我们报告了在剑鱼座30区发现的一颗o型双星VFTS 352，它是迄今为止已知的质量最大、最早的光谱型过接触系统。我们推导出该系统的三维几何形状，其轨道周期P球= 1.1241452 (4)？>天，组分有效温度- t1 = 42 540±280 K, T2 = 41 120±290 K -动力质量- m1 = 28.63±0.30 M⊙？>和m2 = 28.85±0.30 M⊙。？与单星演化模型相比，VFTS 352的组分相对于它们的动力质量来说，分别高出2700 K和1100 K左右。这些结果可以很自然地解释为混合增强的结果，理论上预测会发生在非常短周期的潮汐锁定系统中。VFTS 352组分是迄今为止确定的两个最佳候选组分，可以经历所谓的化学均匀演化。VFTS 352的未来是不确定的。如果这两颗恒星合并，就会产生一颗快速旋转的恒星。相反，如果恒星继续均匀演化，并在它们的罗氏叶内不断缩小，就可以避免合并。在这种情况下，潮汐可能会抵消风的旋转，这样VFTS 352的组件在其寿命结束时可能会满足坍缩情景中长伽马射线暴（GRB）祖先的要求。无论VFTS 352的组成部分是否成为GRB的前身，这种情况都使VFTS 352作为黑洞双星的前身变得有趣，因此作为黑洞-黑洞合并的潜在引力波源。

The contact phase expected to precede the coalescence of two massive stars is poorly characterized due to the paucity of observational constraints. Here we report on the discovery of VFTS 352, an O-type binary in the 30 Doradus region, as the most massive and earliest spectral type overcontact system known to date. We derived the 3D geometry of the system, its orbital period P orb = 1.1241452 ( 4 ) ?> day, components’ effective temperatures—T1 = 42 540 ± 280 K and T2 = 41 120 ± 290 K—and dynamical masses— M 1 = 28.63 ± 0.30 M ⊙ ?> and M 2 = 28.85 ± 0.30 M ⊙ . ?> Compared to single-star evolutionary models, the VFTS 352 components are too hot for their dynamical masses by about 2700 and 1100 K, respectively. These results can be explained naturally as a result of enhanced mixing, theoretically predicted to occur in very short-period tidally locked systems. The VFTS 352 components are two of the best candidates identified so far to undergo this so-called chemically homogeneous evolution. The future of VFTS 352 is uncertain. If the two stars merge, a very rapidly rotating star will be produced. Instead, if the stars continue to evolve homogeneously and keep shrinking within their Roche Lobes, coalescence can be avoided. In this case, tides may counteract the spin down by winds such that the VFTS 352 components may, at the end of their life, fulfill the requirements for long gamma-ray burst (GRB) progenitors in the collapsar scenario. Independently of whether the VFTS 352 components become GRB progenitors, this scenario makes VFTS 352 interesting as a progenitor of a black hole binary, hence as a potential gravitational wave source through black hole–black hole merger.

DISCOVERY OF THE MASSIVE OVERCONTACT BINARY VFTS 352: EVIDENCE FOR ENHANCED INTERNAL MIXING

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