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arXiv 1302.6296astro-ph.SR
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自转最快的O型星VFTS102的前身星双星合并通道

The binary merger channel for the progenitor of the fastest rotating O-type star VFTS102

Dengkai Jiang, Zhanwen Han, Liheng Yang, Lifang Li

摘要:

VFTS 102的预计旋转速度为500 km s $>$,是旋转最快的O型星。我们发现,它的高转速可以理解的框架内的二元合并。在双星合并通道中,VFTS 102的前身双星会在主序星上的两个组成部分仍然存在的情况下演化为接触,然后合并成一颗快速旋转的单星。利用Eggleton的恒星演化程序,我们计算了VFTS 102的双星演化,并在轨道周期-质量比($P-q$)平面上绘制出了它的初始参数。我们发现初始质量比为$q_0 \la 0.7$的VFTS 102的前身双星的初始轨道周期应短于$3.76-4.25$ \,天,而高于此质量比时,其初始轨道周期应短于$1.44-1.55$ \,天。VFTS 102的前身会在快速质量转移阶段或随后的缓慢质量转移阶段演化成接触,并可能最终合并成一颗快速旋转的大质量恒星。此外,我们进行了蒙特卡罗模拟调查的二进制合并通道。我们估计了合并成单星的双星的比例,以及可能从双星合并通道中产生的单星的比例。结果表明,约8.7%的双星会演化为接触并合并成快速旋转的单星,约17.1%的单星可能产生于双星合并通道,并具有与VFTS 102相似的性质。这表明双星合并通道可能是形成VFTS 102这样快速旋转大质量恒星的主要通道之一。

英文摘要:

VFTS102 has a projected rotational velocity ($>$500\,km s$^{-1}$) and would appear to be the fastest rotating O-type star. We show that its high rotational velocity could be understood within the framework of the binary merger. In the binary merger channel, the progenitor binary of VFTS102 would evolve into contact while two components are still on the main sequence, and then merge into a rapidly rotating single star. Employing Eggleton's stellar evolution code, we performed binary stellar evolution calculations and mapped out the initial parameters of the progenitor of VFTS102 in the orbital period-mass ratio ($P-q$) plane. We found that the progenitor binary of VFTS102 with initial mass ratio $q_0 \la 0.7$ should have an initial orbital period shorter than $3.76-4.25$\,days, while above this mass ratio it should have an initial orbital period shorter than $1.44-1.55$\,days. The progenitor of VFTS102 would evolve into contact during the rapid mass transfer phase or during the subsequent slow mass transfer phase, and might ultimately merge into a rapidly rotating massive star. In addition, we performed Monte Carlo simulations to investigate the binary merger channel. We estimated the fraction of binaries that would merge into single stars and the fraction of single stars that might be produced from the binary merger channel. It is found that about 8.7% of binaries would evolve into contact and merge into rapidly rotating single stars, and about 17.1% of single stars might be produced from the binary merger channel and should have similar properties to VFTS102. This suggests that the binary merger channel might be one of the main channels for the formation of rapidly rotating massive stars like VFTS102.

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