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arXiv 1907.06375astro-ph.SRastro-ph.GA
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PG 1610 $+$ 062：一颗挑战经典弹射机制的逃逸B星

PG 1610$+$062: a runaway B star challenging classical ejection mechanisms

Andreas Irrgang, Stephan Geier, Ulrich Heber, Thomas Kupfer, Felix Fürst

备注：
Accepted for publication in A&A (Astronomy and Astrophysics)
发表信息：
A&A 628, L5 (2019)
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摘要：

超高速恒星是罕见的天体，大多数是主序星（MS）B星，它们的速度如此之快，以至于最终会逃离银河系。最近，人们已经表明，流行的希尔斯机制，其中一个双星系统是通过与银河系中心的超大质量黑洞的近距离接触而被破坏的，可能不是它们唯一的弹射机制。对盖亚数据的分析排除了其中一些恒星的银河系中心起源，而是表明它们是极端的盘状失控恒星，以超过经典场景（星团动力学喷射或双星超新星喷射）的预测极限的速度喷射。我们提出了一个新的极端磁盘失控星，PG 1610 $+$ 062，这是一个缓慢的脉动B星明亮到足以详细研究的发现。凯克天文台的ESI光谱定量分析显示PG 1610 $+$ 062是一颗4-5 $M_\odot$的晚期B型MS星，具有低的投影自转速度。丰度（C、N、O、Ne、Mg、Al、Si、S、Ar和Fe）与正常的B星HD 137366不同，表明PG 1610 $+$ 062有点富含金属。基于我们的分光光度距离（17.3 kpc）和盖亚第二次数据发布的自行，运动学分析表明PG 1610 $+$ 062可能以$550\pm40$ km s $^{-1}$的速度从船底座-人马座螺旋臂中喷出，这超出了经典极限。因此，这颗恒星是最极端的MS盘失控恒星中的前五名，并且在已知化学成分的五颗恒星中仅排名第二。

英文摘要：

Hypervelocity stars are rare objects, mostly main-sequence (MS) B stars, traveling so fast that they will eventually escape from the Milky Way. Recently, it has been shown that the popular Hills mechanism, in which a binary system is disrupted via a close encounter with the supermassive black hole at the Galactic center, may not be their only ejection mechanism. The analyses of Gaia data ruled out a Galactic center origin for some of them, and instead indicated that they are extreme disk runaway stars ejected at velocities exceeding the predicted limits of classical scenarios (dynamical ejection from star clusters or binary supernova ejection). We present the discovery of a new extreme disk runaway star, PG 1610$+$062, which is a slowly pulsating B star bright enough to be studied in detail. A quantitative analysis of spectra taken with ESI at the Keck Observatory revealed that PG 1610$+$062 is a late B-type MS star of 4-5 $M_\odot$ with low projected rotational velocity. Abundances (C, N, O, Ne, Mg, Al, Si, S, Ar, and Fe) were derived differentially with respect to the normal B star HD 137366 and indicate that PG 1610$+$062 is somewhat metal rich. A kinematic analysis, based on our spectrophotometric distance (17.3 kpc) and on proper motions from Gaia's second data release, shows that PG 1610$+$062 was probably ejected from the Carina-Sagittarius spiral arm at a velocity of $550\pm40$ km s$^{-1}$, which is beyond the classical limits. Accordingly, the star is in the top five of the most extreme MS disk runaway stars and is only the second among the five for which the chemical composition is known.

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