质量传递对IT库中寿命-旅行时间离散的解释
Mass Transfer as an Explanation for the Lifetime-Travel Time Discrepancy in IT Librae
摘要：
食双星天秤座IT是一个不寻常的系统，由两颗B型恒星组成，位于银道面上方约1千秒差距。这颗双星可能是从它的出生地被抛出的，但它到达当前位置的飞行时间超过了主星的演化寿命。在这里，我们提出了一个新的高色散光谱和开普勒K2任务的精致的光变曲线的研究，以确定系统的属性和解决时间尺度的差异。我们从径向速度测量中得到了一个修正的光谱轨道，并通过比较重建的和模型的光谱（$T_1 = 23.8 \pm 1.8$ kK，$T_2 = 13.7 \pm 2.5$ kK）来确定组件的有效温度。我们使用光变曲线（ELC）代码来模拟K2光变曲线，并且从拟合的倾斜度，我们推导出组分质量（$M_1 = 9.6 \pm 0.6 M_\odot$，$M_2 = 4.2 \pm 0.2 M_\odot$）和平均半径（$R_1 = 6.06 \pm 0.16 R_\odot$，$R_2 = 5.38 \pm 0.14 R_\odot$）。第二颗恒星相对于它的质量来说是过于明亮的，似乎充满了它的洛希瓣。这表明天秤座IT是一个后质量转移系统，其中当前的次级恒星是质量供体星。目前的主星是通过质量吸积而再生的，其演化年龄对应于质量转移阶段以来的时间。因此，双星的真实年龄大于抛射飞行时间，从而解决了时间尺度的差异。
英文摘要：
The eclipsing binary IT Librae is an unusual system of two B-type stars that is situated about 1 kpc above the galactic plane. The binary was probably ejected from its birthplace in the disk, but the implied time-of-flight to its current location exceeds the evolutionary lifetime of the primary star. Here we present a study of new high dispersion spectroscopy and an exquisite light curve from the Kepler K2 mission in order to determine the system properties and resolve the timescale discrepancy. We derive a revised spectroscopic orbit from radial velocity measurements and determine the component effective temperatures through comparison of reconstructed and model spectra ($T_1 = 23.8 \pm 1.8$ kK, $T_2 = 13.7 \pm 2.5$ kK). We use the Eclipsing Light Curve (ELC) code to model the K2 light curve, and from the inclination of the fit, we derive the component masses ($M_1 = 9.6 \pm 0.6 M_\odot$, $M_2 = 4.2 \pm 0.2 M_\odot$) and mean radii ($R_1 = 6.06 \pm 0.16 R_\odot$, $R_2 = 5.38 \pm 0.14 R_\odot$). The secondary star is overluminous for its mass and appears to fill its Roche lobe. This indicates that IT~Librae is a post-mass transfer system in which the current secondary was the mass donor star. The current primary star was rejuvenated by mass accretion, and its evolutionary age corresponds to the time since the mass transfer stage. Consequently, the true age of the binary is larger than the ejection time-of-flight, thus resolving the timescale discrepancy.
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