在KOI-74的开普勒数据中由多普勒波束和罗默延迟对椭球调制的质量比
Mass ratio from Doppler beaming and Rømer delay versus ellipsoidal modulation in the Kepler data of KOI-74
摘要：
本文对一颗轨道为5.2天的食A星+白矮星双星KOI-74进行了光变曲线分析和视向速度研究。除了覆盖系统轨道的新光谱学之外，我们还使用了212天公开的开普勒观测数据，并提出了第一个完整的光变曲线拟合这些数据，模拟了日食和凌日，椭球调制，反射和多普勒波束。马尔可夫链蒙特卡罗模拟用于确定系统参数和不确定性估计。我们的研究结果与早期的研究一致，除了我们发现87.0 \pm 0.4 \degree，这是显着低于以前发表的值的倾斜度。我们发现，由径向速度幅值（q=0.104 \pm 0.004）导出的质量比与由椭球调制（q=0.052 \pm 0.004}，假设共转）导出的质量比不一致。这是以前发现的，但由于我们的倾角较小，差异甚至比以前报道的更大。考虑到A星的快速旋转，发现通过将质量比降低到q=0.047 \pm 0.004来进一步增加差异。这些结果表明，一个必须非常小心，在使用的椭球调制信号的振幅在一个紧密的二进制来确定质量比，当共转的证据是不牢固的建立。从光变曲线中检测到的多普勒光束中可以推断出的径向速度被发现与我们的光谱径向速度测定一致。我们还报告了紧凑双星光曲线中罗默延迟的首次测量结果。该延迟量为-56 \pm 17 s，并且与从径向速度振幅导出的质量比一致。质量比q=0.104 \pm 0.004的确定无疑地表明KOI-74的伴星是一颗低质量的白矮星。
英文摘要：
We present a light curve analysis and radial velocity study of KOI-74, an eclipsing A star + white dwarf binary with a 5.2 day orbit. Aside from new spectroscopy covering the orbit of the system, we used 212 days of publicly available Kepler observations and present the first complete light curve fitting to these data, modelling the eclipses and transits, ellipsoidal modulation, reflection, and Doppler beaming. Markov Chain Monte Carlo simulations are used to determine the system parameters and uncertainty estimates. Our results are in agreement with earlier studies, except that we find an inclination of 87.0 \pm 0.4\degree, which is significantly lower than the previously published value. We find that the mass ratio derived from the radial velocity amplitude (q=0.104 \pm 0.004) disagrees with that derived from the ellipsoidal modulation (q=0.052 \pm 0.004} assuming corotation). This was found before, but with our smaller inclination, the discrepancy is even larger than previously reported. Accounting for the rapid rotation of the A-star is found to increase the discrepancy even further by lowering the mass ratio to q=0.047 \pm 0.004. These results indicate that one has to be extremely careful in using the amplitude of an ellipsoidal modulation signal in a close binary to determine the mass ratio, when a proof of corotation is not firmly established. The radial velocities that can be inferred from the detected Doppler beaming in the light curve are found to be in agreement with our spectroscopic radial velocity determination. We also report the first measurement of Rømer delay in a light curve of a compact binary. This delay amounts to -56 \pm 17 s and is consistent with the mass ratio derived from the radial velocity amplitude. The firm establishment of this mass ratio at q=0.104 \pm 0.004 leaves little doubt that the companion of KOI-74 is a low mass white dwarf.
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