用TESS填补短周期sdBV + dM双星中同步和非同步sdBs之间的空白：TIC 137608661，一个具有明确旋转分裂的新系统
Filling the gap between synchronized and non-synchronized sdBs in short-period sdBV+dM binaries with TESS: TIC 137608661, a new system with a well defined rotational splitting
摘要：
TIC 137608661/TYC 4544 -2658-1/FBS 0938 +788是TESS太空任务发现的一颗新的sdBV+dM反射效应双星，轨道周期为7.21小时。除了轨道频率及其谐波，TIC 137608661的傅立叶变换还显示了sdB星的许多g模式脉动频率。振幅谱特别容易解释，因为我们立即看到几个等间隔频率的旋转三元组。这些三重态的中心频率在周期上是等间隔的，平均周期间隔为270.12 s，对应于连续的l=1模式。从1.25 μHz的平均频率间隔，我们推导出sdB星深层的自转周期为4.6天，明显长于轨道周期。在少数通过星震学测量sdB旋转的sdB+dM双星中，TIC 137608661是轨道周期和核心旋转周期最短的非同步系统。只有NY Vir的轨道周期较短，但它是同步的。从TIC 137608661的光谱跟踪，我们测量了sdB星的径向速度，确定了它的大气参数，并估计了恒星表面的旋转速率。这种测量使我们能够排除外层的同步旋转，并提出了一种差动旋转，表面旋转速度比核心快，这在其他一些类似的系统中发现。此外，TIC 137608661的光谱能量分布的分析，以及sdB脉动特性和asteroseismic模型之间的比较，给我们提供了进一步的元素来约束系统。
英文摘要：
TIC137608661/TYC4544-2658-1/FBS0938+788 is a new sdBV+dM reflection-effect binary discovered by the TESS space mission with an orbital period of 7.21 hours. In addition to the orbital frequency and its harmonics, the Fourier transform of TIC137608661 shows many g-mode pulsation frequencies from the sdB star. The amplitude spectrum is particularly simple to interpret as we immediately see several rotational triplets of equally spaced frequencies. The central frequencies of these triplets are equally spaced in period with a mean period spacing of 270.12 s, corresponding to consecutive l=1 modes. From the mean frequency spacing of 1.25 μHz we derive a rotation period of 4.6 days in the deep layers of the sdB star, significantly longer than the orbital period. Among the handful of sdB+dM binaries for which the sdB rotation was measured through asteroseismology, TIC137608661 is the non-synchronized system with both the shortest orbital period and the shortest core rotation period. Only NY Vir has a shorter orbital period but it is synchronized. From a spectroscopic follow-up of TIC137608661 we measure the radial velocities of the sdB star, determine its atmospheric parameters, and estimate the rotation rate at the surface of the star. This measurement allows us to exclude synchronized rotation also in the outer layers and suggests a differential rotation, with the surface rotating faster than the core, as found in few other similar systems. Furthermore, an analysis of the spectral energy distribution of TIC137608661, together with a comparison between sdB pulsation properties and asteroseismic models, gives us further elements to constrain the system.
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