Eccentric binaries - Tidal flows and periastron events
Eccentric binaries - Tidal flows and periastron events
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DOI：
10.1051/0004-6361/201015874
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发表时间：
2011-02
影响因子：
6.5
通讯作者：
E. Moreno;G. Koenigsberger;D. Harrington
中科院分区：
文献类型：
--
作者：
E. Moreno;G. Koenigsberger;D. Harrington
上下文。许多双星系统显示出在近星通道周围增强活动的证据，表明潮汐相互作用与这些近星效应之间存在联系。目标。这项研究的目的是研究恒星表面受到双星伴星扰动时的随时间响应。这里主要讨论潮汐切变能量耗散。方法。我们推导了一个数学表达式，用于计算由双星表面层潮汐相互作用驱动的粘性流的动能耗散率u E。通过将模型计算网格的结果与Hut （1981, AA 2008, EAS Pub）的分析预测进行比较，对该方法进行了验证。爵士。， 29,67)。结果。我们关于平均（轨道周期以上）能量耗散（Eave）与轨道间距的依赖关系的结果与Hut（1981）对轨道间距在近日点rper/R1 > 8 （R1为恒星半径）的模型双星的结果一致。该模型还再现了中等偏心率（e≤0.3）的预测伪同步角速度。此外，对于圆形轨道，我们的方法产生了与Zahn（1977,2008）给出的对流包络相同的同步时间尺度与轨道分离。计算给出了u E在恒星表面的分布，并表明它通常集中在赤道纬度，最大值通常位于四个明确定义的经度附近，对应于最快的方位角速度扰动。最大振幅出现在星周附近，超同步旋转的恒星则稍晚一些。在非常偏心的双星中，u E在表面上的分布随着轨道相位的变化而发生显著变化，在近日点之后出现了小的空间结构。对一个参数与δ Sco相似的高偏心双星系统（e = 0.94, P = 3944.7 d）的探索性计算表明，u Eave在近日点之前的82天内变化了~ 5个数量级，这表明近日点周围表面性质的突然和大幅度变化确实可能有助于在这个轨道阶段周围观察到的活动。
Context. A number of binary systems present evidence of enhanced activity around periastron passage, suggesting a connection between tidal interactions and these periastron effects. Aims. The aim of this investigation is to study the time-dependent response of a star’s surface as it is perturbed by a binary companion. Here we focus on the tidal shear energy dissipation. Methods. We derive a mathematical expression for computing the rate of dissipation, u E, of the kinetic energy by the viscous flows that are driven by tidal interactions on the surface layer of a binary star. The method is tested by comparing the results from a grid of model calculations with the analytical predictions of Hut (1981, AA 2008, EAS Pub. Ser., 29, 67). Results. Our results for the dependence of the average (over orbital cycle) energy dissipation, u Eave, on orbital separation are consistent with those of Hut (1981) for model binaries with an orbital separation at periastron rper/R1 > 8, where R1 is the stellar radius. The model also reproduces the predicted pseudo-synchronization angular velocity for moderate eccentricities (e ≤ 0.3). In addition, for circular orbits our approach yields the same scaling of synchronization timescales with orbital separation as given by Zahn (1977, 2008) for convective envelopes. The computations give the distribution of u E over the stellar surface, and show that it is generally concentrated at the equatorial latitude, with maxima generally located around four clearly defined longitudes, corresponding to the fastest azimuthal velocity perturbations. Maximum amplitudes occur around periastron passage or slightly thereafter for supersynchronously rotating stars. In very eccentric binaries, the distribution of u E over the surface changes significantly as a function of orbital phase, with small spatial structures appearing after periastron. An exploratory calculation for a highly eccentric binary system with parameters similar to those of δ Sco (e = 0.94, P = 3944.7 d) indicates that u Eave changes by ∼5 orders of magnitude over the 82 days before periastron, suggesting that the sudden and large amplitude variations in surface properties around periastron may, indeed, contribute toward the activity observed around this orbital phase.