Nonradial oscillations of tidally distorted stars and asteroseismology

1. 研究了一个紧密双星系统中δ Scuti型恒星θ Tucanae的脉动特性。这颗恒星的脉动被描述为13个频率，其中一个频率对应于双星轨道周期。而质量比仅为0.0896。主星的振荡似乎不太可能是由这样一个光伴星引起的。我们提出了一个新的场景来解释这个神秘的特征；如果轨道周期恰好接近主星的四极g模式，则g模式与轨道运动共振。随着频率的降低，g模特征谱变得非常密集，从而更容易发生共振。作为共振的结果，恒星向它的伴星被拉长，径向p模特征函数被变形为具有轴对称的四极分量，其对称轴与伴星的方向一致。p模特征函数的四极分量对视亮度变化的贡献随时间变化，在功率谱上产生了等间距为轨道频率倍的三重态精细结构。研究了轨道相θ Tucanae的着色行为。结果表明，两个周期可以很好地描述颜色变化。较短的周期与次要的椭球形状有关。每个轨道周期发生一次的反射效应导致深极小值和浅极小值交替发生。测试了10种脉动模式与轨道运动的共振。结果表明，主导脉动模式与椭球效应有一定的共振关系。作为一个参加国际观测活动的团队，我们对Procyon进行了光谱观测，以探测它的类似太阳的振荡。我们现在进行数据分析。

1. Pulsational properties of θ Tucanae, one of the δ Scuti type stars in a close binary system, were investigated. Pulsation of this star is described by 13 frequencies, and one of them corresponds to the binary orbital period. However, the mass ratio is only 0.0896. It seems unlikely that oscillation of the primary star is excited by such a light companion. We proposed a new scenario to explain this enigmatic feature ; if the orbital period happens to be close to a quadrupole g-mode of the primary star, the g-mode resonates with the orbital motion. The g-mode eigenspectrum becomes so dense with the decrease of frequency that resonance becomes more likely to occur. As a consequence of resonance, the star is elongated toward its companion, and the radial p-mode eigenfunction is deformed to have an axially symmetric quadrupole component, whose symmetry axis coincides with the direction of the companion. The contribution of the quadrupole component of the p-mode eigenfunction to the apparent luminosity variation changes with time, and a triplet fine structure with an equal spacing of the double of orbital frequency is produced in the power spectrum.2. The color behavior of θ Tucanae with orbital phase was investigated. It was shown that the color variation is well described by two periods. The shorter period is connected to the ellipsoidal shape of the secondary. A reflection effect occurring once each orbital period causes alternative deep and shallow minima. Ten pulsational modes were tested for resonance with the orbital motion. It was found that the dominant pulsation mode shows a definite resonance with the ellipsoidal effect.3. We made spectroscopic observation of Procyon as a team attending the international observational campaign of this star, in order to detect its solar-like oscillations. We are now going on the data analysis.