ON THE DYNAMICS AND TIDAL DISSIPATION RATE OF THE WHITE DWARF IN 4U 1820-30
ON THE DYNAMICS AND TIDAL DISSIPATION RATE OF THE WHITE DWARF IN 4U 1820-30
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4U 1820-30白矮星的动力学和潮汐耗散率
DOI：
10.1088/0004-637x/747/1/4
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
N. Murray
中科院分区：
文献类型：
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作者：
S. Prodan;N. Murray
有人认为，低质量X射线双星4U 1820-30的光变曲线中的170天周期是由于存在第三个与双星轨道有很大倾角的天体。我们表明，这种长周期的运动出现，如果系统是在一个Kozai共振的稳定的不动点周围的振动。我们表明，质量转移驱动系统朝着这个固定点和计算，无论是分析和通过数值积分，周期的天平动是为了170天时，相互倾斜是Kozai临界值附近。双星的非零偏心率，加上潮汐耗散，意味着双星周期的变化率将比标准质量转移模型所暗示的要慢，甚至是相反的符号。如果这170天的周期是由天平动产生的，那么与表面现象相反，内双星的轨道周期会随时间增加;在这种情况下，（e/0.009）2 Q/k2 <$2.5 × 109，其中k2 <$0.01是潮汐勒夫数，e = 0.009是内双星的基准偏心率。观测到的负周期导数似乎不太可能是由小于预期（但为正）的值与先前提出的系统在宿主球状星团NGC 6624引力场中的加速度相结合而产生的。观察到的和预期的期间衍生物之间的差异需要进一步调查。
It has been suggested that the 170 day period in the light curve of the low-mass X-ray binary 4U 1820-30 arises from the presence of a third body with a large inclination to the binary orbit. We show that this long-period motion arises if the system is librating around the stable fixed point in a Kozai resonance. We demonstrate that mass transfer drives the system toward this fixed point and calculate, both analytically and via numerical integrations, that the period of libration is of order 170 days when the mutual inclination is near the Kozai critical value. The non-zero eccentricity of the binary, combined with tidal dissipation, implies that the rate of change of the binary period would be slower than, or even of opposite sign to, that implied by standard mass transfer models. If the 170 day period results from libration, then, contrary to appearances, the orbital period of the inner binary is increasing with time; in that case, (e/0.009)2Q/k2 ≳ 2.5 × 109, where k2 ≈ 0.01 is the tidal Love number and e = 0.009 is the fiducial eccentricity of the inner binary. It appears unlikely that the observed negative period derivative results from the smaller than expected (but positive) value of combined with the previously suggested acceleration of the system in the gravitational field of the host globular cluster NGC 6624. The discrepancy between the observed and the expected period derivative requires further investigation.