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arXiv 0902.1315astro-ph.SR
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利用X射线观测研究Eta Carinae的双星相互作用

Using X-Ray Observations to Explore the Binary Interaction in Eta Carinae

Amit Kashi, Noam Soker

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MNRAS, in press. 21 pages, 5 figures
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摘要：

本文研究了利用巨质量双星Eta Carinae的X射线光变曲线、对硬X射线源的柱密度和发射量度（密度平方乘以体积）来确定其半长轴的方向。硬X射线发射源是激波次级风。我们认为，就其本身而言，所观察到的X射线通量不能告诉我们很多关于半长轴的方向。对双星系统的一些未知参数进行微调，可以拟合几乎任何倾角和取向的X射线光变曲线。另一方面，柱密度和X射线发射测量对取向施加强约束。我们改进了我们以前的计算，并表明，柱密度是更兼容的方向，在大多数时间的次要-热，质量较低的恒星-是后面的主星。第二次接近观察者只有很短的时间接近近星点通过。10周X射线深度最小值，这是由于排放量的大幅减少，意味着在此期间，规则的二次风基本上被抑制。这种抑制最有可能是由于主要的发光蓝变星（LBV）的密集风的质量吸积。赤道面的吸积作用可能导致极流的形成。我们认为，极外流有助于软X射线发射的X射线最低期间，另一个来源是在尾部的冲击二次风。每五年半一次的近星点通过都会发生吸积，这一结论意味着在19世纪的20次海山二大爆发期间，吸积的速度要高得多。

英文摘要：

We study the usage of the X-ray light curve, column density toward the hard X-ray source, and emission measure (density square times volume), of the massive binary system Eta Carinae to determine the orientation of its semi-major axis. The source of the hard X-ray emission is the shocked secondary wind. We argue that, by itself, the observed X-ray flux cannot teach us much about the orientation of the semi-major axis. Minor adjustment of some unknown parameters of the binary system allows to fit the X-ray light curve with almost any inclination angle and orientation. The column density and X-ray emission measure, on the other hand, impose strong constrains on the orientation. We improve our previous calculations and show that the column density is more compatible with an orientation where for most of the time the secondary - the hotter, less massive star - is behind the primary star. The secondary comes closer to the observer only for a short time near periastron passage. The ten-week X-ray deep minimum, which results from a large decrease in the emission measure, implies that the regular secondary wind is substantially suppressed during that period. This suppression is most likely resulted by accretion of mass from the dense wind of the primary luminous blue variable (LBV) star. The accretion from the equatorial plane might lead to the formation of a polar outflow. We suggest that the polar outflow contributes to the soft X-ray emission during the X-ray minimum; the other source is the shocked secondary wind in the tail. The conclusion that accretion occurs at each periastron passage, every five and a half years, implies that accretion had occurred at a much higher rate during the 20 Great Eruption of Eta Carinae in the 19th century.

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