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arXiv 1107.4458astro-ph.SR
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利用聚束效应测量类日双星的自旋轨道对准

On using the beaming effect to measure spin-orbit alignment in stellar binaries with Sun-like components

Avi Shporer, Tim Brown, Tsevi Mazeh, Shay Zucker

摘要:

光束效应(又名多普勒增强)会导致观测到的发光物体的通量发生变化,这是由于观测到的径向速度变化。本文描述了双星系统在食时由聚束效应引起的光度信号,其中的恒星成分是晚型类太阳恒星。这个信号的形状对被食恒星的自转轴和轨道角动量轴之间的角度很敏感,因此可以进行测量。我们表明,在日食期间,实际上有两个效果,叠加在已知的日食光变曲线。一种效应是由食星的旋转产生的,是光谱罗斯特-麦克劳克林效应的光度模拟,因此它包含了关于天空投射的自旋轨道角的信息。另一种效应是由日食期间两颗恒星发出的信号之间的不同加权差产生的。我们给出了近似的解析表达式的振幅的两种效果,并提出了一个数值模拟,我们显示的光变曲线的两种效果为不同的轨道取向,低质量比恒星食双星系统。我们表明,虽然整体信号很小,它可以检测到在主日食时,使用开普勒长Cadence数据的明亮系统积累了整个任务寿命。

英文摘要:

The beaming effect (aka Doppler boosting) induces a variation in the observed flux of a luminous object, following its observed radial velocity variation. We describe a photometric signal induced by the beaming effect during eclipse of binary systems, where the stellar components are late type Sun-like stars. The shape of this signal is sensitive to the angle between the eclipsed star's spin axis and the orbital angular momentum axis, thereby allowing its measurement. We show that during eclipse there are in fact two effects, superimposed on the known eclipse light curve. One effect is produced by the rotation of the eclipsed star, and is the photometric analog of the spectroscopic Rossiter-McLaughlin effect, thereby it contains information about the sky-projected spin-orbit angle. The other effect is produced by the varying weighted difference, during eclipse, between the beaming signals of the two stars. We give approximated analytic expressions for the amplitudes of the two effects, and present a numerical simulation where we show the light curves for the two effects for various orbital orientations, for a low mass ratio stellar eclipsing binary system. We show that although the overall signal is small, it can be detected in the primary eclipse when using Kepler Long Cadence data of bright systems accumulated over the mission lifetime.

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