CoRoT-Exo-2a光球层的磁活动。年轻类太阳恒星中的活动黑子和短期黑子周期
Magnetic activity in the photosphere of CoRoT-Exo-2a. Active longitudes and short-term spot cycle in a young Sun-like star
摘要：
空间实验CoRoT最近探测到一颗热木星穿过一颗活跃的G7 V恒星（CoRoT-Exo-2a）的盘面，这颗恒星可以被认为是太阳的一个很好的代理，年龄约为0.5 Gyr。我们提出了一个点建模的光学可变性的恒星在142天的不间断的观测进行了前所未有的光度精度的CoRoT。我们应用现场建模方法，以前测试的情况下，太阳模拟太阳总辐照度的变化。为了模拟CoRoT-Exo-2a的光变曲线，我们考虑了冷斑的光度效应以及太阳光斑的光度效应，采用太阳类比。在CoRoT-Exo-2a的光球上发现了两个最初位于相对半球的活动天体，其自转周期为4.522 $\pm$ 0.024天。在观测的时间跨度内，它们的间距变化约80度。根据这种变化，估计表面差异旋转的相对幅度低于约1%。在活跃的日冕中形成的单个斑点的角速度大约比经度方向的小1%。总的斑点面积显示出一个周期为28.9 $\pm$ 4.3天的周期振荡，这是接近10倍的会合周期的行星所看到的旋转活跃的彗星。在太阳类比的基础上讨论了这些结果对CoRoT-Exo-2a内旋的影响。一个可能的磁性恒星行星相互作用的周期性变化的斑点面积建议。或者，28.9-d周期可能与在恒星的次光球层中传播的罗斯比型波有关。
英文摘要：
The space experiment CoRoT has recently detected transits by a hot Jupiter across the disc of an active G7V star (CoRoT-Exo-2a) that can be considered as a good proxy for the Sun at an age of approximately 0.5 Gyr. We present a spot modelling of the optical variability of the star during 142 days of uninterrupted observations performed by CoRoT with unprecedented photometric precision. We apply spot modelling approaches previously tested in the case of the Sun by modelling total solar irradiance variations. To model the light curve of CoRoT-Exo-2a, we take into account both the photometric effects of cool spots as well as those of solar-like faculae, adopting solar analogy. Two active longitudes initially on opposite hemispheres are found on the photosphere of CoRoT-Exo-2a with a rotation period of 4.522 $\pm$ 0.024 days. Their separation changes by approximately 80 degrees during the time span of the observations. From this variation, a relative amplitude of the surface differential rotation lower than about 1 percent is estimated. Individual spots form within the active longitudes and show an angular velocity about 1 percent smaller than that of the longitude pattern. The total spotted area shows a cyclic oscillation with a period of 28.9 $\pm$ 4.3 days, which is close to 10 times the synodic period of the planet as seen by the rotating active longitudes. The implications of such results for the internal rotation of CoRoT-Exo-2a are discussed on the basis of solar analogy. A possible magnetic star-planet interaction is suggested by the cyclic variation of the spotted area. Alternatively, the 28.9-d cycle may be related to Rossby-type waves propagating in the subphotospheric layers of the star.
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