Magnetic activity in the photosphere of CoRoT-Exo-2a Active longitudes and short-term spot cycle in a young Sun-like star
Magnetic activity in the photosphere of CoRoT-Exo-2a Active longitudes and short-term spot cycle in a young Sun-like star
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DOI：
10.1051/0004-6361:200810591
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发表时间：
2009-01-01
影响因子：
6.5
通讯作者：
Weiss, W. W.
中科院分区：
文献类型：
--
作者：
Lanza, A. F.;Pagano, I.;Weiss, W. W.
上下文空间实验CoRoT最近探测到一颗热木星穿过一颗活跃的G7 V星星（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. Aims。我们提出了一个点建模的光学可变性的星星在142天的不间断观测的CoRoT前所未有的光度精度。我们申请现场建模方法以前测试的情况下，太阳的建模总太阳辐照度的变化，一个很好的代理太阳作为一个星星的光通量变化。通过最大熵正则化模型，获得了最好的结果，在映射的表面亮度不均匀性。为了模拟CoRoT-Exo-2a的光变曲线，我们采用太阳类比的方法，同时考虑了冷斑和类太阳光斑的光度效应。在CoRoT-Exo-2a的光球上发现了两个最初位于相对半球的活跃天体，自转周期为4.522 +/- 0.024天。在观测的时间跨度内，它们的间距变化约为80度。根据这种变化，估计表面差异旋转的相对幅度低于1%。个别斑点形成于活跃的日冕中，其角速度比经度图案的角速度低1%。总的斑点区域显示出一个周期为28.9 +/- 4.3天的周期振荡，这接近于旋转活动行星所看到的行星会合周期的10倍。我们讨论了类太阳光斑对我们模型的影响，发现光斑对CoRoT-Exo-2a光通量变化的贡献明显小于目前的太阳。这些结果的影响的内部旋转的CoRoT-Exo-2a进行了讨论，太阳类比的基础上。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周期可能与在星星的亚光球层中传播的Rossby型波有关。
Context. 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.Aims. 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.Methods. We apply spot modelling approaches previously tested in the case of the Sun by modelling total solar irradiance variations, a good proxy for the optical flux variations of the Sun as a star. The best results in terms of mapping of the surface brightness inhomogeneities are obtained by means of maximum entropy regularized models. To model the light curve of CoRoT-Exo-2a, we take into account the photometric effects of both cool spots and solar-like faculae, adopting solar analogy.Results. Two active longitudes initially on opposite hemispheres are found on the photosphere of CoRoT-Exo-2a with a rotation period of 4.522 +/- 0.024 days. Their separation changes by approximate to 80 degrees during the time span of the observations. From this variation, a relative amplitude of the surface differential rotation lower than similar to 1 percent is estimated. Individual spots form within the active longitudes and show an angular velocity similar to 1 percent lower than that of the longitude pattern. The total spotted area shows a cyclic oscillation with a period of 28.9 +/- 4.3 days, which is close to 10 times the synodic period of the planet as seen by the rotating active longitudes. We discuss the effects of solar-like faculae on our models, finding indications of a facular contribution to the optical flux variations of CoRoT-Exo-2a being significantly smaller than in the present Sun.Conclusions. The implications of such results for the internal rotation of CoRoT-Exo-2a are discussed, based on 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.