Multi-color photometry with SOFIA: Spots on the solar-like star CoRoT-2A and their effect on its exoplanet CoRoT-2b

我和我的合作者将观测到系外行星CoRoT-2b在它非常活跃的主星CoRoT-2A前的一次凌日。我们将首次能够同时获得准天基、短节奏的光学和近红外测光，持续时间超过3小时。SOFIA数据将为我们提供调查两个问题所需的信息：(a)系外行星半径是否膨胀？目前的研究表明，许多类木星系外行星的半径比理论预测的要大得多。利用CoRoT数据，我们的小组已经表明，主恒星的活动会导致行星参数（即行星半径）测定的系统误差。我们的SOFIA观测将使我们能够检查行星膨胀的半径有多少是由恒星表面的恒星黑子引起的。这一结果将帮助我们了解观测到的膨胀是否真的是由于一个尚未理解的物理过程导致的行星膨胀，还是恒星活动影响光曲线的某种结果。(b)星黑子的物理性质是什么？光曲线可以用来重建恒星表面的黑点。对于这项任务，凌日行星是特别有趣的：当行星穿过恒星盘时，它会扫描恒星表面，所有的亮度不均匀都会被印在凌日的轮廓上。本课题组已经利用该方法利用CoRoT卫星的数据重建了CoRoT- 2a近半年的地表演变。SOFIA的观测将为我们提供更多的近红外信息，这是CoRoT没有提供的。这是第一次有可能测量CoRoT-2A表面斑点的温度，而不考虑斑点的未知大小。如果我们能够在观测中分辨出单个黑点的本影和半影，那么我们也将有可能首次测量另一颗类太阳恒星上黑点的结构和本影/半影温度。

My collaborators and I will observe one transit of the exoplanet CoRoT-2b in front of its very active host-star CoRoT-2A. For the first time we will be able to obtain quasi-space-based, short-cadence photometry in the optical and the near-infrared simultaneously for an uninterrupted time period of more than 3 hours. The SOFIA data will provide us with the information necessary to investigate two issues:(a) Are exoplanetary radii inflated?Current research shows that many Jupiter-like exoplanets have radii much larger than theoretical predictions. Using CoRoT data our group has already shown that the activity of the host-star causes systematic errors in the determination of planetary parameters, i.e., the planet radius. Our SOFIA observations will allow us to examine how much of the planet's inflated radius is caused by starspots on the stellar surface. The result will help us to understand whether the observed inflation really is due to an yet not understood physical process expanding the planet or some consequence of stellar activity affecting the lightcurves.(b) What are the physical properties of starspots?Lightcurves can be used to reconstruct dark spots on the surface of a star. For this task, transiting planets are of special interest: When the planet moves across the stellar disk, it scans the surface of the star and all brightness inhomogeneities are imprinted onto the profile of the transit. Our group has already used this method to reconstruct the surface evolution of CoRoT-2A over a time period of almost half a year using the data of the CoRoT satellite. The SOFIA observations will give us additional information in the near-infrared, which was not provided by CoRoT. For the first time, it will be possible to measure the temperature of spots on the surface of CoRoT-2A independent of the unknown size of the spots. If we are able to resolve the umbra and penumbra of an individual spot in our observations, it will also be possible to measure - for the very first time - the structure and umbra/penumbra temperatures of spots on another solar-like star.