Limb Darkening and Planetary Transits: Testing Center-to-limb Intensity Variations and Limb-darkening Directly from Model Stellar Atmospheres
Limb Darkening and Planetary Transits: Testing Center-to-limb Intensity Variations and Limb-darkening Directly from Model Stellar Atmospheres
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肢体变暗和行星凌日：直接从恒星大气模型测试中心到肢体的强度变化和肢体变暗
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发表时间：
2017
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通讯作者：
J. B. Lester
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作者：
H. Neilson;Joseph T. McNeil;R. Ignace;J. B. Lester
恒星微变和振荡(MOST)、开普勒和各种地面调查所采用的凌日方法使太阳系外行星的特征描述达到了前所未有的精度。这些结果足够精确，足以开始在百万分之几百的水平上测量行星大气组成、行星扁率、恒星黑子和其他现象。然而，这些结果取决于我们对恒星边缘暗化的理解，也就是说，当行星运行时，整个恒星盘上的强度分布被顺序地阻挡了。通常，恒星边缘变暗被认为是一个简单的参数化，有两个系数，这两个系数要么来自恒星大气模型，要么直接拟合。在这项工作中，我们重新审视了这一假设，并使用平面平行的Atlas和球对称的SATLAS程序直接从模型恒星大气中心到边缘强度变化(CLIV)计算了合成的行星凌日光曲线。我们将这些光曲线与使用最佳匹配肢体变暗参数构造的光曲线进行比较。我们发现，采用参数恒星边缘变暗规律会导致系统与更接近几何模型的恒星大气CLIV存在系统差异，在凌日中心约为50-100ppm，在出入口处最高可达300ppm。虽然这些误差很小，但它们是系统性的，而且它们似乎限制了测量次要影响所需的精度。我们的结果也可能对渡越光谱产生重大影响。
The transit method, employed by Microvariability and Oscillation of Stars (MOST), Kepler, and various ground-based surveys has enabled the characterization of extrasolar planets to unprecedented precision. These results are precise enough to begin to measure planet atmosphere composition, planetary oblateness, starspots, and other phenomena at the level of a few hundred parts per million. However, these results depend on our understanding of stellar limb darkening, that is, the intensity distribution across the stellar disk that is sequentially blocked as the planet transits. Typically, stellar limb darkening is assumed to be a simple parameterization with two coefficients that are derived from stellar atmosphere models or fit directly. In this work, we revisit this assumption and compute synthetic planetary-transit light curves directly from model stellar atmosphere center-to-limb intensity variations (CLIVs) using the plane-parallel Atlas and spherically symmetric SAtlas codes. We compare these light curves to those constructed using best-fit limb-darkening parameterizations. We find that adopting parametric stellar limb-darkening laws leads to systematic differences from the more geometrically realistic model stellar atmosphere CLIV of about 50–100 ppm at the transit center and up to 300 ppm at ingress/egress. While these errors are small, they are systematic, and they appear to limit the precision necessary to measure secondary effects. Our results may also have a significant impact on transit spectra.