具有极冠和海洋闪烁的系外行星的傅立叶光谱
Fourier spectra from exoplanets with polar caps and ocean glint
摘要：
系外行星微弱的轨道相位相关反射信号包含了行星表面的信息，如类地行星上大陆和海洋的分布。这种光变曲线通常在时域中进行研究，但由于来自静止表面的信号是（准）周期性的，傅立叶级数的分析可以提供一种替代的补充方法。我们研究了简单几何构型的反射光变曲线的傅里叶光谱。取决于它的大气特性，一个在宜居带的旋转行星可能有圆形的极地冰盖。另一方面，潮汐锁定的行星可能有对称的圆形海洋面对恒星。这些情况很有趣，因为冰盖边缘的高对比度和海洋中主星的闪烁可能会产生可识别的轨道周期性光变曲线，这也可以在傅立叶域中解释。我们推导出一个简单的一般表达式的准周期光变曲线的傅立叶系数的朗伯行星表面的的朗伯映射。计算了理想情况下的光变曲线及其光谱的解析表达式，并研究了光谱峰对关键参数倾角、结晶度和帽尺寸的依赖关系。
英文摘要：
The weak orbital-phase dependent reflection signal of an exoplanet contains information on the planet surface, such as the distribution of continents and oceans on terrestrial planets. This light curve is usually studied in the time domain, but because the signal from a stationary surface is (quasi)periodic, analysis of the Fourier series may provide an alternative, complementary approach. We study Fourier spectra from reflected light curves for geometrically simple configurations. Depending on its atmospheric properties, a rotating planet in the habitable zone could have circular polar ice caps. Tidally locked planets, on the other hand, may have symmetric circular oceans facing the star. These cases are interesting because the high-albedo contrast at the sharp edges of the ice-sheets and the glint from the host star in the ocean may produce recognizable light curves with orbital periodicity, which could also be interpreted in the Fourier domain. We derive a simple general expression for the Fourier coefficients of a quasiperiodic light curve in terms of the albedo map of a Lambertian planet surface. Analytic expressions for light curves and their spectra are calculated for idealized situations, and dependence of spectral peaks on the key parameters inclination, obliquity, and cap size is studied.
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