Exploring the potential of exoplanet polarimetry

由于高精度偏振仪的不断发展，对系外行星的偏振辐射的研究有望提供必要的见解，作为对通过“经典技术”获得的观测数据的补充。在过去二十年中，已经开展了广泛的研究，目的是确定大气和表面属性(陆块、海洋)的各种物理性质对系外行星产生的偏振信号的影响。然而，在光学到红外波段的可观测偏振并不仅仅由系外行星的偏振来决定。特别是，必须考虑到潜在存在的系外环和系外行星的吸收和散射、系外系统的局部碎片盘、星际介质的尘埃相以及本征极化恒星辐射的影响。该项目的主要目标是：(A)研究可能干扰和改变系外行星极化信号的外部极化源的影响；(B)制定观测战略，以便能够区分系外行星的极化信号和各种外部源的极化信号，分离系外行星的极化信号，并量化由于外部源的贡献而产生的不确定程度。虽然这些目标雄心勃勃，但对于查明系外行星极化研究的局限性和克服这些局限性的方法，从而开发系外行星极化的潜力，它们是至关重要的。因此，这项研究的结果将对已有的以及未来的系外行星的数值和观测极化研究提供必要的补充。

Thanks to the ongoing development of high-precision polarimeters, the investigation of the polarized radiation of exoplanets is expected to provide essential insights, complementary to those observables obtained through "classical techniques". An already broad range of studies has been performed during the past two decades with the goal to identify the impact of various physical properties of atmospheric and surface properties (land masses, oceans) on the resulting polarization signal of exoplanets. However, the OBSERVABLE polarization at optical to infrared wavelengths is not determined by that of the exoplanet alone. In particular, the absorption and scattering by potentially existing exoplanetary rings and exomoons, the local debris disk of the exoplanetary system, the dust phase of the interstellar medium as well as the impact of intrinsically polarized stellar radiation have to be taken into account. The main goals of this project are (A) To study the impact of external sources of polarization that potentially interfere with and modify the polarization signal of exoplanets and (B) To derive observing strategies that allow discriminating between the polarization signal of the exoplanet and that of various external sources, to separate the polarization signal of the exoplanet, and to quantify the level of uncertainty due the contribution of the external sources. While these goals are ambitious, they are essential for the identification of limitations of polarimetric exoplanet studies and approaches to overcome them and thus for exploiting the potential of exoplanet polarimetry. As such, the results of this study will provide a necessary complement to already existing as well as future numerical and observational polarization studies of exoplanets.