黑镜：旋转增宽对用高分辨率光谱学寻找飞马座51 b反射光的影响
Black Mirror: The impact of rotational broadening on the search for reflected light from 51 Pegasi b with high resolution spectroscopy
摘要：
恒星和它们的行星在光学波长上的极端对比度使得分离系外行星大气反射的光具有挑战性。然而，这些反射特性揭示了大气中发生的关键过程，它们也跨越了包括潜在的O $_2$生物特征的波长。高分辨率互相关光谱（HRCCS）为开发提取系外行星反射光谱的技术提供了一个强大的途径。我们的目标是提取非过境热木星51 Peg b的光学反射光谱，通过调整旨在去除红外HRCCS中的碲的技术，而不是去除光学恒星线。重要的是，我们研究了迄今为止被忽视的影响，扩大反射的主恒星光谱由于恒星旋转和行星的轨道速度之间的差异。我们使用了484，R=115000的光学光谱51 Peg b从HARPS-N和HARPS，我们对准准确的恒星静止帧，以有效地去除污染的宿主星。然而，一些恒星残留物仍然存在，可能是由于恒星活动。我们与适当扩大的合成恒星模型交叉相关，以寻找行星的多普勒频移光谱。我们未检测到来自51 Peg b的显著反射光，并报告了对比度的S/N=3上限，包括增宽时为76.0 ppm（7.60 x10 $^{-5}$），不包括增宽时为24.0 ppm（2.40 x10 $^{-5}$）。这些上限排除了先前声称的探测的半径和半径组合。增宽会显著影响HRCCS提取反射光谱的能力，在确定行星的对比度、半径和半径时必须加以考虑。非同步系统（Prot、$_{\star}\ne$ Porb）受到的影响最大，包括大多数热彗星以及位于某些M矮星传统宜居带中的地球大小的行星。
英文摘要：
The extreme contrast ratios between stars and their planets at optical wavelengths make it challenging to isolate the light reflected by exoplanet atmospheres. Yet, these reflective properties reveal key processes occurring in the atmospheres, and they also span wavelengths that include the potential O$_2$ biosignature. High resolution cross-correlation spectroscopy (HRCCS) offers a robust avenue for developing techniques to extract exoplanet reflection spectra. We aimed to extract the optical reflected light spectrum of the non-transiting hot Jupiter 51 Peg b by adapting techniques designed to remove tellurics in infrared HRCCS to instead remove optical stellar lines. Importantly, we investigated the so far neglected impact of the broadening of the reflected host star spectrum due to the difference between the stellar rotation and the planet's orbital velocity. We used 484, R=115000 optical spectra of 51 Peg b from HARPS-N and HARPS, which we aligned to the exact stellar rest frame in order to effectively remove the contaminating host star. However, some stellar residuals remained, likely due to stellar activity. We cross-correlated with an appropriately broadened synthetic stellar model to search for the planet's Doppler-shifting spectrum. We detect no significant reflected light from 51 Peg b and report a S/N=3 upper limit on the contrast ratio of 76.0 ppm (7.60x10$^{-5}$) when including broadening, and 24.0 ppm (2.40x10$^{-5}$) without. These upper limits rule out radius and albedo combinations of previously claimed detections. Broadening can significantly impact the ability of HRCCS to extract reflected light spectra and must be considered when determining the contrast ratio, radius, and albedo of the planet. Asynchronous systems (Prot,$_{\star}\ne$ Porb) are most affected, including most hot Jupiters as well as Earth-size planets in the traditional habitable zones of some M-dwarfs.
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