PEPSI系外行星凌星巡天（PETS）IV：评估KELT-20b的大气化学
The PEPSI Exoplanet Transit Survey (PETS) IV: Assessing the atmospheric chemistry of KELT-20b
AI总结：
本研究利用LBT/PEPSI高分辨率发射光谱评估超热木星KELT-20b的大气化学，确认Fe I为主要光学不透明度来源，可能引起温度逆温，并探讨了与文献结果的差异及未来研究方向。
摘要：
大多数超热木星（UHJs）显示出温度逆温的证据，即在一定的压力范围内，温度随高度增加而升高。当大气中存在某种在较高高度吸收恒星辐射的物质时，就可能发生温度逆温。然而，造成这种吸收的物质仍未被识别。特别是，已知UHJ KELT-20b存在温度逆温。利用LBT/PEPSI的高分辨率发射光谱，我们研究了可能引起KELT-20b逆温的原子和分子不透明度来源，并探索了其大气化学。我们以17σ的显著性确认了Fe I的存在。我们还报告了Ni I的 tentative 4.3σ探测。在PEPSI蓝臂中名义上4.5σ的Mg I发射探测，实际上很可能归因于Mg I交叉相关模板与光谱中Fe I谱线之间的混叠。我们无法重现最近对Cr I的探测，同时我们的波长覆盖范围不足以稳健地检验过去对Fe II和Si I的探测。结合对TiO等分子物种的非探测，这表明Fe I很可能是KELT-20b白天侧大气中主要的光学不透明度来源，并可能导致了温度逆温。我们探索了调和我们的结果与文献中差异的方法，并指出了理解大气变率的未来路径。
英文摘要：
Most ultra hot Jupiters (UHJs) show evidence of temperature inversions, in which temperature increases with altitude over a range of pressures. Temperature inversions can occur when there is a species that absorbs the stellar irradiation at a relatively high level of the atmospheres. However, the species responsible for this absorption remains unidentified. In particular, the UHJ KELT-20b is known to have a temperature inversion. Using high resolution emission spectroscopy from LBT/PEPSI we investigate the atomic and molecular opacity sources that may cause the inversion in KELT-20b, as well as explore its atmospheric chemistry. We confirm the presence of Fe I with a significance of 17$σ$. We also report a tentative $4.3σ$ detection of Ni I. A nominally $4.5σ$ detection of Mg I emission in the PEPSI blue arm is likely in fact due to aliasing between the Mg I cross-correlation template and the Fe I lines present in the spectrum. We cannot reproduce a recent detection of Cr I, while we do not have the wavelength coverage to robustly test past detections of Fe II and Si I. Together with non-detections of molecular species like TiO, this suggests that Fe I is likely to be the dominant optical opacity source in the dayside atmosphere of KELT-20b and may be responsible for the temperature inversion. We explore ways to reconcile the differences between our results and those in literature and point to future paths to understand atmospheric variability.
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