利用碰撞参数（impact parameter）减轻凌（transit）光源效应：来自 TRAPPIST-1 的初步见解

本文探讨了恒星活动对系外行星（exoplanet）透射光谱的影响，重点分析了凌光源效应（TLS effect）。研究通过以 TRAPPIST-1 为测试平台，评估了活动区（active region）的纬度分布如何影响不同碰撞参数下的凌光源效应强度，并指出了大气表征的最佳碰撞参数范围。

arXiv:2608.20450v1 Announce Type: new Abstract: Stellar activity complicates exoplanet transmission spectra, particularly for smaller planets around M dwarfs with JWST. The transit light source (TLS) effect, the imprinting of spectral differences between the average stellar disk and the occulted transit chord onto the transmission spectrum, makes it challenging to directly use the out-of-transit spectrum to correct for stellar contamination. Theory and observations suggest that spots may concentrate towards higher latitudes when the Coriolis force is substantial relative to buoyancy, leaving the equatorial region relatively quiet. Here, we evaluate how the latitudinal distribution of active regions shapes the strength of the TLS effect for planets spanning a range of impact parameters ($b$), using TRAPPIST-1 as a testbed. We first construct a fiducial model to illustrate two distribution regimes. With our model, the moderate-$b$ outer TRAPPIST-1 planets (f, g, h) occult a more typical region of the stellar disk than the inner planets and are thereby less affected by the TLS effect, though their bias may vary more from visit-to-visit as these active regions evolve with time. More generally, our results imply an impact parameter "sweet spot" for atmospheric characterization, independent of the sign of the active region temperature contrast, whose location