TNG 的 GAPS 计划 —— LXIII. 光致蒸发之谜：探索 TOI-5398 b 大气信号的神秘本质
The GAPS programme at TNG -- LXIII. Photo-evaporating puzzle: Exploring the enigmatic nature of TOI-5398 b atmospheric signal
AI总结：
本研究利用 HARPS-N 与 GIANO-B 高分辨率凌星观测及互相关、单线分析，表征年轻温暖土星 TOI-5398 b，并探测到指示光致蒸发的 Hα、He I 及 Na I 信号。
摘要：
大气表征是理解系外行星系统的关键，可提供有关行星当前和过去状况的洞见。通过分析 Hα 和 He I 三重线等关键谱线，我们能够经由大气光致蒸发追溯行星的演化。尽管超热木星多年来一直是研究焦点，但关注正转向更小、更冷的行星；由于信号较弱，这类行星更具研究挑战，需要更精确的技术。本研究旨在表征 TOI-5398 b 的大气，它是一颗温暖土星，以 10.59 天的轨道围绕一颗年轻（650 Myr）的 G 型恒星运行。该系统还拥有一颗较小的内行星 TOI-5398 c，轨道周期为 4.77 天。两颗行星都因靠近宿主恒星而成为大气研究的理想对象，这种近距离会驱动强烈的光致蒸发，尤其是行星 b；其高达 288 的透射光谱度量使其成为首要目标。我们分析了使用 HARPS-N 和 GIANO-B 高分辨率光谱仪观测一次凌星所得的数据，采用互相关和单线分析来搜寻原子物种。在此观测期间，行星 c 也在发生凌星，因此我们调查了信号的来源。基于光致蒸发模型，我们将该信号主要归因于行星 b，预计它会损失更多质量。我们探测到了 Hα 和 He I 三重线，它们是光致蒸发的关键标志，分别对应 2.33 Rp 和 1.65 Rp 的大气高度。ATES 模型支持我们的观测，预测行星 b 具有相似的 He I 吸收，并表明 He/H 比值为 1/99。此外，我们通过单线分析探测到了 Na I 双重线，不过互相关并未揭示其他原子物种。
英文摘要：
Atmospheric characterization is key to understanding exoplanetary systems, offering insights into the planets current and past conditions. By analyzing key lines like H alpha and the He I triplet, we can trace the evolution of planets through atmospheric photo-evaporation. While ultra-hot Jupiters have been the focus for years, attention is shifting toward smaller, colder planets, which are more challenging to study due to weaker signals, requiring more precise techniques. This study aims to characterize the atmosphere of TOI-5398 b, a warm Saturn with a 10.59-day orbit around a young (650 Myr) G-type star. The system also hosts a smaller inner planet, TOI-5398 c, with a 4.77-day orbit. Both planets are ideal for atmospheric studies due to their proximity to the host star, which drives strong photo-evaporation, especially in planet b, whose high transmission spectroscopy metric (288) makes it a prime target. We analyzed data from a transit observed with the HARPS-N and GIANO-B high-resolution spectrographs, using cross-correlation and single-line analysis to search for atomic species. During this observation, planet c was also transiting, so we investigated the source of the signals. Based on photo-evaporation models, we attribute the signal mainly to planet b, which is expected to lose more mass. We detected H alpha and He I triplets, key markers of photo-evaporation, corresponding to atmospheric heights of 2.33 Rp and 1.65 Rp, respectively. The ATES models supported our observations, predicting a similar He I absorption for planet b and suggesting an He/H ratio of 1/99. Additionally, we detected an Na I doublet via single-line analysis, though cross-correlation did not reveal other atomic species.
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