迈向氦观测与大气逃逸解释的统一框架
Toward a unified framework for helium observations and interpretation of atmospheric escape
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中文总结 AI 辅助
该研究构建大气逃逸观测的统一框架，对比NIRPS、JWST/NIRSpec等仪器能力，明确高、低分辨率观测的互补性，为系外行星大气逃逸研究提供方法支撑。
中文摘要 AI 辅助
大气逃逸被认为是塑造系外行星统计特征与演化的关键过程。近红外亚稳态氦三重线（~10833埃的HeI）是流体动力学外流最有力的示踪剂之一。近年来，大量仪器被用于探测和表征膨胀的高层大气：高分辨率（HR）光谱仪可对该三重线进行光谱分辨，主要用于探测大气逃逸的动力学；更近的是，JWST（低分辨率，LR）探测到了此前地面观测因夜长限制而遗漏的延展外流。由于观测透射光谱是通过仪器卷积退化的恒星光谱之比计算得到的，我们证明，直接将理论透射光谱与仪器轮廓卷积会导致推断偏差，且分辨率越低偏差越显著。该结论对大气逃逸研究尤为重要，也适用于更广泛的低分辨率大气反演场景。遵循恰当的比较方法，我们研究了高分辨率与低分辨率观测在大气逃逸测量中的互补性，对比了三种仪器（NIRPS、JWST/NIRSpec、JWST/NIRISS）探测和表征外流的能力，发现NIRPS与JWST/NIRISS对相同氦信号最为敏感，而JWST/NIRSpec可提升暗弱目标的过剩吸收探测限。通过研究不同外流构型，我们表明，低分辨率空间观测无法用于推断行星附近高层大气的动力学，最适合测量外流尾的空间延展范围。我们因此强调，大气逃逸的高分辨率与低分辨率观测具有互补性，后者可改进基线重建。
英文摘要
Atmospheric escape is considered a key process in shaping exoplanet demographics and evolution. The near-infrared metastable helium triplet (HeI at ~10833Å) is one of the most powerful tracers of hydrodynamical outflows. In recent years, a large variety of instruments have been used to detect and characterize expanding upper atmospheres. High-resolution (HR) spectrographs, which can spectrally resolve the lines of the triplet, have been mostly used to probe the dynamics of atmospheric escape. More recently, JWST (low-resolution, LR) detected extended outflows that were missed by previous ground-based observations due to night-length constraints. Since the observed transmission spectrum is computed from the ratio of stellar spectra degraded by instrumental convolution, we demonstrate that directly convolving a theoretical transmission spectrum with the instrument's profile leads to inference biases as resolution decreases. This conclusion is particularly important for atmospheric escape studies but also holds in the more general context of LR atmospheric retrievals. Following the proper comparison methodology, we then investigated the complementarity of HR and LR observations for atmospheric escape measurements, comparing the capability of three instruments (NIRPS, JWST/NIRSpec, and JWST/NIRISS) to detect and characterize outflows. We find that NIRPS and JWST/NIRISS are mostly sensitive to the same helium signatures, while JWST/NIRSpec improves the detection limit of excess absorption for faint targets. Studying different outflow configurations, we show that LR space-based measurements cannot be used to infer the dynamics of the upper atmosphere close to the planet, and are best employed to measure the spatial extent of outflowing tails. We thus highlight the complementarity between HR and LR observations of atmospheric escape, the latter improving baseline reconstruction.
