AI 中文总结
SPACE计划观测发现亚海王星HD 191939 b的透射光谱无明显特征，其大气或为超太阳金属丰度，霾与云形成可能削弱吸收特征，为研究亚海王星大气演化提供了观测依据。
AI 中文摘要
亚海王星的大气为研究其内部结构与演化历史提供了窗口，有助于揭示这类常见却神秘的系外行星的起源。然而，塑造亚海王星透射光谱的物理与化学过程，尤其是云与霾的形成机制，尚未得到充分理解。为探究透射光谱与紫外线辐射之间可能存在的关联，SPACE（亚海王星大气表征实验）计划利用哈勃空间望远镜（HST）对一系列亚海王星及其主恒星进行观测，使用广角相机3（WFC3）测量行星在1.1微米至1.7微米波段的透射光谱，利用空间望远镜成像光谱仪（STIS）测量恒星的紫外线光谱。本文呈现SPACE计划中对HD 191939 b的观测结果，其透射光谱中未发现显著光谱特征。该数据以2.0σ至3.2σ的显著性水平提供了中等证据，反对其为无云且金属丰度与太阳相当的大气模型，虽该模型仍有可能，但可信度较低。HD 191939 b的超太阳金属丰度可能与行星质量越小大气金属丰度越高的已知趋势相符。在HD 191939 b的零反照率平衡温度（880±20）K下，烃类霾形成与云凝结过程均可能高效发生，尤其在超太阳金属丰度的大气中，可能进一步削弱吸收特征。
英文摘要
The atmospheres of sub-Neptunes provide a window into their internal structure and history, shedding light on the origin of this common, but enigmatic, class of exoplanets. However, the physical and chemical processes that shape sub-Neptunes' transmission spectra, in particular cloud and haze formation, are not well understood. To identify possible correlations between transmission spectra and UV irradiation, the SPACE (Sub-neptune Planetary Atmosphere Characterization Experiment) Program observed an array of sub-Neptunes and their host stars using the Hubble Space Telescope (HST), measuring the planets' transmission spectra between $1.1\,μ$m and $1.7\,μ$m with the Wide Field Camera 3 (WFC3) and the stars' UV spectra with the Space Telescope Imaging Spectrograph (STIS). Here, we present the observations of HD 191939 b carried out as part of the SPACE Program, which reveal no significant spectral features in the transmission spectrum. The data deliver moderate evidence at significance levels between $2.0\,σ$ and $3.2\,σ$ against a cloud-free atmosphere with solar metallicity, rendering this scenario unlikely, but still possible. A super-solar metallicity of HD 191939 b might be consistent with the known trend of increasing atmospheric metallicity with decreasing planet mass. Both hydrocarbon haze formation and cloud condensation can be efficient at HD 191939 b's zero-albedo equilibrium temperature of $(880\pm 20)\,$K, particularly in atmospheres with super-solar metallicity, possibly additionally muting absorption features.
Comments20 pages, 12 figures, 3 tables. Accepted to AJ
