Constraints on atmospheric water abundance and cloud deck pressure in the warm Neptune GJ 3470 b via CARMENES transmission spectroscopy

Observations of cooler atmospheres of super-Earths and Neptune sized objects often show ŕat transmission spectra. The most likely cause of this trend is the presence of aerosols (i.e. clouds and hazes) in the atmospheres of such objects. Highresolution spectroscopy provides an opportunity to test this hypothesis by targeting molecular species whose spectral line cores extend above the level of such opaque decks. In this work, we analyse high-resolution infrared observations of the warm Neptune GJ 3470 b taken over two transits using CARMENES (R ∼ 80,000) and look for signatures of H2O (previously detected using HST WFC3+Spitzer observations) in these transits with a custom pipeline fully accounting for the effects of data cleaning on any potential exoplanet signal. We őnd that our data are potentially able to weakly detect (∼ 3𝜎) an injected signal equivalent to the best-őt model from previous HST WFC3+Spitzer observations However, we do not make a signiőcant detection using the actual observations. Using a Bayesian framework to simultaneously constrain the H2O Volume Mixing Ratio (VMR) and the cloud top pressure level, we select a family of models compatible with the non detection. These are either very high VMR, cloud-free models, solar-abundance models with a high cloud deck, or sub-solar abundance models with a moderate cloud deck. This is a broader range compared to published results from low-resolution spectroscopy, but is also compatible with them at a 1𝜎 level.

对超级地球（super-Earths）与海王星级天体的低温大气的观测通常呈现出平坦的透射光谱（transmission spectra）。造成这一现象的最可能原因是这类天体大气中存在气溶胶（aerosols，即云和霾）。
高分辨率光谱学（High-resolution spectroscopy）为验证该假说提供了可行路径：可选取谱线芯高于这类不透明云盖（opaque decks）的分子组分作为观测目标。
本研究针对暖海王星GJ 3470 b开展了两次凌星期间的高分辨率红外观测，使用分辨率约80000的CARMENES仪器，并通过一套充分考虑数据清洗对潜在系外行星信号（exoplanet signal）影响的自定义数据处理流程，在此次凌星数据中搜寻水（H₂O）的特征光谱信号——此前该天体的水信号已通过哈勃空间望远镜（HST）宽场相机3（WFC3）+斯皮策太空望远镜（Spitzer）的观测被探测到。
我们发现，本次观测数据具备以约3倍标准差（3σ）弱探测到等效于此前HST WFC3+Spitzer观测最优拟合模型的注入信号的潜力，但针对实际观测数据并未获得显著的探测结果。
我们采用贝叶斯框架（Bayesian framework）同时约束水的体积混合比（Volume Mixing Ratio，VMR）与云顶压强层级，并筛选出了与本次非探测结果兼容的一系列模型：这些模型要么为极高体积混合比的无云模型，要么为拥有高云盖的太阳丰度模型，或是拥有中等云盖的亚太阳丰度模型。
相较于已发表的低分辨率光谱学（Low-resolution spectroscopy）研究结果，本次得到的模型参数范围更广，但在1倍标准差（1σ）水平上仍与前者兼容。

搜集汇总

背景与挑战

背景概述

该数据集通过CARMENES高分辨率红外光谱观测温暖海王星GJ 3470 b，旨在约束其大气中的水丰度和云层压力。分析表明，数据与多种模型兼容，包括高水丰度无云模型、高云层的太阳丰度模型或中等云层的次太阳丰度模型，结果与先前低分辨率光谱观测在1σ水平一致。