We present an atmospheric characterization study of two medium sized planets bracketing the radius of Neptune: HD 106315 c (R$_{\rm{P}}$=4.98 $\pm$ 0.23 R$_{\oplus}$) and HD 3167 c (R$_{\rm{P}}$=2.740$_{-0.100}^{+0.106}$ R$_{\oplus}$). We analyse spatially scanned spectroscopic observations obtained with the G141 grism (1.125 - 1.650 $\mu$m) of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope. We use the publicly available Iraclis pipeline and TauREx3 atmospheric retrieval code and we detect water vapor in the atmosphere of both planets with an abundance of $\log_{10}[\mathrm{H_2O}]=-2.1^{+0.7}_{-1.3}$ ($\sim$5.68$\sigma$) and $\log_{10}[\mathrm{H_2O}]=-4.1^{+0.9}_{-0.9}$ ($\sim$3.17$\sigma$) for HD 106315 c and HD 3167 c, respectively. The transmission spectrum of HD 106315 c shows also a possible evidence of ammonia absorption ($\log_{10}[\mathrm {NH_3}]=-4.3^{+0.7}_{-2.0}$, $\sim$1.97$\sigma$ -even if it is not significant-), whilst carbon dioxide absorption features may be present in the atmosphere of HD 3167 c in the $\sim$1.1-1.6~$\mu$m wavelength range ($\log_{10}[\mathrm{CO_{2}}]= -2.4^{+0.7}_{-1.0}$, $\sim$3.28$\sigma$). However the CO$_2$ detection appears significant, it must be considered carefully and put into perspective. Indeed, CO$_2$ presence is not explained by 1D equilibrium chemistry models, and it could be due to possible systematics. The additional contribution of clouds, CO and CH$_4$ are discussed. HD 106315 c and HD 3167 c will be interesting targets for upcoming telescopes such as the James Webb Space Telescope (JWST) and the Atmospheric Remote-Sensing Infrared Exoplanet Large-Survey (Ariel).

中文翻译：

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ARES IV：使用 HST/WFC3 摄像机探测两颗温暖小行星 HD 106315c 和 HD 3167c 的大气

我们展示了对海王星半径范围内两颗中等大小行星的大气特征研究：HD 106315 c (R$_{\rm{P}}$=4.98 $\pm$ 0.23 R$_{\oplus}$) 和 HD 3167 c (R$_{\rm{P}}$=2.740$_{-0.100}^{+0.106}$ R$_{\oplus}$)。我们分析了使用哈勃太空望远镜上的宽视场相机 3 (WFC3) 的 G141 棱镜 (1.125 - 1.650 $\mu$m) 获得的空间扫描光谱观测结果。我们使用公开可用的 Iraclis 管道和 TauREx3 大气检索代码，我们检测到两颗行星大气中的水蒸气丰度为 $\log_{10}[\mathrm{H_2O}]=-2.1^{+0.7}_{ -1.3}$ ($\sim$5.68$\sigma$) 和 $\log_{10}[\mathrm{H_2O}]=-4.1^{+0.9}_{-0.9}$ ($\sim$3.17$\sigma $) 分别用于 HD 106315 c 和 HD 3167 c。HD 106315 c 的透射光谱也显示了氨吸收的可能证据（$\log_{10}[\mathrm {NH_3}]=-4.3^{+0.7}_{-2.0}$, $\sim$1.97$\ sigma$ -即使它不显着-），而在 $\sim$1.1-1.6~$\mu$m 波长范围内（$\log_{10} [\mathrm{CO_{2}}]= -2.4^{+0.7}_{-1.0}$, $\sim$3.28$\sigma$）。然而，CO$_2$ 检测似乎很重要，必须仔细考虑并正确看待。事实上，一维平衡化学模型无法解释 CO$_2$ 的存在，这可能是由于可能的系统学造成的。讨论了云、CO 和 CH$_4$ 的额外贡献。