ARES IV: Probing the Atmospheres of the Two Warm Small Planets HD 106315c and HD 3167c with the HST/WFC3 Camera

We present an atmospheric characterization study of two medium-sized planets bracketing the radius of Neptune: HD 106315c (R-P.=.4.98 +/- 0.23 R-circle plus) and HD 3167c (R-P = 2.740(-0.100)(+0.100) R-circle plus). We analyze spatially scanned spectroscopic observations obtained with the G141 grism (1.125-1.650 mu m) of the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope. We use the publicly available Iraclis pipeline and TauREx3 atmospheric retrieval code and detect water vapor in the atmosphere of both planets, with an abundance of log(10)[H2O] -2.1(-1.3)(+0.7) (similar to 5.68 sigma) and = log(10)[H2O] = -4.1(-0.9)(+0.9) (similar to 3.17s) for HD 106315c and HD 3167c, respectively. The transmission spectrum of HD 106315c also shows possible evidence of ammonia absorption (log(10)[NH3] = -4.3(-2.0)(+0.7), similar to 1.97 sigma, even if it is not significant), while carbon dioxide absorption features may be present in the atmosphere of HD 3167c in the similar to 1.1-1.6 mu m wavelength range (log(10)[CO2] = -2.4(-1.0)(+0.7), similar to 3.28 sigma). However, the CO2 detection appears significant, and it must be considered carefully and put into perspective. Indeed, CO2 presence is not explained by 1D equilibrium chemistry models, and it could be due to possible systematics. The additional contributions of clouds, CO, and CH4 are discussed. HD 106315c and HD 3167c will be interesting targets for upcoming telescopes such as the James Webb Space Telescope and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey.

Automated summary

An atmospheric characterization study of two medium-sized planets revealed the presence of water vapor, ammonia, and carbon dioxide absorption features. These findings make HD 106315c and HD 3167c interesting targets for future telescope observations.