부산대학교 도서관

We present a transmission spectrum for the Neptune-size exoplanet HD 106315 cfrom optical to infrared wavelengths based on transit observations from theHubble Space Telescope/Wide Field Camera 3, K2, and Spitzer. The spectrum showstentative evidence for a water absorption feature in the $1.1 - 1.7\mu$mwavelength range with a small amplitude of 30 ppm (corresponding to just $0.8\pm 0.04$ atmospheric scale heights). Based on an atmospheric retrievalanalysis, the presence of water vapor is tentatively favored with a Bayesfactor of 1.7 - 2.6 (depending on prior assumptions). The spectrum is mostconsistent with either enhanced metallicity, high altitude condensates, orboth. Cloud-free solar composition atmospheres are ruled out at $>5\sigma$confidence. We compare the spectrum to grids of cloudy and hazy forward modelsand find that the spectrum is fit well by models with moderate cloud lofting orhaze formation efficiency, over a wide range of metallicities ($1 - 100\times$solar). We combine the constraints on the envelope composition with an interiorstructure model and estimate that the core mass fraction is $\gtrsim0.3$. Witha bulk composition reminiscent of that of Neptune and an orbital distance of0.15 AU, HD 106315 c hints that planets may form out of broadly similarmaterial and arrive at vastly different orbits later in their evolution.