WASP-31b and host star radius compared with IMACS

These transits were observed with IMACS on the Magellan Baade Telescope at Las Campanas Observatory as part of the ACCESS project. We investigate the presence of clouds/hazes in the upper atmosphere of this planet, as well as the contribution of stellar activity on the observed features.

In addition, we search for absorption features of the alkali elements NaI and KI, with particular focus on KI, for which there have been two previously published disagreeing results. Observations with Hubble Space Telescope (HST)/STIS detected KI, whereas ground-based low- and high- resolution observations did not. We use equilibrium and nonequilibrium chemistry retrievals to explore the planetary and stellar parameter space of the system with our optical data combined with existing near-IR observations.