New ACCESS observations of WASP-31b: Is there Potassium in its atmosphere?

We present a new optical (400-900nm) transmission spectrum of the hot Jupiter WASP-31b (M=0.48M_{M_j} ; R= 1.54R_{R_J}; P=3.406 days), obtained by combining three transits observed with IMACS on the Baade Telescope at Las Campanas Observatory, Chile. In our analysis we investigate the presence of clouds/hazes in the upper atmosphere of this planet. In addition, we search for absorption features by the alkali elements Na I and K I, with particular focus on K I, for which there are currently two contradicting observation results. Observations with HST/STIS detected K I whereas the VLT/FORS2  observations did not. The K I feature is particularly important because the detection of K I can be contaminated by Earth’s O2 telluric features, making it paramount to investigating if the inconsistency is because of a disadvantage with ground based telescopes, the lack of high enough resolution, or ineffective systematic corrections. These observations were made as part of ACCESS (Arizona-CfA-Catolica-Carnegie Exoplanet Spectroscopy Survey), which aims at providing the largest uniform sample of visible transmission spectra of giant exoplanets. We expect ACCESS will also play a key role in providing optical exoplanet transmission spectra in the JWST era.

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