WASP-52b. The effect of star-spot correction on atmospheric retrievals

We perform atmospheric retrievals on the full optical to infrared (0.3-5 μ m) transmission spectrum of the inflated hot Jupiter WASP-52b by combining HST/STIS, WFC3 IR, and Spitzer/IRAC observations. As WASP-52 is an active star that shows both out-of-transit photometric variability and star-spot crossings during transits, we account for the contribution of non-occulted active regions in the retrieval. We recover a 0.1-10× solar atmospheric composition, in agreement with core accretion predictions for giant planets, and no significant contribution of aerosols. We also obtain a <3000 K temperature for the star-spots, a measure which is likely affected by the models used to fit instrumental effects in the transits, and a 5 per cent star-spot fractional coverage, compatible with expectations for the host star's spectral type. Such constraints on the planetary atmosphere and on the activity of its host star will inform future JWST GTO observations of this target.