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

TL;DR

This study performs atmospheric retrievals on WASP-52b's transmission spectrum, accounting for starspot effects, and finds atmospheric composition consistent with core accretion models and starspot properties aligned with stellar type expectations.

Contribution

It introduces a method to incorporate starspot correction into atmospheric retrievals for active stars, improving accuracy of exoplanet atmospheric characterization.

Findings

Atmospheric composition between 0.1-10 times solar.

Starspots have a temperature below 3000 K.

Starspot fractional coverage is about 5%.

Abstract

We perform atmospheric retrievals on the full optical to infrared ($0.3-5 \, \mu \mathrm{m}$) 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 which shows both out-of-transit photometric variability and starspot crossings during transits, we account for the contribution of non-occulted active regions in the retrieval. We recover a $0.1-10\times$ solar atmospheric composition, in agreement with core accretion predictions for giant planets, and a weak contribution of aerosols. We also obtain a $<3000$ K temperature for the starspots, a measure which is likely affected by the models used to fit instrumental effects in the transits, and a 5% starspot 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.