Starspot occultations in infrared transit spectroscopy: the case of WASP-52b

TL;DR

This study analyzes the impact of starspot occultations on infrared transit spectroscopy of exoplanets, demonstrating that different modeling approaches yield consistent water vapor detection, and highlights potential challenges for future JWST observations.

Contribution

It provides the first detailed analysis of starspot occultations in infrared transit spectra and compares modeling methods, emphasizing their robustness and implications for upcoming JWST data.

Findings

Different modeling methods produce consistent transmission spectra.

Water vapor detection remains robust despite starspot modeling.

Starspot crossings could pose challenges for JWST transit observations.

Abstract

Stellar activity is one of the main obstacles to high-precision exoplanet observations and has motivated extensive studies in detection and characterization problems. Most efforts focused on unocculted starspots in optical transit spectrophotometry, while the impact of starspot crossings is assumed to be negligible in the near-infrared. Here, we present \textit{HST}/WFC3 transit observations of the active star WASP-52, hosting an inflated hot Jupiter, which present a possible starspot occultation signal. By using this data set as a benchmark, we investigated whether the masking of the transit profile distortion or modeling it with both a starspot model and a Gaussian process affects the shape of the transmission spectrum. Different methods produced spectra with the same shape and a robust detection of water vapor, and with $\lesssim 1 \sigma$ different reference radii for the planet. The solutions of all methods are in agreement and reached a similar level of precision. Our WFC3 light curve of WASP-52b hints that starspot crossings might become more problematic with \textit{JWST}'s higher sensitivity and complete coverage of the transit profile.