A Panchromatic Characterization of the Evening and Morning Atmosphere of WASP-107 b: Composition and Cloud Variations, and Insight into the Effect of Stellar Contamination

TL;DR

This study uses JWST data to analyze the day-night atmospheric differences of exoplanet WASP-107 b, revealing temperature, composition, and cloud variations, and examines how stellar contamination affects these measurements.

Contribution

It provides the first detailed limb-resolved transmission spectra of WASP-107 b across multiple JWST instruments, highlighting the impact of stellar contamination on atmospheric characterization.

Findings

Confirmed temperature differences between evening and morning limbs.

Detected variations in SO₂ and CO₂ abundances.

Identified significant cloud coverage on the morning limb.

Abstract

Limb-resolved transmission spectroscopy has the potential to transform our understanding of exoplanetary atmospheres. By separately measuring the transmission spectra of the evening and morning limbs, these atmospheric regions can be individually characterized, shedding light into the global distribution and transport of key atmospheric properties from transit observations alone. In this work, we follow up the recent detection of limb asymmetry on the exoplanet WASP-107 b (Murphy et al. 2024) by reanalyzing literature observations of WASP-107 b using all of JWST's science intruments (NIRISS, NIRCam, NIRSpec, and MIRI) to measure its limb transmission spectra from $\sim$1-12 $\mu$m. We confirm the evening--morning temperature difference inferred previously and find that it is qualitatively consistent with predictions from global circulation models. We find evidence for evening--morning variation in SO$_2$ and CO$_2$ abundance, and significant cloud coverage only on WASP-107 b's morning limb. We find that the NIRISS and NIRSpec observations are potentially contaminated by occulted starspots, which we leverage to investigate stellar contamination's impact on limb asymmetry measurements. We find that starspot crossings can significantly bias the inferred evening and morning transmission spectra depending on when they occur during the transit, and develop a simple correction model which successfully brings these instruments' spectra into agreement with the uncontaminated observations.