Speaker
Description
With the James Webb Space Telescope (JWST) ushering in a new era of exoplanet observations, accurately characterising exoplanet atmospheres is more crucial than ever for understanding their chemical compositions and potential habitability. A key observational technique for this is transmission spectroscopy, which measures the wavelength-dependent decrease in starlight as an exoplanet transits its host star. These variations in transit depth—the fraction of starlight blocked by the planet—across different wavelengths produce a transmission spectrum, which encodes information about the planet’s atmospheric properties. However, stellar activity—such as spots, faculae, and convective granulation patterns on the stellar surface—introduces additional wavelength-dependent variations that can contaminate the observed transmission spectrum. These stellar signals can mimic or obscure the atmospheric signatures of the planet, complicating the accurate retrieval of atmospheric properties.
To address these challenges, we employed a comprehensive approach by conducting multi-band photometric and spectroscopic monitoring contemporaneous with JWST observations. Initially, we applied this methodology to GJ 1214 using data from various facilities, including CARMENES, SNO, MuSCAT-2 and TJO. We utilised the StarSim tool to determine the properties of active regions on GJ 1214 and simulate the effects of stellar activity on transmission spectra. We also trained neural network models to predict the stellar activity corrections for transit spectroscopy based on the input contemporaneous monitoring data. Our models provided corrections with a scatter under 100 parts per million (ppm) in transit depth.
Our work establishes a robust framework for mitigating stellar activity in future JWST observations and missions like Ariel, paving the way for more precise and reliable exoplanet atmospheric studies. Building on these promising results, we will apply our methodology to other targets of interest, including TRAPPIST-1, for which we have already gathered data (CARMENES, MuSCAT-2, TJO, Danish 1.54 m Telescope) contemporaneous with JWST observations and conducted preliminary analyses.
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