Description
Active stars can possess surface heterogeneities such as star spots and faculae that are often hidden within atmosphere observations and can thus complicate the interpretation of transmission spectra. When a planet transits a star with surface heterogeneities the reference light source (which is regularly taken from an average of the full stellar disc) may not be representative of the light actually occulted by the planet. This discrepancy can contaminate the transmission spectrum with features from the stellar spectrum, introducing bias to otherwise excellent targets for atmospheric characterisation, such as HAT-P-18b and WASP-52b.
To improve this characterisation process for exoplanets around active stars, we couple the modelling of atmospheric features alongside stellar features, accounting for spot umbra and penumbra as well as faculae, with retrievals from NEMESISPY. We present a comparison of the spectra and spot models for these two planets.
