Stellar Photospheric Contamination as a Tool for Indirect Characterisation of Hot Jupiter Atmospheres

The direct characterisation of exoplanetary atmospheres remains observationally challenging, especially for close-in gas giants around bright stars. However, recent theoretical work by Jermyn & Kama (2018) suggests an indirect pathway: highly irradiated hot Jupiters with evaporating atmospheres may transfer a fraction of their atmospheric material onto their host stars. This process, known as stellar photospheric contamination, could imprint the chemical composition of the exoplanet's upper atmosphere onto the stellar spectrum, offering a new means of atmospheric characterisation.

In this study, we explore the conditions under which such contamination may occur, focusing on star–planet systems involving F and A-type host stars. These stars, with their relatively thin convective zones and high ultraviolet output, are particularly susceptible to detectable enrichment from planetary material. Using a sample of well-characterised hot Jupiters orbiting F-type stars, we model the vertical pressure–temperature (P–T) profiles of their atmospheres, identifying species likely to escape and potentially accumulate on the stellar surface.

We then examine how the architecture of each system (e.g. orbital separation, planetary atmosphere evaporation rates) affects the efficiency and detectability of contamination. Our approach combines theoretical atmospheric structure modelling with current and archival spectral data to assess the feasibility of this technique using existing high-resolution spectrographs and to define instrumental requirements for future observations.

Our results demonstrate that photospheric contamination is a promising, underutilised method for tracing the chemical fingerprints of exoplanet atmospheres. This work opens new avenues for synergy between stellar spectroscopy and planetary atmospheric studies, offering a complementary tool to direct detection techniques.