Eclipsing binaries with very low mass stars: Exploring the radius inflation problem with CHEOPS

There are numerous examples in the literature of low-mass stars (<0.3 Msol) that have radii larger than those predicted by theoretical models. This “radius inflation” problem indicates missing physics in current stellar models that has a direct impact on the analysis and interpretation of observations for transiting exoplanet systems orbiting low-mass stars. Though there have been many proposed causes of this problem such as increased stellar magnetism, metallicity or tidal interactions there has been no definitive conclusion drawn in the literature. To address this problem, we have used the exoplanetary follow-up satellite CHEOPS to obtain high-precision photometry for a sample of 20 eclipsing binaries. Our targets are low mass stars orbiting solar-type stars with a range of metallicities. We seek to provide a sample of homogeneous and precise radius and effective temperature measurements and search them for any possible trends of radius inflation with metallicity, age, etc. Early results include targets that both do and do not show signs of radius inflation, with hints of a trend for metal-rich stars to be more likely to show radius inflation.