2025MNRAS.540..612C

The identification of late-type binary stars with low-mass M companions is crucial for testing and calibrating models of stellar structure and evolution. We use data from the Transiting Exoplanet Survey Satellite (TESS) along with Ultraviolet and Visual Echelle Spectrograph (UVES)/High Accuracy Radial Velocity Planet Searcher (HARPS) spectroscopy to study five eclipsing binaries with late M-dwarf secondaries. At least four of these companions are placed near the fully convective boundary, and we obtained mass and radius measurements with an accuracy better than 4 per cent. The bright F/G primaries enable spectroscopic observations during total eclipses and facilitate the characterization of the primaries through precise atmospheric analysis. We observe no strong proof of radius inflation in these systems compared with stellar evolution models. These results are not consistent with the idea that the observed inflation in stellar radius combines with the lower effective temperature predicted by low-mass stellar models. Our low-mass systems provide precise and consistent measurements that can be utilized in further investigations of radius inflation, contributing five significant data points to the mass-radius diagram of convective M dwarfs.