Classical Cases of Non-Solar Mixing Length in Low Mass Stars

We used geometric radii to constrain the mixing length in detached eclipsing binaries and stars with interferometrically measured diameters, testing literature prescriptions that go beyond a fixed, solar-calibrated mixing length parameter. Other than magnetically inflated fast rotators we found no population level trends for the mixing lengths in eclipsing binaries, calling into question the existence of a ubiquitous calibration beyond the Sun. The mixing length in the interferometric sample on the other hand displayed a strong dependence on metallicity, with very metal poor stars reaching very subsolar mixing lengths. Such a strong metallicity dependence has implications for the absolute age scale and the observed age-metallicity relation in the oldest Galactic populations.