High-precision masses and distances of stars

Stellar masses are often unknown or poorly constrained, which limits our ability to test models of stellar structure and evolution. To meaningfully compare theoretical predictions that use different input physics and chemical compositions, we require mass measurements with relative uncertainties below 1%. Such precision can only be reliably achieved in binary systems, where spectroscopy and astrometry can be combined to derive dynamical masses. For standard stars, my recent work has demonstrated that mass and distance can be determined with accuracies as high as 0.03%. In the case of binary Cepheids, which are particularly valuable as primary distance indicators, I have obtained some of the most precise distances currently available. These results enable direct tests of Gaia parallaxes and of the period-luminosity relations that underpin the extragalactic distance scale. In this contribution, I present the latest results obtained by combining high-resolution spectroscopy and long-baseline interferometry for both standard stars and binary Cepheids.