= Stellar mass determination
{title2=$M_1+M_2=4\pi^2a^3/(GP^2)$}
Orbital dynamics gives the most direct stellar masses: a resolved binary orbit and distance determine the relative semimajor axis, and <Kepler's third law> gives the total mass. The barycentric size or radial-velocity amplitude ratio gives individual masses. An <eclipsing binary> inclination removes the sine-cubed projection factor from spectroscopic masses; a single-lined <binary mass function> alone does not uniquely determine both masses. Surface-gravity/radius and stellar-track estimates are model-dependent and are calibrated against dynamical binary measurements.
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