2000ApJ...544L..65D

Hipparcos proper motions and trigonometric parallaxes allow the derivation of secular parallaxes that fix the distances to individual stars in the Hyades to an accuracy of ∼2%. The resulting color-absolute magnitude diagram for 92 high-fidelity single members of the cluster displays a very narrow main sequence, with two turnoffs and associated gaps. These occur at the locations where the onset of surface convection affects the B-V colors, as predicted by Böhm-Vitense 30 years ago. The new distances provide stringent constraints on the transformations of colors and absolute magnitudes to effective temperatures and luminosities and on models of stellar interiors.