THE ORBIT OF ALPHA EQUULEI MEASURED WITH LONG-BASE-LINE OPTICAL INTERFEROMETRY - COMPONENT MASSES, SPECTRAL TYPES, AND EVOLUTIONARY STATE

We present the orbit of the double-lined spectroscopic binary alpha-Equulei, and masses and absolute magnitudes for its components, from observations with the Mark III Optical Interferometer. Our orbit with the spectroscopic results of Rosvick & Scarfe [MNRAS, 252, 68 (1991)] imply masses and 1-sigma or uncertainties of 2.13 +/- 0.29 M. for the G primary and 1.86 +/- 0.21 M. for the A secondary. The magnitude differences that we measure at the four observed wavelengths are consistent with a G5 III primary and an A5 V secondary, with an uncertainty of about 1.5 subtypes. We compare the masses, magnitude differences, and absolute magnitudes determined here with the evolutionary models of VandenBerg [ApJS, 58, 711 (1985)] and infer that the metallicity Z=Z.. The masses of the G and A components from the orbital fit agree with the evolutionary masses (2.36-2.75 M. and 2.01-2.14 M., respectively) that fit their derived colors and absolute magnitudes. The best-fit age from the evolutionary model is 0.5-0.65 Gyr. The parallax of the system obtained from combining the spectroscopic and interferometric data, for which the term "orbital parallax" has been suggested, is given by pi(orb)=0".01808+/-0".00076.