First Results from the CHARA Array. V. Binary Star Astrometry: The Case of 12 Persei

We have obtained high-resolution orbital data with the CHARA Array for the bright star 12 Persei, a resolved double-lined spectroscopic binary. We describe the data reduction process, which can give precision in separation of up to 25 μas along a given baseline. For this object we find a semimajor axis of a=53.18+/-0.15 mas, which is 0.3% smaller than that of Barlow and coworkers, but with much improved precision. The inclination angle i increases to 128.17d+/-0.14d, compared to 126.77d+/-0.56d of Barlow and coworkers, again with better precision. We also found an intensity ratio for the components in the K' band (λ=2.13 μm) of r=0.72+/-0.01, or ΔK^'=0.409+/-0.013, after allowing for the partial resolution of the components. Assuming the spectral types of the components, we find that ΔV=0.51, as compared to 0.57 by Barlow and coworkers. The revised masses (M_p=1.382+/-0.019 and M_s=1.240+/-0.017 M_solar) are found to be 5.8% larger than those of Barlow and coworkers, and the components are thus even more overmassive. The overall accuracy in the masses is about 1.3%, now primarily limited by the spectroscopically determined radial velocities. The precision of the masses due to the interferometrically derived ``visual'' orbit alone is only about 0.2%.