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 17 ± 0 14, compared to 126 77 ± 0 56 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 Δ K ' = 0.409 ± 0.013, after allowing for the partial resolution of the components. Assuming the spectral types of the components, we find that Pub Lclchangemark =" ins ">Δ V = 0.51, as compared to 0.57 by Barlow and coworkers. The revised masses (Pub Lclchangemark =" ins "> M p = 1.382 ± 0.019 and M s = 1.240 ± 0.017 M ⊙ ) 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%.