A 3-DIMENSIONAL SOLUTION FOR THE ORBIT OF CAPELLA

We have combined new radial velocities of both components of Capella, obtained at McDonald and Kitt Peak, with those recently published by B atten et al. (1991, PASP, 103, 623), and with interferometric observat ions, mainly from the Second CHARA Catalog, to derive a new three-dime nsional orbit of the Capella system. Our results agree well with those of Bagnuolo and Hartkopf (1989, AJ, 98, 2275), as well as with those of Batten et al., and yield masses accurate to +/-3%. The cooler compo nent, which is the fainter star visually but the more luminous one bol ometrically, is the more massive. The mass ratio differs from unity by more than four times its uncertainty, and this lends strong support t o the hypothesis that the cool component has begun to consume its core helium. If so, it may be possible to reconcile, qualitatively at leas t, the orbit's circularity and the stars' rotational velocities with t heories of synchronization and circularization, such as that of the Ta ssouls (1992, ApJ, 395, 259)