2000. The American Astronomical Society. All rights reserved. Printed in U.S.A.( THE VISUAL ORBIT AND EVOLUTIONARY STATE OF 12 BOOTIS

We report on the determination of the visual orbit of the double-lined spectroscopic binary system 12 Bootis with data obtained by the Palomar Testbed Interferometer in 1998 and 1999. 12 Boo is a nearly equal-mass double-lined binary system whose spectroscopic orbit is well known. We have estimated the visual orbit of 12 Boo from our interferometric visibility data Ðtted both separately and in conjunction with archival and CORAVEL radial velocity data. Our 12 Boo orbit is in good agreement with the spectroscopic results, and the physical parameters implied by a combined Ðt to our visibility data and radial velocity data result in precise component masses. In particular, the orbital parallax of the system is determined to be 27.09 ^ 0.41 mas, and masses of the two components are determined to be 1.435 ^ 0.023 and 1.409 ^ 0.020 respectively. Somewhat remarkably, even though the two com-