The Visual Orbit and Evolutionary State of 12 Bootis

We report on the determination of the visual orbit of the double-linedspectroscopic binary system 12 Bootes with data obtained by the Palomar TestbedInterferometer in 1998 and 1999. 12 Boo is a nearly equal-mass double-linedbinary system whose spectroscopic orbit is well known. We have estimated thevisual orbit of 12 Boo from our interferometric visibility data fit bothseparately and in conjunction with archival radial velocity data. Our 12 Booorbit is in good agreement with the spectroscopic results, and the physicalparameters implied by a combined fit to our visibility data and radial velocitydata result in precise component masses. In particular, the orbital parallax ofthe system is determined to be 27.09 $\pm$ 0.41 mas, and masses of the twocomponents are determined to be 1.435 $\pm$ 0.023 M$_{\sun}$ and 1.409 $\pm$0.020 M$_{\sun}$, respectively. Somewhat remarkably, even though the two components are nearly equal mass,the system exhibits a significant brightness difference between the componentsin the near infrared and visible. We attribute this brightness difference toevolutionary differences between the two components in their transition betweenmain sequence and giant evolutionary phases, and based on theoreticalisochrones we can estimate a system age. Further, because the atmospheres ofthe two components are becoming more convective, we project the systemcomponents are currently at or near synchronous rotation, and the system orbitis in the process of circularizing.Comment: 32 pages, 7 figures + 2 data tables, ApJ in pres