Testing Stellar Models With An Improved Physical Orbit for 12 Boötis

In a previous publication we reported on the binary system 12 Boötis and its evolutionary state. In particular the 12 Boo primary component is in a rapid phase of evolution, hence accurate measurement of its physical parameters makes it an interesting test case for stellar evolution models. Here we report on a significantly improved determination of the physical orbit of the double-lined spectroscopic binary system 12 Boo. We have a 12 Boo interferometry dataset spanning six years with the Palomar Testbed Interferometer, a smaller amount of data from the Navy Prototype Optical Interferometer, and a radial velocity dataset spanning 14 years from the Harvard-Smithsonian Center for Astrophysics. We have updated the 12 Boo physical orbit model with our expanded interferometric and radial velocity datasets. The revised orbit is in good agreement with previous results, and the physical parameters implied by a combined fit to our visibility and radial velocity data result in precise component masses and luminosities. In particular, the orbital parallax of the system is determined to be 27.719 ± 0.015 mas, and masses of the two components are determined to be 1.4160 ± 0.0049 M⊙ and 1.3740 ± 0.0045 M⊙, respectively. These mass determinations are more precise than the previous report by a factor of four to five. As indicated in the previous publication, even though the two components are nearly equal in mass, the system exhibits a significant brightness difference between the components in the near infrared and visible. We attribute this brightness difference to evolutionary differences between the two components in their transition between main sequence and giant evolutionary phases, and based on theoretical models we can estimate a system age of approximately 3.2 Gyr. Michelson Science Center, California Institute of Technology Department of Physics and Astronomy, Georgia State University Harvard-Smithsonian Center for Astrophysics European Southern Observatory