The Angular Diameter of λ Bootis

Using the CHARA Array and the Palomar Testbed Interferometer, the chemically peculiar star lambda Bootis has been spatially resolved. We have measured the limb darkened angular diameter to be theta(LD) = 0.533 +/- 0.029 mas, corresponding to a linear radius of R-star 1.70 +/- 0.10 R-circle dot. The measured angular diameter yields an effective temperature for lambda Boo of T-eff 8887 +/- 242 K. Based on literature surface gravity estimates spanning log g = 4.0-4.2 cm s(-2), we have derived a stellar mass range of M-star = 1.1-1.7 M-circle dot. For a given surface gravity, the linear radius uncertainty contributes approximately sigma(M-star) = 0.1-0.2 M-circle dot to the total mass uncertainty. The uncertainty in the mass (i.e., the range of derived masses) is primarily a result of the uncertainty in the surface gravity. The upper bound of our derived mass range (log g = 4.2, M-star = 1.7 +/- 0.2 M-circle dot) is consistent with 100-300 Myr solar metallicity evolutionary models. The mid-range of our derived masses (log g = 4.1, M-star = 1.3 +/- 0.2 M-circle dot) is consistent with 2-3 Gyr metal-poor evolutionary models. A more definitive surface gravity determination is required to determine a more precise mass for lambda Boo.