The Angular Diameter of λ Boötis

Using the CHARA Array and the Palomar Testbed Interferometer, the chemically peculiar star λ Boötis has been spatially resolved. We have measured the limb darkened angular diameter to be θ_LD=0.533+/-0.029 mas, corresponding to a linear radius of R_*=1.70+/-0.10 R_solar. The measured angular diameter yields an effective temperature for λ Boo of T_eff=8887+/-242 K. Based on literature surface gravity estimates spanning logg=4.0-4.2 cm s^-2, we have derived a stellar mass range of M_*=1.1-1.7 M_solar. For a given surface gravity, the linear radius uncertainty contributes approximately σ(M_*)=0.1-0.2 M_solar 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 (logg=4.2, M_*=1.7+/-0.2 M_solar) is consistent with 100-300 Myr solar metallicity evolutionary models. The midrange of our derived masses (logg=4.1, M_*=1.3+/-0.2 M_solar) 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 λ Boo.