Measurement of the Surface Gravity of η Bootis

Direct angular size measurements of the G0 IV subgiant η Boo from the Palomar Testbed Interferometer are presented, with a limb-darkened angular size of θ_LD=2.1894^+0.0055_-0.0140 mas, which indicates a linear radius of R=2.672+/-0.028 R_solar. A bolometric flux estimate of F_bol=(22.1+/-0.28)×10^-7 ergs cm^-2 s^-1 is computed, which indicates an effective temperature of T_eff=6100+/-28 K and a luminosity of L=8.89+/-0.16 L_solar for this object. Similar data are established for a check star, HD 121860. The η Boo results are compared to, and confirm, similar parameters established by the MOST asteroseismology satellite. In conjunction with the mass estimate from the MOST investigation, a surface gravity of logg=3.817+/-0.016 [cm s^-2] is established for η Boo.