Measurement of the Surface Gravity of η Bootis

Direct angular size measurements of the G0IV subgiant $\eta$ Boo from thePalomar Testbed Interferometer are presented, with limb-darkened angular sizeof $\theta_{LD}= 2.1894^{+0.0055}_{-0.0140} $ mas, which indicate a linearradius of $R=2.672 \pm 0.028 R_\odot$. A bolometric flux estimate of $F_{BOL} =22.1 \pm 0.28\times 10^{-7}$ erg cm$^{-2}$s$^{-1}$ is computed, which indicatesan effective temperature of $T_{EFF}=6100 \pm 28$ K and luminosity of $L = 8.89\pm 0.16 L_\odot$ for this object. Similar data are established for a checkstar, HD 121860. The $\eta$ Boo results are compared to, and confirm, similarparameters established by the {\it MOST} asteroseismology satellite. Inconjunction with the mass estimate from the {\it MOST} investigation, a surfacegravity of $\log g=3.817 \pm 0.016$ [cm s$^{-2}$] is established for $\eta$Boo.Comment: To appear in March 1, 2007 ApJ v657 n