Measurement of the Surface Gravity of $\eta$ Boo

Abstract

Direct angular size measurements of the G0IV subgiant $\eta$ Boo from the Palomar Testbed Interferometer are presented, with limb-darkened angular size of ${\theta }_{LD}=2.1894_{-0.0140}^{+0.0055}$ mas, which indicate a linear radius of $R=2.672\pm 0.028R_{\odot }$. A bolometric flux estimate of $F_{BOL}=22.1\pm 0.28\times 10^{-7}$ erg cm${}^{-2}$s${}^{-1}$ is computed, which indicates an effective temperature of $T_{EFF}=6100\pm 28$ K and luminosity of $L=8.89\pm 0.16L_{\odot }$ for this object. Similar data are established for a check star, HD 121860. The $\eta$ Boo results are compared to, and confirm, similar parameters established by the {\it MOST} asteroseismology satellite. In conjunction with the mass estimate from the {\it MOST} investigation, a surface gravity of $\log g=3.817\pm 0.016$ [cm s${}^{-2}$] is established for $\eta$ Boo.

To appear in March 1, 2007 ApJ v657 n1

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