The Angular Diameter of $\lambda$ Boötis}

Abstract

Using the CHARA Array and the Palomar Testbed Interferometer, the chemically peculiar star $\lambda$ Boötis has been spatially resolved. We have measured the limb darkened angular diameter to be ${\theta }_{LD}=0.533\pm 0.029$ mas, corresponding to a linear radius of $R_{\star }=1.70\pm 0.10R_{\odot }$. The measured angular diameter yields an effective temperature for $\lambda$ Boo of $T_{eff}=8887\pm 242$ K. Based upon literature surface gravity estimates spanning $\log (g)=4.0-4.2$ $[{\mathrm{cms}}^{-2}]$, we have derived a stellar mass range of $M_{\star }=1.1-1.7$ $M_{\odot }$. For a given surface gravity, the linear radius uncertainty contributes approximately $\sigma (M_{\star })=0.1-0.2M_{\odot }$ 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 ($\log (g)=4.2,M_{\star }=1.7\pm 0.2M_{\odot }$) is consistent with 100-300 MYr solar-metallicity evolutionary models. The mid-range of our derived masses ($\log (g)=4.1,M_{\star }=1.3\pm 0.2M_{\odot }$) 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.

Accepted for publication in The Astrophysical Journal

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