The Effective Temperature of Arcturus

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Abstract
We construct an empirical energy distribution for Arcturus from published scans, integrate it to obtain the total flux, and combine the latter with precise interferometric measurements of the limb-darkened angular diameter to derive the effective temperature. We conclude that the best value that can be derived within the framework of the associated assumptions is Teff = 4290 ± 30 K. We then select a grid of model-atmosphere energy distributions by Kurucz and extract Teff/log g/[Fe/H] by a least-squares fit to the adopted energy distribution. With the value of Teff already constrained, we could investigate values for the surface gravity and metallicity of Arcturus; our results are log g = 1.9, [Fe/H] = -0.68, and R = 23 R⊙. However, we discuss evidence that relevant grids of models may not contain sufficient opacity.