The Effective Temperature of Arcturus

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 T eff = 4290 ± 30 K. We then select a grid of model-atmosphere energy distributions by Kurucz and extract T eff /log g /[Fe/H] by a least-squares fit to the adopted energy distribution. With the value of T eff 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.