Absolute dimensions of eclipsing binaries. XIII. AI Phoenicis : a casestudy in stellar evolution.

The masses, radii, and chemical composition of evolved F + K-type eclipsing binary AI Phe are redetermined. The masses for the stars are 1.20 solar for the hotter, less-evolved star, and 1.24 solar for the cooler, larger subgiant component. The orbital eccentricity is e = 0.188 + or - 0.002. The metal abundance of AI Phe is determined to be (Fe/H) = -0.14 + or - 0.1, corresponding to Z = 0.012 + or - 0.003. New stellar evolution sequences are computed with the VandenBerg (1983) code for the observed masses of the two components, for a helium abundance that is required to satisfy the luminosity constraints of the data, and for a value of the mixing-length parameter that has been calibrated from a solar model. These models fit the observed properties of AI Phe with remarkable precision. The success of standard evolution theory in modeling AI Phe strongly suggests that convective overshooting is unimportant in stars with masses near 1.25 solar.