2010A&A...516A..42C

Double-lined, detached eclipsing binaries are our main source for accurate stellar masses and radii. In this paper we focus on the 1.15-1.70M_☉ interval where convective core overshoot is gradually ramped up in theoretical evolutionary models. We aim to determine absolute dimensions and abundances for the F-type detached eclipsing binary BKPeg, and to perform a detailed comparison with results from recent stellar evolutionary models, including a sample of previously studied systems with accurate parameters. uvby light curves and uvbyβ standard photometry were obtained with the Stroemgren Automatic Telescope, ESO, La Silla, and high-resolution spectra were acquired with the FIES spectrograph at the Nordic Optical Telescope, La Palma. The 5.49d period orbit of BKPeg is slightly eccentric (e=0.053). The two components are quite different with masses and radii of (1.414±0.007M_☉, 1.988±0.008R_☉) and (1.257±0.005M_☉, 1.474±0.017R_☉), respectively. The measured rotational velocities are 16.6±0.2 (primary) and 13.4±0.2 (secondary) km/s. For the secondary component this corresponds to (pseudo)synchronous rotation, whereas the primary component seems to rotate at a slightly lower rate. We derive an iron abundance of [Fe/H]=-0.12±0.07 and similar abundances for Si, Ca, Sc, Ti, Cr and Ni. The stars have evolved to the upper half of the main-sequence band. Yonsei-Yale and Victoria-Regina evolutionary models for the observed metal abundance reproduce BKPeg at ages of 2.75 and 2.50Gyr, respectively, but tend to predict a lower age for the more massive primary component than for the secondary. We find the same age trend for three other upper main-sequence systems in a sample of well studied eclipsing binaries with components in the 1.15-1.70M_☉ range. We also find that the Yonsei-Yale models systematically predict higher ages than the Victoria-Regina models. The sample includes BWAqr, and as a supplement we have determined a [Fe/H] abundance of -0.07±0.11 for this late F-type binary. We propose to use BK Peg, BW Aqr, and other well-studied 1.15-1.70M_☉ eclipsing binaries to fine-tune convective core overshoot, diffusion, and possibly other ingredients of modern theoretical evolutionary models.