Absolute dimensions of detached eclipsing binaries - II. The metallic-lined system XY Ceti

We present phase-resolved spectroscopy and extensive survey photometry of the detached eclipsing binary system XY Cet, which is composed of two metallic-lined stars. We measure their masses to be 1.773 ± 0.016 and 1.615 ± 0.014 M_⊙ and their radii to be 1.873 ± 0.035 and 1.773 ± 0.029 R_⊙, resulting in logarithmic surface gravities of 4.142 ± 0.016 and 4.149 ± 0.014 (cgs). We determine effective temperatures of 7870 ± 115 and 7620 ± 125 K. The projected rotational velocities are 34.4 ± 0.4 and 34.1 ± 0.4 km s^-1, which are close to synchronous. Theoretical models cannot match all of these properties, but come closest for a solar helium and metal abundance and an age in the region of 850 Myr. We obtain the individual spectra of the two stars by the spectral disentangling method, and compare them to synthetic spectra calculated for the measured effective temperatures and a solar chemical composition. Both stars show enhanced abundances of iron-group elements and clear deficiencies of Ca I and Sc II, confirming their classification as Am stars. We also find strong overabundances of Zr II and the rare-earth species La II, Ce II and Nd II, a hallmark of chemically peculiar A stars. XY Cet is a prime candidate for detailed spectroscopic analyses of metallic-lined stars whose masses and radii are known to accuracies of 1-2 per cent.