The chemical composition of Algol systems - I. The secondary in U Cep.

An abundance analysis of the G8 III secondary of the U Cep system is performed on the basis of the Reticon spectra 430 A wide, centered at wavelengths of 6200, 6320, and 8620 A, and obtained with a resolution of 1.9 A. A rotational velocity of 90 + or - 8 km/s applied to the spectrum of the standard star Kappa Gem is found to provide an excellent fit to the secondary's spectrum, indicating that the star is rotating synchronously. A spectrum-synthesis analysis of the secondary's chemical composition reveals normal abundances of metals (Fe/H = 0.0 + or - 0.3) and s-process elements, which are consistent with the values expected from theories of close-binary evolution. It is noted that the Ca II IR triplet lines are weak in the secondary of U Cep relative to standard stars and that a weakening of the IR absorption lines is likely to be accompanied by enhanced chromospheric emission in the Ca II H and K lines.