THE BINARY-SYSTEM O-PER - ORBITAL ELEMENTS, COMPONENT PARAMETERS, ANDHELIUM ABUNDANCE

The radial velocities V-r of the components of the binary system o Per were measured from high-resolution, high signal-to-noise ratio CCD sp ectra. These data and all of the previously published V-r determinatio ns were used to refine the orbital elements. The following effective t emperatures and surface gravities were obtained: T-eff = 22700 +/- 150 0 K, logg = 3.4 +/- 0.2 for the primary component (star A) and T-eff= 21000 +/- 1500 K, logg = 4.0 +/- 0.2 for the secondary component (star B). The rotational velocity was found from HeI and MgII lines to be v sini = 89 +/- 4 km s(-1) for star A and vsini = 87 +/- 3 km s(-1) for stal B. The helium abundance derived from blue (lambda < 5000 Angstrom ) HeI lines turned out to be enhanced in component A (He/H = 0.18 +/- 0.01) and nearly normal in component B (He/H = 0.11 +/- 0.01). The rel ative ages of the components, t(A)/t(MS) = 0.96 and t(B)/t(MS) = 0.54, which were estimated from evolutionary calculations, suggest that the primary is near completion of the main-sequence phase. while the seco ndary is only halfway through this phase. These data together with our previous results for-binary early B stars lend support to the age dep endence of the helium abundance. This dependence can be explained by m ixing in the main-sequence phase. it is concluded that binarity strong ly affects the mixing pattern.