CHEMICAL-COMPOSITION OF COMPONENT-A AND COMPONENT-B OF THE HG-MN CHEMICALLY-PECULIAR ECLIPSING SB2 STAR AR-AUR

Results of a spectroscopic study of the unique eclipsing SB2 system AR Aur with chemically-peculiar components of approximately equal mass a re reported. The high-dispersion (1.7 Angstrom mm(-1)) spectra obtaine d on the BTA telescope for ten phases of the orbital period were spect rophotometrically reduced. Lines in the region 3850 - 4600 Angstrom we re identified, and the chemical composition of each component was dete rmined for 18 elements. The primary component (Sp B9 V) is shown to be a typical Hg-Mn star. The chemical composition of the secondary compo nent (Sp B9.5 V) is also abnormal, but differs from that of the primar y. Our result is in conflict with the view that the atmospheric chemic al composition of the components of approximately equal mass in AR Aur reflects the chemical composition of the parent matter from which the y were formed on the same time scale. If chemical anomalies are brough t about solely in the surface layers, then, since the orbital and axia l rotations of the system are synchronized, they can only set in after the rotation the components has been synchronized. The difference in the chemical compositions of the components suggests that the effects responsible for the emergence of anomalies are very subtle (slight dif ferences in mass, temperature, or star-formation time).