CHEMICAL-COMPOSITION OF THE CP HG-MN COMPONENTS OF APPROXIMATELY EQUAL MASS IN THE SB2 SYSTEM-46 DRACONIS

We have performed the most complete (to date) atmospheric-abundance an alysis of the components of approximately equal mass in the SB2 system 46 Dra using the high-resolution, S/N = > 200 CCD spectra obtained wi th the echelle spectrograph of the 2.7-m McDonald Observatory telescop e. The abundances of 25 elements were determined from lines in the wid e spectral range 3800 to 9000 A. The rotation of the components is sho wn to be synchronized and coaxial with the orbital motion. The chemica l anomalies of both components were found to be generally similar: an underabundance of He, C, N, O, and Al; a nearly solar abundance of iro n-peak elements; and considerable overabundances of P, Mn, Ga, Sr, Y, Zr, Pa, Pt, Au, and Hg, which increase with increasing atomic number. However, we found significant differences in the abundances of some el ements in components A and B, similar to those that were previously de tected in the analogous SB2 system AR Aur: an underabundance of Al and Ni in component A with a smaller anomaly or a normal abundance of the se two elements in component B. Component A shows a considerably great er overabundance of Ga and considerably smaller overabundances of Sr a nd Pt than component B does. There are also differences between the sy stems themselves: in contrast to AR Aur, in which only component A exh ibits great overabundances of Y, Ba, and Hg, these elements are equall y greatly enhanced in both components of 46 Dra. The most striking dif ference between components A and B of 46 Dra, which are similar in all physical parameters, is the difference in the isotopic composition of mercury which was first detected by Cowley and Aikman (1975) and conf irmed in this study. It is concluded that the abundance difference bet ween the components could arise after the synchronization of the rotat ion and the arrival of the stars at the main sequence.