ORBITAL COPLANARITY IN SOLAR-TYPE BINARY-SYSTEMS - IMPLICATIONS FOR PLANETARY SYSTEM FORMATION AND DETECTION

The equatorial inclinations of solar-type stars within visual binary s ystems are computed by combining v sin i measurements with rotational period information, or with expected rotational velocities based upon the age of the star in question. These inclinations are then compared with the orbital inclinations of the systems to test the alignment bet ween the equatorial and orbital planes, and how the tendency for or ag ainst coplanarity varies as a function of parameters such as spectral type, separation, eccentricity, etc. The results are extended to plane tary systems in order to determine the appropriateness of basing plane tary search strategies upon a parent star's equatorial inclination, an d to address issues in planetary system formation and evolution, inclu ding the stability of planetary orbits within binary systems. During t he course of this project new or improved v sin i measurements are mad e for over 30 solar-type stars within binary systems, and (for the pur poses of the study) tentative orbits are computed for thirteen long-pe riod systems. The results suggest that approximate coplanarity between the equatorial and orbital planes exists for solar-type binary system s with separations less than 30-40 AU. The coplanarity tendency, as we ll as this ''critical separation,'' is not significantly affected by m ost of the other parameters studied. The one significant exception occ urs with hierarchical multiple systems, where noncoplanarity may exist at relatively small separations. If it is assumed that planetary dist ances in our solar system are typical, the results suggest there is no reason to expect planets to orbit in planes significantly different f rom that of the parent star's equator, in turn suggesting that planeta ry formation models and search strategies dependent upon this assumpti on are valid from this standpoint. The results also suggest that nonco planarity between the components of a binary system is not a significa nt issue in addressing the stability of planetary orbits within the sy stem.