THE KINEMATICS OF YOUNG DISK POPULATION SUPERCLUSTER MEMBERS

A discussion of the total space motions of early-type members of young disk population superclusters, derived from distances based on a photometric calibration of four-color and Hbeta photometry, shows an increase in total velocity with increasing radial distance from the Sun, within each supercluster. The rate of increase with distance varies from supercluster to supercluster because it results from the interaction of two effects-an "expansion" that involves the total space motion and a "rotation" that involves only the V-velocity because it arises from the requirement that supercluster members have isoperiodic, galactic orbits. The ratio of the velocity in the direction of galactic rotation ( V-velocity) to the total space motion determines the size of the resultant effect from the contradictory "rotation" and "expansion" terms. The expansion term is 40 to 45 km/s/kpc in the superclusters discussed, whereas the rotation term is dV/dX= - (B-A)=26 km/s/kpc, where B and A are the constants of galactic rotation.