ABSOLUTE MAGNITUDES AND KINEMATIC PROPERTIES OF CEPHEIDS

A maximum likelihood statistical parallax analysis of classical Cepheids has been performed to determine the relative solar motion, Oort constants, velocity ellipsoid parameters, and zero points of the PL and PLC relations. The analysis is based upon 90 proper motions drawn from the list of Karimova and Pavlovskaya and upon the analytical approach of Hawley et al. Our results give a best estimate for the mean absolute magnitude of Cepheids at log P = 0.8 of <M(v)> = -3.46 +/- 0.33 mag. This estimate for the Cepheid absolute magnitude zero point is highly stable against refinements in the mathematical technique and against additional Cepheid proper motion data of quality similar to the existing proper motions. Improvement in this value will likely come only from a marked improvement in the quality of the Cepheid proper motions. We also determine solar motion components along the axes (pi, theta, z) of (-6.8, -14.3, -10.0) km s-1 with uncertainties less than +/- 2 km s-1. The velocity ellipsoid components on the same axes are (11.9, 9.9, 2.1) km s-1 with similar uncertainties. We obtain values for the Oort constants of A = 14.5 +/- 2.4 km s-1 kpc-1 and -5.9 +/- 3.3 km s-1 kpc-1, although we suggest that the value of B is probably too positive because of limitations in the proper motion data base.