Kinematics of Nearby Gas and Stars

The kinematic properties of gas and stars in the solar neighborhood are described in terms of the line of sight component of a three dimensional first order Taylor series expansion of the local velocity field. The types of object analyzed are: (1) 21 cm absorbing clouds; (2) intercloud medium; (3) main sequence B-stars closer than 200 pc; (4) B-stars of luminosity class ranging from I to IV; (5) main sequence A stars; (6) K-giant stars. The least squares fitting procedure used to derive the 10 coefficients describes each of the six velocity fields was essentially the same for comparison. Marked departures from circular motion are found in most cases, but the only systematic trend is a correlation between delta u/delta x and stellar spectral type, where the gas behaves like a medium younger than the early type stars. It is indicated that the standard plane-parallel model provides a good description for the intercloud medium, but is inadequate for the absorbing clouds. A velocity ellipsoid description of the residuals is presented for each type of object. The influence of the Gould belt on local kinematics is discussed.