OB Stars in the Solar Neighborhood. II. Kinematics

Using the spatial classification method and the structural parametersestimated for the Gould Belt (GB) and the local Galactic disk (LGD) from aprevious paper, we have evaluated spatial membership probabilities for a sampleof O and B stars from the Hipparcos catalogue (ESA 1997) with available propermotions and radial velocity data. Thus being able to study the space velocityfields of both systems, we conclude that the GB and the LGD present differentstatistical distributions, both in the velocity space as well as in the phasespace. In the light of the existence of both systems we analyze differentkinematic aspects in the vicinity of the Sun, and we find the GB to beresponsible for the highly negative vertex deviation found for the OB stars inthe solar neighborhood. We also find that the GB sensibly alters the estimationof Oort's constants in the Galactic disk; thus, in order to establishcomparisons with other kinematic studies based in older stellar populations, acareful pruning of the GB members must be performed. Further analysis of the GBvelocity field and the moving groups that contribute to it suggest thepossibility that the GB can be the result of a chance superposition of movinggroups. We propose for future investigations the dynamical analysis of thesemoving groups in order to probe the origin of the GB.Comment: 23 pages (including 4 figures). To be published in the Astronomical Journal (accepted May 17th, 2006