Ob stars in the solar neighborhood. II. kinematics

Abstract

Using the spatial classification method and the structural parameters estimated for the Gould Belt (GB) and the local Galactic disk (LGD) from a previous paper, we have evaluated spatial membership probabilities for a sample of O and B stars from the Hipparcos catalog (Perryman and coworkers) with available proper motions and radial velocity data. Thus, being able to study the space velocity fields of both systems, we conclude that the GB and the LGD present different statistical distributions, both in velocity space and in phase space. In light of their possible existence as distinct systems, we analyze different kinematic aspects in the vicinity of the Sun, and we find the GB to be responsible for the highly negative vertex deviation found for the OB stars in the solar neighborhood. We also find that the GB noticeably alters the estimation of the Oort constants in the Galactic disk; thus, in order to establish comparisons with other kinematic studies based on older stellar populations, a careful pruning of the GB members must be performed. Further analysis of the GB velocity field and the moving groups that contribute to it suggest the possibility that the GB can be the result of a chance superposition of moving groups. We propose for future investigations the dynamical analysis of these moving groups in order to probe the origin of the GB.