The Kinematics of Stars Emerging from Expanding Shells: An Analysis of the Gould Belt

Abstract

Using the available data for nearby stars from the Hipparcos catalog, we derive the velocity ellipsoid of dwarf O-B5.5 stars belonging to the Gould Belt (GB). The resulting vertex deviation for the whole sample of 252 stars is lv ~ -64° ± 20°, and this value is modified to lv = 22° ± 8° when the members of the Pleiades moving group are removed from the sample. This implies the existence of, at least, two different kinematic groups defining the GB system. We also model the evolution of a supershell in the solar neighborhood and obtain a fit to the shape and kinematics of the gas in the GB. Assuming that the expanding shell is also forming stars, we obtain the corresponding velocity fields for the shell and its newly formed stars. The average vertex deviation value resulting from these models for the new stars (assuming different velocity dispersion values and cutoff distances) is lv ≃ 20° and is consistent with the observed value when the Pleiades moving group members are excluded from the GB.