Apex and Kinematical Structure of Castor and Ursa Major Moving Stellar Groups

Abstract

Based on space velocity components UVW and using a recent dataset for Castor and Ursa Major moving groups, we compute the apex position with two methods. Classical convergent procedures give (A_cp, D_cp) = (80$_{.}^{\circ}$7830, –17$_{.}^{\circ}$2598; Castor, 298$_{.}^{\circ}$334, –34$_{.}^{\circ}$6405; UMa) for Castor and Ursa Major groups. According to the AD-map method we deduce the apex position (A₀, D₀) = (79$_{.}^{\circ}$5514, –17$_{.}^{\circ}$3948; Castor, 304$_{.}^{\circ}$767, ‒35$_{.}^{\circ}$2045; UMa) for these two objects. These results are in good agreement with other published coordinated. Also, we calculate all parameters with a model of stream velocity ellipsoidal motions, which reveals inner kinematical structure. Finally, we consider the intrinsic variations considered with late-type moving groups (streams) for the longitude of the vertex versus temperature (spectral types).