Details of the spatial structure and kinematics of the Castor and Ursa Major streams

TL;DR

This paper analyzes the spatial structure and movement of the Castor and Ursa Major streams, revising star memberships and comparing their kinematics to understand their relation and implications for the Galactic disk's morphology.

Contribution

It provides a detailed comparison of the Castor and Ursa Major streams' parameters and their spatial and kinematic relationship, including revised memberships and apex determinations.

Findings

Castor stream occupies a smaller volume than UMa stream.

The two streams move in almost opposite directions, separated by 225 degrees on the apex diagram.

Stars of both streams are spatially intermixed, with Castor inside UMa.

Abstract

A list of the Castor stream members is compiled based on the data from various authors. The membership probabilities for some stars are revised based on the individual apex, multiplicity, observational errors, and peculiarity. The apex of the Castor moving group is determined using the apex diagram method. The parameters of the Castor and Ursa Major streams are compared and the positions of the two streams on the apex diagram are found to differ by 225deg, implying that the two groups move in almost opposite directions. Stars of both moving groups are intermixed in space, the Castor stream occupies a smaller volume than the UMa stream and is located inside it. Our results can be useful for understanding the morphology of the Galactic disk in the Sun's vicinity.