New Members of Upper Scorpius from Gaia DR1


Accepted for publication in the journal Astronomy and Astrophysics.

Abstract

Selecting a cluster in proper motion space is an established method for identifying members of a star forming region. The first data release from Gaia (DR1) provides an extremely large and precise stellar catalogue, which when combined with the Tycho-2 catalogue gives the 2.5 million parallaxes and proper motions contained within the Tycho-Gaia Astrometric Solution (TGAS). We aim to identify new member candidates of the nearby Upper Scorpius subgroup of the Scorpius-Centaurus Complex within the TGAS catalogue. In doing so, we also aim to validate the use of the DBSCAN clustering algorithm on spatial and kinematic data as a robust member selection method. We constructed a method for member selection using a density-based clustering algorithm (DBSCAN) applied over proper motion and distance. We then applied this method to Upper Scorpius, and evaluated the results and performance of the method. We identified 167 member candidates of Upper Scorpius, of which 78 are new, distributed within a 10° radius from its core. These member candidates have a mean distance of 145.6 ± 7.5 pc, and a mean proper motion of (-11.4, -23.5) ± (0.7, 0.4) mas/yr. These values are consistent with measured distances and proper motions of previously identified bona-fide members of the Upper Scorpius association.