Proper Motions in Kapteyn Selected Area 103: A Preliminary Orbit for the Virgo Stellar Stream

TL;DR

This paper measures proper motions in a specific sky area to analyze the Virgo Stellar Stream's orbit, suggesting it is tidal debris from a disrupted system possibly linked to the globular cluster NGC 2419.

Contribution

It provides the first absolute proper motions for SA 103 and proposes a preliminary orbit for the VSS, linking it to a potential disrupted progenitor.

Findings

VSS has a pericenter of 11 kpc and an apocenter of ~90 kpc.

One RR Lyrae star in SA 103 is confirmed as a VSS member.

NGC 2419 may be the nucleus of the disrupted system.

Abstract

We present absolute proper motions in Kapteyn Selected Area (SA) 103. This field is located 7 degrees west of the center of the Virgo Stellar Stream (VSS, Duffau et al. 2006), and has a well-defined main sequence representing the stream. In SA 103 we identify one RR Lyrae star as a member of the VSS according to its metallicity, radial velocity and distance. VSS candidate turnoff stars and subgiant stars have proper motions consistent with that of the RR Lyrae star. The 3D velocity data imply an orbit with a pericenter of 11 kpc and an apocenter of ~90 kpc. Thus, the VSS comprises tidal debris found near the pericenter of a highly destructive orbit. Examining the six globular clusters at distances larger than 50 kpc from the Galactic center, and the proposed orbit of the VSS, we find one tentative association, NGC 2419. We speculate that NGC 2419 is possibly the nucleus of a disrupted system of which the VSS is a part.