Close encounters involving RAVE stars beyond the 47 Tucanae tidal radius

TL;DR

This study uses precise 6D phase-space data from RAVE to identify stars that had close past encounters with the globular cluster 47 Tucanae, revealing potential extratidal members and ejected stars through orbit integration.

Contribution

It introduces a Monte Carlo orbit integration method considering uncertainties and Galactic potential models to identify past close encounters with 47 Tucanae.

Findings

Identified 20 stars with close encounters to 47 Tucanae.

Nine stars likely tidally stripped from the cluster.

Eleven stars probably ejected or unassociated.

Abstract

The most accurate 6D phase-space information from the Radial Velocity Experiment (RAVE) was used to integrate the orbits of 105 stars around the galactic globular cluster 47 Tucanae, to look for close encounters between them in the past, with a minimum distance approach less than the cluster tidal radius. The stars are currently over the distance range 3.0 kpc $<$ d $<$ 5.5 kpc. Using the uncertainties in the current position and velocity vector for both, star and cluster, 105 pairs of star-cluster orbits were generated in a Monte Carlo numerical scheme, integrated over 2 Gyr and considering an axisymmetric and non-axisymmetric Milky-Way-like Galactic potential, respectively. In this scheme, we identified 20 potential cluster members that had close encounters with the globular cluster 47 Tucanae, all of which have a relative velocity distribution (V$_{rel}$) less than 200 km s$^{-1}$ at the minimum distance approach. Among these potential members, 9 had close encounters with the cluster with velocities less than the escape velocity of 47 Tucanae, therefore a scenario of tidal stripping seems likely. These stars have been classified with a 93\% confidence level, leading to the identification of extratidal cluster stars. For the other 11 stars, V$_{rel}$ exceeds the escape velocity of the cluster, therefore they were likely ejected or are unassociated interlopers.