The Milky Way Bulge Extra-Tidal Star Survey: NGC 6569
Abstract
We present spectroscopic evidence for tidal debris associated with the bulge globular cluster NGC 6569, based on medium-resolution (R ~ 11,000) Anglo-Australian Telescope spectra of 303 stars. Targets were selected using Blanco DECam Bulge Survey (BDBS) photometry and Gaia DR3 astrometry, spanning 7-30 arcmin (~1-5 rt, where rt is the King-model tidal radius) from the cluster center. Orbit-based modeling predicts a strongly time-variable Jacobi radius, with rJ ~ 8-11 arcmin near pericenter and ~18-22 arcmin near apocenter, so stars just outside rt can be unbound and feeding leading and lagging tidal tails. We identify 40 stars with kinematics and abundances consistent with previous, or borderline, cluster membership. The seven highest-quality candidates (S/N > 30) have mean [Fe/H] = -0.83 +/- 0.14 and [alpha/Fe] = +0.38 +/- 0.06 dex, matching the bound population. Interpreting these stars as recently stripped debris implies a present-day mass-loss rate of 1.0-1.6 solar masses per Myr, or 5.6 +/- 1.3% of the current cluster mass per Gyr. These results indicate ongoing tidal stripping of NGC 6569 and quantify its contribution to the bulge field. This paper is part of the Milky Way Bulge Extra-Tidal Star Survey (MWBest) and is our first detailed debris study of a massive bulge globular cluster.
Cite
@article{arxiv.2512.19074,
title = {The Milky Way Bulge Extra-Tidal Star Survey: NGC 6569},
author = {Joanne Hughes and Andrea Kunder and Kevin Covey and Kathryn Devine and Kristen A. Larson and Carlos Campos and Adrian M. Price-Whelan and Joseph E. McEwen and Gabriel I. Perren and Christian I. Johnson and Craig Horton and Luke Smith and Sarah Torset and Cynthia Luna and Matthew Kolmanovsky and Fiona Kovisto and Leander Villarta and Vy Vuong and Iulia T. Simion and Kyle Webster and Erika Silva and Catherine A. Pilachowski and R. Michael Rich and Justin A. Kader and Andreas J. Koch-Hansen and Meridith Joyce and Sean McAdam and Faith Benda},
journal= {arXiv preprint arXiv:2512.19074},
year = {2026}
}
Comments
31 pages, 10 figures, 8 tables. Accepted for publication in The Astronomical Journal 19 December, 2025. Updated to correct typos