The Milky Way Bulge Extra-Tidal Star Survey: NGC 6569

Joanne Hughes; Andrea Kunder; Kevin Covey; Kathryn Devine; Kristen A. Larson; Carlos Campos; Adrian M. Price-Whelan; Joseph E. McEwen; Gabriel I. Perren; Christian I. Johnson; Craig Horton; Luke Smith; Sarah Torset; Cynthia Luna; Matthew Kolmanovsky; Fiona Kovisto; Leander Villarta; Vy Vuong; Iulia T. Simion; Kyle Webster; Erika Silva; Catherine A. Pilachowski; R. Michael Rich; Justin A. Kader; Andreas J. Koch-Hansen; Meridith Joyce; Sean McAdam; Faith Benda

arXiv · 2512.19074

The Milky Way Bulge Extra-Tidal Star Survey: NGC 6569

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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.

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Joanne Hughes, Andrea Kunder, Kevin Covey, Kathryn Devine, Kristen A. Larson, Carlos Campos, Adrian M. Price-Whelan, Joseph E. McEwen, Gabriel I. Perren, Christian I. Johnson, Craig Horton, Luke Smith, Sarah Torset, Cynthia Luna, Matthew Kolmanovsky, Fiona Kovisto, Leander Villarta, Vy Vuong, Iulia T. Simion, Kyle Webster, Erika Silva, Catherine A. Pilachowski, R. Michael Rich, Justin A. Kader, Andreas J. Koch-Hansen, Meridith Joyce, Sean McAdam, Faith Benda. 2025-12-22. The Milky Way Bulge Extra-Tidal Star Survey: NGC 6569. https://arxiv.org/abs/2512.19074

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