Baumgardt, H.; Hilker, M.; Sollima, A.; Bellini, A. (2019). "Mean proper motions, space orbits, and velocity dispersion profiles of Galactic globular clusters derived from Gaia DR2 data". Monthly Notices of the Royal Astronomical Society. 482 (4): 5138–5155. arXiv:1811.01507. doi:10.1093/mnras/sty2997.{{cite journal}}: CS1 maint: unflagged free DOI (link)
Baumgardt, H.; Hilker, M.; Sollima, A.; Bellini, A. (2019). "Mean proper motions, space orbits, and velocity dispersion profiles of Galactic globular clusters derived from Gaia DR2 data". Monthly Notices of the Royal Astronomical Society. 482 (4): 5138–5155. arXiv:1811.01507. doi:10.1093/mnras/sty2997.{{cite journal}}: CS1 maint: unflagged free DOI (link)