Shapley, Harlow; Sawyer, Helen B., A Classification of Globular Clusters, Harvard College Observatory Bulletin, August 1927, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.
Baumgardt, H.; Vasiliev, E., Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data, Monthly Notices of the Royal Astronomical Society, 2021, 505 (4): 5957–5977, Bibcode:2021MNRAS.505.5957B, arXiv:2105.09526, doi:10.1093/mnras/stab1474.
Baker, JoDee M.; et al, Variable Stars in Metal-Rich Globular Clusters. III. NGC 6539, The Astronomical Journal, January 2007, 133 (1): 139–146, Bibcode:2007AJ....133..139B, doi:10.1086/509638.
D'Amico, N.; et al, Green, D. W. E. , 编, Millisecond Pulsar in NGC 6539, IAU Circular, May 1990, 5013: 1, Bibcode:1990IAUC.5013....1D.
Baumgardt, H.; Vasiliev, E., Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data, Monthly Notices of the Royal Astronomical Society, 2021, 505 (4): 5957–5977, Bibcode:2021MNRAS.505.5957B, arXiv:2105.09526, doi:10.1093/mnras/stab1474.
Baumgardt, H.; Vasiliev, E., Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data, Monthly Notices of the Royal Astronomical Society, 2021, 505 (4): 5957–5977, Bibcode:2021MNRAS.505.5957B, arXiv:2105.09526, doi:10.1093/mnras/stab1474.
Baker, JoDee M.; et al, Variable Stars in Metal-Rich Globular Clusters. III. NGC 6539, The Astronomical Journal, January 2007, 133 (1): 139–146, Bibcode:2007AJ....133..139B, doi:10.1086/509638.