Baumgardt, H.; Vasiliev, E. (August 2021), "Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data", Monthly Notices of the Royal Astronomical Society, 505 (4): 5957–5977, arXiv:2105.09526, Bibcode:2021MNRAS.505.5957B, doi:10.1093/mnras/stab1474.
Lee, Jae-Woo; Carney, Bruce W. (November 2006), "VI Photometry of Globular Clusters NGC 6293 and NGC 6541: The Formation of the Metal-poor Inner Halo Globular Clusters", The Astronomical Journal, 132 (5): 2171–2186, arXiv:astro-ph/0606711, Bibcode:2006AJ....132.2171L, doi:10.1086/507412.
Baumgardt, H.; Vasiliev, E. (August 2021), "Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data", Monthly Notices of the Royal Astronomical Society, 505 (4): 5957–5977, arXiv:2105.09526, Bibcode:2021MNRAS.505.5957B, doi:10.1093/mnras/stab1474.
Lee, Jae-Woo; Carney, Bruce W. (November 2006), "VI Photometry of Globular Clusters NGC 6293 and NGC 6541: The Formation of the Metal-poor Inner Halo Globular Clusters", The Astronomical Journal, 132 (5): 2171–2186, arXiv:astro-ph/0606711, Bibcode:2006AJ....132.2171L, doi:10.1086/507412.
Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.
Baumgardt, H.; Vasiliev, E. (August 2021), "Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST, and literature data", Monthly Notices of the Royal Astronomical Society, 505 (4): 5957–5977, arXiv:2105.09526, Bibcode:2021MNRAS.505.5957B, doi:10.1093/mnras/stab1474.
Lee, Jae-Woo; Carney, Bruce W. (November 2006), "VI Photometry of Globular Clusters NGC 6293 and NGC 6541: The Formation of the Metal-poor Inner Halo Globular Clusters", The Astronomical Journal, 132 (5): 2171–2186, arXiv:astro-ph/0606711, Bibcode:2006AJ....132.2171L, doi:10.1086/507412.