Geisler, Doug; et al, Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo, The Publications of the Astronomical Society of the Pacific, September 2007, 119 (859): 939–961, Bibcode:2007PASP..119..939G, arXiv:0708.0570, doi:10.1086/521990.
Geisler, Doug; et al, Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo, The Publications of the Astronomical Society of the Pacific, September 2007, 119 (859): 939–961, Bibcode:2007PASP..119..939G, arXiv:0708.0570, doi:10.1086/521990.
Abell, George O. Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey. Publications of the Astronomical Society of the Pacific. 1955, 67 (397): 258. Bibcode:1955PASP...67..258A. doi:10.1086/126815.
Geisler, Doug; et al, Chemical Abundances and Kinematics in Globular Clusters and Local Group Dwarf Galaxies and Their Implications for Formation Theories of the Galactic Halo, The Publications of the Astronomical Society of the Pacific, September 2007, 119 (859): 939–961, Bibcode:2007PASP..119..939G, arXiv:0708.0570, doi:10.1086/521990.
Abell, George O. Globular Clusters and Planetary Nebulae Discovered on the National Geographic Society-Palomar Observatory Sky Survey. Publications of the Astronomical Society of the Pacific. 1955, 67 (397): 258. Bibcode:1955PASP...67..258A. doi:10.1086/126815.