Lee, Jae-Woo (2019), "Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH Photometry. V. cn′JWL as a Surrogate cnJWL Index and NGC 6723", The Astrophysical Journal, 883 (2): 166, arXiv:1908.06670, doi:10.3847/1538-4357/ab3d34, S2CID201070324
Lee, Jae-Woo (2019), "Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH Photometry. V. cn′JWL as a Surrogate cnJWL Index and NGC 6723", The Astrophysical Journal, 883 (2): 166, arXiv:1908.06670, doi:10.3847/1538-4357/ab3d34, S2CID201070324
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Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.
Lee, Jae-Woo (2019), "Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH Photometry. V. cn′JWL as a Surrogate cnJWL Index and NGC 6723", The Astrophysical Journal, 883 (2): 166, arXiv:1908.06670, doi:10.3847/1538-4357/ab3d34, S2CID201070324