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Puzia, Thomas H.; Kissler‐Patig, Markus; Goudfrooij, Paul (2006). «Extremely α‐Enriched Globular Clusters in Early‐Type Galaxies: A Step toward the Dawn of Stellar Populations?». The Astrophysical Journal. 648: 383–388. Bibcode:2006ApJ...648..383P. arXiv:astro-ph/0605210. doi:10.1086/505679
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T. S. van Albada, Norman Baker (1973). «On the Two Oosterhoff Groups of Globular Clusters». Astrophysical Journal. 185: 477–498. Bibcode:1973ApJ...185..477V. doi:10.1086/152434
Puzia, Thomas H.; Kissler‐Patig, Markus; Goudfrooij, Paul (2006). «Extremely α‐Enriched Globular Clusters in Early‐Type Galaxies: A Step toward the Dawn of Stellar Populations?». The Astrophysical Journal. 648: 383–388. Bibcode:2006ApJ...648..383P. arXiv:astro-ph/0605210. doi:10.1086/505679
Sanchez-Salcedo, F. J. (1997). «On the Stringent Constraint on Massive Dark Clusters in the Galactic Halo». Astrophysical Journal Letters v.487. 487: L61. Bibcode:1997ApJ...487L..61S. doi:10.1086/310873
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Lauren J. Bryant. «What Makes Stars Tick». Indiana University Research & Creative Activity. Consultado em 7 de setembro de 2005