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Hertzprung, Ejnar (1908). «Über die Sterne der Unterabteilung c und ac nach der Spektralklassifikation von Antonia C. Maury». Astronomische Nachrichten179 (24): 373–380. doi:10.1002/asna.19081792402. Bibcode: 1909AN....179..373H.
Vandenberg, D.A.; Brogaard, K.; Leaman, R.; Casagrande, L. (2013). «THE AGES OF 55 GLOBULAR CLUSTERS AS DETERMINED USING AN IMPROVED $\Delta V^{\rm HB}_{\rm TO}$ METHOD ALONG WITH COLOR-MAGNITUDE DIAGRAM CONSTRAINTS, AND THEIR IMPLICATIONS FOR BROADER ISSUES». The Astrophysical Journal775 (2): 134. doi:10.1088/0004-637X/775/2/134. Bibcode: 2013ApJ...775..134V.