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Keenan, Philip C.; McNeil, Raymond C. (). „The Perkins catalog of revised MK types for the cooler stars”. The Astrophysical Journal Supplement Series. 71: 245. doi:10.1086/191373. ISSN0067-0049.
Parsons, Sidney B.; Ake, Thomas B. (). „Ultraviolet and Optical Studies of Binaries with Luminous Cool Primaries and Hot Companions. V. The EntireIUESample”. The Astrophysical Journal Supplement Series. 119 (1): 83–104. doi:10.1086/313152. ISSN0067-0049.