Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
Evans, D. S.; Edwards, D. A. (August 1981), "Photoelectric observations of lunar occultations. XII", Astronomical Journal, 86: 1277−1287, Bibcode:1981AJ.....86.1277E, doi:10.1086/113008.
Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
Evans, D. S.; Edwards, D. A. (August 1981), "Photoelectric observations of lunar occultations. XII", Astronomical Journal, 86: 1277−1287, Bibcode:1981AJ.....86.1277E, doi:10.1086/113008.