Johnson, H. L.; Morgan, W. W. (1953). “Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas”. The Astrophysical Journal117: 313. Bibcode: 1953ApJ...117..313J. doi:10.1086/145697. ISSN0004-637X.
Keenan, Philip C.; McNeil, Raymond C. (1989). “The Perkins catalog of revised MK types for the cooler stars”. The Astrophysical Journal Supplement Series71: 245. Bibcode: 1989ApJS...71..245K. doi:10.1086/191373. ISSN0067-0049.
Johnson, H. L.; Morgan, W. W. (1953). “Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas”. The Astrophysical Journal117: 313. Bibcode: 1953ApJ...117..313J. doi:10.1086/145697. ISSN0004-637X.
Keenan, Philip C.; McNeil, Raymond C. (1989). “The Perkins catalog of revised MK types for the cooler stars”. The Astrophysical Journal Supplement Series71: 245. Bibcode: 1989ApJS...71..245K. doi:10.1086/191373. ISSN0067-0049.
Johnson, H. L.; Morgan, W. W. (1953). “Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas”. The Astrophysical Journal117: 313. Bibcode: 1953ApJ...117..313J. doi:10.1086/145697. ISSN0004-637X.
Keenan, Philip C.; McNeil, Raymond C. (1989). “The Perkins catalog of revised MK types for the cooler stars”. The Astrophysical Journal Supplement Series71: 245. Bibcode: 1989ApJS...71..245K. doi:10.1086/191373. ISSN0067-0049.