"The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2013-12-03, retrieved 2012-01-16
Snowden, Michael S.; Young, Arthur (March 2005), "Radial Velocities of Late-Type Field Subgiant Stars", The Astrophysical Journal Supplement Series, 157 (1): 126–137, Bibcode:2005ApJS..157..126S, doi:10.1086/423711.
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.
Snowden, Michael S.; Young, Arthur (March 2005), "Radial Velocities of Late-Type Field Subgiant Stars", The Astrophysical Journal Supplement Series, 157 (1): 126–137, Bibcode:2005ApJS..157..126S, doi:10.1086/423711.
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.
"The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2013-12-03, retrieved 2012-01-16