Keenan, Philip C.; McNeil, Raymond C. The Perkins catalog of revised MK types for the cooler stars. Astrophysical Journal Supplement Series. 1989, 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
Mullan, D. J.; MacDonald, J. Onset of Mass Loss in Red Giants: Association with an Evolutionary Event. The Astrophysical Journal. 2003, 591 (2): 1203. Bibcode:2003ApJ...591.1203M. doi:10.1086/375446.
Samus, N. N.; Durlevich, O. V.; et al. VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007–2013). VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 2009, 1. Bibcode:2009yCat....102025S.
Keenan, Philip C.; McNeil, Raymond C. The Perkins catalog of revised MK types for the cooler stars. Astrophysical Journal Supplement Series. 1989, 71: 245. Bibcode:1989ApJS...71..245K. doi:10.1086/191373.
Mullan, D. J.; MacDonald, J. Onset of Mass Loss in Red Giants: Association with an Evolutionary Event. The Astrophysical Journal. 2003, 591 (2): 1203. Bibcode:2003ApJ...591.1203M. doi:10.1086/375446.