Johnson, H. L.; et al, UBVRIJKL photometry of the bright stars, Communications of the Lunar and Planetary Laboratory, 1966, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
Houk, N., Michigan catalogue of two-dimensional spectral types for the HD stars 4, Ann Arbor: Dept. of Astronomy, University of Michigan, 1988, Bibcode:1988mcts.book.....H.