H. L. Johnson et al., UBVRIJKL photometry of the bright stars, in Communications of the Lunar and Planetary Laboratory, vol. 4, n. 99, 1966, pp. 99, Bibcode:1966CoLPL...4...99J.
Nancy Houk et al., Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 2, Dept. of Astronomy, University of Michigan, 1978, Bibcode:1978mcts.book.....H.