Col Reference--- ---------
R1 Hoag A.A., et al. 1961, Publ. US. Nav. Obs. 17, 347 (pe)
R2 Hoag A.A., et al. 1961, Publ. US. Nav. Obs. 17, 347 (pg)
R3 Purgathofer A. 1964, Ann. Univ. Sternw. Wien 26 no 2
R4 Mathews R.T. 1963, Publ. Goodsell Obs. no 14
R5 Massey P. et al. 1995, Astrophys. J. 454, 151
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