Walter F.M., A. Brown, R.D. Mathieu, P.C. Myers, and F.J. Vrba, The Astronomical Journal 96, 297 (1988).
Walter F.M., A. Brown, J.L. Linsky, A.E. Rydgren, F.J. Vrba, M. Roth, L. Carrasco, P.F. Chugainov, N.I. Shakovskaya, and C.L. Imhoff, The Astrophysical Journal 314, 297 (1987).