1. Abbott, D.C. & Conti, P.S., 1987, ARA&A, 25, 113.
2. Beals, C.C., 1938, Trans. IAU, 6, 248.
3. Conti, P.S., Leep, E.M., & Perry, D.N., 1983, ApJ, 268, 228.
4. Hamann, W.-R., Koesterke, L., & Wessolowski, U., 1993, A&A, 274, 397.
5. Hillier, D.J., 1997, in: J.M. Vreux, A. Detal, D. Fraipont-Caro, E. Gosset, & G. Rauw, (Eds.), Wolf-Rayet Stars in the Framework of Stellar Evolution, Proc. 33rd Liege International Astrophysical Colloquium, University de Liege, p. 509.