1. Allen, D.A., Harvey, P.M., Swings, J.P. 1972, A&A 20 , 333
2. Allen, D.A., Barton, J.R., Wallace, P.T. 1981, MNRAS 196, 797
3. Annuk, K. 1991, in: K.A. van der Hucht & B. Hidayat, B., Wolf-Rayet Stars and Interrelations with Other Massive Stars in Galaxies, Proc. IAU Symp. No. 143 (Dordrecht: Kluwer), p. 245
4. Cohen, M., Barlow, M.J., Kuhi, L.V. 1975, A&A 40, 291
5. Cohen, M., Kuhi, L.V. 1977, MNRAS 180, 37