1. Abbott, D.C. and Hummer, D.G.: 1982, this volume.
2. Aller, L.H.: 1968, “Planetary Nebulae”: IAU Symposium No. 34, p. 339.
3. Aller, L. H.: 1976, Mem. de la Soc. Roy. des Sci. de Liege, 6 eme Ser., p 271.
4. Barlow, M. J. and Hummer, D.: 1982, “Wolf-Rayet Stars”: IAU Symp. No. 99, C. de Loore, ed. (D. Reidel: Dordrecht).
5. Benvenuti, P, Perinotto, M. and Willis, A.J.: 1982, “Wolf-Rayet Stars”, C. de Loore, ed., (D. Reidel: Dordrecht.)