1. Middlehurst, B., Aller, L.H. (eds.): Nebulae and Interstellar Matter, Stars and Stellar Systems. Chicago, University of Chicago Press, Vol. 7 (1968).
2. Les Nebuleuses Planetaires, Mem. Soc. R. Sci. Liège 6th Series, Vol. 5 (1973).
3. Int. Astron. Union Symp.,1968
4. Int. Astron. Union Symp.,1978
5. Aller, L.H.: Gaseous Nebulae, Chapman and Hall, London (1956).