1. Hack, M., Struve, O.: Stellar Spectroscopy — Peculiar Stars, Osservatorio Astronomico, Trieste (1970).
2. Underhill, A.B.: The Early Type Stars, Reidel, Dordrecht (1966); see also Stars and Stellar Systems 6, Univ. Chicago Press, Chicago (1960) 411.
3. Int. Astron. Union Symp.,1976
4. Jaschek, M., Groth, H.G., (eds.): Int. Astron. Union Symp. 98, in preparation.
5. Struve, O.: Astrophys. J. 95 (1942) 134.