1. Böhm-Vitense, E.: 1981,Ann. Rev. Astron. Astrophys. 19, 295.
2. Deutsch, A. J.: 1964,Ann. Report Mt. Wilson Palomar Observ., p. 11.
3. Engvold, O.: 1977,Physica Scripta 16, 48.
4. Faraggiana, R. and Hack, M.: 1971,Astron. Astrophys. 15, 55.
5. Hack, M., Rusconi, L., Sedmak, G., Engin, S., and Yilmaz, N.: 1982,Astron. Astrophys. 113, 250.