1. Allen, C. W.: 1973,Astrophysical Quantities, (3rd ed.), Athlone Univ. Press, London.
2. Altenhoff, W. J. and Wendker, H. J.: 1973,Nature 241, 37.
3. Altenhoff, W. J., Oster, L., and Wendker, H. J.: 1979,Astron. Astrophys. 73, L21.
4. Babcock, H. W.: 1947,Astrophys. J. 105, 105.
5. Babcock, H. W.: 1960, in J. L. Greenstein (ed.),Stellar Atmospheres, Chicago University Press, p. 283.