1. D. S. Hall, in Multiple Periodic Variable Stars, Proceedings of the IAU Coll. No. 29, Budapest, 1975, Ed. by W. S. Fitch (Reidel, Dordrecht, 1976), p. 287.
2. S. V. Berdyugina, Living Rev. Solar Phys. 2, 8 (2005).
3. S. V. Berdyugina and L. Tuominen, Astron. Astrophys. 336, L25 (1998).
4. D. Sokoloff and N. Piskunov, Mon. Not. R. Astron. Soc. 334, 925 (2002).
5. D. S. Hall and J. M. Kreiner, Acta Astron. 30, 387 (1980).