1. E. X. Parker and J. Chinese, Astron. Astrophys. 1(2), 99 (2001).
2. B. W. Lites, Sunspot: Theory and Observations, Ed. by J. H. Thomas and N. O. Weiss (1992), p. 261.
3. N. I. Kobanov, Solar Phys. 125, 25 (1990).
4. E. B. Georgakilas and S. Koutchmy, Astron. Astrophys. 363, 306 (2000).
5. B. Montesinos and J. H. Thomas, Nature 390, 485 (1997).