1. Gafeira, R., Fonte, C.C., Pais, M.A., Fernandes, J.: The Sun: New Tools and Ideas in Observational Solar Astrophysics Proceedings EWASS. Rome (2012)
2. Hathaway, D.H., Choudhary, D.P.: Solar Phys. 250, 269 (2008)
3. McIntosh, P.: Solar Phys. 125, 251 (1990)
4. Zirin, H.: Astrophysics of the Sun, vol. 440. Cambridge University Press, Cambridge (1988)
5. Schlichenmaier, R., Gonzalez, N.B., Rezaei, R., Waldmann, T.A.: Astron. Nachr. 330, 563 (2010)