1. Athay, R. G., Low, B.C., and Rompolt, B.: 1987, Solar Phys. 110, 359.
2. Bendlin, C., Stellmacher, G., and Wiehr, E.: 1988, Astron. Astrophys. 197, 274.
3. Bommier, V., Leroy, J. L., and Sahal-Bréchot, S.: 1986a, Astron. Astrophys. 156, 79.
4. Bommier, V., Leroy, J. L., and Sahal-Bréchot, S.: 1986b, Astron. Astrophys. 156, 90.
5. Brickhouse, N. S. and Landman, D. A.: 1987, Astrophys. J. 313, 463.