1. Brault, J.W. and Noyes, R.W.: 1984, Astrophys. J. (Letters)
269, 61.
2. Carlsson, M., Rutten, R.J., and Shchukina, N.G.: 1992, Astron. Astrophys. 253, 567.
3. Chang, E.S., Avrett, E.H., Mauas, P.J., Noyes, R.W., and Loeser, R.: 1991 Astrophys. J. (Letters)
379, 79.
4. Clark, T.A., Courts, G.R., and Jennings, R.E.: 1971, Phil. Trans. A. 270, 55.
5. Coates, R.J.: 1958, Astrophys. J. 128, 83.