1. Burbidge, G. R., and Burbidge, E. M., The Observatory, 75, 212 (1955). Bierman, L., and Lust, R., in Stellar Atmospheres, edit. by Greenstein, J. L. (Chicago, 1960).
2. Parker, E., Astrophys. J., 121, 49 (1955).
3. Schatzman, E., Ann. d'Astrophys., 25, 18 (1962).
4. Herbig, G., Astrophys. J., 125, 612 (1957).
5. Henyey, L., et. al., P.A.S.P., 67, 154 (1955).