1. Aller, L. H.: 1953, Astrophysics, the Atmosphere of the Sun and the Stars, Ronald Press, N.Y.
2. Aller, L. H.: 1961, The Abundance of the Elements, Interscience Publisher, N.Y.
3. Beck, D. R. and Sinanoğlu, O.: 1972, Phys. Rev. Letters 28, 945.
4. Chamberlain, J. W.: 1961, Physics of the Aurora and Airglow, Acad. Press.
5. Corney, A. and Williams, O. M.: 1972, J. Phys. B: Atom Mol. Phys. 5, 686.