1. Abt, H. A. 1983, Ann. Rev. Astr. Ap., 21, 343.
2. Abt, H. A., and Levy, S. G. 1976, Ap. J. Suppl., 30, 273.
3. Arquilla, R. 1984, Ph. D. thesis, University of Massachusetts.
4. Baudry, A., Cernicharo, J., Perault, M., de la Noe, J., and Despois, D. 1981, Astr. Ap., 194, 101.
5. Beichman, C. A., and Chaisson, E. J. 1974, Ap. J. (Letters), 190, L21.