1. Aitken, D.K., 1981 in IAU Symposium 96, Infrared Astronomy, ed. C.G. Wynn-Willians and D.P. Cruikshank (D.Reidel), 207.
2. Allen, C.W., 1973: Astrophysical Quantities (3rd ed.: London: Athlone).
3. Bregman, J.D., Dinerstein, H.L, Goebel, J.H., Lester, D.F., Witteborn, F.C. and Rank, D.M., 1983, Ap.J., 274, 666.
4. Crawford, M.K., Tielens, A.G.G. and Allamandola, L.J., 1985, Ap. J. Letts., 293, L45.
5. Dulley, W.W. and Williams, D.A., 1981, Mon. Not. Roy. Astrn. Soc., 196, 269.