1. Askins, B.S. 1976. Applied Optics. 15, 2860–2864.
2. Babcock, et al. 1974. Astron. J. 79, 1479–1487.
3. Barbon, R., Capaccioli, M., Tarenghi, M. 1975. Astron. Astrophys. 38, 315–321.
4. Baum, W.A. 1955. in Trans. IAU. Vol. 9, 681–686.
5. Baum, W.A. 1962. Stars and Stellar System, Vol. 2., Astronomical Techniques, W.A. Hiltner, Ed. pp1–33. Univ. of Chicago Press.