A list of optically warped spiral galaxies with basic position and geometric parameters is presented in Sanchez-Saavedra, M.L., Battaner, E., & Florido, E. MNRAS, 246, 458-462, 1990. The sample is based on all northern-hemisphere NGC spiral galaxies with log R₂₅ > 0.57 as inspected on the Palomar Observatory Sky Survey plates.

The galaxies were classified on a four-point scale:

0 = no warp

1 = barely perceptible warp

2 = clear warp

3 = very clear warp

The frequency of warps was found to be high with 42 out of the 86 galaxies examined being observed to exhibit a warp. Because of geometric projection effects it is concluded that the true fraction of warps is even higher than that directly observed, perhaps 83%.

Proceedings of a workshop on warped disks and inclined rings can be found in "Warped Disks and Inclined Rings around Galaxies" eds. S. Casertano, P.D. Sackett, & F.H. Briggs, Cambridge University Press, Cambridge 1991.

Addition discussion can be found in

1. Florido, E., Battaner, E., Prieto, M., Mediavilla, E., & Sanchez-Saavedra, M.L., Mon. Not. R. Astron. Soc. 193, 251 (1991)
2. Kamphuis, J., & Briggs, F., Astron. Astrophys. 335, 253 (1992)
3. Quillen, A.C., Zeeuw, P.T. de, Phinney, E.S., & Phillips, T.G., Astrophys. J. 121, 391 (1992)