Distribution and motions of HI in M 31.

Based on high-resolution H I data obtained from a new survey of M31 made with the Westerbork SRT in the 21-cm line of atomic hydrogen, a new model has been constructed. The model is an extension of the model derived for the inner part of the Galaxy by Burton and Liszt (1978); only the main characteristics are discussed, details being deferred to a paper in preparation. In the model, M31 is assumed to have a warp, where the degree of warp that varies as the sine of azimuth. The line of nodes of the warp runs parallel to the major axis of M31 in such a manner that it bends toward the observer on the near side of the Galaxy and away on the far side. The rotation curve is flat at a circular velocity of 260 km/s beyond 5.2 kpc, rising linearly from 0 km/s at the center to the maximum velocity. Position-velocity maps for the Galaxy and the model are given. A detailed comparison of the characteristics of the M31 and the Milky Way warps is promised in the upcoming paper.