Spiral Structure in M31.

Luminous spiral arm features in M31 are presented as they would appear if the galaxy were to be viewed flat-on. The logarithmic spiral which best fits the star arms is r - 30'e0 130 The arms trail in rota[ion. Like other spirals studied by Danver, the pitch steepens somewhat to the inside and becomes lightly shallower to the outside. The derived pitch angle for the M31 spiral is it = 830, which is tightly wound compared to the average for spiral galaxies of it = 750 Even though M31 is tightly wound, it is pointed out that the distance between arms in M31 is about 4 kpc, or more than twice the distance that ippears to separate arms in our own Milky Way system. The spiral pattern outlined by 688 emission nebulae in M31 and the tilt of their plane are difficult to [nterpret. They occur predominantly between 8 and 14 kpc from the center and in some places they out[ine arm segments very well. If it is assumed that all emission nebulae are in a single, flat plane, however, [hen there is no projection factor which will give a rectified picture which looks like a continuous spiral rve. The most acceptable interpretation seems to be that the major part of M31 has an inclination of = t6 . The disk, however, is raised on the near side out of the plane to an inclination near i = 110, and this deformation persists into the vicinity of M32. M32 appears to be responsible for the deformation of the M31 plane, but since M32 appears projected off the end of a major spiral arm, it is possible that the perturbation may not be purely gravitational but may instead be partially or wholly plasma-magnetic.