Optical counterparts for X-ray sources in M 31.

Einstein Observatory X-ray position (both IPC and HRI) for 117 sources around M31 have been examined with 1000 A/mm slitless spectral plates obtained at the prime focus of the Canada-France-Hawaii Telescope (CFHT). A variety of possible counterparts is found within the error circles of the source positions, including globular clusters, foreground stars, faint blue stars, and a compact galaxy. For about half of the sources, no candidate object sufficiently near the X-ray position was visible on the plates which reach to a B-mag of about -3.5. Crowding in the nucleus of M31 made it impossible to examine the source positions less than 2 to 3 arcmin from the center of the galaxy. This paper lists all sources with their suggested optical identifications and gives finding charts for some of the stars. A brief comparison is made among the X-ray sources in M31, the Magellanic Clouds, and the Galaxy.