Absolute stellar proper motions with reference to galaxies of the M 81 group

We report on the measurement of absolute proper motions of stars of magnitude 7 to 14.5 in a $2^\circ \times 2^\circ$ field in the region of the M 81 group of galaxies. This work is part of the Bonn program for the extragalactic link of Hipparcos. The proper motions were determined from a collection of photographic plates covering the time interval from 1894 to 1994. The absolute reference system for the proper motions is represented by the galaxies M 81, M 82 and NGC 3077, for which accurate optical reference positions were obtained by means of an image cross-correlation technique. For the majority of stars, the internal proper motion accuracy is better than 1 mas/a. The precision of the realization of the absolute system is found to be around 1 mas/a. In total, our measurements yield absolute proper motions for 24 Hipparcos stars and positions, proper motions and photometry for 330 additional stars including a number of visual binaries and high proper motion stars. Among the latter one G-type sub dwarf is identified. The results are relevant as a contribution to the Hipparcos link, but also as a database for kinematic investigations