Photometric investigation of the central region of the M31 Andromeda nebula

Photoelectric UBV observations of the central region of M 31 were carried out in 166 points at the distances 54''-351'' from the center. The results are used to study the structure of the central condensation (bulge) of M 31. It is shown that the isophotes of the surface brightness are approximated by the ellipses with different semi-axes ratio eta=b/a (from approximately 0.9 to approximately 0.6) and position angles (from approximately 70 deg -60 deg to approximately 45 deg). The central condensation has the complex structure, possibly with a bar. The surface brightness distribution is represented by the de Vaucouleur formula (asup(1/4)), as well as by some other ones (asup(1/3) and asup(1/5)). The nucleus is located asymmetrically in the central condensation. The maximum displacement is equal to 22'' to North-West from the center of the most distant considered U isophote with a=368''. The apparent displacement of the nucleus with respect to the distant isophotes is due to the distribution of dust matter revealed by color data (the colors B-V and U-B correspond to dust distribution in the central condensation of M 31. The stellar population changes when approaching the center of M 31 where the red giants are dominating