Structure and stellar content of dwarf galaxies - I. B and R photometry of dwarf galaxies in the M 81 group

We have carried out CCD photometry in the Cousins B and R bands of 25 dwarf galaxy members and suspected members of the M 81 group of galaxies. Based on azimuthally averaged brightness profiles we have derived total magnitudes, effective radii, effective surface brightnesses, as well as galaxy diameters at various isophotal levels in both photometric bands. Best-fitting exponential parameters and B - R colour gradients are also given for these galaxies. The data will be interpreted, along with those of another supplementary paper, in Paper III of this series (to appear in the main journal). In two appendices we discuss the nature of a clustering of unusual low-surface brightness objects in the south-east corner of the M 81 group and show the luminosity function of its presently known members.