BV RI imaging of M 51-type pairs - II. Bulge and disk parameters

We present decompositions of azimuthally averaged surface brightness :profi les in optical B, V, R and I-bands for a sample of 40 M 51-type interacting galaxies. The profiles were modelled by an exponential disk and a spherica l bulge described either by the R-1/4 law or by an exponential function. Ha lf of the galaxies were well fitted by both bulge models, whereas for 35% t he exponential function was a better choice. Special care was taken on elim inating superpositions of the companion galaxies. The mean B-band central s urface brightness mu(0) was found to be 21.5 mag arcsec(-2), which is near to the value originally found by Freeman (1970), but the scatter was fairly large. Galaxy interactions have strongly modified the disks in many of the galaxies in the sample. For example, six of them had extremely flat bright ness profiles outside the exponential part of the disk, and many showed sig nificant isophotal twists.