Optical structure and star formation in blue compact dwarf galaxies .1. Observations and profile decomposition

We present new B and R CCD surface photometry for a sample of 4 Blue Compact Dwarf Galaxies (BCDs) and 2 higher luminosity starburst galaxies. We find that the BCD surface brightness profiles (SBPs) can be generally well fitted by the sum of the light of 3 distinct components: 1) an exponential component at large radii, with or without a central flattening which describes the underlying older stellar population; 2) a plateau component at intermediate radii and 3) a gaussian component at small radii. The last 2 components describe the ongoing starburst superimposed on the older stellar component. We apply the 3-component decomposition scheme to 8 more BCDs from the literature and, for the total sample of 14 galaxies, derive structural properties such as central surface brightness and scale length, and perform a deprojection to obtain the luminosity density distribution for each component. We also derive B-R color profiles and find that BCDs show generally a reddening outwards, followed by a blueing beyond a transition radius.