We report the results of a surface photometry study of a sample of 23 Blue Compact Dwarf Galaxies, selected from the two surveys of Byurakan. An atlas of isophotal maps and brightness distribution profiles has been produced.
From these profiles, we classify the objects in three groups:
1) 7 objects whose brightness distributions are described by an exponential
law, supposed to be characteristic of disk-like (flattened) galaxies. These
objects seem to be closely related to classical Magellanic irregulars. We
could not draw any conclusion on their flattening without kinematical data.
2) 10 objects whose brightness distributions are described by an r1/4 law valid for classical luminous spheroidal systems. These galaxies have generally smooth isophotes at all levels of brightness, except in the very center. Many of them however show obvious departures from axisymmetry as boxy isophotes, off-centered "nuclei'' or double central components. The discovery of a significant fraction of r1/4 galaxies in a sample of BCDGs confirms and extends previous results by Kunth et al. (1988) and Loose & Thuan (1983).
3) 4 intermediate types showing a superimposition of a r1/4 law and a exponential law. Their isophotal maps show irregular patterns in the inner parts surrounded by a regular envelope. Two remaining objects escape any classification.
Two galaxies are members of close physical pairs (Mk 1480-81 and Mk 1308) and may be influenced by tidal interaction effects that could be responsible for the presently observed burst. The other objects have no known physical neighbour. However, a number of features observed in their images may be linked to recent past interactions or ongoing merging phenomena (boxy internal isophotes, double nuclei structures, asymmetric envelopes). It is still premature to draw conclusions on the triggering agents of the starburst without complementary spectro-imaging investigations that are presently under progress.
The color distribution of our sample is representative of a blue galaxy population. However, some objects exhibit strong color gradients implying the presence of stellar populations of evolutionary states distinct from that of the blue star-forming region.
The luminosity-radius relationship has been investigated and the selection bias towards objects with a centrally located burst that provides excess of light in B band is obvious in the data. This bias itself takes origin in the selection mode of the original surveys.
The high median values of the mean surface brightness inside the effective radius, the significantly large mean value of the concentration index and the average short scale length of the brightness distribution as measured by the effective radii altogether demonstrate that our sample indeed contains "compact'' dwarf galaxies in overwhelming majority.
A more quantitative discussion will take place upon completion of this surface photometry survey on an extended sample of more than 50 objects.
Acknowledgements
Part of this research was supported by PICS
(Programme International de Coopération Scientifique) 
of
CNRS between France and Armenia. The financial support of International
Association for the Promotion of Cooperation with Scientist from the
Independent States of the former Soviet Union (INTAS) is gratefully
acknowledged. Special thanks go to Jivan Stepanian who kindly communicated
finding charts, accurate coordinates, redshifts and provisional magnitudes
for many unpublished objects in the SBS.