STARBURSTS IN THE CLUMPY IRREGULAR GALAXY VV-523

The following is a study of the irregular clumpy galaxy VV 523 (NGC 39 91 - UGC 6933 - IRAS 11549+3237). High angular resolution BRI CCD imag es were obtained using the 2m, Bernard Lyot telescope at the Observato ire du Pic du Midi. Long slit spectra with dispersions of 33 and 260 A ngstrom mm(-1) were obtained with the Carelec spectrograph using the 1 .93 m telescope at the Observatoire de Haute Provence. Three emitting regions A, B and C are resolved along the slit. A wavelet analysis ena bled detection of about twenty clumps and also measurements of their s ize (about 300 pc) and brightness. The measurements were interpreted u sing the evolutionary population synthesis models of Mas-Hesse and Kun th. The model was constrained by matching the metallicity, H beta equi valent widths, and colour measurements. We found that we were dealing with instantaneous starbursts rather than continuous star formation. O ur data are consistent with an Initial Mass Function slope of 3 and th e ages of the starbursts were found to be between 5 and 6.6 mega-years . The model may be used to predict the visible, infrared and UV proper ties observed. The burst region total mass is estimated to be about 4 10(7) M. while the rotational mass of the galaxy is 2.7 10(10) M.. A c orrelation is found between the location on the galaxy and the colour of the clumps; our spectroscopic data show that it corresponds to a va riation in starburst ages. This feature may be interpreted as a conseq uence of a self-propagating, star formation mechanism.