In this paper we present some results concerning the effects of two instantaneous starbursts , separated by a quiescent period , on the dynamical and chemical evolution of blue compact dwarf galaxies .
In particular , we compare the model results to the galaxy IZw18 , which is a very metal-poor , gas-rich dwarf galaxy , possibly experiencing its first or second burst of star formation .
We follow the evolution of a first weak burst of star formation followed by a second more intense one occurring after several hundreds million years .
We find that a galactic wind develops only during the second burst and that metals produced in the burst are preferentially lost relative to the hydrogen gas .
We predict the evolution of several chemical abundances ( H , He , C , N , O , \alpha -elements , Fe ) in the gas inside and outside the galaxy , by taking into account in detail the chemical and energetical contributions from type II and Ia supernovae .
We find that the abundances predicted for the star forming region are in good agreement with the HII region abundances derived for IZw18 .
We also predict the abundances of C , N and O expected for the HI gas to be compared with future FUSE abundance determinations .
We conclude that IZw18 must have experienced two bursts of star formation , one occurred \sim 300 Myr ago and a present one with an age between 4-7 Myr .
However , by taking into account also other independent estimates , such as the color-magnitude diagram and the spectral energy distribution of stars in IZw18 , and the fact that real starbursts are not instantaneous , we suggest that it is more likely that the burst age is between 4 and 15 Myr .