Star formation and stellar populations in the Wolf-Rayet(?) luminous compact blue galaxy IRAS 08339+6517

Aims. IRAS 08339+6517 is a luminous infrared and Ly alpha-emitting starburst galaxy that possesses a dwarf companion object at a projected distance of 56 kpc. An H I tidal tail has recently been detected between both galaxies, suggesting that about 70% of the neutral gas has been ejected from them. Methods. We present deep broad-band optical images, together with narrow band H alpha CCD images, and optical intermediate-resolution spectroscopy of both galaxies. Results. The images reveal interaction features between both systems and strong Ha emission in the inner part of IRAS 08339+6517. The chemical composition of the ionized gas of the galaxies is rather similar. The analysis of their kinematics also indicates interaction features and reveals an object that could be a candidate tidal dwarf galaxy or a remnant of an earlier merger. Our data suggest that the Hi tail has been mainly formed from material stripped from the main galaxy. We find weak spectral features that could be attributed to the presence of Wolf-Rayet stars in this starburst galaxy and estimate an age of the most recent burst of around 4 - 6 Myr. A more evolved underlying stellar population, with a minimal age between 100 - 200 Myr, is also detected and fits an exponential intensity profile. A model which combines 85% young and 15% old populations can explain both the spectral energy distribution and the H I Balmer and He I absorption lines presented in our spectrum. The star formation rate of the galaxy is consistently derived using several calibrations, giving a value of similar to 9.5 M-. yr(-1). Conclusions. IRAS 08339+6517 does satisfy the criteria of a luminous compact blue galaxy, rare objects in the local universe but common at high redshifts, being a very interesting target for detailed studies of galaxy evolution and formation.