We present spectroscopic observations in the near-ultraviolet, optical
, and near-infrared of the superstar clusters (hereafter SSC A and SSC
B) in NGC 1569. Previous studies have suggested that they are in a po
ststarburst phase. However, our data suggest a younger mean age and a
significant age spread. The spectrum of SSC A shows the Wolf-Rayet (W-
R) feature at 4686 Angstrom, with a luminosity equivalent to 20-40 WNL
stars. This qualifies NGC 1569 as a W-R galaxy. The small Palmer jump
detected in both clusters also suggests strongly the presence of very
massive (and therefore very young) stars. Evolutionary synthesis mode
ls are used to constrain the star formation scenario by explaining the
spectral energy distribution, the Palmer jump, the equivalent width (
EW) of the W-R bump, and the near-infrared Ca II triplet in absorption
. No single-age stellar population fits all these constraints. We prop
ose a two-burst model, with the younger burst having an age of 3 Myr (
2 Myr for SSC B) and the older one having an age of 9 Myr (8 Myr for S
SC B), to explain the simultaneous presence of hot massive stars and r
ed supergiants. We speculate that sequential star formation is taking
place in the SSCs of NGC 1569, with the younger burst probably located
in the surroundings of and initiated as a consequence of the energeti
c stellar activity of the older central compact cluster. A deficit of
ionized gas was found around the SSCs, which we ascribe to the strong
stellar winds and supernova explosions of the older burst removing the
gas from the vicinity of the clusters.