\documentstyle[paasms4,pptwocol]{preprint}
\input pub.sty

\begin{document}

\title{ARE THE SUPER STAR CLUSTERS OF NGC~1569\\
~\\
IN A POST-STARBURST PHASE?}

\author{Rosa M. Gonz\'alez Delgado\/\thanks{Visiting astronomer, Kitt Peak 
National Observatory, NOAO, operated by AURA, Inc.\ under cooperative agreement 
with the National Science Foundation.} and Claus Leitherer\\
\\
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD
21218\\
\\
Electronic mail: gonzalez@stsci.edu; leitherer@stsci.edu\\
\and
Timothy Heckman\/\samethanks{1}\\
\\
Department of Physics \& Astronomy, JHU, Baltimore, MD 21218\\
\\
Electronic mail: heckman@pha.jhu.edu\\
\and
Miguel Cervi\~no\\
\\
LAEFF-INTA, Apdo. 50727, E-28080 Madrid, Spain\\
\\
Electronic mail: mcs@laeff.esa.es}

\pub{ApJ}
\recacc{3 November 1996}{17 January 1997}

\maketitle

\abstract{
We present spectroscopic observations in the near ultraviolet, optical, and
near infrared of the Super Star Clusters (hereafter SSC~A and SSC~B) in NGC~1569. 
Previous studies have suggested that they are in a post-starburst phase.  However, 
our data suggest a younger mean age and a significant age spread. The spectrum of 
SSC~A shows the Wolf-Rayet (WR) feature at 4686~\AA, with a luminosity equivalent 
to 20--40 WNL stars. This qualifies NGC~1569 as a WR galaxy. The small Balmer jump 
detected in both clusters also suggests strongly the presence of very massive (and 
therefore very young) stars. Evolutionary synthesis models are used to constrain the 
star formation scenario by explaining the spectral energy distribution (SED), the 
Balmer jump, the equivalent width (ew) of the WR bump, and the near infrared Ca~II 
triplet in absorption. No single age stellar population fits all these constraints.
We propose a two-burst model, with the younger burst age of 3~Myr (2~Myr for SSCB), 
and the older one with an age of 9~Myr (8~Myr for SSC~B), to explain the simultaneous
presence of hot massive stars and red 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
energetic stellar activity of the older central compact cluster. A deficit of ionized 
gas was found around the SSCs, that we ascribe to the strong stellar winds and supernova 
explosions of the older burst removing the gas from the vicinity of the clusters.}