The starburst-interstellar medium interaction in NGC 1569. I. Location andnature of HeII sources using Hubble Space Telescope WFPC2 imagery

We present the detection of He II sources in the Im galaxy NGC 1569 from Hu bble Space Telescope WFPC2 imagery. Of the 15 detections, seven were Wolf-R ayet stars, five were stellar clusters with associated He II emission, and three were sources of unknown origin. The detected Wolf-Rayet stars' colors and magnitudes are similar to those of Large Magellanic Cloud late-type WN stars. The physical origins of the other He II sources are discussed. We c onclude that the equivalent of 51 +/- 19 WNL stars have been detected in NG C 1569, and we have estimated the total Wolf-Rayet population in NGC 1569 a s 78 +/- 51. These numbers are compared with the Wolf-Rayet stellar populat ions in the SMC, LMC, Milky Way, and other starburst galaxies relative to t heir luminosities, dynamical masses, and ionized gas masses. Previous to th is study, Wolf-Rayet stars in NGC 1569 were not detected using ground-based imagery but were only indicated through long-slit spectroscopy. This is th e first time the exact locations of the Wolf-Rayet stars in this nearby, we ll-studied, "poststarburst" galaxy have been determined.