The Starburst–Interstellar Medium Interaction in NGC 1569. I. Location and Nature of H[CLC]e[/CLC] [CSC]ii[/CSC] Sources Using [ITAL]HUBBLE SPACE TELESCOPE[/ITAL] WFPC2 Imagery

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Abstract
We present the detection of He II sources in the Im galaxy NGC 1569 from Hubble Space Telescope WFPC2 imagery. Of the 15 detections, seven were Wolf-Rayet 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 conclude that the equivalent of 51 ± 19 WNL stars have been detected in NGC 1569, and we have estimated the total Wolf-Rayet population in NGC 1569 as 78 ± 51. These numbers are compared with the Wolf-Rayet stellar populations in the SMC, LMC, Milky Way, and other starburst galaxies relative to their luminosities, dynamical masses, and ionized gas masses. Previous to this study, Wolf-Rayet stars in NGC 1569 were not detected using ground-based imagery but were only indicated through long-slit spectroscopy. This is the first time the exact locations of the Wolf-Rayet stars in this nearby, well-studied, "poststarburst" galaxy have been determined.
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