The Distance to the Massive Galactic Cluster Westerlund 2 from a Spectroscopic and HST Photometric Study

  title={The Distance to the Massive Galactic Cluster Westerlund 2 from a Spectroscopic and HST Photometric Study},
  author={Carlos A. Vargas Alvarez and Henry A. Kobulnicky and David Bradley and Sheila J. Kannappan and Mark A. Norris and Richard Jacob Cool and Brendan P. Miller},
  journal={The Astronomical Journal},
We present a spectroscopic and photometric determination of the distance to the young Galactic open cluster Westerlund 2 using WFPC2 imaging from the Hubble Space Telescope (HST) and ground-based optical spectroscopy. HST imaging in the F336W, F439W, F555W, and F814W filters resolved many sources previously undetected in ground-based observations and yielded photometry for 1136 stars. We identified 15 new O-type stars, along with two probable binary systems, including MSP 188 (O3 + O5.5). We… 
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