The distance to the young open cluster Westerlund 2
  A new X-ray, {\it UBVR}$I_c$, and {\it JHK$s$} study of the young cluster
Westerlund 2 was undertaken to resolve discrepancies tied to the cluster's
distance. Existing spectroscopic observations for bright cluster members and
new multi-band photometry imply a reddening relation towards Westerlund~2
described by $E_{U-B}/E_{B-V}=0.63 + 0.02\;E_{B-V}$. Variable-extinction
analyses for Westerlund~2 and nearby IC 2581 based upon spectroscopic distance
moduli and ZAMS fitting yield values of $R_V=A_V/E_{B-V}=3.88\pm0.18$ and
$3.77\pm0.19$, respectively, and confirm prior assertions that anomalous
interstellar extinction is widespread throughout Carina (e.g., Turner 2012).
The results were confirmed by applying the color difference method to {\it
UBVR$I_c$JH$K_s$} data for 19 spectroscopically-observed cluster members,
yielding $R_V=3.85\pm0.07$. The derived distance to Westerlund~2 of
$d=2.85\pm0.43$ kpc places the cluster on the far side of the Carina spiral
arm. The cluster's age is no more than $\tau \sim2\times10^6$ yr as inferred
from the cluster's brightest stars and an X-ray (Chandra) cleaned analysis of
its pre-main-sequence demographic. Four Wolf-Rayet stars in the cluster core
and surrounding corona (WR20a, WR20b, WR20c, and WR20aa) are likely cluster
members, and their inferred luminosities are consistent with those of other
late-WN stars in open clusters. The color-magnitude diagram for Westerlund~2
also displays a gap at spectral type B0.5 V with associated color spread at
higher and lower absolute magnitudes that might be linked to close binary
mergers. Such features, in conjunction with the evidence for mass loss from the
WR stars, may help to explain the high flux of $\gamma$ rays, cosmic rays, and
X-rays from the direction towards Westerlund~2.
