We present first results from a high resolution multi-band survey of the
Westerlund 2 region with the Hubble Space Telescope. Specifically, we imaged
Westerlund 2 with the Advanced Camera for Surveys through the F555W, F814W,
and F658N filters and with the Wide Field Camera 3 in the F125W, F160W,
and F128N filters. We derive the first high resolution pixel-to-pixel map of
the color excess E(B−V)g of the gas associated with the cluster, combining
the Hα (F658N) and Paβ (F128N) line observations. We
demonstrate that, as expected, the region is affected by significant
differential reddening with a median of E(B−V)g=1.87~mag. After separating
the populations of cluster members and foreground contaminants using a
(F814W−F160W) vs. F814W color-magnitude diagram, we identify a pronounced
pre-main-sequence population in Westerlund 2 showing a distinct turn-on. After
dereddening each star of Westerlund 2 individually in the color-magnitude
diagram we find via over-plotting PARSEC isochrones that the distance is in
good agreement with the literature value of ∼4.16±0.33~kpc. With
zero-age-main-sequence fitting to two-color-diagrams, we derive a value of
total to selective extinction of RV=3.95±0.135. A spatial density map of
the stellar content reveals that the cluster might be composed of two clumps.
We estimate the same age of 0.5-2.0 Myr for both clumps. While the two clumps
appear to be coeval, the northern clump shows a ∼20% lower stellar
surface density.Comment: 24 pages, 27 figures, 7 tables; Accepted for publication to The
Astronomical Journa