  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 H$\alpha$ ($F658N$) and Pa$\beta$ ($F128N$) 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 $\sim4.16 \pm 0.33$~kpc. With
zero-age-main-sequence fitting to two-color-diagrams, we derive a value of
total to selective extinction of $R_V=3.95 \pm 0.135$. 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 $\sim 20 \%$ lower stellar
surface density.

Solar and Stellar Astrophysics