Is the massive star cluster Westerlund 2 double? : A high resolution multi-band survey with the Hubble Space Telescope

Westerlund 2 (Wd2) is one of the most massive young star clusters known in the Milky Way. The close proximity (4.16 kpc) to the Sun, and the young age (2.0 Myr) allow us to study star formation in detail at a high spatial resolution. We present results from our recent deep multi-band survey in the optical and near-infrared obtained with the Hubble Space Telescope. We demonstrated that, as expected, the region is affected by significant differential reddening with a median value of E(B − V) g = 1.87 mag. The distance was inferred from the dereddened color-magnitude diagrams using Padova isochrones. Analyzing the spatial distribution of stars we found that Wd2 consists of two sub-clumps, namely the main cluster of Westerlund 2 and a less well populated clump located to the North. We estimated the same age of 0.1–2.0 Myr for both sub-clumps, thus we conclude that they are likely coeval.