Astron. J., 150, 78 (2015/September-0)
A high-resolution multiband survey of westerlund 2 with the Hubble Space Telescope. I. Is the massive star cluster double?
ZEIDLER P., SABBI E., NOTA A., GREBEL E.K., TOSI M., BONANOS A.Z., PASQUALI A., CHRISTIAN C., DE MINK S.E. and UBEDA L.
Abstract (from CDS):
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) versus F 814W 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 e 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.
H II regions - infrared: stars - open clusters and associations: individual: Westerlund 2 - stars: early-type - stars: pre-main sequence - techniques: photometric
In Table 7: 10:24:01.920 -57:45:32 is a probable misprint for 10:24:00.20 -57:45:32.6, and 10:23:00.480 -57:45:24.01 for 10:24:00.48 -57:45:24.0.
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