A new X-ray , UBVR I _ { c } , and 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 \pm 0.18 and 3.77 \pm 0.19 , 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 UBVR I _ { c } JH K _ { s } data for 19 spectroscopically-observed cluster members , yielding R _ { V } = 3.85 \pm 0.07 .
The derived distance to Westerlund 2 of d = 2.85 \pm 0.43 kpc places the cluster on the far side of the Carina spiral arm .
The cluster ’ s age is no more than \tau \sim 2 \times 10 ^ { 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 .