Westerlund 2

Hubble Space Telescope image of the cluster Westerlund 2 and its surroundings

Westerlund 2 is an obscured compact young star cluster (perhaps even a super star cluster[1]) in the Milky Way, with an estimated age of about one or two million years. It contains some of the hottest, brightest, and most massive stars known. The cluster resides inside a stellar breeding ground known as Gum 29, located 20,000 light-years away in the constellation Carina.[2]

Composition

The cluster contains a dozen O stars, of which at least three are eclipsing binaries, many pre–main sequence stars and two Wolf–Rayet stars: the binary WR20a and the single star WR20b, all of spectral type WN6ha. They are probably not actually Wolf-Rayet stars, i.e. they are core-hydrogen-burning stars, just like the sun, but due to their large mass loss rate they appear to be Wolf Rayet stars.[3]

It was shown recently that the core of the cluster contains several examples of rare very hot stars.[4] Just outside the cluster a massive eclipsing binary WR20a is found at 30 arcseconds (about 1.1 pc in projection), the bright yellow spot just on the lower right side of the cluster center.

Discovery

Westerlund 2 surrounded by stellar nursery RCW 49.

As its name indicates, the Westerlund 2 cluster was discovered by Bengt Westerlund in the sixties[5] but its stellar content was assessed only in later years[6]

References

  1. ↑ Y. Fukui et al. "Cloud-cloud collision which triggered formation of the super star cluster RCW38". arXiv:1504.05391.
  2. ↑ "Hubble Space Telescope Celebrates 25 Years of Unveiling the Universe". NASA. April 23, 2015.
  3. ↑ Rauw et al. (4 March 2005). "The spectrum of the very massive binary system WR 20a (WN6ha + WN6ha): Fundamental parameters and wind interactions". Astronomy & Astrophysics 432 (3): 985–998. doi:10.1051/0004-6361:20042136.
  4. ↑ Rauw et al. (1 March 2007). "Early-type stars in the core of the young open cluster Westerlund 2". Astronomy & Astrophysics 463 (3): 981–991. doi:10.1051/0004-6361:20066495.
  5. ↑ Bengt Westerlund (1 March 1961). "A Heavily Reddened Cluster in Ara.". Astronomical Journal 70: 57. Bibcode:1961AJ.....66T..57W. doi:10.1086/108585.
  6. ↑ Moffat et al. (1 August 1961). "New Wolf-Rayet stars in Galactic open clusters - Sher 1 and the giant H II region core Westerlund 2". Astronomical Journal 102: 642–653. Bibcode:1991AJ....102..642M. doi:10.1086/115897.

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