Westerlund 2

Starbox begin
name=WR 20a Starbox observe
epoch=J2000
ra=10h 23m 58.02s
dec=-57° 45' 48.9"'
appmag_v=15.0
constell=Carina Starbox character
class=WN6ha + WN6ha
b-v=-0.33
u-b=?
variable=Eclipsing Starbox astrometry
radial_v=0.0
prop_mo_ra=0.0
prop_mo_dec=0.0
parallax=0.0| p_error=0.0
distance= 7900 ± 600
absmag_v=13.5 Starbox detail
mass=82.7 +/- 5.5 and 81.9 +/- 5.5
radius= 19.3 +/- 0.5 and 19.3 +/- 0.5
luminosity=(1.15 +/-0.15) 10^6
temperature=43000 +/- 2000
metal=?
rotation=?
age=?
orbital period 3.7 daysStarbox catalog
names= GEN# +4.38020004, THA 35-II-36, Cl* Westerlund 2, MSP 240, 2MASS J10235800-5745489, UBV M 40466, Cl Westerlund 2 4.

Westerlund 2 is a young massive obscured star cluster 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 contains a dozen of 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 "Wolf-Rayet stars in disguise", i.e. they are core hydrogen burning stars, just like the sun. Due to their large mass loss rate the appear to be Wolf Rayet stars.

The core of the cluster contains at least five O6-7V stars within a radius of 15 arcsec. 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.

The system is located 20,000 light-years from the earth towards the southern constellation Carina. It was discovered by a team led by Krzysztof Stanek of Harvard University using the Las Campanas Observatory in Chile.

[http://chandra.harvard.edu/photo/2008/wd2/wd2.jpgChandra Image of Westerlund 2]

WR20a is one of the most massive binary system known to day, for which the masses of the components are accurately measured. Each star in the system has about eighty times the mass of our sun. It not clear why this system is located away form the center of the cluster. It is possible that the system was formed in the core, but that it got ejected by dynamical inteactions.

Every 3.6 days the two star in this system revolve around each other. Although the stars are in very tight orbit, both stars in the system are detached. It is to be expexted that within a million years the two will expand and come into contact. A large Nitrogen abundance has been measured on the surface of the stars, about six times the Nitrogen abundance of measured in the sun. This nitrogen is probably produced in deeper layers of the star and mixed towards the surface by rotational mixing.

WR20b seems to be single star, slightly fainter than the faintest star of WR20a.

References

* [http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=WR20a&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id Simbad]
* [http://chandra.harvard.edu/photo/2008/wd2/wd2_hand.html Chandra Image of Westerlund 2]
* [http://arxiv.org/abs/astro-ph/0405338 Bonanos et al 2004: The light curve of WR20a]
* [http://arxiv.org/abs/astro-ph/0404551 Rauw et al 2004: The radial velocity curve WR20a]