Chandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund2

Details Chandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund2 Chandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund2

2008-01-04

arxiv.org/abs/0801.0647v1

Astron.Astrophys.483:171-182,2008

Astronomy and Astrophysics

Astrophysics

accepted by A&A, 10 pages, 7 figures (available in jpg)

Scientific paper

10.1051/0004-6361:20078851

Results: The two Wolf-Rayet stars WR20a (WN6ha+WN6ha) and WR20b (WN6ha) were analyzed in detail. They are both very luminous and display very hard spectra, but WR20b does not seem to vary. On the contrary, WR20a, a known eclipsing, colliding-wind binary, brightens in the X-ray domain during the eclipses, i.e. when the collision is seen face-on. This can be explained by the properties of the wind-wind collision zone, whose high density leads to a large absorbing column (2 10^24 cm^-2).All twelve O-type stars previously classified spectroscopically, two eclipsing binaries previously identified and nine newly identified O-type star candidates are detected in the high energy domain; ten of them could be analyzed spectroscopically. Four are overluminous, but the others present typical L_X/L_BOL ratios, suggesting that several O-type objects are actually binaries. Variability at the ~2sigma level was detected for a majority of the sources, of unknown origin for the putatively single objects. Faint, soft, diffuse emission pervades the entire field-of-view but no clear structure can be identified, even at the position of a blister proposed to be at the origin of the TeV source HESS J1023-575. Finally, the X-ray properties of PMS objects were also investigated, in particular the brightest flaring ones. They provided an additional argument in favor of a large distance (~8kpc) for the cluster.

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