Reference : Chandra monitoring of the very massive binary WR20a and the young massive cluster Wes...
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Earth sciences & physical geography
http://hdl.handle.net/2268/2777
Chandra monitoring of the very massive binary WR20a and the young massive cluster Westerlund 2
English
Nazé, Yaël mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Sciences spatiales >]
Rauw, Grégor mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE) - Sciences spatiales >]
Manfroid, Jean mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO) >]
2008
Astronomy and Astrophysics
EDP Sciences
483
1
171-182
Yes (verified by ORBi)
International
0004-6361
Les Ulis
France
[en] X-rays : stars ; stars : individual : WR20a ; stars : individual : WR20b ; galaxy : open clusters and associations : individual : Westerlund 2
[en] Context. Westerlund 2 is a young and massive, obscured stellar cluster of our Galaxy. It harbors the most massive star with well-determined parameters, WR20a (82 + 83 M-circle dot), a dozen very early O-type stars (O3-7), and a wealth of PMS stars. Although of clear significance, this star cluster has not been well-studied. Aims. The high-energy properties of this cluster, especially those of its early-type stars are examined in detail. The variability of the X-ray sources is investigated. Methods. A monitoring of the field was performed using three Chandra observations. This dataset probes daily as well as monthly to yearly timescales and provides the deepest X-ray view of the cluster to date. Results. The two Wolf-Rayet stars WR20a (WN6ha+WN6ha) and WR20b (WN6ha) were analyzed in detail. They are both luminous and display hard spectra, but WR20b does not appear to vary. In contrast, WR20a, a known eclipsing, colliding-wind binary, brightens in the X-ray domain during 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 x 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 those could be analyzed spectroscopically. Four are overluminous, but the others have typical LX/LBOL ratios, suggesting that several O-type objects are actually binaries. Variability at the similar to 2 sigma level is detected for a majority of the sources, of unknown origin for 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 correspond to the TeV source HESS J1023-575. The X-ray properties of PMS objects, in particular the brightest flaring ones, are also investigated. They provided an additional argument in favor of a large distance (similar to 8 kpc) for the cluster.
Researchers ; Professionals
http://hdl.handle.net/2268/2777
10.1051/0004-6361:20078851
http://arxiv.org/abs/0801.0647

File(s) associated to this reference

Fulltext file(s):

FileCommentaryVersionSizeAccess
Open access
0801.pdfAuthor postprint194.6 kBView/Open

Bookmark and Share SFX Query

All documents in ORBi are protected by a user license.