Article (Scientific journals)
Early-type stars in the core of the young open cluster Westerlund 2
Rauw, Grégor; Manfroid, Jean; Gosset, Eric et al.
2007In Astronomy and Astrophysics, 463 (3), p. 981-991
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Keywords :
Galaxy : open clusters and associations : individual : Westerlund 2; stars : early-type; stars : binaries : eclipsing; stars : fundamental parameters; stars : individual : WR20a
Abstract :
[en] Aims. The properties of the early-type stars in the core of the Westerlund 2 cluster are examined in order to establish a link between the cluster and the very massive Wolf-Rayet binary WR 20a as well as the H II complex RCW 49. Methods. Photometric monitoring as well as spectroscopic observations of Westerlund 2 are used to search for light variability and to establish the spectral types of the early-type stars in the cluster core. Results. The first light curves of the eclipsing binary WR 20a in B and V filters are analysed and a distance of 8 kpc is inferred. Three additional eclipsing binaries, which are probable late O or early B-type cluster members, are discovered, but none of the known early O-type stars in the cluster displays significant photometric variability above 1% at the 1-sigma level. The twelve brightest O-type stars are found to have spectral types between O3 and O6.5, significantly earlier than previously thought. Conclusions. The distance of the early-type stars in Westerlund 2 is established to be in excellent agreement with the distance of WR20a, indicating that WR20a actually belongs to the cluster. Our best estimate of the cluster distance thus amounts to 8.0 +/- 1.4 kpc. Despite the earlier spectral types, the currently known population of early-type stars in Westerlund 2 does not provide enough ionizing photons to account for the radio emission of the RCW49 complex. This suggests that there might still exist a number of embedded early O-stars in RCW49.
Disciplines :
Earth sciences & physical geography
Author, co-author :
Rauw, Grégor  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE)
Manfroid, Jean  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)
Gosset, Eric ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE)
Nazé, Yaël  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE)
Sana, H.
De Becker, Michaël  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Groupe d'astrophysique des hautes énergies (GAPHE)
Foellmi, C.
Moffat, A. F. J.
Language :
English
Title :
Early-type stars in the core of the young open cluster Westerlund 2
Publication date :
March 2007
Journal title :
Astronomy and Astrophysics
ISSN :
0004-6361
eISSN :
1432-0746
Publisher :
Edp Sciences S A, Les Ulis Cedex A, France
Volume :
463
Issue :
3
Pages :
981-991
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 06 January 2009

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