Reference : A spectroscopic investigation of early-type stars in the young open cluster Westerlund 2
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Space science, astronomy & astrophysics
A spectroscopic investigation of early-type stars in the young open cluster Westerlund 2
Rauw, Grégor mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Sciences spatiales]
Sana, H. [Sterrenkundig Instituut "Anton Pannekoek", Universiteit van Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands]
Nazé, Yaël mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique observationnelle (sol et espace)]
Astronomy and Astrophysics
EDP Sciences
Yes (verified by ORBi)
Les Ulis
[en] binaries: eclipsing ; stars: early-type ; open clusters and associations: individual: Westerlund 2 ; Sun: fundamental parameters ; stars: individual: WR 20b ; stars: individual: Westerlund 2 MSP 18
[en] Context. The distance of the very young open cluster <ASTROBJ>Westerlund 2</ASTROBJ>, which contains the very massive binary system <ASTROBJ>WR 20a</ASTROBJ> and is likely associated with a TeV source, has been the subject of much debate. <BR /> Aims: We attempt a joint analysis of spectroscopic and photometric data of eclipsing binaries in the cluster to constrain its distance. <BR /> Methods: A sample of 15 stars, including three eclipsing binaries (<ASTROBJ>MSP 44</ASTROBJ>, <ASTROBJ>MSP 96</ASTROBJ>, and <ASTROBJ>MSP 223</ASTROBJ>) was monitored with the FLAMES multi-object spectrograph. The spectroscopic data are analysed together with existing B V photometry. <BR /> Results: The analysis of the three eclipsing binaries clearly supports the larger values of the distance, around 8 kpc, and rules out values of about 2.4 - 2.8 kpc that have been suggested in the literature. Furthermore, our spectroscopic monitoring reveals no clear signature of binarity with periods shorter than 50 days in either the WN6ha star <ASTROBJ>WR 20b</ASTROBJ>, the early O-type stars <ASTROBJ>MSP 18</ASTROBJ>, <ASTROBJ>MSP 171</ASTROBJ>, <ASTROBJ>MSP 182</ASTROBJ>, <ASTROBJ>MSP 183</ASTROBJ>, <ASTROBJ>MSP 199</ASTROBJ>, and <ASTROBJ>MSP 203</ASTROBJ>, or three previously unknown mid O-type stars. The only newly identified candidate binary system is <ASTROBJ>MSP 167</ASTROBJ>. The absence of a binary signature is especially surprising for WR 20b and MSP 18, which were previously found to be bright X-ray sources. <BR /> Conclusions: The distance of Westerlund 2 is confirmed to be around 8 kpc as previously suggested based on the spectrophotometry of its population of O-type stars and the analysis of the light curve of WR 20a. Our results suggest that short-period binary systems are not likely to be common, at least not among the population of O-type stars in the cluster. Based on observations collected at the European Southern Observatory (Cerro Paranal, Chile).Appendix A is available in electronic form at <A href=""></A>

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