A spectroscopic investigation of early-type stars in the young open cluster Westerlund 2

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

Abstract :

[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="http://www.aanda.org">http://www.aanda.org</A>

Disciplines :

Space science, astronomy & astrophysics

Author, co-author :

Rauw, Grégor ; Université de Liège - ULiège > 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 ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique observationnelle (sol et espace)

Language :

English

Title :

A spectroscopic investigation of early-type stars in the young open cluster Westerlund 2

Publication date :

01 November 2011

Journal title :

Astronomy and Astrophysics

ISSN :

0004-6361

eISSN :

1432-0746

Publisher :

EDP Sciences, Les Ulis, France

Volume :

535

Pages :

A40

Peer reviewed :

Peer Reviewed verified by ORBi

Additional URL :

http://adsabs.harvard.edu/abs/2011A%26A...535A..40R

Commentary :

http://de.arxiv.org/abs/1109.1086

Available on ORBi :

since 12 December 2011

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Bibliography

Abdo, A.A., Ackermann, M., Ajello, M., et al. 2010, ApJS, 188, 405
Ackermann, M., Ajello, M., Baldini, L., et al. 2011, ApJ, 726, 35
Aharonian, F., Akhperjanian, A. G., Bazer-Bachi, A. R., et al. 2007, A&A, 467, 1075
Ascenso, J., Alves, J., Beletsky, Y., & Lago, M. T. V. T. 2007, A&A, 466, 137
Babel, J., & Montmerle, T. 1997, ApJ, 485, L29
Bonanos, A. Z., Stanek, K. Z., Udalski, A., et al. 2004, ApJ, 611, L33
Bonnell, I. A., Vine, S. G., & Bate, M. R. 2004, MNRAS, 349, 735
Churchwell, E., Whitney, B. A., Babler, B. L., et al. 2004, ApJS, 154, 322
Crowther, P. A., Schnurr, O., Hirschi, R., et al. 2010, MNRAS, 408, 731
Curcio, J. A., Drummeter, L. F., & Knestrick, G. L. 1964, Appl. Opt., 3, 1401
De Becker, M., Rauw, G., Manfroid, J., & Eenens, P. 2006, A&A, 456, 1121
Fukui, Y., Furukawa, N., Dame, T. M., et al. 2009, PASJ, 61, L23
Fullerton, A. W., Gies, D. R., & Bolton, C. T. 1996, ApJS, 103, 475
Furukawa, N., Dawson, J. R., Ohama, A., et al. 2009, ApJ, 696, L115
Hammersley, J. M., & Handscomb, D. C. 1964, Monte Carlo Methods (New York: Wiley)
Herbig, G. 1995, ARA&A, 33, 19
Hillwig, T. C., Gies, D. R., Bagnuolo, W. G. Jr., et al. 2006, ApJ, 639, 1069
Kerton, C. R., Ballantyne, D. R., & Martin, P. G. 1999, AJ, 117, 2485
Leonard, P. J. T., & Duncan, M. J. 1990, AJ, 99, 608
Mahy, L., Nazé, Y., Rauw, G., et al. 2009, A&A, 502, 937
Martins, F., & Plez, B. 2006, A&A, 457, 637
Moffat, A. F. J., Shara, M. M., & Potter, M. 1991, AJ, 102, 642
Nazé, Y. 2009, A&A, 506, 1055
Nazé, Y., Rauw, G., & Manfroid, J. 2008, A&A, 483, 171
Niemela, V. S., Gamen, R. C., Barbá, R. H., et al. 2008, MNRAS, 389, 1447
Rauw, G., Crowther, P. A., Eenens, P. R. J., Manfroid, J., & Vreux, J. M. 2002, A&A, 392, 563
Rauw, G., De Becker, M., Nazé, Y., et al. 2004, A&A, 420, L9
Rauw, G., Crowther, P. A., De Becker, M., et al. 2005, A&A, 432, 985
Rauw, G., Manfroid, J., Gosset, E., et al. 2007, A&A, 463, 981 (Paper I)
Rauw, G., Nazé, Y., Fernández Lajús, E., et al. 2009, MNRAS, 398, 1582
Sana, H., Rauw, G., Nazé, Y., Gosset, E., & Vreux, J.-M. 2006, MNRAS, 372, 661
Sana, H., Gosset, E., Nazé, Y., Rauw, G., & Linder, N. 2008, MNRAS, 386, 447
Sana, H., Gosset, E., & Evans, C. J. 2009, MNRAS, 400, 1479
Schmidt-Kaler, T. 1982, Physical Parameters of the Stars, Landolt-Börnstein Numerical Data and Functional Relationships in Science and Technology, New Series, Group VI, Vol. 2b (Berlin: Springer)
Schnurr, O., Casoli, J., Chené, A.-N., Moffat, A. F. J., & St-Louis, N. 2008, MNRAS, 389, L38
Schnurr, O., Moffat, A. F. J., Villar-Sbaffi, A., St-Louis, N., & Morrell, N. I. 2009, MNRAS, 395, 823
Schwartz, R. D., Persson, S. E., & Hamann, F. W. 1990, AJ, 100, 793
Shara, M. M., Moffat, A. F. J., Smith, L. F., & Potter, M. 1991, AJ, 102, 716
Shara, M. M., Moffat, A. F. J., Smith, L. F., et al. 1999, AJ, 118, 390
Smith, L. F., Shara, M. M., & Moffat, A. F. J. 1996, MNRAS, 281, 163
Southworth, J. 2007, in Binary Stars as Critical Tools and Tests in Contemporary Astrophysics, ed. W. I. Hartkopf, P. Harmanec, & E. F. Guinan, Proc. IAU Symp., 240, 264
Stevens, I. R., Blondin, J. M., & Pollock, A. M. T. 1992, ApJ, 386, 265
Taylor, W. D., Evans, C. J., Sana, H., et al. 2011, A&A, 530, L10
Telting, J. H., Schrijvers, C., Ilyin, I. V., et al. 2006, A&A, 452, 945
Thé, P. S. 1966, Contr. from Bosscha Observ. Lembang, 35
Uzpen, B., Kobulnicky, H. A., Olsen, A. G., et al. 2005, ApJ, 629, 512
van der Hucht, K. A. 2001, NewAR, 45, 135
Walborn, N. R. 1980, ApJS, 44, 535
Walborn, N. R. 2001, in Eta Carinae and other mysterious stars: the hidden opportunities of emission spectroscopy, ed. T. R. Gull, S. Johansson, & K. Davidson, ASP Conf. Ser., 242, 217
Walborn, N. R., & Howarth, I. D. 2000, PASP 112, 1446
Weidner, C., Kroupa, P., & Bonnell, I. A. D. 2010, MNRAS, 401, 275
Whiteoak, J. B. Z., & Uchida, K. I. 1997, A&A, 317, 563