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The magnetic field of the B1/B2V star σ Lup

Published online by Cambridge University Press:  12 July 2011

Huib F. Henrichs ,
Katrien Kolenberg ,
Benjamin Plaggenborg ,
Stephen C. Marsden ,
Ian A. Waite  and
Gregg A. Wade
Huib F. Henrichs
Affiliation:
Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, 1098XH Amsterdam, Netherlands, email: h.f.henrichs@uva.nl
Katrien Kolenberg
Affiliation:
Institut für Astronomie, Universität Wien, Türkenschanzstrasse 17, A-1180 Vienna, Austria
Benjamin Plaggenborg
Affiliation:
Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, 1098XH Amsterdam, Netherlands, email: h.f.henrichs@uva.nl
Stephen C. Marsden
Affiliation:
Anglo-Australian Observatory, PO Box 296, Epping, NSW 1710, Australia
Ian A. Waite
Affiliation:
Faculty of Sciences, University of Southern Queensland, Toowoomba, Qld 4350Australia
Gregg A. Wade
Affiliation:
Dept. of Physics, Royal Military College of Canada, Kingston, Canada
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Abstract

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The ultraviolet stellar wind lines of the photometrically periodic variable early B-type star σ Lupi were found to behave very similarly to what has been observed in known magnetic B stars, although no periodicity could be determined. AAT spectropolarimetric measurements with SEMPOL were obtained. We detected a longitudinal magnetic field with varying strength and amplitude of about 100 G with error bars of typically 20 G. This type of variability supports an oblique magnetic rotator model. We fold the equivalent width of the 4 usable UV spectra in phase with the well-known photometric period of 3.019 days, which we identify with the rotation period of the star. The magnetic field variations are consistent with this period. Additional observations with ESPaDOnS attached to the CFHT strongly confirmed this discovery, and allowed to determine a precise magnetic period. Like in the other magnetic B stars the wind emission likely originates in the magnetic equatorial plane, with maximum emission occurring when a magnetic pole points towards the Earth. The 3.0182 d magnetic rotation period is consistent with the photometric period, with maximum light corresponding to maximum magnetic field. No helium or other chemical peculiarity is known for this object.

Keywords

stars: magnetic fieldstechniques: polarimetricstars: atmospheresstars: individual (σ Lup)stars: early-typestars: windsoutflowsstars: rotation
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 6 , Symposium S272: Active OB stars: structure, evolution, mass loss, and critical limits , July 2010 , pp. 192 - 193
Copyright
Copyright © International Astronomical Union 2011

References

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