4 research outputs found
Discovery of the magnetic field in the B1/B2V star sigma Lupi
The ultraviolet stellar wind lines of the photometrically periodic variable
early B-type star sigma 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.Comment: 2 pages, 2 figures, to appear in the proceedings of IAU Symposium
272, Active OB stars - structure, evolution, mass loss, and critical limit