Discovery of the magnetic field of the B1/B2V star σ Lupi

Henrichs, H. F. and Kolenberg, K. and Plaggenborg, B. and Marsden, S. C. and Waite, I. A. and Landstreet, J. and Grunhut, J. and Oksala, M. and Wade, G. (2012) Discovery of the magnetic field of the B1/B2V star σ Lupi. In: American Institute of Physics Conference (STARPOL 2011): Stellar Polarimetry: From Birth to Death, 27-30 Jun 2011, Madison, WI. United States.

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Abstract

In our search for new magnetic massive stars we use the strongest indirect indicator of a magnetic field in B stars, which is periodic variability of UV stellar wind lines occurring in a velocity range symmetric around zero. Our aim is to obtain follow-up spectropolarimetry to search for a magnetic field in magnetic candidate stars. We quantify UV wind line variability, and analyse its time behaviour. The B1/B2Vstar σ Lupi emerged as a new magnetic candidate star. AAT spectropolarimetric measurements with SEMPOL were obtained. The stellar wind line variations of σ Lupi are similar to what is known in magnetic B stars, but no periodicity could be determined. We detected a longitudinal magnetic field with varying strength and amplitude of about 100 G with error bars of typically 20 G, which supports an oblique magnetic-rotator configuration. The equivalent width variations of the UV lines, the magnetic and the optical line variations are consistent with the well-known photometric period of 3.02 days, which we identifywith the rotation period of the star. Additional observations with ESPaDOnS attached to the CFHT strongly confirmed this discovery, and allowed to determine a precise magnetic period. Further analysis revealed that σ Lupi is a helium-strong star, with an enhanced nitrogen abundance and an underabundance of carbon, and has a spotted surface. We conclude that σ Lupi is a magnetic oblique rotator, and is a He-strong star. It is the fourth B star for which a magnetic field is discovered from studying only its wind variability. Like in the other magnetic B stars the wind emission originates in the magnetic equator, with maximum emission occurring when a magnetic pole points towards the Earth. The 3.01819 d magnetic rotation period is consistent with the photometric period, with maximum light corresponding to maximum magnetic field. A full paper will be submitted to Astronomy & Astrophysics.


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Item Type: Conference or Workshop Item (Commonwealth Reporting Category E) (Paper)
Refereed: Yes
Item Status: Live Archive
Additional Information: © 2012 American Institute of Physics. Copyright of AIP Conference Proceedings is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. Accepted Version from arXiv deposited in accordance with the copyright policy of the publisher.
Faculty / Department / School: Historic - Faculty of Sciences - Department of Biological and Physical Sciences
Date Deposited: 08 Jan 2013 06:40
Last Modified: 26 Apr 2018 04:27
Uncontrolled Keywords: magnetic fields; massive stars; star spots; abundances
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
02 Physical Sciences > 0204 Condensed Matter Physics > 020404 Electronic and Magnetic Properties of Condensed Matter; Superconductivity
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020106 High Energy Astrophysics; Cosmic Rays
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1063/1.3701907
URI: http://eprints.usq.edu.au/id/eprint/21546

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