Article (Scientific journals)
The rapid rotation and complex magnetic field geometry of Vega
Petit, Pascal; Lignières, F.; Wade, G. A. et al.
2010In Astronomy and Astrophysics, 523, p. 41
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Keywords :
stars: magnetic field; stars: rotation; stars: atmospheres; stars: imaging; stars: individual: Vega
Abstract :
[en] Context. The recent discovery of a weak surface magnetic field on the normal intermediate-mass star Vega raises the question of the origin of this magnetism in a class of stars that was not previously known to host detectable magnetic fields. <br />Aims: We aim to confirm the field detection reported by Lignières et al. (2009, A&A, 500, L41) and provide additional observational constraints about the field characteristics, by modelling the large-scale magnetic geometry of the star and by investigating a possible seasonal variability of the reconstructed field topology. <br />Methods: We analyse a total of 799 high-resolution circularly-polarized spectra collected with the NARVAL and ESPaDOnS spectropolarimeters during 2008 and 2009. Using about 1100 spectral lines, we employ a cross-correlation procedure to compute, from each spectrum, a mean polarized line profile with a signal-to-noise ratio of about 20 000. The technique of Zeeman-Doppler Imaging is then used to determine the rotation period of the star and reconstruct the large-scale magnetic geometry of Vega at two different epochs. <br />Results: We confirm the detection of circularly polarized signatures in the mean line profiles. The signal shows up in four independent data sets acquired with both NARVAL and ESPaDOnS. The amplitude of the polarized signatures is larger when spectral lines of higher magnetic sensitivity are selected for the analysis, as expected for a signal of magnetic origin. The short-term evolution of polarized signatures is consistent with a rotational period of 0.732 ± 0.008 d. The reconstruction of the magnetic topology unveils a magnetic region of radial field orientation, closely concentrated around the rotation pole. This polar feature is accompanied by a small number of magnetic patches at lower latitudes. No significant variability in the field structure is observed over a time span of one year. <br />Conclusions: The repeated observational evidence that Vega possesses a weak photospheric magnetic field strongly suggests that a previously unknown type of magnetic stars exists in the intermediate-mass domain. Vega may well be the first confirmed member of a much larger, as yet unexplored, class of weakly-magnetic stars now investigatable with the current generation of stellar spectropolarimeters.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Petit, Pascal
Lignières, F.;  Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, France
Wade, G. A.;  Department of Physics, Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, Ontario, Canada
Aurière, M.;  Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, France
Böhm, T.;  Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, France
Bagnulo, S.;  Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK
Dintrans, B.;  Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, France
Fumel, Aurélie ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique et traitement de l'image
Grunhut, J.;  Department of Physics, Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, Ontario, Canada
Lanoux, J.;  Centre d'Étude Spatiale des Rayonnements, Université de Toulouse, CNRS, France
Morgenthaler, A.;  Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, France
Van Grootel, Valérie  ;  Laboratoire d'Astrophysique de Toulouse-Tarbes (LATT)
Language :
English
Title :
The rapid rotation and complex magnetic field geometry of Vega
Publication date :
November 2010
Journal title :
Astronomy and Astrophysics
ISSN :
0004-6361
eISSN :
1432-0746
Publisher :
EDP Sciences, Les Ulis, France
Volume :
523
Pages :
41
Peer reviewed :
Peer Reviewed verified by ORBi
Commentary :
9 pages, 8 figures
Available on ORBi :
since 22 January 2012

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