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Pollux: a stable weak dipolar magnetic field but no planet?

Published online by Cambridge University Press:  07 August 2014

Michel Aurière ,
Renada Konstantinova-Antova ,
Olivier Espagnet ,
Pascal Petit ,
Thierry Roudier ,
Corinne Charbonnel ,
Jean-François Donati  and
Gregg A. Wade
Michel Aurière
Affiliation:
IRAP, Université de Toulouse & CNRS, Toulouse, France email: [email protected]
Renada Konstantinova-Antova
Affiliation:
IRAP, Université de Toulouse & CNRS, Toulouse, France email: [email protected] Institute of Astronomy and NAO, Bulgarian Academy of Sciences, Sofia, Bulgaria
Olivier Espagnet
Affiliation:
IRAP, Université de Toulouse & CNRS, Toulouse, France email: [email protected]
Pascal Petit
Affiliation:
IRAP, Université de Toulouse & CNRS, Toulouse, France email: [email protected]
Thierry Roudier
Affiliation:
IRAP, Université de Toulouse & CNRS, Toulouse, France email: [email protected]
Corinne Charbonnel
Affiliation:
IRAP, Université de Toulouse & CNRS, Toulouse, France email: [email protected] Geneva Observatory, University of Geneva, Versoix, Switzerland
Jean-François Donati
Affiliation:
IRAP, Université de Toulouse & CNRS, Toulouse, France email: [email protected]
Gregg A. Wade
Affiliation:
Department of Physics, Royal Military College of Canada, Kingston, Ontario, Canada
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Abstract

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Pollux is considered as an archetype of a giant star hosting a planet: its radial velocity (RV) presents sinusoidal variations with a period of about 590 d, which have been stable for more than 25 years. Using ESPaDOnS and Narval we have detected a weak (sub-gauss) magnetic field at the surface of Pollux and followed up its variations with Narval during 4.25 years, i.e. more than for two periods of the RV variations. The longitudinal magnetic field is found to vary with a sinusoidal behaviour with a period close to that of the RV variations and with a small shift in phase. We then performed a Zeeman Doppler imaging (ZDI) investigation from the Stokes V and Stokes I least-squares deconvolution (LSD) profiles. A rotational period is determined, which is consistent with the period of variations of the RV. The magnetic topology is found to be mainly poloidal and this component almost purely dipolar. The mean strength of the surface magnetic field is about 0.7 G. As an alternative to the scenario in which Pollux hosts a close-in exoplanet, we suggest that the magnetic dipole of Pollux can be associated with two temperature and macroturbulent velocity spots which could be sufficient to produce the RV variations. We finally investigate the scenarii of the origin of the magnetic field which could explain the observed properties of Pollux.

Keywords

Stars: individual: PolluxStars: late typeStars: magnetic field
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 9 , Symposium S302: Magnetic Fields throughout Stellar Evolution , August 2013 , pp. 359 - 362
Copyright
Copyright © International Astronomical Union 2014 

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