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THÈSE
THÈSE
En vue de l’obtention du
DOCTORAT DE L’UNIVERSITÉ DE TOULOUSE
Délivré par : l’Université Toulouse 3 Paul Sabatier (UT3 Paul Sabatier)
Présentée et soutenue le 30/10/2015 par :
Élodie HÉBRARD
Magnétométrie stellaire et Imagerie Zeeman-Doppler appliquées à la
recherche d’exoplanètes par mesures vélocimétriques
JURY
Clément Baruteau IRAP
Andrew Cameron Saint Andrews
Magali Deleuil LAM
Thierry Forveille IPAG
Gaitee Hussain ESO
Anne-Marie Lagrange IPAG
Julien Morin LUPM
Claire Moutou LAM-CFHT
Michel Rieutord IRAP
École doctorale et spécialité :
SDU2E : Astrophysique, Sciences de l’Espace, Planétologie
Unité de Recherche :
Institut de Recherche en Astrophysique et Planétologie (UMR 5277)
Directeur(s) de Thèse :
Jean-François Donati et Xavier Delfosse
Rapporteurs :
Magali Deleuil et Thierry Forveille

Stellar Magnetometry and Zeeman-Doppler Imaging in exoplanets
research using the radial velocity method.
Abstract
Forthcoming instruments dedicated to exoplanets detection through the radial velocity method
are numerous, and increasingly more accurate. However this method is indirect : orbiting planets
are detected and characterised from variations on the spectrum of the host star. We are therefore
sensitive to all activity phenomena impacting the spectrum and producing a radial velocity signal
(pulsation, granulation, spots, magnetic cycle...). The detection of rocky Earth-like planets around
main-sequence stars, and of hot Jupiters into young systems, are currently limited by the intrinsic
magnetic activity of the host stars. The radial velocity fluctuations caused by activity (activity jitter)
can easily mimic and hide signals from such planets, whose amplitude is of a few m/s and hundreds
of m/s, respectively. As a result, the detection threshold of exoplanets is largely set by the stellar
activity level.
Currently, efforts are invested to overcome this intrinsic limitation. During my PhD, I studied how
to take advantage of imaging tomographic techniques (Zeeman-Doppler imaging, ZDI) to characterise
stellar activity and magnetic field topologies, ultimately allowing us to filter out the activity jitter. My
work is based on spectropolarimetric observations of a sample of weakly-active M-dwarfs, and young
active T Tauri stars. Using a modified version of ZDI, we are able to reconstruct the distribution
of active regions, and then model the induced stellar signal allowing us to clean RV curves from
the activity jitter. First tests demonstrate that this technique can be efficient enough to recover the
planet signal, especially for the more active ones.
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Remerciments
our m’avoir soutenu ou inspiré ou guidé (patiemment), ou pour m’avoir fait confiance, et
même parfois pour avoir soumis mes nerfs à rude épreuve il faut bien l’admettre ;-) ...
à toutes les personnes qui m’ont accompagné, de près ou de loin,
durant ces trois années et même plus,
je tiens sincèrement à vous aremercier, je n’y serais jamais arrivée sans vous.
a. Sophie, maman, papa, Jean-François, Xavier, Rim, Sandrine, Pierre, Aurélien, Clément, Agathe, Nicolas, Renaud,
Julien, François, Isabelle, Guillaume, Giovanni, Bertrand, Stéphane, Frédéric, Pablo, Hayley, Pascal, Geneviève, l’équipe
SPIRou, .....