Modelling the magnetic activity and filtering radial velocity curves of young Suns : the weak-line T Tauri star LkCa 4
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We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri star LkCa 4 within the Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets (MaTYSSE) programme, involving ESPaDOnS at the Canada–France–Hawaii Telescope. Despite an age of only 2 Myr and a similarity with prototypical classical T Tauri stars, LkCa 4 shows no evidence for accretion and probes an interesting transition stage for star and planet formation. Large profile distortions and Zeeman signatures are detected in the unpolarized and circularly polarized lines of LkCa 4 using Least-Squares Deconvolution (LSD), indicating the presence of brightness inhomogeneities and magnetic fields at the surface of LkCa 4. Using tomographic imaging, we reconstruct brightness and magnetic maps of LkCa 4 from sets of unpolarized and circularly polarized LSD profiles. The large-scale field is strong and mainly axisymmetric, featuring a ≃2 kG poloidal component and a ≃1 kG toroidal component encircling the star at equatorial latitudes – the latter making LkCa 4 markedly different from classical T Tauri stars of similar mass and age. The brightness map includes a dark spot overlapping the magnetic pole and a bright region at mid-latitudes – providing a good match to the contemporaneous photometry. We also find that differential rotation at the surface of LkCa 4 is small, typically ≃5.5 times weaker than that of the Sun, and compatible with solid-body rotation. Using our tomographic modelling, we are able to filter out the activity jitter in the radial velocity curve of LkCa 4 (of full amplitude 4.3 km s−1) down to an rms precision of 0.055 km s−1. Looking for hot Jupiters around young Sun-like stars thus appears feasible, even though we find no evidence for such planets around LkCa 4.
Donati , J-F , Hébrard , E , Hussain , G , Moutou , C , Grankin , K , Boisse , I , Morin , J , Gregory , S G , Vidotto , A A , Bouvier , J , Alencar , S H P , Delfosse , X , Doyon , R , Takami , M , Jardine , M M , Fares , R , Cameron , A C , Ménard , F , Dougados , C & Herczeg , G 2014 , ' Modelling the magnetic activity and filtering radial velocity curves of young Suns : the weak-line T Tauri star LkCa 4 ' Monthly Notices of the Royal Astronomical Society , vol 444 , no. 4 , pp. 3220-3229 . DOI: 10.1093/mnras/stu1679
Monthly Notices of the Royal Astronomical Society
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2014 The Authors, Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
SGG acknowledges support from the Science & Technology Facilities Council (STFC) via an Ernest Rutherford Fellowship [ST/J003255/1]. SHPA acknowledges financial support from CNPq, CAPES and Fapemig.
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