SPIRou spectropolarimetry of the T Tauri star TW Hydrae: magnetic fields, accretion and planets - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
Journal Articles Monthly Notices of the Royal Astronomical Society Year : 2024

SPIRou spectropolarimetry of the T Tauri star TW Hydrae: magnetic fields, accretion and planets

L Lehmann
L Arnold
  • Function : Author
N Cook
Á Kóspál
  • Function : Author
M Takami
  • Function : Author
Sylvie Cabrit
Guillaume Hébrard
R Doyon
  • Function : Author

Abstract

In this paper we report near-infrared observations of the classical T Tauri star TW Hya with the SPIRou high-resolution spectropolarimeter and velocimeter at the 3.6-m Canada-France-Hawaii Telescope in 2019, 2020, 2021 and 2022. By applying Least-Squares Deconvolution (LSD) to our circularly polarized spectra, we derived longitudinal fields that vary from year to year from -200 to +100 G, and exhibit low-level modulation on the 3.6 d rotation period of TW Hya, despite the star being viewed almost pole-on. We then used Zeeman-Doppler Imaging to invert our sets of unpolarized and circularly-polarized LSD profiles into brightness and magnetic maps of TW Hya in all 4 seasons, and obtain that the large-scale field of this T Tauri star mainly consists of a 1.0-1.2 kG dipole tilted at about 20° to the rotation axis, whereas the small-scale field reaches strengths of up to 3-4 kG. We find that the large-scale field is strong enough to allow TW Hya to accrete material from the disc on the polar regions at the stellar surface in a more or less geometrically stable accretion pattern, but not to succeed in spinning down the star. We also report the discovery of a radial velocity signal of semiamplitude 11.1+3.3-2.6 m s-1 (detected at 4.3 ) at a period of 8.3 d in the spectrum of TW Hya, whose origin may be attributed to either a non-axisymmetric density structure in the inner accretion disc, or to a 0.55+0.17-0.13 Jupiter mass candidate close-in planet (if orbiting in the disc plane), at an orbital distance of 0.075 ± 0.001 au.
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Dates and versions

hal-04752307 , version 1 (24-10-2024)

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J -F Donati, P Cristofari, L Lehmann, Claire Moutou, Silvia Alencar, et al.. SPIRou spectropolarimetry of the T Tauri star TW Hydrae: magnetic fields, accretion and planets. Monthly Notices of the Royal Astronomical Society, 2024, 531 (3), pp.3256-3278. ⟨10.1093/mnras/stae1227⟩. ⟨hal-04752307⟩
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