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Magnetic topologies of young suns: the weak-line T Tauri stars TWA 6 and TWA 8A

Abstract : We present a spectropolarimetric study of two weak-line T Tauri stars (wTTSs), TWA 6, and TWA 8A, as part of the MaTYSSE (Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets) programme. Both stars display significant Zeeman signatures that we have modelled using Zeeman Doppler Imaging (ZDI). The magnetic field of TWA 6 is split equally between poloidal and toroidal components, with the largest fraction of energy in higher order modes, with a total unsigned flux of 840 G, and a poloidal component tilted 35° from the rotation axis. TWA 8A has a 70 per cent poloidal field, with most of the energy in higher order modes, with an unsigned flux of 1.4 kG (with a magnetic filling factor of 0.2), and a poloidal field tilted 20° from the rotation axis. Spectral fitting of the very strong field in TWA 8A (in individual lines, simultaneously for Stokes I and V) yielded a mean magnetic field strength of 5.9 ± 0.2 kG. The higher field strengths recovered from spectral fitting suggests that a significant proportion of magnetic energy lies in small-scale fields that are unresolved by ZDI. So far, wTTSs in MaTYSSE appear to show that the poloidal-field axisymmetry correlates with the magnetic field strength. Moreover, it appears that classical T Tauri stars (cTTSs) and wTTSs are mostly poloidal and axisymmetric when mostly convective and cooler than ˜4300 K, with hotter stars being less axisymmetric and poloidal, regardless of internal structure.
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https://hal-obspm.ccsd.cnrs.fr/obspm-02399750
Contributor : Jean-Francois Donati <>
Submitted on : Monday, December 9, 2019 - 11:26:55 AM
Last modification on : Wednesday, April 8, 2020 - 1:48:56 AM

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C. A. Hill, C. P. Folsom, J.-F. Donati, G. J. Herczeg, G. A. J. Hussain, et al.. Magnetic topologies of young suns: the weak-line T Tauri stars TWA 6 and TWA 8A. Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2019, 484 (4), pp.5810-5833. ⟨10.1093/mnras/stz403⟩. ⟨obspm-02399750⟩

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