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

C. A. Hill, C. P. Folsom, J. -F. Donati, G. J. Herczeg, G. A. J. Hussain, S. H. P. Alencar, S. G. Gregory

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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 6.0 ± 0.5 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....
Original languageEnglish
Pages (from-to)5810-5833
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Volume484
Issue number4
DOIs
Publication statusPublished - 11 Apr 2019

Keywords

  • Magnetic fields
  • Stars: formation
  • Stars: imaging
  • Stars: individual: TWA 6
  • Stars: individual: TWA 8A
  • Techniques: polarimetric

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    Gregory, Scott

    • Physics - Lecturer in Astrophysics (joint appointment: 50% Mathematics 50% Physics)

    Person: Academic

    Cite this

    Hill, C. A., Folsom, C. P., Donati, J. -F., Herczeg, G. J., Hussain, G. A. J., Alencar, S. H. P., & Gregory, S. G. (2019). Magnetic topologies of young suns: the weak-line T Tauri stars TWA 6 and TWA 8A. Monthly Notices of the Royal Astronomical Society, 484(4), 5810-5833. https://doi.org/10.1093/mnras/stz403