Magnetic topologies of young suns: the weak-line T Tauri stars TWA 6 and TWA 8A. Issue 4 (11th February 2019)

• Record Type: Journal Article
• Authors: Hill, C A; Folsom, C P; Donati, J-F; Herczeg, G J; Hussain, G A J; Alencar, S H P; Gregory, S G
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 484:Issue 4(2019)
• Page Start: 5810
• Page End: 5833
• Publication Date: 2019-02-11
• Subjects: techniques: polarimetric -- stars: formation -- stars: imaging -- stars: individual: TWA 6 -- stars: individual: TWA 8A -- magnetic fields; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz403
• Languages: English
• ISSNs: 0035-8711

Abstract

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.