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Optical & Infrared
Interferometry Group
Smith, K., Pestalozzi, M., Güdel, M., Conway, J., Benz,
A.O.,
VLBI Observations of T Tauri South
Astronomy and Astrophysics, 406, 957 (2003)
Abstract
We report observations of the T Tauri system at 8.4 GHz with a VLBI
array comprising the VLBA, VLA and Effelsberg 100 m telescopes. We
detected a compact source offset approximately 40 mas from the best
infrared position of the T Tau Sb component. This source was
unresolved, and constrained to be less than 0.5 mas in size,
corresponding to 0.07 AU or 15 Rsun at a distance of 140 pc. The other
system components (T Tau Sa, T Tau N) were not detected in the VLBI
data. The separate VLA map contains extended flux not accounted for by
the compact VLBI source, indicating the presence of extended emission
on arcsecond scales. The compact source shows rapid variability, which
together with circular polarization and its compact nature indicate
that the observed flux arises from a magnetically-dominated region.
Brightness temperatures in the MK range point to gyrosynchrotron as the
emission mechanism for the steady component. The rapid variations are
accompanied by dramatic changes in polarization, and we record an at
times 100% polarized component during outbursts. This strongly suggests
a coherent emission process, most probably an electron cyclotron maser.
With this assumption it is possible to estimate the strength of the
local magnetic field to be 1.5-3 kilogauss.
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