Multi-epoch VLBA observations of T Tauri South

In this Letter, we present a series of seven observations of the compact, non-thermal radio source associated with T Tauri South made with the Very Long Baseline Array over the course of one year. The emission is found to be composed of a compact structure most certainly originating from the magnetosphere of an underlying pre-main sequence star, and a low-brightness extension which may result from reconnection flares at the star-disk interface. The accuracy of the absolute astrometry offered by the VLBA allows very precise determinations of the trigonometric parallax and proper motion of T Tau South. The proper motion derived from our VLBA observations agrees with that measured with the VLA over a similar period to better than 2 mas yr$^{-1}$, and is fully consistent with the infrared proper motion of T Tau Sb, the pre-main sequence M star with which the radio source has traditionally been associated. The parallax, $\pi$ = 7.07 $\pm$ 0.14 mas, corresponds to a distance of 141.5$^{+2.8}_{-2.7}$ pc.