M ar 2 00 1 Circumstellar structure of RU Lupi down to au scales

We have used the technique of spectro-astrometry to study the milli-arcsecond scale structure of the emission lines in the T Tauri star RU Lupi. The wings of the Hα emission are found to be displaced from the star towards the southwest (blue wing) and northeast (red wing) with angular scales of 20-30 milli-arcsecs. This structure is consistent with a bipolar outflow from the star. From a study of the variability of the intensity and position spectra we argue that a combination of magnetically-driven bipolar outflow and accreting gas contribute to the Hα emission. On the other hand, the [OI] and [SII] emission are displaced from the star to the southwest but at much larger distances than the Hα, hundreds of milli-arcsecs for the high-velocity component (HVC) and down to 30 milli-arcsecs for the low-velocity components (LVC). The presence of both red-shifted and blue-shifted outflows in Hα but only a blue-shifted outflow in the forbidden lines can be explained if the disc obscures the red-shifted forbidden line outflow, but a disc gap with outer radius 3-4 au allows the red-shifted Hα to be seen. This gap could be induced by an unseen companion.