Circumstellar structure of RU Lupi down to au scales

Abstract

We have used the technique of spectro-astrometry to study the milliarcsecond 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 south-west (blue wing) and north-east (red wing) with angular scales of 20-30mas. 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 contributes to the Hα emission. On the other hand, the [Oi] and [Sii] emission are displaced from the star to the south-west but at much larger distances than the Hα, hundreds of milliarcseconds for the high-velocity component (HVC) and down to 30mas for the low-velocity components (LVCs). The presence of both redshifted and blueshifted outflows in Hα but only a blueshifted outflow in the forbidden lines can be explained if the disc obscures the redshifted forbidden line outflow, but a disc gap with outer radius 3-4au allows the redshifted Hα to be seen. This gap could be induced by an unseen companion.