Circumstellar structure of RU Lupi down to au scales

Abstract

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 H-alpha emission are found to be displaced from the star towards the south-west (blue wing) and north-east (red wing) with angular scales of 20-30 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 H-alpha 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 H-alpha, 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 H-alpha 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 H-alpha to be seen. This gap could be induced by an unseen companion.Comment: accepted for publication in MNRA

Tracing the potential planet-forming regions around seven pre-main-sequence stars

“…Our measurements of RU Lup can be simulated equally with an active disk model with or without a dust-free gap. A disk model with a gap was formerly proposed by Takami et al (2001) based on spectro-astrometric observations. viii.…”

“…The apparent lack of redshifted line components results from an obscuration of the dorsal outflow by the circumstellar disk (Eislöffel et al 2000). Takami et al (2001) found that the Hα line in the spectrum of RU Lup, which is evident predominatly in the innermost regions, shows both blueshifted and redshifted wings. This finding is explained by an inner disk gap that allows regions behind the disk to be observed.…”

“…Based on spectro-astrometric observations, Takami et al (2001) suggested that an inner gap in the circumstellar disk of RU Lup exists between ∼2 AU and ∼4 AU (20-30 mas) as justified by the following arguments. Because of the positional displacement of the extended wings, the emission of forbidden lines such as [OI] and [SII] in the spectra of RU Lup is assumed to arise in a collimated large-scale outflow.…”

“…The gap could be evoked by an unseen (planetary) companion. Since the wings of the Hα line shows the same positional displacement as the forbidden lines, Takami et al (2001) suggested that the Hα line originates predominantly in the outflow.…”

Linear polarization in forbidden lines of the T Tauri star RY Tauri

“…However, higher spatial resolution is still required to approach the launching region of outflows close to the central star. Recently, new observational efforts such as spectro-astrometry (Takami et al 2001) and long slit spectroscopy with an adaptive optics (Pyo et al 2003(Pyo et al , 2006 have been made to reveal the circumstellar structure of TTSs down to AU scales.…”