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Strong infrared circular polarization resulting from dust scattering in reflection nebulae in the Orion OMC-1 star-formation region has been observed. Circular polarization at shorter wavelengths might have been important in inducing chiral asymmetry in interstellar organic molecules that could be subsequently delivered to the early Earth by comets, interplanetary dust particles, or meteors. This could account for the excess of L-amino acids found in the Murchison meteorite and could explain the origin of the homochirality of biological molecules.

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Abstract. We present spectro-astrometric observations for 28 southern pre-main sequence (PMS) stars and investigate their circumstellar environment down to AU scales. The structures detected in the "position spectra" include: (1) almost all the known binary companions in our sample (Sz 68, Sz 41, HO Lup, VW Cha, S CrA, AS 205), (2) companion candidates which have not been detected by infrared speckle techniques (T CrA, MWC 300), (3) monopolar and bipolar jets (AS 353A, CS Cha), (4) a combination of jets and a bow shock (VV CrA), and (5) a combination of a jet and stellar companion (R CrA). Results in known binaries show that this technique is capable of detecting binaries with separations down to ∼10 milliarcsec. Both components in each binary appear to have strikingly similar profiles in Hα emission, indicating a similarity of circumstellar activity (mass accretion and/or a wind), and supporting the scenario of core fragmentation for the mechanism of binary formation. The bipolar Hα jet in CS Cha has a spatial scale of ∼1.5 AU, similar to that previously observed in RU Lup, and likely be heated by a mechanism other than shocks. From the spatial scale, velocity, and Hα luminosity, we estimate the mean hydrogen density in the AU-scale bipolar flows to be > ∼ 10 7 cm −3 . The bipolar geometry in these jets can be explained by the presence of a disc gap/hole at AU scales, which could be induced by a gas-giant planet at the ice condensation radius.

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

We find considerable spatial variability suggesting active processes with conservation between species. The most variable regions are just below the Venus cloud deck, and these may be related to changes in atmospheric circulation or virga events.