  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 H-alpha 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 H-alpha 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 H-alpha 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.
