Abstract
We present spectro-imaging and adaptive optics observations in the lines of [O I] 6300 Å, [S II] 6716, 6731 Å and [N II] 6583 Å aimed at constraining the ejection and collimation mechanisms in active pre-main sequence stars. We first discuss narrow-band high-angular resolution (0.1 arcsec =15 AU) observations of the jets from CW Tau, DG Tau and RW Aur. The morphology of the inner regions of the wind is revealed in unprecedented detail. All 3 jets are resolved beyond 56 AU and show similar widths of 30 AU at projected distances of =~ 100 AU . The jet in DG Tau appears more perturbed, suggesting strong interaction with the ambient medium and/or jet axis variations. We investigate in detail the excitation conditions in the DG Tau and RW Aur microjets from spectro-imaging observations. In both sources, line ratios at distances > 70-100 AU are best reproduced by shock models suggesting that time variability plays an essential role at these spatial scales. The inner regions of the jets show however lower excitation conditions and may remain undisturbed by shocks.