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Fig. 5. Channel maps in three different velocity intervals (HVC:[—400,—250], IVC:[-250,-100], LVC:[—100,+10] km s^1) of the optical emission lines of the DG Tau microjet reconstructed from IFS+AO data (OASIS/CFHT combined with AO correction). Angular resolution is 0."4, velocity resolution 100 km s-1. Figure from [29]

-2 0 2 4 -2 0 2 4 -2 0 2 4 -2 0 2 4 Offset (arcsec)

-2 0 2 4 -2 0 2 4 -2 0 2 4 -2 0 2 4 Offset (arcsec)

Fig. 6. Position-velocity diagram of the DG Tau (Left) and RW Aur (Right) microjets in the [Fe ii] 1.644 |lm obtained with IRCS/SUBARU (AO+long-slit spectrograph). Angular resolution is 0."2 angular resolution and velocity resolution 30 km s_1. Figures taken from [37] and [38]

Fig. 6. Position-velocity diagram of the DG Tau (Left) and RW Aur (Right) microjets in the [Fe ii] 1.644 |lm obtained with IRCS/SUBARU (AO+long-slit spectrograph). Angular resolution is 0."2 angular resolution and velocity resolution 30 km s_1. Figures taken from [37] and [38]

Using the method developed by [3, 14, 29] also derive the variation of plasma parameters (ne, Te, xe, and total hydrogen density nH) along the jet axis for the RW Aur and DG Tau microjets (Fig. 7). Similar studies have been conducted from STIS/HST data on these 2 microjets [2, 5, 46], and on the HH 30 [4] and Th 28 [3] microjets. In these 4 jets, strong gradients in excitation conditions are observed below 1", illustrating the crucial importance of high-angular resolution (Fig. 7). Both the electronic and hydrogen densities and the excitation temperature strongly decrease with distance from the source. In contrast, the ionization fraction is seen to rapidly level off to values between 0.03 and 0.5. In DG Tau, the degree of excitation (xe, Te) clearly increases with flow velocity [5, 29]. The more accurate derivation of nH and jet radius allows for a better estimate of mass-loss rates in these flows, a crucial parameter for launching models. Newly derived ejection to accretion rates are still uncertain by a factor 10 but typically range between 1 and 10%. See [7] for a detailed discussion of the remaining uncertainties in the derivation of mass-loss rates.

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