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Appendix A: Physical structure of previously analysed jets

In this appendix we present the results obtained by applying spectral diagnostics to HH 1 (jet and bow), HH 2, HH 83, and HH 24. These jets have been already analysed in previous papers with the same diagnostics, but are re-analysed here with higher spatial sampling ( $\Delta x \sim 1.2$ $^{\prime\prime}$) and an improved version of the diagnostic code as explained in Sect. 3. The values presented are used for investigating dust reprocessing in these jets (see Sect. 5).

A.1 HH 1/2: the jet and its terminal bows

The physical structure of the HH 1 jets and its terminal bows has been previously analysed by Solf & Böhm (1991), Nisini et al. (2005), and Böhm & Solf (1985), Solf et al. (1988), Eislöffel et al. (1994), Bally et al. (2002). In our observations the slit is aligned along the jet and it covers the fainter western/eastern parts of HH 1 and HH 2 respectively, i.e. the knots B and G, which are located to the west of the HH 1 bow apex (knot F), and the knots L, J, G, B, T, and Q located to the east of the bright H and A knots in HH 2.

The results obtained by applying the BE technique to the HH 1 jet are shown in Fig. A.1. The values for the physical parameters are in a good agreement with the ones obtained in Nisini et al. (2005) but here the spatial sampling is two times better.

\begin{figure} \par\includegraphics[width=8.cm]{12408fA1.eps} \end{figure} Figure A.1:

Variation of the physical parameters for the HH 1 jet as a function of distance from the source. From top to bottom panel: intensity profiles of the optical lines, the electron density, $n_{\rm e}$, in units of 103 cm-3, the ionisation fraction, $x_{\rm e}$, the temperature, $T_{\rm e}$, in units of 104 K, and the total density, $n_{\rm H}$, in units of 104 cm-3.
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\begin{figure} \par\includegraphics[width=13cm]{12408fA2.eps} \end{figure} Figure A.2:

Analysis of the excitation conditions in the HH 1 jet and its terminal bows HH 1 and HH 2 as a function of distance from the source. From top to bottom panel: intensity profiles of the optical lines, the electron density, $n_{\rm e}$, in units of 103 cm-3, and the [N II]/[O I] ratio.
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We could not apply the diagnostic to the terminal bows. The BE technique, in fact, relies on the assumption of low excitation conditions, i.e. S being totally ionised but there is no S++, and oxygen and nitrogen are ionised at most once (Bacciotti & Eislöffel 1999). This assumption is satisfied for the jet where gas interacts with material already in motion from previous outflow events, but may not be correct when dealing with the terminal bows. This picture is confirmed by proper motions studies by Bally et al. (2002) which indicate shock velocities lower than 30 km s-1  in the jet and velocity jumps of up to 100-200 km s-1  in the bows. Moreover, Böhm & Solf (1985) and Solf et al. (1988) detected many high excitation lines in HH 1 and HH 2 such as O++, S++, and Ar+++.

Even if in our case the slit covers the lateral part of the bows the excitation conditions may still be too high. This is indicated by the detection of the high excitation [Ar III]$\lambda $7135.8 line in our spectra and by the fact that the [N II] lines, which are faint in the jet, show strong emission in the bows, comparable to the [S II] lines (see the upper panel of Fig. A.2).

In order to compare the physical conditions in the jet and in the bows we computed the electron density, $n_{\rm e}$, and the [N II]/[O I]  ratio along all the slit length. The electron density does not show large differences. It varies between 0.05- $4\times 10^3$ cm-3  along all the jet. While in the jet $n_{\rm e}$  is decreasing with distance from the source, both in the HH 1 and in HH 2 bows, on the contrary, there is a decreasing trend going from the shock apex toward the source. This is expected behind a shock front and confirms the results found by Böhm & Solf (1985) and Solf et al. (1988). Our values of $n_{\rm e}$  are lower than those inferred by Böhm & Solf (1985), however, because of the different slit alignment (on the brightest spots at the apex of HH 1 and HH 2 for Böhm & Solf 1985, and on the bows wings in our case) and show that the density in the two bows is maximum at the apex and fades towards the wings. The [N II]/[O I]  ratio is a good indicator of excitation conditions and, in particular, of the ionisation state of the gas. Figure A.2 shows that [N II]/[O I]  is <1 in the jet and in knot L, while it is >1 in the HH 1 and HH 2 bows, indicating that the excitation level is much higher in the bows, and a higher value of $x_{\rm e}$  is expected.

A.2 HH 83: the physical structure of the inner knots

The physical structure of the HH 83 jet has been already derived in Podio et al. (2006). Thanks to the high S/N of these data, however, we obtained a sampling which is four times larger in comparison to previous results. Moreover the good quality of the data, which allowed us to properly subtract the continuum emission from the reflection nebula Re 17 (Rolph et al. 1990), and the use of the improved diagnostic code allowed us to estimate the gas physical conditions in the inner part of the jet, where emission from the [N II] lines is comparable to the [S II]  and [O I] emission.

The derived parameters, shown in Fig. A.3, indicate that the excitation conditions are very high in the knots close to the source (knots from A to D) with $n_{\rm e}$ $\sim$ 400-700 cm-3, and high values of the ionisation fraction and temperature ($x_{\rm e}$ $\sim$ 0.4-0.7, and $T_{\rm e}$ $\sim$ 1.5- $2\times 10^4$ K).

\begin{figure} \par\includegraphics[width=6.5cm]{12408fA3.eps} \end{figure} Figure A.3:

Variation of the physical parameters for the HH 83 jet as a function of distance from the source. From top to bottom panel: intensity profiles of the optical lines, the electron density, $n_{\rm e}$, in units of 103 cm-3, the ionisation fraction, $x_{\rm e}$, the temperature, $T_{\rm e}$, in units of 104 K, and the total density, $n_{\rm H}$, in units of 103 cm-3.
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A.3 The HH 24 jets

The physical parameters along the jets HH 24 C, E, and A, have already been derived in Bacciotti & Eislöffel (1999) and Podio et al. (2006). In our observations the slit has been aligned along the axis HH 24 M-A-E and thus only partially covers the knots of the HH 24 C jet up to 40 $\hbox{$^{\prime\prime}$ }$ (knot C6). This is why the line profiles in the upper panel of Fig. A.4 show fainter emission in the knots of group C, contrary to what was found in Podio et al. (2006), where the slit was aligned along the HH 24 C jet. The variation of the physical parameters obtained by applying the BE technique is shown in Fig. A.4. The sampling is improved by around one third with respect to previous analyses (Bacciotti & Eislöffel 1999; Podio et al. 2006) allowing us to highlight the different excitation conditions in the various groups of knots detected in the HH 24 complex (HH 24 A, HH 24 M/E, and HH 24 C) and supporting the idea that these knots may belong to different jets.

\begin{figure} \par\includegraphics[width=13cm]{12408fA4.eps} \end{figure} Figure A.4:

Variation of the physical parameters for the HH 24 C/E jet as a function of distance from the source. From top to bottom panel: intensity profiles of the optical lines, the electron density, $n_{\rm e}$, in units of 103 cm-3, the ionisation fraction, $x_{\rm e}$, the temperature, $T_{\rm e}$, in units of 104 K, and the total density, $n_{\rm H}$, in units of 104 cm-3.
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