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\section{Results}
\label{sect:results}
The last section already showed that for all parameters consistent with the theoretical and observational constraints the stellar wind is enclosed in a finite region by a shock front. This shock front generally reaches a maximum cylindrical radius of only several AUs, but a much larger height above the accretion
disk. While a detailed numerical treatment disk for external presure profiles with high pressure in the plane of the
post-shock cooling disk and a large presure gradient (fiducial model in Fig.~\ref{fig:result}). A shallower pressure profile leads to a stellar wind region that is wider. In CTTS, no stellar wind zone is
beyond resolved within the
scope more massive and wider disk wind in the available imaging, limiting it to a width of
a few AU. Our calculations show that this
work, scenario is compatible with the
shape known properties of the
shock front indicates that the post-shock zone will also be rather narrow in $\omega$. stellar wind. The
highest post-shock temperatures are generally reached at biggest uncertainty is probably the
base value of the
jet when external presure. As discussed above, different simulations in the
stellar wind encounters literature predict similar pressure profiles, but the
inner disk rim or at normalisation of the pressure depends to a large
$z$ when degree on the
shock front intersects disk magnetic field, which is only poorly constaint. In our calculation, we have scaled the pressure such that the post-shock densities are compatible with observations of the jet
axis. Thus, and we find a fiducial model that is compatible with the X-ray emission from the
position jet that we set out to explain. However, the magnitude of the
hottest post-shock cooling plasma must pressure is a free parameter in our model and if it could be
very close to determined more accurately, that will confirm or rule-out the
jet axis. scenario we suggest in this article.
The
temperature in highest post-shock temperatures are generally reached at the base of the jet when the stellar wind encounters the inner disk rim or at large $z$ when the shock front intersects the jet axis. Thus, the position of the hottest post-shock cooling plasma must be very close to the jet axis. In our fiducial model
stays just below 1~MK -- too little to explain X-ray emission in the jets (Fig.~\ref{fig:result}, solid red line),
but the temperature is just sufficient to produce X-ray emission. Paper~I showed that a small
changes faction, about $10^{-3}$, of the total mass loss rate in the
parameters, well within outflow is enough to power the
observational and theoretical constraints, are sufficient observed X-ray emission at the base of DG~Tau's jet. Figure~\ref{fig:rhocool} shows the pre-shock number densities $n_0$ for the four models from Fig.~\ref{fig:results}. A detailed treatment of the post-shock region is beyond the scope of this paper, but an upper limit on the post-shock cooling length $d_{\mathrm{cool}}$ can be derived according to
drive \citet{http://adsabs.harvard.edu/abs/2002ApJ...576L.149R}:
\begin{equation}
d_{\mathrm{cool}} \approx 20.9 \mathrm{ AU}
\left(\frac{10^5\mathrm{ cm}^{-3}}{n_0}\right)
\left(\frac{v_{\mathrm{shock}}}{500\textnormal{ km s}^{-1}}\right)^{4.5}\ .
\end{equation}
The derivation for this formula assumes a cylindrical cooling flow. In contrast, the
maximal temperatures over 1~MK external pressure will continue to compress the gas, as it starts cooling. Since denser gas emits more radiation and thus cools faster, $d_{\mathrm{cool}}$ is only an upper limit. With this in mind, figure~\ref{fig:rhocool} (lower panel) indicates that the cooling lenghts for
our fiducial model is consistent with the X-ray observations that do not resolve the wind shock \citep{2008A&A...488L..13S}. On the other hand, a model with a wind mass loss rate of only $10^{-10}$~M$_{\odot}$~yr$^{-1}$, has a much larger $d_{\mathrm{cool}}$. Since only a
very small fraction of the
stellar mass loss
(other lines in is heated to X-ray emitting temperatures (Fig.\ref{fig:result}, rightmost panel) this scenario does not provide enough X-ray luminosity to explain the observations (paper~I). This model shows that the external presure that confines the wind must be within an order of magnitude or so form the
figure). values we assumed for our fiducial model. Significantly higher pressures require unrealistically fast outflows to push the shock front out to 40~AU and lower presures do not allow a mass flux high enough to power the X-ray luminosity.
Paper~I showed that a small faction, about $10^{-3}$, In our model, it is irrelevant how much of the
total mass loss rate in the outflow external pressure is
enough to power provided by the
observed X-ray emission at magnetic field in the
base disk wind and how much by thermodynamic pressure. The region of
DG~Tau's jet. All but interest is still within the
fiducial scenario Alfv\'en surface (see references in
Fig.~\ref{fig:result} have a significant, but small fraction Sect.~\ref{sect:boundary}), so the influence of the
stellar magntic field probably dominates. Otherwise, the disk wind
that gets heated would also have to
$>1.5$~MK and thus can easily emit X-rays. In be very dense (probably too dense to be consistent with observations) to provide this
article, we concentrate on the stellar wind mass loss, but in the observations pressure. Observationally, it is difficult to distinguish the stellar wind from the disk wind. The slower jet components observed further away from the jet axis carry much of the mass flow \citep{2000ApJ...537L..49B}. Their origin is probably the inner region of the disk and not the star \citep{2003ApJ...590L.107A}. Thus, it is fully consistent that our model predicts a mass loss fraction larger than $10^{-3}$ of the stellar wind at X-ray emitting temperatures. If the disk wind dominates over the stellar wind in mass loss, then the fraction of hot gas in the (stellar plus inner disk) jet might still be small.