Astron. Astrophys. 333, 989-1000 (1998)

5. Conclusions and summary

Adopting a spatial approach we have been able to follow the growth of a perturbation as it advanced in space, advected by the flux. In addition we could include the whole extension of the jet in the numerical domain, and not only a portion, as in the temporal approach. This would favor the direct application of the results to the astrophysical context of YSO jets, as attempted in Paper IV.

On the other side, the finite extent of the grid set a limit on the duration of the simulations, since when the perturbation reached the right boundary, we could not advance any more, neither in space nor in time. As a consequence we could be looking at a situation in which the latest phase is not yet fully evolved, or it is not yet present in the domain. Another important difference of the spatial approach vs the temporal one is the presence of a 'head', which is a region formed by the front shock, that is evolving with time.

The results obtained in the calculations can be summarized as follows:

• 1. For cylindrical geometry and radiation is very effective in suppressing the matter entrainment, and we see the generation of a great deal of biconical shocks that evolve very little in time, apart from a merging event.
• 2. Dense () cylindrical jets evolve in a very different fashion: radiation does not suppress entrainment; moreover, the shocks are closer each other and not clearly distinguishable. Matter entrainment bears different characteristics with respect to the adiabatic case, being due to very localized ejection of cold filaments that drag the external medium.
• 3. Equal density () radiative, symmetrically perturbed, slab jets evolve faster than cylindrical ones, display a low number of shocks that tend to merge in a single structure; entrainment is not reduced by radiation.

As discussed before, radiative cylindrical jets with present a series of 10-15 quasi-equally spaced line emission knots, and in Paper IV we show how the relative calculations can be applied to HH jets with morphological properties such as HH34 and HH111. Instead, calculations for radiative high density jets () lead to very different morphologies, as summarized in point 2; as a consequence of this, and identifying the shocked region with the line emitting regions of YSO jets, the high density case could be relevant for sources like L 1551 IRS 5, where the emission knots are few and not clearly identified (Ray 1996). Moreover, as discussed by Reipurth & Heathcote (1997) for the HH47 jet, HST images show that mass entrainment appears localized around shocks instead being due to a widespread turbulence, in agreement with our findings for high density jets discussed above.

© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998

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