Emission lines from rotating proto-stellar jets with variable velocity profiles. I. Three-dimensional numerical simulation of the non-magnetic case

摘要

Using the Yguazu-a three-dimensional hydrodynamic code, we have computed aset of numerical simulations of heavy, supersonic, radiatively cooling jetsincluding variabilities in both the ejection direction (precession) and the jetvelocity (intermittence). In order to investigate the effects of jet rotationon the shape of the line profiles, we also introduce an initial toroidalrotation velocity profile, in agreement with some recent observational evidencefound in jets from T Tauri stars which seems to support the presence of arotation velocity pattern inside the jet beam, near the jet production region.Since the Yguazu-a code includes an atomic/ionic network, we are able tocompute the emission coefficients for several emission lines, and we generateline profiles for the H, [O I]6300, [S II]6716 and [N II]6548 lines. Usinginitial parameters that are suitable for the DG Tau microjet, we show that thecomputed radial velocity shift for the medium-velocity component of the lineprofile as a function of distance from the jet axis is strikingly similar forrotating and non-rotating jet models. These findings lead us to put forwardsome caveats on the interpretation of the observed radial velocity distributionfrom a few outflows from young stellar objects, and we claim that these datashould not be directly used as a doubtless confirmation of themagnetocentrifugal wind acceleration models.