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

TL;DR

This study uses 3D hydrodynamic simulations to analyze how rotation affects emission line profiles in proto-stellar jets, challenging the assumption that observed velocity shifts confirm magnetocentrifugal acceleration.

Contribution

It introduces a non-magnetic, rotating jet model with detailed emission line calculations, highlighting that rotation alone can produce velocity shifts similar to non-rotating jets.

Findings

Radial velocity shifts are similar in rotating and non-rotating models.

Rotation effects on line profiles may be misinterpreted as evidence of magnetocentrifugal acceleration.

Simulations suggest caution in using velocity shifts as definitive indicators of jet launching mechanisms.

Abstract

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