A Unified Model for Bipolar Outflows from Young Stars: Kinematic Signatures of Jets, Winds, and Their Magnetic Interplay with the Ambient Toroids

TL;DR

This paper presents a unified model of bipolar outflows from young stars, analyzing their kinematic signatures through simulations that reveal complex structures, instabilities, and velocity features consistent with observations.

Contribution

It introduces a comprehensive model linking jets, winds, and magnetic interactions to observed outflow structures and kinematics in young stellar objects.

Findings

Outflows form bubble-like structures with mixing layers beyond thin-shell models.

Jet profiles show broad base narrowing along the axis, indicating collimation.

Kinematic signatures match observed features in Class 0 to II systems.

Abstract

Kinematic signatures of the jet, winds, multicavities, and episodic shells arising in the unified model of bipolar outflows developed in Shang et al.\ (2020), in which an outflow forms by radially directed, wide-angle toroidally magnetized winds interacting with magnetized isothermal toroids, are extracted in the form of position--velocity diagrams. Elongated outflow lobes, driven by magnetized winds and their interplay with the environment, are dominated by extended bubble structures with mixing layers beyond the conventional thin-shell models. The axial cylindrically stratified density jet carries a broad profile near the base, across the projected velocity of the wide-angle wind, and narrows down along the axis with the collimated flow. The reverse shock encloses the magnetized free wind, forms an innermost cavity, and deflects the flow pattern. Shear, Kelvin--Helmholtz instabilities, and pseudopulses add fine and distinctive features between the jet--shell components, and the fluctuating jet velocities. The broad webbed velocity features connect the extremely high and the low velocities across the multicavities, mimicking nested outflowing slower-wind components. Rings and ovals in the perpendicular cuts trace multicavities at different heights, and the compressed ambient gap regions enrich the low-velocity features with protruding spikes. Our kinematic signatures capture the observed systematics of the high-, intermediate-, and low-velocity components from Class 0 to II jet--outflow systems in molecular and atomic lines. The nested shells observed in HH 212, HH 30, and DG Tau B are naturally explained. Outflows as bubbles are ubiquitous and form an inevitable integrative outcome of the interaction between wind and ambient media.