Velocity segregation in a clump-like outflow with a non-top hat velocity cross-section

TL;DR

The paper presents a model explaining high velocity clumps in planetary nebulae and star formation outflows, showing that velocity stratification leads to a linear velocity-position relation similar to observed 'Hubble law' features.

Contribution

It introduces a simple ejection model with velocity stratification that reproduces observed velocity structures in outflows, supported by analytic and numerical results.

Findings

Model produces a linear velocity vs. position ramp.

Reproduces observed 'Hubble law' clumps.

Supports stratified ejection as a mechanism in outflows.

Abstract

High velocity clumps joined to the outflow source by emission with a "Hubble law" ramp of linearly increasing radial velocity vs. distance are observed in some planetary nebulae and in some outflows in star formation regions. We propose a simple model in which a "clump" is ejected from a source over a period $\tau_0$, with a strong axis to edge velocity stratification. This non-top hat cross section results in the production of a highly curved working surface (initially being pushed by the ejected material, and later coasting along due to its inertia). From both analytic models and numerical simulations we find that this working surface has a linear velocity vs. position ramp, and therefore reproduces in a qualitative way the "Hubble law clumps" in planetary nebulae and outflows from young stars.