The ubiquity of turbulence in the expanding kinematics of the ionized shells of Galactic planetary nebulae

TL;DR

This study analyzes residual velocities in 105 Galactic planetary nebulae, revealing pervasive turbulence that is slightly higher in inner zones and more prominent in nebulae with H-poor central stars.

Contribution

It provides the largest analysis to date of turbulence in planetary nebulae using high-dispersion spectra, highlighting the prevalence and characteristics of turbulence.

Findings

Residual velocities are transonic or slightly supersonic in PNe.

Higher residual velocities are observed in inner zones of PNe.

PNe with H-poor central stars show higher residual velocities.

Abstract

We present an analysis of the residual velocities from a sample of 105 Galactic planetary nebulae (PNe), the largest done to date on this subject. The analysis has been carried out with long-slit, high dispersion echelle spectra. The data were drawn from the San Pedro M\'artir Kinematic Catalogue of Galactic Planetary Nebulae. The residual velocity is identified with turbulence in the plasma and is derived by decomposing the emission line profiles into their structural contributors. Turbulence seems pervasive throughout all the PNe in the sample. We find the values for the residual velocities in the sample to be either transonic or slightly supersonic in the ionized environment. When residual velocities of [N II], [O III] and He II in the same PNe are compared, there is a tendency for the residual velocities of the higher ionized ion to be larger by about 5-10 km s$^{-1}$, indicating that the turbulent structure is larger in the inner zones of the PN. We find in general no clear correlation between the residual velocities and other nebular parameters such as morphology, global expansion velocities, ionization degree and binary cores. The only exception is the case of PNe with H-poor ([WR]-type) central stars, where we confirm previous results that have consistently shown higher residual velocities for this group of PNe as compared to those with H-rich central star atmospheres. Turbulence seems to be a localised, random, dissipative process occurring in the inner sections of the shell and may affect its early evolution.