Low velocity streams inside the planetary nebula H 2-18. A 3D photoionization and kinematical reconstruction

TL;DR

This study uses 3D photoionization and kinematic modeling of the planetary nebula H 2-18 to reveal complex internal structures and velocity fields, enhancing understanding of nebular shaping processes without requiring energetic jets.

Contribution

It introduces a detailed 3D model that uncovers hidden dense structures and consistent kinematics, improving upon previous models of planetary nebulae.

Findings

Discovery of a dense, cylindrical inner structure within the nebula.

Shared isotropic velocity field with increasing velocity away from the star.

No evidence of energetic jets, with low velocities explaining nebular shapes.

Abstract

Aims. Numerous planetary nebulae show complicated inner structures not obviously explained. For one such object we undertake a detailed 3D photoionization and kinematical model analysis for a better understanding of the underlying shaping processes. Methods. We obtained 2D ARGUS/IFU spectroscopy covering the whole nebula in selected, representative emission lines. A 3D photoionization modelling was used to compute images and line profiles. Comparison of the observations with the models was used to fine-tune the model details. This predicts the approximate nebular 3D structure and kinematics. Results. We found that within a cylindrical outer nebula there is a hidden, very dense, bar-like or cylindrical inner structure. Both features are co-axial and are inclined to the sky by 40 deg. A wide asymmetric one-sided plume attached to one end of the bar is proposed to be a flat structure. All nebular components share the same kinematics, with an isotropic velocity field which monotonically increases with distance from the star before reaching a plateau. The relatively low velocities indicate that the observed shapes do not require particularly energetic processes and there is no indication for the current presence of a jet. The 3D model reproduces the observed line ratios and the detailed structure of the object significantly better than previous models.