Formation and X-ray emission from Hot Bubbles in Planetary Nebulae. I. Hot Bubble formation

TL;DR

This study uses high-resolution simulations to investigate hot bubble formation and evolution in planetary nebulae, focusing on the effects of hydrodynamical mixing and thermal conduction on their dynamics and X-ray emission.

Contribution

It provides new insights into how thermal conduction and hydrodynamical mixing influence hot bubble dynamics and stability in planetary nebulae.

Findings

Thermal conduction prevents bubble pressure loss by sealing gaps in the shell.

Models without conduction show significant mass mixing into the hot bubble.

Bubble dynamics differ markedly depending on the inclusion of thermal conduction.

Abstract

We carry out high resolution two-dimensional radiation-hydrodynamic numerical simulations to study the formation and evolution of hot bubbles inside planetary nebulae (PNe). We take into account the evolution of the stellar parameters, wind velocity and mass-loss rate from the final thermal pulses during the asymptotic giant branch (AGB) through to the post-AGB stage for a range of initial stellar masses. The instabilities that form at the interface between the hot bubble and the swept-up AGB wind shell lead to hydrodynamical interactions, photoevaporation flows and opacity variations. We explore the effects of hydrodynamical mixing combined with thermal conduction at this interface on the dynamics, photoionization, and emissivity of our models. We find that even models without thermal conduction mix significant amounts of mass into the hot bubble. When thermal conduction is not included, hot gas can leak through the gaps between clumps and filaments in the broken swept-up AGB shell and this depressurises the bubble. The inclusion of thermal conduction evaporates and heats material from the clumpy shell, which expands to seal the gaps, preventing a loss in bubble pressure. The dynamics of bubbles without conduction is dominated by the thermal pressure of the thick photoionized shell, while for bubbles with thermal conduction it is dominated by the hot, shocked wind.