Hot bubbles of planetary nebulae with hydrogen-deficient winds I. Heat conduction in a chemically stratified plasma

TL;DR

This study investigates how chemical composition influences heat conduction in planetary nebulae bubbles, revealing that hydrogen-deficient compositions slightly alter temperature gradients but have minimal impact on observable X-ray properties.

Contribution

The paper extends heat conduction modeling to chemically stratified plasmas, enabling more accurate simulations of hydrogen-deficient planetary nebulae.

Findings

Heat conduction in hydrogen-deficient PNe is nearly as efficient as in hydrogen-rich cases.

The bubble temperature slightly increases with the new heat conduction model.

X-ray emission properties are largely unaffected by chemical composition differences.

Abstract

Heat conduction has been found a plausible solution to explain discrepancies between expected and measured temperatures in hot bubbles of planetary nebulae (PNe). While the heat conduction process depends on the chemical composition, to date it has been exclusively studied for pure hydrogen plasmas in PNe. A smaller population of PNe show hydrogen-deficient and helium- and carbon-enriched surfaces surrounded by bubbles of the same composition; considerable differences are expected in physical properties of these objects in comparison to the pure hydrogen case. The aim of this study is to explore how a chemistry-dependent formulation of the heat conduction affects physical properties and how it affects the X-ray emission from PN bubbles of hydrogen-deficient stars. We extend the description of heat conduction in our radiation hydrodynamics code to work with any chemical composition. We then compare the bubble-formation process with a representative PN model using both the new and the old descriptions. We also compare differences in the resulting X-ray temperature and luminosity observables of the two descriptions. The improved equations show that the heat conduction in our representative model of a hydrogen-deficient PN is nearly as efficient with the chemistry-dependent description; a lower value on the diffusion coefficient is compensated by a slightly steeper temperature gradient. The bubble becomes somewhat hotter with the improved equations, but differences are otherwise minute. The observable properties of the bubble in terms of the X-ray temperature and luminosity are seemingly unaffected.