Hot bubbles of planetary nebulae with hydrogen-deficient winds

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 carbonenriched 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.

Formation and X-ray emission from hot bubbles in planetary nebulae – II. Hot bubble X-ray emission

“…For instance, at early times we could expect the abundances to be dominated by hot, shocked stellar wind material, while at later times nebular abundances will determine the spectral characteristics. This is more relevant for the case of PNe with [WR]-type nuclei and has been recently explored by Sandin et al (2016).…”

“…However, they favoured the numerical results from their efficient conduction method, arguing that the low-efficiency conduction method results in limb-brightened synthetic X-ray surface brightness profiles, which did not match some observations at the time. This group has recently extended its numerical simulations to study the X-ray emission from PNe with hydrogen-deficient winds (Sandin et al 2016).…”

Planetary Nebulae: Sources of Enlightenment

“…Radiation-hydrodynamic simulations of these hot bubbles and their x-ray emission have been carried out by several groups. Steffen, Schönberner, & Warmuth (2008) and Sandin et al (2016) demonstrated the importance of thermal conduction at the interface between the shocked wind and the nebular gas. Toalá & Arthur (2014 performed high-resolution two-dimensional calculations following the evolution of these hot bubbles.…”

X-ray Studies of Planetary Nebulae

“…Supporting evidence for heat conduction has been found from multi-wavelength studies of the 10 5 K transition region (see Ruiz et al 2013 and the contribution by Guerrero in this volume). Studies of heat conduction in nebula with distinct chemical compositions are ongoing (see Sandin et al 2016 and the contribution by Schoenberner in this volume). Other predictions of heat conduction models, such as the radial distribution of hot bubble emission (Freeman & Kastner 2016) and mixing of nebular and fast wind elemental abundances (Maness & Vrtilek 2003) are limited by the capabilities of the two modern X-ray observatories.…”