Spatially-resolved spectroscopic investigation of the born-again planetary nebula A 78

TL;DR

This study uses spatially-resolved spectroscopy to analyze the chemical and physical properties of the born-again planetary nebula A 78, revealing complex morphology, unusual abundance ratios, and inhomogeneous dust distribution, suggesting a possible binary evolution.

Contribution

It provides detailed spatially-resolved chemical and physical analysis of A 78, highlighting new insights into its morphology, dust distribution, and possible binary evolution path.

Findings

Inner knots confirm born-again nature with VLTP-like abundances

High Ne/O ratio suggests alternative evolutionary scenarios

Inhomogeneous extinction correlates with dust-rich regions

Abstract

We present the analysis of spatially-resolved spectroscopic observations of the born-again planetary nebula (PN) A 78 that are used to investigate the chemistry and physical properties of its three main morphological components, namely the inner knots, its eye-like structure, and the low surface-brightness outer nebula. The H-poor chemical abundances of the inner knots confirm the born-again nature of A 78, with a N/O abundances ratio consistent with the predictions of very late thermal pulses (VLTP). On the other hand, the high Ne/O is not expected in VLTP events, which prompts a possible different evolutionary path may be involving a binary system. The low N/O ratio and He/H abundances of the outer shell are indicative of a low-mass progenitor, whereas the chemical abundances of the eye-like structure, which results from the interaction between the H-poor born-again material and the outer nebula, evidence their mixture. Unlike previous works, the extinction is found to be inhomogeneous, being much higher towards the H-poor inner knots, where the presence of large amounts of C-rich dust has been previously reported. Dust-rich material seems to diffuse into outer nebular regions, resulting in zones of enhanced extinction.