Spectral variability of the born-again ejecta in A 58

Abstract

Born-again planetary nebulae (PNe) allow investigating stellar evolution, dust production, and nebular shocks in human timescales. Here we present an analysis of multi-epoch optical spectroscopic observations of the born-again PN A 58 around V605 Aql, which experienced a very late thermal pulse (VLTP) about a century ago. The H-deficient ejecta has experienced a considerable brightening in the time period considered, from 1996 to 2021, with notable changes also in many emission line ratios. Neither the reduction of the extinction caused by the dilution of the ejecta nor the increase of the ionizing photon flux from the central star seem capable to produce these spectral changes, which are instead attributed to shocks in the bipolar H-poor outflow dissociating molecular material and propagating through the outer nebula.