Ionization structure and chemical abundances of the Wolf-Rayet nebula NGC6888 with integral field spectroscopy

TL;DR

This study uses integral field spectroscopy to analyze the ionization, chemical composition, and kinematics of the Wolf-Rayet nebula NGC6888, revealing complex spatial variations and shock interactions.

Contribution

It provides detailed spatially-resolved maps and chemical abundance analysis of NGC6888, highlighting shock signatures and nebular evolution scenarios.

Findings

Electron densities range from <100 to 360 cm^(-3)

Nitrogen abundance varies up to a factor of 10 across regions

Oxygen is slightly underabundant, helium is overabundant

Abstract

This work aims to search for the observational footprints of the interactions between the interstellar medium (ISM) and stellar winds in the Wolf-Rayet (WR) nebula NGC6888 in order to understand its ionization structure, chemical composition, and kinematics. We have collected a set of integral field spectroscopy observations across NGC6888, obtained with PPAK in the optical range performing both 2D and 1D analyses. Attending to the 2D analysis in the northeast part of NGC6888, we have generated maps of the extinction structure and electron density. We produced statistical frequency distributions of the radial velocity and diagnostic diagrams. We have found that the spectra of a localized region to the southwest of this pointing can be represented well by shock models. Furthermore, we performed a thorough study of integrated spectra in nine regions over the whole nebula. We derived electron densities ranging from <100 to 360 cm^(-3). The electron temperature varies from ~7700 K to ~10200 K. A strong variation of up to a factor 10 between different regions in the nitrogen abundance has been found: N/H appears lower than the solar abundance in those positions observed at the edges and very enhanced in the observed inner parts. Oxygen appears slightly underabundant with respect to solar value, whereas the helium abundance is found to be above it. Finally, we provide a scenario for the evolution of NGC6888 to explain the features observed. This scheme consists of a structure of multiple shells.