Planetary nebulae with Wolf-Rayet-type central stars -- I. The case of the high-excitation NGC 2371

TL;DR

This paper analyzes the planetary nebula NGC 2371 with a Wolf-Rayet central star, revealing its complex multipolar morphology, high ionization, and evolutionary history through detailed spectroscopic and imaging data.

Contribution

It provides a detailed morphological and spectroscopic analysis of NGC 2371, highlighting its bipolar structure and evolutionary implications, with new insights into its dense knots and high-ionization features.

Findings

NGC 2371 has a multipolar, bipolar morphology with lobes and a central cavity.

Dense knots are likely the oldest structures, remnants of earlier ejections.

Spectral analysis confirms the central star as a [WO1] type.

Abstract

We present the analysis of the planetary nebula (PN) NGC 2371 around the [Wolf-Rayet] ([WR]) star WD 0722$+$295. Our Isaac Newton Telescope (INT) Intermediate Dispersion Spectrograph (IDS) spectra, in conjunction with archival optical and UV images, unveil in unprecedented detail the high-ionisation of NGC 2371. The nebula has an apparent multipolar morphology, with two pairs of lobes protruding from a barrel-like central cavity, a pair of dense low-ionisation knots misaligned with the symmetry axis embedded within the central cavity, and a high excitation halo mainly detected in He II. The abundances from the barrel-like central cavity and dense knots agree with abundance determinations for other PNe with [WR]-type CSPNe. We suggest that the densest knots inside NGC 2371 are the oldest structures, remnant of a dense equatorial structure, whilst the main nebular shell and outer lobes resulted from a latter ejection that ended the stellar evolution. The analysis of position-velocity diagrams produced from our high-quality spectra suggests that NGC 2371 has a bipolar shape with each lobe presenting a double-structure protruding from a barrel-like central region. The analysis of the spectra of WD 0722$+$295 results in similar stellar parameters as previously reported. We corroborate that the spectral sub-type corresponds with a [WO1] type.