Herschel observations of the nebula M1-67 around the Wolf-Rayet star WR 124

TL;DR

This study uses Herschel infrared observations combined with optical imaging to analyze the composition, structure, and origin of the nebula M1-67 around WR 124, revealing a dusty, clumpy nebula with processed material ejected during a specific stellar evolutionary phase.

Contribution

It provides the first detailed infrared spectroscopic analysis of M1-67, estimating dust mass, composition, and linking nebular ejection to a RSG/YSG phase of a 32 Msun star.

Findings

Nebula extends up to 1 pc with clumpy dust and ionized gas.

Dust mass estimated at 0.22 solar masses with large grains.

Ejection occurred during a RSG/YSG phase of the star.

Abstract

Infrared Herschel imaging and spectroscopic observations of the nebula M1-67 around the Wolf-Rayet star WR 124 have been obtained along with optical imaging observations. The infrared images reveal a clumpy dusty nebula that extends up to 1 pc. The comparison with the optical images shows that the ionized gas nebula coincides with the dust nebula, the dust and the gas being mixed together. A photodissociation region is revealed from the infrared spectroscopic analysis. The analysis of the infrared spectrum of the nebula, where forbidden emission lines of ionized elements were detected, showed that the nebula consists of mildly processed material with the calculated abundance number ratios being N/O = 1.0 +/- 0.5 and C/O = 0.46 +/- 0.27. Based on a radiative transfer model, the dust mass of the nebula was estimated to be 0.22 Msun with a population of large grains being necessary to reproduce the observations. The comparison of the mass-loss rate and the abundance ratios to theoretical models of stellar evolution led to the conclusion that the nebular ejection took place during a RSG/YSG evolutionary phase of a central star with an initial mass of 32 Msun.