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

¹ Institut d’Astrophysique et de Géophysique, Université de Liège, Quartier Agora, Allée du 6 août, 19C−Bât. B5c, 4000 Liège ( Sart-Tilman), Belgium
e-mail: C.VamvatiraNakou@alumni.ulg.ac.be
² Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, Bus 2401, 3001 Leuven, Belgium
³ Koninklijke Sterrenwacht van België, Ringlaan 3, 1180 Brussels, Belgium
⁴ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

Received: 30 October 2015
Accepted: 29 January 2016

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 M_⊙ 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 M_⊙.