Dust in the Wolf-Rayet Nebula M1-67

The Wolf-Rayet nebula M1-67 around WR124 is located above the Galactic plane in a region mostly empty of interstellar medium, which makes it the perfect target to study themass-loss episodes associated with the late stages of massive star evolution. Archive photometric observations from Wide-field Infrared Survey Explorer (WISE), Spitzer (MIPS), and Herschel (PACS and SPIRE) are used to construct the spectral energy distribution (SED) of the nebula in the wavelength range of 12-500 mu m. The infrared (photometric and spectroscopic) data and nebular optical data from the literature are modelled simultaneously using the spectral synthesis code CLOUDY, where the free parameters are the gas density distribution and the dust grain-sized distribution. The infrared SED can be reproduced by dust grains with two size distributions: an MRN power-law distribution with grain sizes between 0.005 and 0.05 mu m and a population of large grains with representative size of 0.9 mu m. The latter points towards an eruptive origin for the formation of M1-67. The model predicts a nebular ionized gas mass of M-ion = 9.2(-1.5)(+1.6) M-circle dot and the estimated mass-loss rate during the dust formation period is M approximate to 6 x 10(-4) M-circle dot yr(-1). We discuss the implications of our results in the context of single and binary stellar evolution and propose that M1-67 represents the best candidate for a post-common envelope scenario in massive stars.