Integral field spectroscopy of M1-67. A Wolf-Rayet nebula with LBVN
  appearance
  This work aims to disentangle the morphological, kinematic, and chemical
components of the nebula M1-67 to shed light on its process of formation around
the central Wolf-Rayet (WR) star WR124. We have carried out integral field
spectroscopy observations over two regions of M1-67, covering most of the
nebula in the optical range. Maps of electron density, line ratios, and radial
velocity were created to perform a detailed analysis of the two-dimensional
structure. We studied the physical and chemical properties by means of
integrated spectra selected over the whole nebula. Photoionization models were
performed to confirm the empirical chemical results theoretically. In addition,
we analysed infrared spectroscopic data and the MIPS 24micron image of M1-67
from Spitzer. We find that the ionized gas of M1-67 is condensed in knots
aligned in a preferred axis along the NE-SW direction, like a bipolar
structure. Both electron density and radial velocity decrease in this direction
when moving away from the central star. From the derived electron temperature,
Te~8200 K, we have estimated chemical abundances, obtaining that nitrogen
appears strongly enriched and oxygen depleted. From the last two results, we
infer that this bipolarity is the consequence of an ejection of an evolved
stage of WR124 with material processed in the CNO cycle. The infrared study has
revealed that the bipolar axis is composed of ionized gas with a low ionization
degree that is well mixed with warm dust and of a spherical bubble surrounding
the ejection at 24micron. Taking the evolution of a 60 Mo star and the temporal
scale of the bipolar ejection into account, we propose that the observed gas
was ejected during an eruption in the luminous blue variable. The star has
entered the WR phase recently without apparent signs of interaction between
WR-winds and interstellar material.
