Integral field spectroscopy of M1-67. A Wolf-Rayet nebula with luminous blue variable nebula appearance⋆
1 Instituto de Astrofísica de Andalucía (IAA – CSIC), Glorieta de la Astronomía S/N, 18008 Granada, Spain
2 Leiden Observatory, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
3 Centro Astronómico Hispano Alemán, Calar Alto, CSIC-MPG, C/Jess Durbán Remn 2-2, 04004 Almería, Spain
4 Departament de Física i Enginyeria Nuclear, EUETIB, Universitat Politécnica de Catalunya, C. Comte Urgell 187, 08036 Barcelona, Spain
Received: 22 November 2012
Accepted: 15 March 2013
Aims. 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.
Methods. 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 obtained and analysed infrared spectroscopic data and the MIPS 24 μm image of M1-67 from Spitzer.
Results. 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. Furthermore, we find two regions placed outside of the bipolar structure with different spectral and chemical properties. 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 24 μm.
Taking the evolution of a 60 M⊙ 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 stage. The star has entered the WR phase recently without apparent signs of interaction between WR-winds and interstellar material.
Key words: ISM: bubbles / ISM: abundances / ISM: kinematics and dynamics / ISM: individual objects: M1-67 / stars: Wolf-Rayet
© ESO, 2013