The dynamics of the nebula M1-67 around the run-away Wolf-Rayet star WR 124

¹ Astronomical Institute, Princetonplein 5, 3584 CC Utrecht, The Netherlands
² SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

Corresponding author: H. J. G. L. M. Lamers, lamers@astro.uu.nl

Received: 18 July 2002
Accepted: 7 November 2002

Abstract

A new point of view on the dynamics of the circumstellar nebula M1-67 around the run-away Wolf-Rayet (WR) star WR 124 is presented. We simulated the outbursts of nebulae with different morphologies, to compare the results to the observed dynamical spectra of M1-67. We found that it has been interacting with the surrounding ISM and has formed a bow shock due to its high velocity of about relative to the local ISM. The star is about 1.3 parsec away from the front of this bow shock. The outbursts that are responsible for the nebula are assumed to be discrete outbursts that occurred inside this bow shock. The ejecta collide with this bow shock shortly after the outburst. After the collision, they are dragged away by the pressure of the ISM, along the surface of the bow shock. The bow shock is oriented in such way that we are looking from the rear into this paraboloid, almost along the main axis. Evidence for this is given firstly by the fact that the far hemisphere is much brighter than the near hemisphere, secondly by the fact that there is hardly any emission found with radial velocities higher than the star's radial velocity, thirdly by the fact that the star looks to be in the centre of the nebula, as seen from Earth, and finally by the asymmetric overall velocity distribution of the nebula, which indicates higher radial velocities in the centre of the nebula, and lower velocities near the edges. We find evidence for at least two discrete outbursts that occurred inside this bow shock. For these outbursts, we find expansion velocities of and dynamical timescales of about 0.8 and yr, which are typical values for LBV outbursts. We therefore conclude that M1-67 originates from several outbursts that occurred inside the bow shock around WR 124, during an LBV phase that preceded the current WR phase of the star.