* Astronomy

Title: WR 148: Identifying the companion of an extreme runaway massive binary
Author: Melissa Munoz, Anthony F.J. Moffat, Grant M. Hill, Tomer Shenar, Noel D. Richardson, Herbert Pablo, Nicole St-Louis, Tahina Ramiaramanantsoa

WR 148 (HD 197406) is an extreme runaway system considered to be a potential candidate for a short-period (4.3173 d) rare WR + compact object binary. Provided with new high resolution, high signal-to-noise spectra from the Keck observatory, we determine the orbital parameters for both the primary WR and the secondary, yielding respective projected orbital velocity amplitudes of 88.1±3.8 km s^-1 and 79.2±3.1 km s^-1 and implying a mass ratio of 1.1±0.1. We then apply the shift-and-add technique to disentangle the spectra and obtain spectra compatible with a WN7ha and an O4-6 star. Considering an orbital inclination of ~67°, derived from previous polarimetry observations, the system's total mass would be a mere 2-3 solar masses , an unprecedented result for a putative massive binary system. However, a system comprising a 37 solar masses secondary (typical mass of an O5V star) and a 33 solar mass primary (given the mass ratio) would infer an inclination of ~18°. We therefore reconsider the previous methods of deriving the orbital inclination based on time-dependent polarimetry and photometry. While the polarimetric results are inconclusive requiring better data, the photometric results favour low inclinations. Finally, we compute WR 148's space velocity and retrace the runaway's trajectory back to the Galactic plane (GP). With an ejection velocity of 198±27 km s^-1 and a travel time of 4.7±0.8 Myr to reach its current location, WR 148 was most likely ejected via dynamical interactions in a young cluster.

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