BAT99 126: A multiple Wolf-Rayet system in the Large Magellanic Cloud
  with a massive near-contact binary
  BAT99 126 is a multiple system in the Large Magellanic Cloud containing a
Wolf-Rayet (WR) star, which has a reported spectroscopic (orbital) period of
25.5 days and a photometric (orbital) period of 1.55 days, and hence is
potentially one of the shortest WR binaries known to date. Such short-period
binary systems containing a WR star in low-metallicity environments are prime
candidate progenitors of black-hole (BH) mergers. By thoroughly analysing the
spectroscopic and photometric data, we aim to establish the true multiplicity
of BAT99 126, characterise the orbit(s) of the system, measure the physical
properties of its individual components, and determine the overall evolutionary
status of the system. Using newly acquired high resolution spectra, we measured
radial velocities and performed a spectral analysis of the individual
components. We estimated the age of the system and derived an evolutionary
scenario for the 1.55-day system. BAT99 126 comprises at least four components.
The 1.55-day photometric signal originates in an eclipsing O+O binary of
spectral types O4 V and O6.5 V, and masses of 36+/-5 MSun and 15+/-2 MSun,
respectively. For the WR star, we derived a spectral type WN2.5-3 and reject
the previously reported 25.5-d period. We find evidence in the composite
spectra of a fourth component, a B1 V star, which shows radial velocity
variation. The configurations of the B-type star, WR star, and possible
additional undetected components remain unknown. We estimated the age of the
system to be 4.2 Myr. The O+O binary likely went through a phase of
conservative mass transfer and is currently a near-contact system. We show that
BAT99 126 is a multiple - quadruple or higher-order - system with a total
initial mass > 160 MSun. The 1.55-day O+O binary most likely will not evolve
towards a BH+BH merger, but instead will merge before the components collapse
to BHs.
