  SMC AB 6 is the shortest-period (6.5d) Wolf-Rayet (WR) binary in the Small
Magellanic Cloud, and is therefore crucial for the study of binary interaction
and formation of WR stars at low metallicity. The WR component in AB 6 was
previously found to be very luminous (logL=6.3[Lsun]) compared to its reported
orbital mass (8Msun), placing it significantly above the Eddington limit.
Through spectroscopy and orbital analysis of newly acquired optical data taken
with UVES, we aim to understand the peculiar results reported for this system
and explore its evolutionary history.
  Results: We find that AB 6 contains at least four stars. The 6.5d period WR
binary comprises the WR primary (WN3:h, star A) and a rather rapidly rotating
early O-type companion (O5.5 V, star B). Static N and He lines suggest the
presence of an emission line star (O5.5 I(f), star C). Finally, narrow
absorption lines portraying a long-term radial velocity variation show the
existence of a fourth star (O7.5 V, star D). Star D appears to form a second
140d period binary together with a fifth stellar member, which is a B-type
dwarf or a black hole. It is not clear that these additional components are
bound to the WR binary. The WR star is found to be less luminous than
previously thought (logL = 5.9[Lsun]) and, adopting 41Msun for star B, more
massive (18Msun). Correspondingly, the WR star does not exceed the Eddington
limit. We derive the initial masses of 60 and 40Msun for stars A and B and an
age of 3.9 Myr for the system. The WR binary likely experienced nonconservative
mass transfer in the past supported by the relatively rapid rotation of star B.
  Conclusion: Our study shows that AB 6 is a multiple -- probably quintuple --
system. This finding resolves the previously reported puzzle of the WR primary
exceeding the Eddington limit and suggests that the WR star exchanged mass with
its companion in the past.
