  The spectrum of the Wolf-Rayet (WR) star WR 63 contains spectral lines of two
different O stars that show regular radial velocity (RV) variations with
amplitudes of ~160 and ~225 km/s on a ~4.03 d period. The light-curve shows two
narrow eclipses that are 0.2 mag deep on the same period as the RV changes. On
the other hand, our data show no significant RV variations for the WR spectral
lines. Those findings are compatible with WR 63 being a triple system composed
of two non-interacting late O stars orbiting a WR star on a period larger than
1000 days. The amplitude of the WR spectral line-profile variability reaches
7-8% of the line intensity and seems related to a 0.04 mag periodic photometric
variation. Large wind density structures are a possible origin of this
variability, but our data are not sufficient to verify this. Our analysis shows
that, should the three stars be bound, they would be coeval with an age of
about 5.9+/-1.4 Myrs. The distance to the O stars is estimated to be 3.4+/-0.5
kpc. Their dynamical masses are 14.3+/-0.1 and 10.3+/-0.1 M_sol. Using
rotating, single star evolutionary tracks, we estimate their initial masses to
be 18+/-2 and 16+/-2 M_sol for the primary and the secondary, respectively.
Regular spectral monitoring is required in the future to detect RV variations
of the WR star that would prove that it is gravitationally bound to the close
O+OB system and to determine its mass.
