  Context. Massive-binary evolution models predict that some systems will go
through an evolutionary phase where the original primary has become a supernova
and left a compact object behind that then orbits a Wolf-Rayet (hereafter, WR)
star. WR 138 is an X-ray bright WR star that has been described as a triple
system, including a compact companion in a short-period orbit. Aims. Our goal
is to search for spectroscopic evidence of a compact companion around WR 138.
Methods. We used optical and X-ray spectra to search for signatures of a
compact companion, which can be revealed by systematic variations in WR optical
spectral lines induced by orbital motion of the compact companion or by hard,
luminous X-rays from accretion onto this companion. Results. The optical
spectra display emission-line profile variations that are most probably caused
by clumps inside the stellar winds. The radial velocities do not vary on a
short time-scale compatible with the suggested orbital period of a putative
compact companion. The X-ray spectra are found to be normal for a WN5-6+OB
system with no indication of accretion by a compact companion. Conclusions.
There is no evidence for the presence of a compact companion, and we therefore
conclude that WR 138 is a normal long-period (P~1521 d) eccentric WR+OB system.

Solar and Stellar Astrophysics