The origin of the magnetic field in massive O-type stars is still under
debate. To model the physical processes responsible for the generation of O
star magnetic fields, it is important to understand whether correlations
between the presence of a magnetic field and stellar evolutionary state,
rotation velocity, kinematical status, and surface composition can be
identified. The O4Ief supergiant zeta Pup is a fast rotator and a runaway star,
which may be a product of a past binary interaction, possibly having had an
encounter with the cluster Trumper 10 some 2Myr ago. The currently available
observational material suggests that certain observed phenomena in this star
may be related to the presence of a magnetic field. We acquired
spectropolarimetric observations of zeta Pup with FORS2 mounted on the 8-m Antu
telescope of the VLT to investigate if a magnetic field is indeed present in
this star. We show that many spectral lines are highly variable and probably
vary with the recently detected period of 1.78d. No magnetic field is detected
in zeta Pup, as no magnetic field measurement has a significance level higher
than 2.4sigma. Still, we studied the probability of a single sinusoidal
explaining the variation of the longitudinal magnetic field measurements.Comment: 12 pages, 2 tables, 8 figures, accepted for publication in Ap
