2002PASP..114..612C

In this paper, we report on an attempt to optically detect localized and/or variable magnetic fields in the single O4 I(n)f star ζ Puppis and in the WC 8 star in the binary star γ² Velorum with the spectropolarimeter Cassegrain echelle spectrograph mounted on the ESO 3.6 m telescope. The spectra cover 5700-6800 Å with resolution element 0.2 Å. These stars are sufficiently bright in principle to obtain Stokes V spectra with excellent signal-to-noise ratio and temporal resolution at this telescope. We discuss several procedures adapted to the extraction of the polarized signal from broad lines to put constraints on the global and local magnetic fields. Despite some instrumental difficulties, we report a null longitudinal component of the global magnetic field measurement in ζ Pup with σ_Bl∼200 G. We also find no significant activity in Stokes V above 3σ_V∼0.3% in 10 minutes in ζ Puppis's observable photospheric lines, in a spectral bandpass of 0.2-3 Å. We also report a null detection above 3σ_V∼0.3% for the emission lines of γ Vel. Spectral variability in natural light for these stars is also discussed. Finally, we discuss the potential of such spectropolarimetric techniques in the context of new-generation spectropolarimeters.