Spectroscopic study of Of^+^ supergiants

O-type supergiants with emission lines (OIf^+^) are considered to be intermediate between these two classes. The scope of this paper is to investigate the spectral variability of three Of^+^ supergiants.

We constituted spectral time series of unprecedented quality for our targets (~200 spectra in total), essentially in the blue domain, covering timescales from a few hours up to a few years. Temporal Variance Spectrum and Fourier analyses were performed in order to characterize their spectral variability.