The B-type variable HD 131120 modelled by rotational modulation

We present ground-based multi-colour Geneva photometry and high-resolution spectra of the variable B-type star HD 131120. All sets of data reveal a monoperiodic star with a period of 1.569 days. We compare the variability of the star with a non-radial g-mode pulsation model and with a rotational modulation model. The latter model appears to be the best explanation for the observed line-profile variations of the star. Moreover, contrary to the pulsational model, it is able to reproduce the behaviour of the first three moments of the Si and He lines as well as the large variability of their equivalent width. We therefore remove the star from the list of new Slowly Pulsating B stars found from Hipparcos data. Based on observations obtained with the Swiss photometric telescope and ESO's CAT/CES telescope, both situated at La Silla, Chile