On the moving subfeatures in the Be star zeta Oph

We analyse a series of line profile observations of the He I 6678 line in x i Oph, A period analysis on these data using the mode and moments of the li ne profile confirms the two previously known periods. We describe a new met hod of mode identification for pulsating stars in which the calculated prof iles are directly fitted to observed profiles. The method yields the full s et of pulsational parameters including the spherical harmonic degree, l, an d azimuthal number, m, Application of the method to these data confirms the mode identifications previously suggested for the two periodicities.: We f ind that the derived pulsational parameters are physically realistic and co nclude that non-radial pulsation is the most likely explanation for the tra velling subfeatures. However, a unique mode identification is still not pos sible - several non-sectorial modes fit the data as well as the usually ado pted sectorial identifications. The predicted photometric amplitudes are in good accord with upper limits derived from photometric observations. We co nclude that xi Oph is a star in the beta Cep instability strip in which two modes of high degree (probably l = 4 and l = 8) are excited. We present an interpretation of these findings in which the cause of the low-order line profile and light variations in periodic Be scars is corotating photospheri c clouds, while the travelling subfeatures are incidental to the Be phenome non and are a result of non-radial pulsation.