1999A&A...351..543Z

We present the results of analyzing Hα spectra of the radio emitting X-ray binary LS I+61 303. For the first time, the same 26.5 d radio period is clearly detected in the Hα emission line. Moreover, the equivalent width and the peak separation of the Hα emission line seem also to vary over a time scale of 1600 days. This points towards the ∼4yr modulation, detected in the radio outburst amplitude, being probably a result of variations in the mass loss rate of the Be star and/or density variability in the circumstellar disk. In addition, the dependence of the peak separation from the equivalent width informs us that the LS I+61 303 circumstellar disk is among the densest of Be-stars.