Evidence of Hα periodicities in LS I+61°303

We present the results of analyzing H alpha spectra of the radio emitting X-ray binary LS I+61 degrees 303. For the first time, the same 26.5 d radio period is clearly detected in the H alpha emission line. Moreover, the equivalent width and the peak separation of the H alpha emission line seem also to vary over a time scale of 1600 days. This points towards the similar to 4 yr 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 degrees 303 circumstellar disk is among the densest of Be-stars.