  We present the results of analyzing H$\alpha$ spectra of the radio emitting
X-ray binary LS I+61303. 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 $\sim4$ 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+61303 circumstellar disk is among the
densest of Be-stars.

Astrophysics