2013A&A...559A..87Z

We report 138 spectral observations of the Hα emission line of the radio- and γ-ray-emitting Be/X-ray binary LSI+61°303 obtained during the period of September 1998 - January 2013. From measuring various Hα parameters, we found that the orbital modulation of the Hα is best visible in the equivalent width ratio EW(B)/EW(R), the equivalent width of the blue hump, and in the radial velocity of the central dip. The periodogram analysis confirmed that the Hα emission is modulated with the orbital and superorbital periods. For the past 20 years the radius of the circumstellar disk is similar to the Roche lobe size at the periastron. It is probably truncated by a 6:1 resonance. The orbital maximum of the equivalent width of Hα emission peaks after the periastron and coincides on average with the X-ray and γ-ray maxima. All the spectra are available upon request from the authors and through the CDS.