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A detailed analysis of more than 800 electronic high-resolution spectra ofgamma Cas, which were obtained during a time interval of over 6000 days (16.84yrs) at several observatories, documents the smooth variations in the densityand/or extend of its circumstellar envelope. We found a clear anticorrelationbetween the peak intensity and FWHM of the H alpha emission, which seems toagree with recent models of such emission lines. The main result of this studyis a confirmation of the binary nature of the object, determination of areliable linear ephemeris T_{min.RV} = HJD (2452081.9$\pm$0.6) +(203.52$\pm$0.08)*E, and a rather definitive set of orbital elements. Weclearly demonstrated that the orbit is circular within the limits of accuracyof our measurements and has a semi-amplitude of radial-velocity curve of4.30$\pm$0.09 (km/s). No trace of the low-mass secondary was found. The timedistribution of our spectra does not allow a reliable investigation of rapidspectral variations, which are undoubtedly present in the spectra. We postponethis investigation for a future study, based on series of dedicated whole-nightspectral observations.

Properties and nature of Be stars: 29. Orbital and long-term spectral variations of \gamma\ Cassiopei\ae