A detailed analysis of more than 800 electronic high-resolution spectra of gamma Cas , which were obtained during a time interval of over 6000 days ( 16.84 yrs ) at several observatories , documents the smooth variations in the density and/or extend of its circumstellar envelope .
We found a clear anticorrelation between the peak intensity and FWHM of the H \alpha emission , which seems to agree with recent models of such emission lines .
The main result of this study is a confirmation of the binary nature of the object , determination of a reliable linear ephemeris T _ { min . RV } = { HJD } ( 2452081.9 \pm 0.6 ) + ( 203 \aas@@fstack { d } 52 \pm 0 % \aas@@fstack { d } 08 ) \times E, and a rather definitive set of orbital elements .
We clearly demonstrated that the orbit is circular within the limits of accuracy of our measurements and has a semi-amplitude of radial-velocity curve of 4.30 \pm 0.09 km s ^ { -1 } .
No trace of the low-mass secondary was found .
The time distribution of our spectra does not allow a reliable investigation of rapid spectral variations , which are undoubtedly present in the spectra .
We postpone this investigation for a future study , based on series of dedicated whole-night spectral observations .