Spectral energy distribution and long-term variations in gamma cassiopeiae

Newly measured continuum energy distribution data of a typical Be star, Cas, is presented in the visible region (3200–8000 Å). The behaviour of the continuum over the broader wavelength range covering the ultraviolet, visible, and infrared regions is summarized. It is found that Cas exhibits large variations in the continuum which are connected with variations in the strength of ultraviolet and infrared excess emissions.From the analysis of the existing data in the visible region it transpires that this star possesses interesting long-term changes of different parameters like colour temperature (T _c ), visual magnitude (m _v ), total strength of Balmer emission lines (E _H ), ratio of violet to red emission component (V/R), and equivalent width of Balmer lines (W _H ). The most interesting aspect is the fact that all these parameters are related with one another during the so-called Great Outburst (GO) period which occurred during 1932–1942. The parametersT _c ,m _v , andE _H are also found to be connected to each other throughout their long-term variations.The present investigation shows that Cas has exhibited three phases—Be, Be shell, and normal B — in the past. Since 1866, the first Be phase, lasting about 60 to 70 years, was followed by spectacular variations of about 10 years duration (1932–1942). During this spectacular episode ending with a quasi-normal B phase, two strong shell phases followed by very intense emission phases were observed. Since then, a new, slowly irregularly increasing Be phase which is still persisting has been observed. So far this last Be phase has not shown any outstanding variable characteristics.The present behaviour of the long-term variation ofm _v shows that since 1985 Cas has again entered a new phase of activity. We hope that this star will again pass through some new outstanding variability phase during the coming decade.