Automated Photometry of γ Cassiopeiae: The Last Roundup

gamma Cassiopeiae (B0.5IVe) is the noted prototype of a subgroup of classical Be stars exhibiting hard thermal X-ray emission. This paper reports results from a 23 yr optical campaign on this star with an automated photometric telescope (APT). A series of unstable long cycles of length 56-91 days has nearly ceased over the last decade. Also, we revise the frequency of the dominant coherent signal at 0.82238 days(-1). This signal's amplitude has nearly disappeared in the last 15 yr but has somewhat recovered its former strength. We confirm the presence of secondary nonradial pulsation signals found by other authors at frequencies 1.24, 2.48, and 5.03 days(-1). The APT data from intensively monitored nights reveal rapidly variable amplitudes among these frequencies. We show that peculiarities in the 0.82 days(-1) waveform exist that can vary even over several days. Although the 0.82 days(-1) frequency is near the star's presumed rotational frequency, because of its phase slippage with respect to a dip pattern in its far-UV light curve, it is preferable to consider the UV pattern, not the 0.82 days(-1) signal, as associated with rotational modulation. We also find hints of the UV dip pattern in periodograms of seasonal data early in our program.

Automated summary

Gamma Cassiopeiae (B0.5IVe) is a classical Be star prototype that exhibits hard thermal X-ray emission. A 23-year optical campaign revealed unstable long cycles and changes in the dominant coherent signal frequency. The star also shows secondary nonradial pulsation signals at multiple frequencies, with rapidly variable amplitudes among these frequencies.