Automated photometry of $\gamma$ Cassiopeiae:the last roundup

TL;DR

This study presents a 23-year optical photometry campaign of Gamma Cassiopeiae, revealing changes in its dominant signals, pulsations, and rotation-related patterns, with implications for understanding its stellar activity and variability.

Contribution

It provides a comprehensive long-term analysis of Gamma Cas's photometric variability, revising the dominant frequency and clarifying the nature of its signals and rotation signature.

Findings

Dominant 0.82 cy/d signal amplitude has nearly disappeared and then recovered.

Confirmed secondary nonradial pulsation signals at specific frequencies.

Identified variability and phase slippage in the 0.82 cy/d waveform.

Abstract

Gamma Cas (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-year optical campaign with an Automated Photometric Telescope (APT) on this star. A series of unstable long cycles of length 56--91 days has nearly ceased over the last decade. Herein, we revise the frequency of the dominant coherent signal at 0.82238 cy/d. This signal's amplitude has nearly disappeared in the last 15 years but has somewhat recovered its former strength. We confirm the presence of secondary nonradial pulsation signals found by other authors at frequencies 1.25, 2.48, and 5.03 cy/d. The APT data from intensively monitored nights reveal rapidly variable amplitudes among these frequencies. We show that peculiarities in the 0.82 cy/d waveform exist that can vary even over several days. Although the 0.82 cy/d frequency is near the star's presumed rotation frequency. However, because of its phase slippage with respect to a dip pattern in the star's far-UV light curve it is preferable to consider the latter pattern, not the 0.82 cy/d signal, that carries a rotation signature. We also find hints of the UV dip pattern in periodograms of early-season APT data.