仙后座γ的旋转和周期变率。II。十五季
Rotational and Cyclical Variability in gamma Cassiopeiae. II. Fifteen Seasons
摘要：
B0.5IVe的恒星Gam Cas是一个非常有趣的恒星，因为它是一小群经典Be星的原型，具有未知来源的硬X射线发射。我们讨论了正在进行的B和V观测的GAM Cas星盘系统获得的APT在1997年至2011年的观测季节的结果。在早期的研究中，Smith、Henry和Vishniac指出，Gam Cas中的光变是由一系列相对突出的周期所主导，这些周期的振幅为0.02-0.03等，长度为2-3个月，叠加在一个1.21天的周期信号上，这个信号小了大约五倍，他们将其归因于旋转。周期长度集中在70天左右。周期长度和振幅的变化每年都在观察。这些作者还发现V带周期比B带周期大30-40%。在本研究中，我们发现持续的证据，这些变化模式和双峰分布的B/V振幅比在长周期。在2010年的观测季节，加姆卡斯经历了一次质量损失事件（爆发），我们新的测光中看到的增亮和变红证明了这一点。这一事件与正在进行的周期的振幅减弱相吻合。Be爆发在次年结束，光变曲线振幅恢复到爆发前的水平。这一行为强化了周期是由全球盘的不稳定性引起的解释。值得注意的是，我们还发现，无论是振幅和旋转波形的不对称性改变了多年。我们审查这种调制所产生的过境的表面磁扰动的参数。最后，限制为5毫等，我们没有发现任何光度变化的证据，对应于加姆卡斯双星周期，203.55天，或前几个谐波。
英文摘要：
The B0.5IVe star gam Cas is of great interest because it is the prototype of a small group of classical Be stars having hard X-ray emission of unknown origin. We discuss results from ongoing B and V observations of the gam Cas star-disk system acquired with an APT during the observing seasons 1997-2011. In an earlier study, Smith, Henry, & Vishniac showed that light variations in gam Cas are dominated by a series of comparatively prominent cycles with amplitudes of 0.02-0.03 mag and lengths of 2-3 months, superimposed on a 1.21-day periodic signal some five times smaller, which they attributed to rotation. The cycle lengths clustered around 70 days. Changes in both cycle length and amplitude were observed from year to year. These authors also found the V-band cycles to be 30-40% larger than the B-band cycles. In the present study we find continued evidence for these variability patterns and for the bimodal distribution of the B/V amplitude ratios in the long cycles. During the 2010 observing season, gam Cas underwent a mass loss event (outburst), as evidenced by the brightening and reddening seen in our new photometry. This episode coincided with a waning of the amplitude in the ongoing cycle. The Be outburst ended the following year, and the light-curve amplitude returned to pre-outburst levels. This behavior reinforces the interpretation that cycles arise from a global disk instability. Remarkably, we also find that both the amplitude and the asymmetry of the rotational waveform changed over the years. We review arguments for this modulation arising from transits of a surface magnetic disturbance. Finally, to a limit of 5 mmag, we find no evidence for any photometric variation corresponding to the gam Cas binary period, 203.55 days, or to the first few harmonics.
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