AAS 207th Meeting, 8-12 January 2006
Session 104 Binary and Variable Stars
Oral, Tuesday, 2:00-3:30pm, January 10, 2006, Balcony B

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[104.01] Rotational and Cyclical Variabiity in gamma Cassiopeia (B0.5e)

M. A. Smith (Catholic University of America), G. W. Henry (Tennessee State University)

We report on robotic telescope (APT) photometric monitoring in B, V Johnson bandpasses over nine years of the classical B0.5e star \gamma Cas. This star is unusual in emiting copious hard X-rays as well as varying over many timescales in the optical. In our work two types of variability stand out: unpredictable cycles of 60-90 day lengths and 2-3% amplitudes, which are slightly larger in the V bandpass, and a colorless, coherent variation with a period of 1.21581{±.00002} days and a full amplitude of 0.5%. The long cycles show irregular glitches and sometimes damp or grow with timescales of even two weeks. The redness of this variation suggests their origin is in the disk. We suggest that an dynamo induced by a magnetorotational instability in the Be disk is responsible for these and associated X-ray variations. The 1.2 day period is undoubtedly a signature of rotational modulation. Its "sawtooth" waveform offers a challenge to any interpretation. However, we suggest it is caused by a helium anomalous distribution on the star's surface. Could \gamma Cas be a multipole, hot analog of magnetic Bp stars?

MAS acknowledges support from NASA Grant NNG05GB60C.

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