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

Details Rotational and Cyclical Variabiity in gamma Cassiopeia (B0.5e) Rotational and Cyclical Variabiity in gamma Cassiopeia (B0.5e)

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aas...20710401s&link_type=abstract

American Astronomical Society Meeting 207, #104.01; Bulletin of the American Astronomical Society, Vol. 37, p.1333

Astronomy and Astrophysics

Astronomy

Scientific paper

We report on robotic telescope (APT) photometric monitoring in B, V Johnson bandpasses over nine years of the classical B0.5e star γ 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 γ Cas be a multipole, hot analog of magnetic Bp stars?
MAS acknowledges support from NASA Grant NNG05GB60C.

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