Seminars : Documents

A Mechanism for creating the hard X-rays of gamma Cas (B0.5e): Clues from Multi-wavelength Observations
Myron Smith (NOIRlab, Tucson, Arizona, USA)

In this talk the X-rays of gamma Cas will be examined. gamma Cas is the prototype of a subgroup of Be stars, the spectra of which exhibit hydrogen line emission, a signature of episodically ejected, flattened disks. Members of the gamma Cas subgroup also emit X-rays ~30 times more intense than the X-rays produced by winds of normal B and Be stars, and host an equally greater high plasma temperature. The mechanism responsible for this emission has been long debated. I will confine attention to one that is most consistent with observations, one positing magnetic interactions between gamma Cas and its disk. In this scenario, small-scale magnetic fields extending from the Be star entangle with a toroidal disk field. The stresses so produced release high energy particle beams that impact the star's surface explosively, resulting in observed X-rays 'flares.' This explanation is implied by correlations of X-ray, UV, and optical light curves. The narrative is also supported by features in X-ray spectra. Altogether, observations suggest an environment near gamma Cas stars unlike from those near other hot massive stars, though there are some similarities to magnetospheres of cool stars, including the Sun.