Feedback from $\gamma$~Cassiopeiae: Large Expanding Cavity, Accelerating
  Cometary Globules, and Peculiar X-ray Emission
  We present wide-field multi-wavelength observations of $\gamma$ Cassiopeiae
(or $\gamma$~Cas for short) in order to study its feedback toward the
interstellar environment. A large expanding cavity is discovered toward
$\gamma$~Cas in the neutral hydrogen (HI) images at a systemic velocity of
about -10 km/s. The measured dimension of the cavity is roughly 2.0 deg
$\times$ 1.4 deg (or 6.0 pc $\times$ 4.2 pc at a distance of 168 pc), while the
expansion velocity is about 5.0$\pm$0.5 km/s. The CO observations reveal
systematic velocity gradients in IC63 (about 20 km/s/pc) and IC59 (about 30
km/s/pc), two cometary globules illuminated by $\gamma$~Cas, proving fast
acceleration of the globules under stellar radiation pressure. The gas
kinematics indicate that the cavity is opened by strong stellar wind, which has
high potential to lead to the peculiar X-ray emission observed in $\gamma$~Cas.
Our result favors a recent new scenario that emphasizes the roles of stellar
wind and binarity in the X-ray emission of the $\gamma$~Cas stars.
