Feedback from γ Cassiopeiae: Large Expanding Cavity, Accelerating Cometary Globules, and Peculiar X-Ray Emission

We present wide-field multiwavelength observations of γ Cassiopeiae (or γ Cas for short) in order to study its feedback toward the interstellar environment. A large expanding cavity is discovered toward γ Cas in the neutral hydrogen (H i ) images at a systemic velocity of about −10 km s −1 . The measured dimension of the cavity is roughly 2.°0 × 1.°4 (or 6.0 pc × 4.2 pc at a distance of 168 pc), while the expansion velocity is ∼5.0 ± 0.5 km s −1 . The CO observations reveal systematic velocity gradients in IC 63 (∼20 km s −1 pc −1 ) and IC 59 (∼30 km s −1 pc −1 ), two cometary globules illuminated by γ 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 γ Cas. Our result favors a new scenario that emphasizes the roles of stellar wind and binarity in the X-ray emission of the γ Cas stars.