Feedback from $\gamma$~Cassiopeiae: Large Expanding Cavity, Accelerating Cometary Globules, and Peculiar X-ray Emission

TL;DR

This study reveals a large expanding cavity and accelerated cometary globules around $ ext{γ}$~Cas, linking stellar wind and binarity to its peculiar X-ray emission through multi-wavelength observations.

Contribution

It provides new evidence of a large HI cavity and accelerated globules around $ ext{γ}$~Cas, highlighting stellar wind and binarity as key factors in its X-ray emission.

Findings

Discovery of a 6x4.2 pc HI cavity with 5 km/s expansion velocity.

Identification of fast-accelerating cometary globules IC63 and IC59.

Linking stellar wind and binarity to the peculiar X-ray emission.

Abstract

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.