Discovery of a [O III] Emission Shell Around the X-ray Binary CI Cam

TL;DR

A large [O III] emission shell was discovered around the X-ray binary CI Cam, likely related to its stellar winds, providing insights into its environment and potential interactions with nearby supernova remnants.

Contribution

This paper reports the serendipitous discovery of an emission shell around CI Cam, a new observation linking stellar winds to large-scale nebular structures.

Findings

Shell size approximately 9.5 by 14.3 parsecs.

Shell is brightest in [O III] emission.

Shell's proximity to a supernova remnant appears coincidental.

Abstract

We report the serendipitous discovery of a $8' \times 12'$ emission shell brightest in [O III] centered on the X-ray binary B[e] star, CI Cameleopardalis (CI Cam). This shell, detected during a survey of optical emission associated with the Galactic supernova remnant G150.3+4.5, is seen outside but immediately adjacent to the remnant's optical filaments along its northwestern edge. Assuming this shell is related to CI Cam's strong winds and transient outbursts, the adoption of CI Cam's Gaia DR3 statistically corrected distance of 4.1$^{+0.3}_{-0.2}$ kpc yields shell dimensions $\simeq$ 9.5 pc $\times$ 14.3 pc. While the distance to the G150.3+4.5 remnant is uncertain, the appearance of CI Cam's emission shell so close to the SNR's optical filaments appears likely to be a chance coincidence.