The Nature and Kinematics of the Emission Nebulae in the Cyg OBI Supershell

Summary

Detailed H_α line investigations of the gas kinematics in the supershell around the Cyg OBI association were carried out. The supershell contains nebulae and CO-cavities around WR and O_f stars which form a hierarchical system of mutually embedded gaseous dust shells. The nebulae around WR 134, 135, 141 and 142 and the SNR G73.9+0.9 are shown to be located at the far edge of the parent molecular cloud at V_lsr ∼ 5 − 10 km s⁻¹. We found high negative velocities up to 70 km s⁻¹ and [OIII]-H_α emission stratification typical for shocks. Both could be associated with stellar wind and SNe. The collective wind and ionizing radiation of the Cyg OBI stars (especially WR) and supernova explosions must play some role in forming the supershell. There are some reasons to suppose that the gas at the sound velocity V_lsr ∼ 12 km s⁻¹ is flowing dowmstream of the ionization front.

Six years ago Lozinskaya & Sitnik, 1988 discovered a hierarchical system of mutually embedded gaseous-dust shells in the Cygnus arm (73 < l < 78°, −0°· 5 < b < 3°). In the sky plane this system consists of several small-size shells around WR and O_f stars (NGC 6888 among them) inside the supershell around Cyg OBI association (Figure 1). The supershell (diameter about 100 pc) and inner shells of different sizes are seen as optical ring nebulae, radio-shells, CO-cavities (Lozinskaya & Sitnik, 1988) and IR supershells (Lozinskaya & Repin,1991; Saken et.al, 1992).