IUE observations of absorption by hot gas in the nebula NGC6888

Abstract

New UV observations of Wolf-Rayet stars obtained with the IUE satellite show narrow absorption components in the highly ionized species of Si IV and C IV. In the case of the WN6 star HD 192163 each resonance transition in the above ions exhibits two components, one undisplaced in wavelength and one blueshifted. The latter components are shown to arise in the nebula NGC 6888 surrounding HD 192163, and these are the first observations of absorption lines arising in a nebula associated with an early-type star. The strengths of the 'interstellar' Si IV and C IV lines in four WR stars and two other early-type stars are compared. There seems to be no correlation in the strengths of these lines with either stellar distance or color excess, suggesting that they arise not in the general interstellar medium but in material more intimately linked with the stars themselves.