The far ultraviolet spectra of γ Cyg and μ Cen

The spectra of the 'pole-on' Be stars γ Cyg and μ Cen have been observed in the region lambdalambda 1000-1450 A with the Princeton Ultraviolet Spectrometer on board the Copernicus satellite. The data include scans of intermediate resolution (0.2 A) with U2 and high resolution scans (0.05 A) of selected suspected shell lines with U1. The spectra of γ Cyg and μ Cen are compared with a complete intermediate resolution Copernicus scan of the equator-on Be star phi Per. The ultraviolet spectra of γ Cyg and μ Cen appear to be identical to those observed in non-Be stars of comparable ground-based spectral type. Neither emission nor shell features are observed. However, numerous strong shell features are seen in phi Per. An upper limit on the column density of hydrogen in the line of sight is computed for γ Cyg from the observed strength of a weak feature at lambda 1130.4 A identified as an Fe III shell line. Estimates for the dimensions of the circumstellar envelope are then obtained. Some implications of the strengths of the Fe III shell lines at lambda 1130 A observed in γ Cyg, μ Cen, phi Per, and other Be stars are discussed. (Auth.)