The Far-Ultraviolet Spectra of Six Stars in Orion

Far-ultraviolet spectra of , 8, , fl, # and ,c Orionis were obtained with an J/2 objective spectrograph carried to 186 km by an Aerobee rocket on October 13, 1965. The lithium fluoride corrector of the Schmidt camera transmitted wavelengths longward of 1200 A. An attitude-control system pointed the rocket toward 8 Ori and then the limit-cycle jitter parallel to the dispersion was reduced by a passive gyroscopic stabilization system. Resolution was about 3 A on a 180-sec exposure. Zero-order images of other stars in the field permitted an absolute calibration of wavelengths to about 1 A. Emission lines of Si iv at 1402.8 A and C iv at 1549.5 A have been identified in 8 and Strong absorption lines of both components of the Si iv doublet and the unresolved C iv doublet were found in 8, , and L shifted to shorter wavelengths by velocities of 1800, 1900, and 3800 km , respectively. The Si iv doublet was present in shifted in the same direction by 1400 km . These displaced resonance absorption lines must be formed in gas escaping from the stars at high velocities, indicating mass loss from these giants and supergiants. Absorption lines about 9 A wide are also visible at 1216 A in and and are attributed to Lyman-a absorption by interstellar hydrogen atoms. For broadening by radiation damping this width corresponds to 1.5 X 10' atoms in the line of sight. This is about one-tenth the density found from the 21-cm radio emission in this direction.