The Far-Ultraviolet Spectra of Six Stars in Orion

Abstract

Far-ultraviolet spectra of , 8, , fl, # and ,c Orionis were obtainedwith an J/2 objective spectrograph carried to 186 km by an Aerobeerocket on October 13, 1965. The lithium fluoride corrector of theSchmidt camera transmitted wavelengths longward of 1200 A. Anattitude-control system pointed the rocket toward 8 Ori and then thelimit-cycle jitter parallel to the dispersion was reduced by a passivegyroscopic stabilization system. Resolution was about 3 A on a 180-secexposure. Zero-order images of other stars in the field permitted anabsolute calibration of wavelengths to about 1 A. Emission lines of Siiv at 1402.8 A and C iv at 1549.5 A have been identified in 8 and Strongabsorption lines of both components of the Si iv doublet and theunresolved C iv doublet were found in 8, , and L shifted to shorterwavelengths by velocities of 1800, 1900, and 3800 km , respectively. TheSi iv doublet was present in shifted in the same direction by 1400 km .These displaced resonance absorption lines must be formed in gasescaping from the stars at high velocities, indicating mass loss fromthese giants and supergiants. Absorption lines about 9 A wide are alsovisible at 1216 A in and and are attributed to Lyman-a absorption byinterstellar hydrogen atoms. For broadening by radiation damping thiswidth corresponds to 1.5 X 10' atoms in the line of sight. This is aboutone-tenth the density found from the 21-cm radio emission in thisdirection.