48Lib 49Lib Cly OI siz Hel O11 SiW CW Hell rSco —|_ 8Sco i200 1300 1400 1500 i600 (700 1300 [400 1500 1600 1700A HD35656 HD35714 HD35623 HI SilZ cIZ NIT Fig. 6 (above). The ultraviolet spectra of wr Scorpii (above) and of & Scorpii (below). Fig. 7 (left). The ultraviolet spectrum of ¢ Orionis. 1200 1300 i400 1500 1600 length scale to an accuracy of 1 A, so that the spectral features can be identified. Both stars show the resonance lines of C IV and Si IV and an excited line of He II; also present are several excited multiplets of C III, which have yet to be studied in detail in the laboratory. Of particular in- 1700A beside one of the zero-order images; the position of this line confirms the wavelength scale determined from the zero-order images. The width of the Lyman-a line corresponds to only onetenth the number of H atoms expected lines of O I, C H, Si II, and Al J, from the 21-cm radio emission in this direction. The resonance-absorption doublet of Si IV and the unresolved doublet of ionization for such het atmospheres; the lines, probably originating in the sion lines appear on the long-wavelength edges of these absorption lines; terest in which are these stars all rather are low absorption states of interstellar medium,give the first direct information on the abundances of these elements between the stars (/6). Spectra, longward from 1200 A,of six OB stars in Orion were obtained on 13 October 1965 with a camera having a lithium fluoride corrector. The spectrum of the O9.5Ib supergiant ¢ Orionis is reproduced in Fig. 7; the zero-order images at the left show that the pointing was not quite so good as on the first flight; the resolution is about 3 A. Nevertheless several remarkable features are visible. The Lyman-q line due to interstellar absorption by hydrogen atoms may be seen 1278 C IV appearfurther to the right. Emis- it is the wavelengths of the emission lines that agree with the laboratory values. The absorption lines are shifted to shorter wavelengths by some 9 A; this shift corresponds to a velocity of 1900 kilometers per second toward the earth. These resonance lines must be formed in an expanding shell of gas around the star, the implication being that the star is losing mass, returning to it the interstellar medium from which the star once formed. The other two supergiant stars, 6 Orionis, O9.5 II, and « Orionis, BOla, and C IV absorption lines. Consequently we suggest that this observed loss of mass was not by chance and that the loss is a continuous phenomenon typical of all hot supergiants. The presence of expanding atmospheres around the BO- and O-type supergiants had been suspected earlier (17) from several weak and very broad features observed in the part of the spectrum accessible to ground-based instruments. Neverthe- less the ultraviolet observations are of tremendous value in confirming unmistakably the earlier inferences and permitting a quantitative estimate of the rate of mass ejection. The full implications of these ultraviolet spectra are yet to be worked out in terms of models for the outermost layers of O and B stars. Within the past year additional ultraviolet stellar spectra have been ob- tained by several investigators using various techniques. During the flight of Gemini 11 on 14 September 1966 the astronauts photographed a number of stars longward of 2200 A, with 15-A which with ¢ Orionis form the belt of resolution. According to Henize, WackOrion, also show the displaced Si IV _ erling, and’ O'Callaghan (78) Canopus SCIENCE, VOL. 158