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