1920 .] 
Astronomical Notes. 
115 
ASTRONOMICAL NOTES. 
The Absorption Spectrum of the Novae. 
By A. C. Gifford. 
In an article on the “ Absorption Spectrum of the Novae ” by Dr 
W. S. Adams, Mount Wilson Observatory, Pasadena, California, it is 
shown that the metallic absorption-lines in the spectrum of Nova Aquilae 
showed a progressive increase in displacement. Thus in the region between 
A. 4250 and A 4600 the values were—June 10, 21*7 angstroms ; June 11, 
22-4 ; June 12, 23-0 ; June 13, 23-7 ; June 15, 24*6. The more refrangible 
components of the hydrogen lines showed a displacement one and a half 
times as great as these. Adams remarks that no adequate explanation 
has been offered as yet to account for these immense displacements. 
Later in the article he comes startlingly close to giving a completely 
satisfying explanation himself. He says, “ The suggestion, however, may 
be made that the absorption-lines are produced in a shell of gas which is 
moving radially outward from the star with a high velocity. If the size 
of this shell is large as compared with that of the body of the star it is 
evident that an area of the shell only equal to that of the star would be 
seen in projection against the latter and would give absorption-lines, and 
that all of the gas within this area would have large components of 
velocity towards the observer. This would result in comparatively narrow 
absorption-lines. The remainder of the gas would give an emission 
spectrum, and the combination of the widely different velocities would 
result in very broad bright bands with their centres nearly undisplaced. 
This is in accordance with observations. With these high velocities the 
interval of two days between the outburst of the star and the appearance 
of the prominent absorption spectrum would be sufficient for the gas to 
reach a great distance from the surface of the star. The hypothesis would , 
however, leave unexplained the apparent acceleration of motion during the 
period of observation of the absorption spectrum ; and the nearly constant 
character of the emission bands after the disappearance of the absorption spectrum 
would point rather to their origin in the star itself .” 
Except for this last sentence (the italics are mine), the above agrees 
exactly with the hypothesis that the outburst is due to the grazing collision 
of two stars, which after the encounter pass on, leaving behind them the 
portions that actually come in one another’s way. 
The coalescence of these portions produces an intensely heated and 
theiefore thermodynamically unstable body. It is this body which gives 
nearly all the light of the new star. It is its spectrum that is recognized 
nearly every time as that of a typical nova. It is the dissipation of this 
body into space that causes the rapid fading of the brilliant radiance. 
The details of each special case depend on the sizes and masses of the 
colliding stars, and on the ratio of the mass of the part struck off to that 
of the original bodies. The smaller this ratio is, the greater will be the 
instability of the third body, and the shorter its life. 
Its constitution is very remarkable. The lighter portions of the two 
stars come into collision first, and therefore occupy originally the central 
region of the body formed. They are almost enwrapped equatorially by 
denser material torn from the deeper portions of the grooves in the wounded 
stars. 
