PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 4 DECEMBER 15, 1918 Number 12 
TEE ABSORPTION SPECTRUM OF THE NOVAE 
By W. S. Adams 
Mount Wilson Observatory, Carnegie Institution of Washington 
Communicated, September 24, 1918 
One of the most remarkable features of the spectrum of novae or temporary 
stars is the presence at a certain stage in their development of absorption lines 
displaced greatly toward the violet end of the spectrum. In the case of the 
elements hydrogen and helium they appear as strong lines forming sharp 
boundaries to the broad emission bands which are the principal characteristic 
of the spectrum of such stars. Occasionally they are double and are subject 
to great variations in character and intensity. In addition to the lines of hy- 
drogen and helium a large number of absorption lines has been observed in 
the spectra of the three brightest novae of recent years, Nova Persei of 1901, 
Nova Geminorum of 1912, and Nova Aquilae of 1918. The identification of 
many of these lines and some features of their displacements form the object 
of this communication. 
Nova Aquilae was first observed at Mount Wilson on June 8. At this time 
the spectrum was essentially continuous, with a few broad and hazy absorption 
bands superposed upon it. Most of these were due to hydrogen and helium 
and were displaced over 20 angstroms toward the violet. Two nights later 
the entire spectrum had changed : a large number of comparatively narrow 
absorption lines had appeared and the hydrogen and helium lines had become 
double. This spectrum had so many points of similarity to that of certain 
stars that a comparison was instituted with a photograph of a Cygni, a star 
of early type with exceptionally strong enhanced lines. It then appeared that 
a considerable number of lines could be identified as common to both spectra 
provided a displacement of about — 23 angstroms at X 4500 were assumed in 
the case of Nova Aquilae. A large proportion of these lines are enhanced but 
some of the stronger arc lines are also represented. In the region of spectrum 
between X 3900 and H/3 ninety lines have been identified with considerable cer- 
tainty, and the origin of many others may be assigned with only slightly less 
probability. 
355 
