174 
A STRONOM Y: ADAMS A ND JO Y Proc. N. A. S. 
A list of 100 stars with distances and absolute magnitudes obtained by 
these methods has formed the basis of an attempt upon our part to investi- 
gate a possible correlation between absolute magnitude and the intensities 
of certain spectral lines similar to that which has been used successfully 
in the case of stars of the later types of spectrum. The material used in- 
cludes the stars for which spectra have been obtained with the Cassegrain 
spectrograph at Mount Wilson, and the values of the parallaxes and 
absolute magnitudes have been taken from the lists of trigonometric par- 
allaxes of various observers, an unpublished investigation by Russell on 
dynamical parallaxes, and the memoir of Rasmuson on moving clusters. 
Corrections have been applied to the dynamical parallaxes to reduce them 
to the values corresponding to the most probable value of the mass of the 
A-type stars. 
No. 
A,» 
A4.+AS 
AfetAT 
Ma7 
9 0.63 +2.4- 
!4- 1.09 2.4 
12 O.^l 
4 0.15 
12 1.59 
7 0.51 
7 1.59 
6 1.16 
II 2.10 
H 2.24 
10 2.56 
4 2.62 
2.0 
2.4 
2.4 
2.2 
2.2 
2.3 
Z.b 
2.3 
2.3 
2.3 
B5 &9 Aq A| Ag A3 A4. A5 Afc A7 Afl A9 fo F| fz 
FIG. 1 
Curves showing the relationship between absolute magnitude and spectral type for 
stars with parallaxes determined trigonometrically, dynamically and from group 
motions. Crosses refer to spectra with sharp lines Ais, points to spectra with diffuse 
or nebulous lines as Ain. In the present case this distinction is not carried into the 
more advanced sub-divisions,. MA7 denotes the absolute magnitudes reduced to 
spectral type A 7 by means of these curves. 
The starting point of the investigation and, as it proved, its most im- 
portant feature, was an accurate determination of spectral type and the 
characteristics of the spectral lines. The stars were classified according 
to the Harvard scale as Ao, Ai, A2, etc., and the spectra were designated w 
or 5 according as the lines are nebulous or sharp. This distinction is 
marked among the stars of the earlier subdivisions but becomes less certain 
at ^5 or later. In addition to these two classes with sharp or nebulous 
lines is the small group of stars, of which a Cygni is the most prominent 
example, which are characterized by the Harvard observers as c-stars. 
These have exceptionally sharp and narrow lines and the enhanced lines 
as a rule are remarkably strong. In most of them the enhanced lines of 
strontium at X4077 and X4215 are very intense. 
