5.1. The A-Systems
The spectral types in the region 3850-4100 are of class A, and hence we shall refer to them as "A-systems"; they are listed in Table I.
These seven galaxies are of three kinds in Hubble's classification: Irr, SBc, and Sc. They seem to have similar stellar populations, and the principal contributors to the total light in the violet region are main-sequence stars of type A. This classification appears to be unique, for the observed broad hydrogen absorption lines could not be produced by a mixture of B- and F-type stars. The spectral type for all of these systems is around F8 at 4340; therefore the degree of compositeness is considerable.