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5.1. The A-Systems

The spectral types in the region lambdalambda 3850-4100 are of class A, and hence we shall refer to them as "A-systems"; they are listed in Table I.

TABLE I
A-SYSTEMS

NGC Hubble

672 SBc
1518 Scp
3319 SBc
3389 Sc
4449 Irr
4559 Sc
4631 Sc

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 lambda 4340; therefore the degree of compositeness is considerable.