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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.


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.