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5.4 Transitions Between SA and SB

Transition galaxies are shown in Plate 5. Those illustrated are among only the most obviously mixed cases previously called S/SB by Hubble and Sandage. De Vaucouleurs emphasizes the transitions more strongly than Hubble by using the SAB notation for galaxies where the bar is quite subtle. For example, five of the eight galaxies in Plate 4 are called SAB by de Vaucouleurs, whereas none of these were called transition cases in the Hubble Atlas. De Vaucouleurs's procedure recognizes the fact that most galaxies possess an incipient bar, as discussed most explicitly by Lindblad and Langebartel (1953). The effect of the finer division in the revised system is that among the 1500 bright galaxies reclassified by de Vaucouleurs (1963b, table 5) there are about equal numbers of SA, SAB, and SB systems, whereas very few transition cases were isolated in the Hubble system (see, e.g., the types listed in HMS 1956).

Plate 5

Plate 5. Transition types between ordinary and barred spirals. The types assigned by various classifiers are listed in table 2.

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