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Published online by Cambridge University Press: 07 February 2017
Concerning the absolute magnitudes of the giant stars contained in the Mt. Wilson catalogue of Adams et al., the following facts are pointed out:
(1) There is a linear relation between the Mt. Wilson magnitudes and the absolute magnitudes derived on account of the Wilson-Bappu effect (Figure 1). The scale factor is 2.3.
(2) The accuracy of the properly scaled Mt. Wilson magnitudes follows from the scatter in relation (1) and the accuracy of the Wilson-Bappu magnitudes (± 0.6). It is ± 0m.6 (mean error).
(3) The assured reliability of the corrected Mt. Wilson magnitudes allows a subdivision into bright, intermediate and faint giants (Figure 2). The 3 subgroups exhibit different 2-colour relations (Figures 3, 4, 5).
(4) The large number of giant stars present in the Mt. Wilson catalogue allows a trustworthy derivation of the mean absolute magnitudes of giant branch stars (Figure 6) and an estimate of its dispersion as well (Figure 7).