The ratio of Sr II 4077 to nearby iron lines (Fe I 4046, 4063, 4071) remains sensitive to luminosity. The violet-system CN bands, with bandhead at 4216 , visible in the supergiant and giant spectra as a concavity in the continuum, show a strong sensitivity to luminosity. Notice as well that the Ca II K and H lines show extremely broad damping wings in the supergiant class. But the criterion affording the greatest discrimination in the luminosity classes is the ratio of the YII 4376 line to Fe I 4383.
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