Properties
The spectrum of Alpha Persei matches a stellar classification of F5 Ib, revealing it to be a supergiant star in the latter stages of its evolution. It has a similar spectrum to Procyon, though the latter star is much less luminous. This difference is highlighted in their spectral designation under the Yerkes spectral classification, published in 1943, where stars are ranked on luminosity as well as spectral typing. Procyon is thus F5 IV, a subgiant star. Since 1943, the spectrum of Alpha Persei has served as one of the stable anchor points by which other stars are classified.
Mirfak has about 7.3 times the Sun's mass and has expanded to roughly 60 times the size of the Sun. It is radiating 5,000 times as much luminosity as the Sun from its outer atmosphere at an effective temperature of 6,350 K, which creates the yellow-white glow of an F-type star. In the Hertzsprung–Russell Diagram, Mirfak lies inside the region in which Cepheid variables are found. It is thus useful in the study of these stars, which are important standard candles.
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