the latter stages of its evolution. It has a similar spectrum to Procyon A, 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 A 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. Alpha Persei has about 8.5 times the Sun's mass and has expanded to roughly 60 times the size of the Sun. It is radiating 5,000 times the luminosity of the Sun from its outer atmosphere at an effective temperature of , which creates the yellow-white glow of an F-type star. In the Hertzsprung–Russell diagram, Alpha Persei 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. Unconfirmed exoplanet In 2010 evidence was presented of a planet orbiting Mirfak. Radial velocity data from repeated observations of the star found a periodic variation with an amplitude of 70.8 ± 1.6 m/s. The proposed planet is estimated to have a minimum mass of approximately 6.6 times that of Jupiter and an orbital period of 128 days, but the claimed period may not be stable over 20 years so the exoplanet is considered doubtful. Rotational modulation due to surface activity such as starspots seem a more likely explanation of the radial velocity variations. In previous publications, periodic radial velocity variations of 87.7 or 77.7 days have been reported, but these have not been confirmed. References Persei, Alpha Perseus (constellation) F-type supergiants Mirfak Alpha Persei Cluster Persei, 33 015863 1017 020902 BD+49 0917