Mirfak
 Location of α Per (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Perseus |
| Right ascension | 03h 24m 19.37009s |
| Declination | +49° 51′ 40.2455″ |
| Apparent magnitude (V) | 1.806 |
| Characteristics | |
| Spectral type | F5 Ib |
| U−B color index | +0.38 |
| B−V color index | +0.483 |
| Astrometry | |
| Radial velocity (Rv) | –2.04 km/s |
| Proper motion (μ) |
RA: +23.75 mas/yr Dec.: -26.23 mas/yr |
| Parallax (π) | 6.44 ± 0.17mas |
| Distance | 510 ± 10 ly (155 ± 4 pc) |
| Absolute magnitude (MV) | –5.1 |
| Details | |
| Mass | 8.5 ± 0.3 M☉ |
| Radius | 68 ± 3 R☉ |
| Surface gravity (log g) | 1.90 ± 0.04 cgs |
| Temperature | 6,350 ± 100 K |
| Metallicity [Fe/H] | –0.02 dex |
| Rotational velocity (v sin i) | 20 km/s |
| Age | 41 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Alpha Persei (α Persei, abbreviated Alpha Per, α Per), also named Mirfak, is the brightest star in the northern constellation of Perseus, just outshining the constellation's best known star, Algol. α Persei has an apparent visual magnitude of 1.8, and is a circumpolar star when viewed from mid-northern latitudes.
Mirfak lies in the midst of a cluster of stars named as the eponymous Alpha Persei Cluster, or Melotte 20, which is easily visible in binoculars and includes many of the fainter stars in the constellation. Determined distance using the trigonometric parallax, places the star 510 light-years (160 parsecs) from the Sun.
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 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 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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