Alpha Persei

Alpha Persei

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 ± 0.17 mas
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
Mirfak, Mirphak, Marfak, Algeneb, Algenib, α Persei, α Per, Alpha Per, 33 Persei, BD+49 917, CCDM J03243+4951A, FK5 120, GC 4041, HD 20902, HIP 15863, HR 1017, IDS 03171+4930 A, PPM 46127, SAO 38787, WDS J03243+4952A.

Alpha Persei (Alpha Per, α Persei, α Per) is the brightest star in the northern constellation of Perseus, just outshining the constellation's best known star, Algol. Known by the traditional names Mirfak and Algenib, it is a circumpolar star when viewed from the latitude of New York City or higher. It has an apparent visual magnitude of 1.8, placing it among the brightest stars in the sky. Mirfak lies in the midst of a cluster of stars eponymously named the Alpha Persei Cluster, or Melotte 20, which is easily visible in binoculars and includes many of the fainter stars in the constellation. The distance to this star has been determined using the parallax technique, putting it away.

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 8.5 times the Sun's mass and has expanded to roughly 60 times the size of the Sun. It is radiating 7,000 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.

Etymology and cultural significance

• The names Mirfak and Algenib are Arabic in origin. The former, meaning 'Elbow' and also written Mirphak, Marfak or Mirzac, comes from the Arabic Mirfaq al-Thurayya, while Algenib, also spelt Algeneb, Elgenab, Gęnib, Chenib or Alchemb, is derived from الجنب al-janb, or الجانب al-jānib, 'the flank' or 'side'. Gamma Pegasi also bears the name Algenib.
• Hinali'i is the name of the star in Native Hawaiian astronomy. The name of the star is meant to commemorate a great tsunami and mark the beginning of the migration of Maui. According to some Hawaiian folklore, Hinali'i is the point of separation between the Earth and the sky that happened during the creation of the Milky Way.
• Assemani alluded to a title on the Borgian globe, Mughammid (مغمد), or Muliammir al Thurayya (ملىمرٱلطرى), the Concealer of the Pleiades, which, from its location, may be for this star.
• This star, together with δ Per, ψ Per, σ Per, γ Per and η Per, has been called the Segment of Perseus.
• In Chinese, 天船 (Tiān Chuán), meaning Celestial Boat, refers to an asterism consisting of α Persei, η Persei, γ Persei, ψ Persei, δ Persei, 48 Persei, μ Persei and HD 27084. Consequently, α Persei itself is known as 天船三 (Tiān Chuán sān, English: the Third Star of Celestial Boat.)