Semi-amplitude (K2)
(secondary) 81.3 km/s Period 4.2 months Apparent magnitude (V) 4.01 | Magnitude 4.01 Constellation Perseus | |
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Phi Persei (Phi Per, φ Persei, φ Per) is a Class B2Vpe, fourth-magnitude star in the constellation Perseus. Phi Persei is binary consisting of a blue main sequence primary of class B2 and an apparent magnitude of 4.01 and a hot subdwarf secondary. Due to its rapid rotation, the primary has a polar radius about 5.5 R☉ and an equatorial radius of about 8.0 R☉. Phi Persei is also a variable star with rapid variations in its brightness and spectrum. The Phi Persei stellar system is located about 716 light-years from Earth.
Naming
Flamsteed followed Ptolemy in treating φ Persei as being in Andromeda and gave it the designation 54 Andromedae. It is isolated from the main stars of Perseus, but lies within its formal borders.
In Chinese, 天大將軍 (Tiān Dà Jiāng Jūn), meaning Heaven's Great General, refers to an asterism consisting of φ Persei, γ Andromedae, 51 Andromedae, 49 Andromedae, χ Andromedae, υ Andromedae, τ Andromedae, 56 Andromedae, β Trianguli, γ Trianguli and δ Trianguli. Consequently, φ Persei itself is known as 天大將軍二 (Tiān Dà Jiāng Jūn èr, English: the Second Star of Heaven's Great General.).