Gamma Persei

Gamma Persei (Gamma Per, γ Persei, γ Per) is a binary star system in the constellation Perseus. The combined apparent visual magnitude of the pair is +2.9, making it the fourth-brightest member of the constellation. The distance to this system is of roughly 221 ly with a 1% margin of error. About 4° to the north of Gamma Persei is the radiance point for the annual Perseid meteor shower.

This is a wide eclipsing binary system with an orbital period of 5,329.8 days (14.6 years). This eclipse was first observed in 1990 and lasted for two weeks. During an eclipse, the primary passes in front of the secondary, causing the magnitude of the system to decrease by 0.55. The primary component of this system is a giant star with a stellar classification of G9 III. It has a projected rotational velocity of 50.0 km s−1 and a lengthy estimated rotation period of 14.6 years. The classification of the secondary remains tentative, with assignments of A3 V and A2(III).

Mass estimates for the two stars remain disparate. Using speckle interferometry, McAlister (1982) obtained mass estimates of for the primary and  for the secondary, where  is the mass of the Sun. He noted that the mass estimate was too high for the given classification of the primary. Martin and Mignard (1998) determined masses for both components based on data from the Hipparcos mission: for the primary and  for the secondary. They admit that the high inclination of the orbit resulted in a large margin of error. Prieto and Lambert (1999) came up with a mass estimate of for the primary, while Pizzolato and Maggio (2000) obtained. Ling et al. (2001) obtained estimates of for the primary and  for the secondary, while Kaler (2001) obtained 2.5 and 1.9, respectively. Diamant et al. (2023) found masses of for A and B respectively.

Name and etymology

 * This star, together with δ Per, ψ Per, σ Per, α 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 γ Persei, η Persei, α Persei, ψ Persei, δ Persei, 48 Persei, μ Persei and HD 27084. Consequently, the Chinese name for γ Persei itself is 天船二 (Tiān Chuán èr, the Second Star of Celestial Boat.)