Xi¹ Ceti

Xi¹ Ceti is a binary star system located in the equatorial constellation of Cetus. Its name is a Bayer designation that is Latinized from ξ¹ Ceti, and is abbreviated Xi¹ Cet or ξ¹ Cet. This system is visible to the naked eye with a combined apparent visual magnitude of +4.36. The distance to this system is approximately 310 light years based on parallax measurements, and it is drifting closer to the Sun with a radial velocity of −4 km/s. The proximity of the star to the ecliptic means it is subject to lunar occultations.

The spectroscopic binary nature of Xi¹ Ceti was discovered in 1901 by William Wallace Campbell using the Mills spectrograph at the Lick Observatory. The pair have a circular orbit with a period of 4.5 years and a separation of 3.8 AU. It is a suspected eclipsing binary with an amplitude of 0.03 in magnitude, which would suggest the orbital plane has a high inclination.

The primary, designated component A, is a mild barium giant star with a stellar classification of G7III Ba0.4 Fe-1. Morgan and Keenan in 1973 had classified it as a bright giant star with an anomalous underabundance of the CN molecule. Evidence has been found for an overabundance of s-process elements, although this is disputed. The star has 3.4 times the mass and 16.8 times the radius of the Sun. The companion, component B, is a small white dwarf companion with 80% of the mass of the Sun and a class of DA4. It was detected in 1985 by its ultraviolet emission.

In Chinese, 天囷 (Tiān Qūn), meaning Circular Celestial Granary, refers to an asterism consisting of α Ceti, κ¹ Ceti, λ Ceti, μ Ceti, ξ¹ Ceti, ξ² Ceti, ν Ceti, γ Ceti, δ Ceti, 75 Ceti, 70 Ceti, 63 Ceti and 66 Ceti. Consequently, the Chinese name for Xi¹ Ceti itself is "the Fifth Star of Circular Celestial Granary", Tiān Qūn Wu.