Zeta Andromedae

Zeta Andromedae (Zeta And, ζ Andromedae, ζ And) is a star system in the constellation Andromeda. It is approximately 189 light-years from Earth.

Zeta Andromedae is the star's Bayer designation. It also has the Flamsteed designation 34 Andromedae and multiple other designations in stellar catalogues.

Location
The star's location is in the northern constellation Andromeda, in which it is the second-most southerly of the stars in this often drawn characteristic shape representing the mythical princess asterism, after η Andromedae.

System
The system is a spectroscopic binary whose is classified as an orange K-type giant with a mean apparent magnitude of +4.08. Due to brightness changes caused by the ellipsoidal shape of that object, the system is also an RS Canum Venaticorum-type variable star. Its brightness varies from magnitude +3.92 to +4.14 with a period of 17.77 days, and its spectrum shows strong and variable Ca II H and K lines. The orbital period of the binary is 17.77 days.

Direct imaging
The primary component of this binary system, Zeta Andromedae Aa, is one of the few stars who has been imaged directly using Doppler imaging and long-baseline infrared interferometry. With direct imaging we can recover additional information about this star.

Direct imaging also allowed observation of starspots (the analogue to sunspots), on this star, and their asymmetric distribution showed that the magnetic field of the star is generated by a mechanism different from the solar dynamo. A Sun-like differential rotation of the star was observed instead.

Visual companions
The WDS notes three visual companions to the eclipsing binary (Aa and Ab, forming binary A). The parallax of the D star has been measured by Gaia proving its distance to be much greater than Zeta Andromedae, probably a distant red giant. The closest companion, B, is likewise a background object. The companion C at $97 "$ shares a common proper motion and a similar parallax.

Naming
In Chinese, 奎宿 (Kuí Sù), meaning Legs (asterism), refers to an asterism consisting of ζ Andromedae, η Andromedae, 65 Piscium, ε Andromedae, δ Andromedae, π Andromedae, ν Andromedae, μ Andromedae, β Andromedae, σ Piscium, τ Piscium, 91 Piscium, υ Piscium, φ Piscium, χ Piscium and ψ1 Piscium. Consequently, the Chinese name for ζ Andromedae itself is 奎宿二 (Kuí Sù èr, the Second Star of Legs).