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

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ζ Andromedae

Location of ζ Andromedae
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Andromeda
Right ascension	00h 47m 20.32547s[1]
Declination	+24° 16′ 01.8408″[1]
Apparent magnitude (V)	3.92 to 4.14[2]
Characteristics
Spectral type	K1III + KV[3]
U−B color index	+0.90[4]
B−V color index	+1.12[4]
R−I color index	+0.59[4]
Variable type	ELL/RS[2]
Astrometry
Radial velocity (Rv)	−24.43 ± 0.1[5] km/s
Proper motion (μ)	RA: −101.17[1] mas/yr Dec.: −81.77[1] mas/yr
Parallax (π)	17.24 ± 0.26 mas[1]
Distance	189 ± 3 ly (58.0 ± 0.9 pc)
Absolute magnitude (MV)	+0.14[3]
Orbit[3]
Period (P)	17.769426
Semi-major axis (a)	2.7 R*
Eccentricity (e)	0.0
Inclination (i)	65 ± 5°
Details
Aa
Mass	2.6 ± 0.4[3] M☉
Radius	15.9 ± 0.8[6] R☉
Luminosity	95.5[3] L☉
Surface gravity (log g)	2.8[3] cgs
Temperature	4,665 ± 140[6] K
Metallicity [Fe/H]	−0.30[3] dex
Rotation	17.77 days[7]
Rotational velocity (v sin i)	41.4 ± 0.2[3] km/s
Ab
Mass	0.75[3] M☉
Other designations
ζ And, Zeta Andromedae, Zeta And, 34 Andromedae, 34 And, BD+23 106, CCDM J00473+2416A, FK5 27, GC 940, HD 4502, HIP 3693, HR 215, IDS 00421+2344 A, PPM 90149, SAO 74267, WDS 00473+2416A.
Database references
SIMBAD	data

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

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.

The system is a spectroscopic binary whose primary 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.^[3] The orbital period of the binary is 17.77 days.

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.^[9] A Sun-like differential rotation of the star was observed instead.^[3]

The WDS notes three visual companions to the eclipsing binary (Aa and Ab, forming binary A).^[4] 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.^[10] The closest companion, B, is likewise a background object.^[11] The companion C at 97″ shares a common proper motion and a similar parallax.^[12]

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, English: the Second Star of Legs).^[14]