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Eta Andromedae

Coordinates: Sky map 00h 57m 12.4000s, +23° 25′ 03.533″
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η Andromedae
Location of η Andromedae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Andromeda
Right ascension 00h 57m 12.400s[1]
Declination +23° 25′ 03.54″[1]
Apparent magnitude (V) 4.403[2]
Characteristics
Spectral type G8III-IV + G8III-IV[3]
U−B color index +0.69[4]
B−V color index +0.94[4]
R−I color index +0.48[4]
Astrometry
η And A
Radial velocity (Rv)−10.30±0.29[5] km/s
Proper motion (μ) RA: −43.008 mas/yr[1]
Dec.: −45.254 mas/yr[1]
Parallax (π)12.5624±0.2525 mas[1]
Distance260 ± 5 ly
(80 ± 2 pc)
Absolute magnitude (MV)0.52±0.06[3]
η And B
Absolute magnitude (MV)1.07±0.07[3]
Orbit[3]
Period (P)115.72±0.01 d
Semi-major axis (a)10.37±0.03 mas
Eccentricity (e)0.006±0.002
Inclination (i)30.5±0.4°
Longitude of the node (Ω)69.4±0.5°
Periastron epoch (T)48013±1 MJD
Argument of periastron (ω)
(secondary)		215±4°
Details
η And A
Mass2.6±0.35[6] M☉
Radius10.7[7] R☉
Luminosity (bolometric)65±3[3] L☉
Surface gravity (log g)2.8[3] cgs
Temperature4,900[3] K
Age800[citation needed] Myr
η And B
Mass2.3±0.31[6] M☉
Radius8.6[7] R☉
Luminosity (bolometric)39±3[3] L☉
Surface gravity (log g)3.0[3] cgs
Temperature4,900[3] K
Other designations
η Andromedae, η And, Eta And, 38 Andromedae, 38 And, BD+22°153, FK5 2060, GC 1136, HD 5516, HIP 4463, HR 271, SAO 74388, PPM 90327, CCDM J00572+2325A, WDS 00572+2325A/Aa[2][8][9]
Database references
SIMBADdata

Eta Andromedae, also named Kui,[10] is a spectroscopic binary star system in the northern constellation of Andromeda. It consists of two G-type evolved stars orbiting each other with a period of 115.7 days and has an overall apparent visual magnitude of approximately 4.403.[2][3] Based on parallax measurements, this system is located at a distance of approximately 260 light years from the Sun.[1] But it is drawing closer with a heliocentric radial velocity of −10.30 km/s.[5]

η Andromedae system as seen from earth orbit, M 33 in background

This star was discovered to be a double-lined spectroscopic binary in a series of spectra taken in 1899 and 1900.[11] Its orbit was computed in 1946 from spectroscopic observations.[12] Because spectroscopy only reveals the radial velocity of a star towards or away from the viewer, such a computation does not determine all orbital elements. In observations made from 1990 to 1992, Eta Andromedae was resolved interferometrically by the Mark III Stellar Interferometer at Mount Wilson Observatory, California, United States. This allowed a more complete orbit to be computed and, in 1993, published.[3]

The primary component has 2.6[6] times the mass of the Sun and 10.7[7] times the Sun's radius. It is radiating 65[3] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,900 K.[3] The fainter secondary member has 2.3[6] times the mass and 8.6[7] times the radius of the Sun. It radiates 39[3] times the luminosity of the Sun at a temperature of 4,900 K.[3]

Eta Andromedae has a visual companion star of apparent visual magnitude 11.5, BD+22°153B, visible 129.2 arcseconds away.[9]

Naming

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In Chinese, 奎宿 (Kuí Sù), meaning Legs (asterism), refers to an asterism consisting of η Andromedae, 65 Piscium, ζ Andromedae, 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 η Andromedae itself is 奎宿一 (Kuí Sù yī, English: the First Star of Legs.)[13] The IAU Working Group on Star Names approved the name Kui for this star on 6 April 2025 and it is now so entered in the IAU Catalog of Star Names.[10]

References

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  1. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  2. ^ a b c "* eta And". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved August 23, 2008.
  3. ^ a b c d e f g h i j k l m n o p Hummel, C. A.; et al. (December 1993). "The spectroscopic binary eta Andromedae: Determination of the orbit by optical interferometry". Astronomical Journal. 106 (6): 2486–2492. Bibcode:1993AJ....106.2486H. doi:10.1086/116816.
  4. ^ a b c HR 271, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line August 23, 2008.
  5. ^ a b Karataș, Yüksel; et al. (2004). "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution". Monthly Notices of the Royal Astronomical Society. 349 (3): 1069–1092. arXiv:astro-ph/0404219. Bibcode:2004MNRAS.349.1069K. doi:10.1111/j.1365-2966.2004.07588.x. S2CID 15290475.
  6. ^ a b c d Pourbaix, D. (August 2000). "Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar masses". Astronomy and Astrophysics Supplement. 145 (2): 215–222. Bibcode:2000A&AS..145..215P. doi:10.1051/aas:2000237. See table 2.
  7. ^ a b c d Eggleton, Peter P.; Yakut, Kadri (July 2017). "Models for 60 double-lined binaries containing giants". Monthly Notices of the Royal Astronomical Society. 468 (3): 3533–3556. arXiv:1611.05041. Bibcode:2017MNRAS.468.3533E. doi:10.1093/mnras/stx598.
  8. ^ Entry 00572+2325, discoverer code MKT 2, components Aa, The Washington Double Star Catalog Archived April 12, 2008, at the Wayback Machine, United States Naval Observatory. Accessed on line August 27, 2008.
  9. ^ a b Entry 00572+2325, discoverer code FOX 116, components AB, The Washington Double Star Catalog Archived April 12, 2008, at the Wayback Machine, United States Naval Observatory. Accessed on line August 23, 2008.
  10. ^ a b "IAU Catalog of Star Names". Retrieved 6 April 2025.
  11. ^ Campbell, W. W.; Wright, W. H. (November 1900). "A list of nine stars whose velocities in the line of sight are variable". Astrophysical Journal. 12: 254–257. Bibcode:1900ApJ....12..254C. doi:10.1086/140765.
  12. ^ Gordon, Katherine C. (January 1946). "The Spectroscopic Binary η Andromedae". Astrophysical Journal. 103: 13–15. Bibcode:1946ApJ...103...13G. doi:10.1086/144783.
  13. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 19 日 Archived 2016-03-03 at the Wayback Machine
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