Astronomy:Eta Andromedae

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Short description: Spectroscopic binary star in the constellation Andromeda
η Andromedae
Andromeda constellation map.svg
Red circle.svg
Location of η Andromedae (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Andromeda
Right ascension  00h 57m 12.4000s[1]
Declination +23° 25′ 03.533″[1]
Apparent magnitude (V) 4.403[1]
Characteristics
Spectral type G8III-IV + G8III-IV[2]
U−B color index +0.69[3]
B−V color index +0.94[3]
R−I color index +0.48[3]
Astrometry
η And A
Radial velocity (Rv)−10.3 ± 0.9[1] km/s
Proper motion (μ) RA: −43.72[1] mas/yr
Dec.: −46.06[1] mas/yr
Parallax (π)13.44 ± 0.75[1] mas
Distance240 ± 10 ly
(74 ± 4 pc)
Absolute magnitude (MV)0.52 ± 0.06[2]
η And B
Absolute magnitude (MV)1.07 ± 0.07[2]
Orbit[2]
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[4] M☉
Luminosity (bolometric)65 ± 3[2] L☉
Surface gravity (log g)2.8[2] cgs
Temperature4900[2] K
Age800 Million years
η And B
Mass2.3 ± 0.31[4] M☉
Luminosity (bolometric)39 ± 3[2] L☉
Surface gravity (log g)3.0[2] cgs
Temperature4900[2] K
Other designations
η Andromedae, η And, Eta And, 38 Andromedae, 38 And, MKT 2, FOX 116A, BD+22°153, CCDM J00572+2325A, FK5 2060, GC 1136, HD 5516, HIP 4463, HR 271, IDS 00519+2253 A, PPM 90327, SAO 74388, WDS 00572+2325A/Aa.[1][5][6]
Database references
SIMBADdata

Eta Andromedae (Eta And, η Andromedae, η And) is a spectroscopic binary star in the constellation of Andromeda. It consists of two G-type subgiant or giant stars orbiting each other with a period of 115.7 days and has an overall apparent visual magnitude of approximately 4.403.[1][2]

History

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

Eta Andromedae was discovered to be a double-lined spectroscopic binary in a series of spectra taken in 1899 and 1900.[7] Its orbit was computed in 1946 from spectroscopic observations.[8] 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.[2]

Naming

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.)[9]

Visual companion

Eta Andromedae has a visual companion star of apparent visual magnitude 11.5, BD+22°153B, visible 129.2 arcseconds away.[6]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 "* eta And". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+eta+And. 
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 The spectroscopic binary eta Andromedae: Determination of the orbit by optical interferometry, C. A. Hummel et al., Astronomical Journal 106, #6 (December 1993), pp. 2486–2492, Bibcode: 1993AJ....106.2486H, doi:10.1086/116816.
  3. ↑ 3.0 3.1 3.2 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.
  4. ↑ 4.0 4.1 Table 2, Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar masses, D. Pourbaix, Astronomy and Astrophysics Supplement 145 (August 2000), pp. 215–222, Bibcode: 2000A&AS..145..215P.
  5. ↑ Entry 00572+2325, discoverer code MKT 2, components Aa, The Washington Double Star Catalog , United States Naval Observatory. Accessed on line August 27, 2008.
  6. ↑ 6.0 6.1 Entry 00572+2325, discoverer code FOX 116, components AB, The Washington Double Star Catalog , United States Naval Observatory. Accessed on line August 23, 2008.
  7. ↑ A list of nine stars whose velocities in the line of sight are variable, W. W. Campbell and W. H. Wright, Astrophysical Journal 12 (November 1900), pp. 254–257, Bibcode: 1900ApJ....12..254C, doi:10.1086/140765.
  8. ↑ The Spectroscopic Binary η Andromedae, Katherine C. Gordon, Astrophysical Journal 103 (January 1946), pp. 13–15, Bibcode: 1946ApJ...103...13G.
  9. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 19 日

External links

Coordinates: Sky map 00h 57m 12.4000s, +23° 25′ 03.533″



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