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Eta Andromedae

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

Eta Andromeda A/B.
Observation data
Epoch J2000.0      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
U−B color index +0.69[2]
B−V color index +0.94[2]
R−I color index +0.48[2]
Component 1
Spectral type G8III-IV[3]
Component 2
Spectral type G8III-IV[3]
Astrometry
Component 1
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 mas[1]
Distance240 ± 10 ly
(74 ± 4 pc)
Absolute magnitude (MV)0.52 ± 0.06[3]
Component 2
Absolute magnitude (MV)1.07 ± 0.07[3]
Orbit[4]
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
Component 1
Mass2.6 ± 0.35[5] M☉
Luminosity (bolometric)65 ± 3[3] L☉
Surface gravity (log g)2.8[3] cgs
Temperature4900[3] K
Age8×108 [3] years
Component 2
Mass2.3 ± 0.31[5] M☉
Luminosity (bolometric)39 ± 3[3] L☉
Surface gravity (log g)3.0[3] cgs
Temperature4900[3] 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][6][7]
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][3]

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.[8] Its orbit was computed in 1946 from spectroscopic observations.[9] 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]

Location

This star's location in the constellation Andromeda can be seen in the following diagram:

Diagram of Andromeda constellation

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, η Andromedae itself is known as 奎宿一 (Kuí Sù yī, English: the First Star of Legs.)[10]

Visual companion

BD+22°153B
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Andromeda
Right ascension 00h 57m 04.9s[11]
Declination +23° 23′ 43″[11]
Apparent magnitude (V) 11.5[11]
Position (relative to η And)
Epoch of observation1997
Angular distance129.2″ [7]
Position angle232° [7]
Database references
SIMBADdata
Other designations
FOX 116B, BD+22°153B, CCDM J00572+2325B, IDS 00519+2253 B, WDS 00572+2325B.[7][11]

The star has a visual companion star of apparent visual magnitude 11.5, BD+22°153B, visible 129.2 arcseconds away.[7]

References

  1. ^ a b c d e f g h i HD 5516 -- Spectroscopic binary, database entry, SIMBAD. Accessed on line August 23, 2008.
  2. ^ 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.
  3. ^ a b c d e f g h i j k l m 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.
  4. ^ Entry 00572+2325, Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory. Accessed on line August 27, 2008.
  5. ^ a b 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.
  6. ^ Entry 00572+2325, discoverer code MKT 2, components Aa, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line August 27, 2008.
  7. ^ a b c d e Entry 00572+2325, discoverer code FOX 116, components AB, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line August 23, 2008.
  8. ^ 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.
  9. ^ The Spectroscopic Binary η Andromedae, Katherine C. Gordon, Astrophysical Journal 103 (January 1946), pp. 13–15, Bibcode:1946ApJ...103...13G.
  10. ^ Template:Zh icon AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 19 日
  11. ^ a b c d BD+22 153B -- Star in double system, database entry, SIMBAD. Accessed on line August 22, 2008.


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