Eta Andromedae
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.
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 00h 57m 12.4000s |
| Declination | +23° 25′ 03.533″ |
| Apparent magnitude (V) | 4.403 |
| Characteristics | |
| Spectral type | G8III-IV + G8III-IV |
| U−B color index | +0.69 |
| B−V color index | +0.94 |
| R−I color index | +0.48 |
| Astrometry | |
| η And A | |
| Radial velocity (Rv) | −10.3 ± 0.9 km/s |
| Proper motion (μ) | RA: −43.72 mas/yr Dec.: −46.06 mas/yr |
| Parallax (π) | 13.44 ± 0.75 mas |
| Distance | 240 ± 10 ly (74 ± 4 pc) |
| Absolute magnitude (MV) | 0.52 ± 0.06 |
| η And B | |
| Absolute magnitude (MV) | 1.07 ± 0.07 |
| Orbit | |
| 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 | |
| Mass | 2.6 ± 0.35 M☉ |
| Luminosity (bolometric) | 65 ± 3 L☉ |
| Surface gravity (log g) | 2.8 cgs |
| Temperature | 4900 K |
| Age | 800 Million years |
| η And B | |
| Mass | 2.3 ± 0.31 M☉ |
| Luminosity (bolometric) | 39 ± 3 L☉ |
| Surface gravity (log g) | 3.0 cgs |
| Temperature | 4900 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
History
Eta Andromedae was discovered to be a double-lined spectroscopic binary in a series of spectra taken in 1899 and 1900. Its orbit was computed in 1946 from spectroscopic observations. 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.
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.)
Visual companion
Eta Andromedae has a visual companion star of apparent visual magnitude 11.5, BD+22°153B, visible 129.2 arcseconds away.
References
External links
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