Eta Andromedae (Eta And, η Andromedae, η And) is a spectroscopic binary star in the constellationofAndromeda. It consists of two G-type subgiantorgiant stars orbiting each other with a period of 115.7 days and has an overall apparent visual magnitude of approximately 4.403.[1][2]
| |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Andromeda |
| Right ascension | 00h57m 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 mas[1] |
| Distance | 240 ± 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 | |
| Mass | 2.6 ± 0.35[4] M☉ |
| Luminosity (bolometric) | 65 ± 3[2] L☉ |
| Surface gravity (log g) | 2.8[2] cgs |
| Temperature | 4900[2] K |
| Age | 800 Million years |
| η And B | |
| Mass | 2.3 ± 0.31[4] M☉ |
| Luminosity (bolometric) | 39 ± 3[2] L☉ |
| Surface gravity (log g) | 3.0[2] cgs |
| Temperature | 4900[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 | |
| SIMBAD | data |
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 InterferometeratMount Wilson Observatory, California, United States. This allowed a more complete orbit to be computed and, in 1993, published.[2]
InChinese, 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]
Eta Andromedae has a visual companion starofapparent visual magnitude 11.5, BD+22°153B, visible 129.2 arcseconds away.[6]
