Eta Andromedae
 Eta Andromeda A/B. |
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| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
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| 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[2] | 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 | ||
| Radial velocity (Rv) | −10.3 ± 0.9[1] km/s | |
| Proper motion: | ||
| RA (μα cos δ) | −43.72[1] mas/yr | |
| Dec. (μδ) | −46.06[1] mas/yr | |
| Parallax (π) | 13.44 ± 0.75[1] mas | |
| Distance | 240 ± 10 ly (74 ± 4 pc) |
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| Absolute magnitude (MV) | 0.52 ± 0.06[2] | 1.07 ± 0.07[2] |
| Details | ||
| Mass | 2.6 ± 0.35[4] M☉ | 2.3 ± 0.31[4] M☉ |
| Surface gravity (log g) | 2.8[2] | 3.0[2] |
| Luminosity (bolometric) | 65 ± 3[2] L☉ | 39 ± 3[2] L☉ |
| Temperature | 4900[2] K | 4900[2] K |
| Age | 8×108 [2] years | |
| Orbit[5] | ||
| Period (P) | 115.72 ± 0.01 d | |
| Semimajor axis (a) | 10.37 ± 0.03 mas | |
| Eccentricity (e) | 0.006 ± 0.002 | |
| Inclination (i) | 30.5 ± 0.4° | |
| Longitude of node (Ω) | 69.4 ± 0.5° | |
| Periastron epoch (T) | 48013 ± 1 MJD | |
| Argument of periastron (ω) (secondary) |
215 ± 4° | |
| Database references | ||
| SIMBAD | data | |
| Other designations | ||
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]
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[edit] History
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.[2]
[edit] Location
This star's location in the constellation Andromeda can be seen in the following diagram:
[edit] Visual companion
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
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|---|---|
| Constellation | Andromeda |
| Right ascension | 00h 57m 04.9s[10] |
| Declination | +23° 23′ 43″[10] |
| Apparent magnitude (V) | 11.5[10] |
| Position (relative to η And) | |
| Epoch of observation | 1997 |
| Angular distance | 129.2″ [7] |
| Position angle | 232° [7] |
| Database references | |
| SIMBAD | data |
| Other designations | |
The star has a visual companion star of apparent visual magnitude 11.5, BD+22°153B, visible 129.2 arcseconds away.[7]
[edit] References
- ^ a b c d e f g h i HD 5516 -- Spectroscopic binary, database entry, SIMBAD. Accessed on line August 23, 2008.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ Entry 00572+2325, Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory. Accessed on line August 27, 2008.
- ^ Entry 00572+2325, discoverer code MKT 2, components Aa, The Washington Double Star Catalog, United States Naval Observatory. Accessed on line August 27, 2008.
- ^ 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.
- ^ 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.
- ^ The Spectroscopic Binary η Andromedae, Katherine C. Gordon, Astrophysical Journal 103 (January 1946), pp. 13–15, Bibcode: 1946ApJ...103...13G.
- ^ a b c d BD+22 153B -- Star in double system, database entry, SIMBAD. Accessed on line August 22, 2008.
[edit] External links
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