Eta Cassiopeiae
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 Eta Cassiopeiae is just left of Alpha Cassiopeiae |
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Cassiopeia |
| Right ascension | 00h 49m 06.2912s[1] |
| Declination | +57° 48′ 54.674″[1] |
| Apparent magnitude (V) | 3.45/7.51[2] |
| Characteristics | |
| Spectral type | G0V/K7V[2] |
| U−B color index | 0.02/1.03 |
| B−V color index | 0.57/1.39 |
| Variable type | RS CVn |
| Astrometry | |
| Radial velocity (Rv) | +10.0±0.1[1] km/s |
| Proper motion (μ) | RA: 1087.07[1] mas/yr Dec.: −559.73[1] mas/yr |
| Parallax (π) | 167.99 ± 0.62[1] mas |
| Distance | 19.42 ± 0.07 ly (5.95 ± 0.02 pc) |
| Absolute magnitude (MV) | 4.59/8.64 |
| Orbit[3] | |
| Companion | Eta Cassiopeiae B |
| Period (P) | 480 yr |
| Semimajor axis (a) | 11.9939" |
| Eccentricity (e) | 0.497 |
| Inclination (i) | 34.76° |
| Longitude of the node (Ω) | 98.42° |
| Periastron epoch (T) | 1889.6 |
| Argument of periastron (ω) (secondary) |
88.59° |
| Details | |
| Mass | 0.95/0.62[2] M☉ |
| Radius | 1.01/0.66[4] R☉ |
| Luminosity | 1.29/0.06[2] L☉ |
| Temperature | 5965 ± 6.4[5]/4,036[2] K |
| Metallicity | [Fe/H] = −0.31[2] |
| Rotation | 6 km/s[2] |
| Age | 2.9-5.8 × 109[6] years |
| Other designations | |
Eta Cassiopeiae (η Cas, η Cassiopeiae) is a star system 19.4 light years away from Earth, in the constellation Cassiopeia. Sometimes the traditional name Achird is used.
In Chinese, 王良 (Wáng Liáng), meaning Wang Liang,[7] refers to an asterism consisting of η Cassiopeiae, β Cassiopeiae, κ Cassiopeiae, α Cassiopeiae and λ Cassiopeiae.[8] Consequently, η Cassiopeiae itself is known as 王良三 (Wáng Liáng sān, English: the Third Star of Wang Liang.)[9]
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[edit] Characteristics
The primary star in the Eta Cassiopeiae system is a yellow dwarf (main sequence) star of spectral type G0V, putting it in the same spectral class as our Sun, which is of spectral type G2V. It therefore resembles what our Sun might look like if we were to observe it from Eta Cassiopeiae. The star is of apparent magnitude 3.45. The star has a cooler and dimmer (magnitude 7.51) orange dwarf companion of spectral type K7V. The system is an RS Canum Venaticorum type variable star and its brightness varies by 0.05 magnitudes.
Based on an estimated semimajor axis of 12″ and a parallax of 0.168″, the two stars are separated by an average distance of 71 AU, where an AU is the average distance between the Sun and the Earth.[10] However, the large orbital eccentricity of 0.497 means that their periapsis, or closest approach, is as small as 36 AU, with an apoapsis of about 106 AUs. For comparison, the semi-major axis of Neptune is 30 AU. There are six dimmer optical components listed in the Washington Double Star Catalog. However, none of them are related to the Eta Cassiopeiae system and are in reality more distant stars.
[edit] See also
- Lists of stars in the constellation Cassiopeia
- Class G Stars
- RS Canum Venaticorum variables
- Eta Cassiopeiae in fiction
[edit] References
- ^ a b c d e f g "SIMBAD query result: V* eta Cas -- Spectroscopic binary". Centre de Données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=V*+eta+Cas. Retrieved 2008-04-10.
- ^ a b c d e f g Fernandes, J.; Lebreton, Y., Baglin, A., Morel, P. (1998). "Fundamental stellar parameters for nearby visual binary stars: eta Cas, XI Boo, 70 OPH and 85 Peg". Astronomy and Astrophysics 338: 455–464. Bibcode 1998A&A...338..455F.
- ^ Strand, K. A. (1969). "The orbit of Eta Cassiopeiae". Astronomical Journal 74: 760–763. Bibcode 1969AJ.....74..760S. doi:10.1086/110853.
- ^ Johnson, H. M.; Wright, C. D. (1983). "Predicted infrared brightness of stars within 25 parsecs of the sun". Astrophysical Journal Supplement Series 53: 643–711. Bibcode 1983ApJS...53..643J. doi:10.1086/190905.—see p. 647.
- ^ Kovtyukh, V. V.; Soubiran, C.; Belik, S. I.; Gorlova, N. I. (2003). "High precision effective temperatures for 181 F-K dwarfs from line-depth ratios". Astronomy and Astrophysics 411 (3): 559–564. arXiv:astro-ph/0308429. Bibcode 2003A&A...411..559K. doi:10.1051/0004-6361:20031378. http://www.aanda.org/articles/aa/full/2003/46/aa3944/aa3944.html. Retrieved 2010-02-15.
- ^ Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". The Astrophysical Journal 687 (2): 1264–1293. Bibcode 2008ApJ...687.1264M. doi:10.1086/591785.
- ^ Wang Liang was a famous charioteer during the Spring and Autumn Period
- ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 9789867332257.
- ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
- ^ Unsöld, Albrecht; Baschek, Bodo (2001). The New Cosmos: An Introduction to Astronomy and Astrophysics (5th ed.). Springer. p. 186. ISBN 3540421777.
[edit] External links
- "Eta Cassiopeiae 2". SolStation. http://www.solstation.com/stars/eta-cass.htm. Retrieved 2005-11-03.
- Kaler, Jim. "Achird". University of Illinois at Urbana-Champaign. http://stars.astro.illinois.edu/sow/Achird.html. Retrieved 2008-04-10.
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