Eta Cassiopeiae
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| Observation data Epoch J2000 |
|
|---|---|
| Constellation (pronunciation) |
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 |
| Visual binary orbit[3] | |
| Companion | Gl 34B |
| 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) | 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 | 6,087/4,036[2] K |
| Metallicity | [Fe/H] = −0.031[2] |
| Rotation | 6 km/s[2] |
| 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. It is known as 王良三 (the Third Star of Wang Liang) in Chinese.[citation needed]
The primary star in the η Cassiopeiae system is a yellow dwarf (main sequence) star of spectral type G3V, 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 η 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.[5] However, the large orbital eccentricity of 0.497 means that their periapsis, or closest approach, is as small as 36 AU. 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 η Cassiopeiae system and are in reality more distant stars.
[edit] See also
[edit] References
- ^ a b c d e f g SIMBAD query result: V* eta Cas -- Spectroscopic binary. Centre de Données astronomiques de Strasbourg. Retrieved on 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.
- ^ Strand, K. A. (1969). "The orbit of Eta Cassiopeiae". Astronomical Journal 74: 760–763.
- ^ 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.—see p. 647.
- ^ Unsöld, Albrecht; Baschek, Bodo (2001). The New Cosmos: An Introduction to Astronomy and Astrophysics, 5th edition, Springer, p. 186. ISBN 3540421777.
[edit] External links
- Eta Cassiopeiae 2. SolStation. Retrieved on 2005-11-03.
- Kaler, Jim. Achird. University of Illinois at Urbana-Champaign. Retrieved on 2008-04-10.
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