Eta Piscium
 
| |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Pisces |
| Right ascension | 01h 31m 29.01026s[1] |
| Declination | +15° 20′ 44.9685″[1] |
| Apparent magnitude (V) | +3.611[2] (3.83 + 7.51)[3] |
| Characteristics | |
| Spectral type | G7 IIIa[4] |
| U−B color index | +0.730[2] |
| B−V color index | +0.976[2] |
| Variable type | γ Cas |
| Astrometry | |
| Radial velocity (Rv) | 13.60±0.42[5] km/s |
| Proper motion (μ) | RA: +27.14[1] mas/yr Dec.: −2.64[1] mas/yr |
| Parallax (π) | 9.33 ± 0.72[1] mas |
| Distance | 350 ± 30 ly (107 ± 8 pc) |
| Orbit[6] | |
| Period (P) | 850.5±66.5 yr |
| Semi-major axis (a) | 1.228±0.144″ |
| Eccentricity (e) | 0.469±0.053 |
| Inclination (i) | 58.5±2.5° |
| Longitude of the node (Ω) | 32.8±2.0° |
| Periastron epoch (T) | 2040.3±66.9 |
| Argument of periastron (ω) (secondary) | 86.9±4.0° |
| Details[5] | |
| η Psc A | |
| Mass | 3.78±0.16 M☉ |
| Radius | 26.48±2.15 R☉ |
| Luminosity | 457 L☉ |
| Surface gravity (log g) | 2.20±0.14 cgs |
| Temperature | 4,937±40 K |
| Metallicity [Fe/H] | −0.13±0.06 dex |
| Rotational velocity (v sin i) | 8.4[7] km/s |
| Age | 220±30 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Eta Piscium (η Piscium), also named Al Pherg,[9] is the brightest star in the constellation Pisces with an apparent visual magnitude of +3.6.[2] Based upon a measured annual parallax shift of 9.33 mas as seen from Earth,[1] it is located roughly 350 light years distant from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.09±0.06 due to interstellar dust. It is a member of the thin disk population of the Milky Way.[5]
This is a binary star[3] system with an orbital period of roughly 850 years, a semimajor axis of 1.2 arc seconds, and an eccentricity of 0.47. The binarity was discovered in 1878 by American astronomy S. W. Burnham.[6] The primary, component A, is an evolved, magnitude 3.83[3] G-type giant star with a stellar classification of G7 IIIa.[4] It has a weak magnetic field with a strength of 0.4±0.2 G,[7] and is a Gamma Cassiopeiae variable.[6] The companion, component B, is a magnitude 7.51 star.[3]
Name and etymology
The star had an obscure Babylonian name Kullat Nūnu−the latter being the Babylonian word for fish and the former "Kullat" referring to either a bucket or the cord that ties the fish together.[10] In Chinese, 右更 (Yòu Gèng), meaning Official in Charge of the Pasturing, refers to an asterism consisting of η Piscium, ρ Piscium, π Piscium, ο Piscium and 104 Piscium. Consequently, η Piscium itself is known as 右更二 (Yòu Gèng èr, English: the Second Star of Official in Charge of the Pasturing.)[11]
References
- 1 2 3 4 5 6 van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, Bibcode:2007A&A...474..653V, arXiv:0708.1752
, doi:10.1051/0004-6361:20078357. - 1 2 3 4 Oja, T. (March 1985), "UBV photometry of stars whose positions are accurately known. II", Astronomy and Astrophysics Supplement Series, 59: 461–464, Bibcode:1985A&AS...59..461O.
- 1 2 3 4 Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, Bibcode:2008MNRAS.389..869E, arXiv:0806.2878 , doi:10.1111/j.1365-2966.2008.13596.x.
- 1 2 Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
- 1 2 3 Maldonado, J.; et al. (June 2013), "The metallicity signature of evolved stars with planets", Astronomy & Astrophysics, 554: 18, Bibcode:2013A&A...554A..84M, arXiv:1303.3418 , doi:10.1051/0004-6361/201321082, A84.
- 1 2 3 Cvetković, Z.; Novaković, B. (March 2010), "Eight new and three recalculated orbits for binaries", Astronomische Nachrichten, 331 (3): 304, Bibcode:2010AN....331..304C, doi:10.1002/asna.200911250.
- 1 2 Aurière, M.; Konstantinova-Antova, R.; Charbonnel, C.; Wade, G. A.; Tsvetkova, S.; Petit, P.; Dintrans, B.; Drake, N. A.; Decressin, T.; Lagarde, N.; Donati, J. F.; Roudier, T.; Lignières, F.; Schröder, K. P.; Landstreet, J. D.; Lèbre, A.; Weiss, W. W.; Zahn, J. P. (February 2015), "The magnetic fields at the surface of active single G-K giants", Astronomy & Astrophysics, 574: 30, Bibcode:2015A&A...574A..90A, arXiv:1411.6230 , doi:10.1051/0004-6361/201424579, A90.
- ↑ "eta Psc". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-30.
- ↑ Pisces Constellation: Facts About the Fishes, retrieved 29 September 2016.
- ↑ Allen, Richard Hinckley (1963) [1899], Star Names: Their Lore and Meaning (rep. ed.), New York, NY: Dover Publications Inc., pp. 328–29, ISBN 0-486-21079-0
- ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 19 日
External links
- Kaler, James B., "KULLAT NUNU (Eta Piscium)", Stars, University of Illinois, retrieved 2017-07-30.