Astronomy:Eta Piscium
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| Observation data 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) |
| Absolute magnitude (MV) | −1.52[6] |
| Orbit[7] | |
| 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[8] km/s |
| Age | 220±30 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Eta Piscium (η Piscium, abbreviated Eta Psc, η Psc) is a binary star and the brightest point of light in the constellation of 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 in the thin disk population of the Milky Way.[5]
The two components are designated Eta Piscium A (formally named Alpherg /ˈælfɜːrɡ/, the traditional name of the system)[10] and B.
Nomenclature
η Piscium (Latinised to Eta Piscium) is the system's Bayer designation. The designations of the two constituents as Eta Piscium A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[11]
The system bore the traditional names Al Pherg (in this context meaning the emptying) and Kullat Nunu. At the time that the sun at the March Equinox entered into Pisces having lay in Aries, the system was in the first ecliptic constellation of the Neo-Babylonians, Kullat Nūnu − 'Nūnu' being Babylonian for fish and 'Kullat' referring to either the bucket or the cord that binds the fish.[12] In 2016, the IAU organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[14] It approved the name Alpherg for the component Eta Piscium A on 1 June 2018 (for its official List).[10]
In Chinese, 右更 (Yòu Gèng), meaning Official in Charge of the Pasturing, refers to an asterism consisting of Eta Piscium, Rho Piscium, Pi Piscium, Omicron Piscium and 104 Piscium. Consequently, the Chinese name for Eta Piscium itself is 右更二 (Yòu Gèng èr, English: the Second Star of Official in Charge of the Pasturing.)[15]
Properties
At its present distance, the visual magnitude of the system is diminished by an extinction factor of 0.09±0.06 due to interstellar dust.
This system's binary nature was discovered in 1878 by an amateur astronomer, S. W. Burnham.[7] It has an orbital period of roughly 850 years, a semimajor axis of 1.2 arc seconds, and an eccentricity of 0.47.
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,[8] and is a Gamma Cassiopeiae variable.[7] The companion, component B, is a magnitude 7.51 star.[3]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V.
- ↑ 2.0 2.1 2.2 2.3 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.
- ↑ 3.0 3.1 3.2 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, doi:10.1111/j.1365-2966.2008.13596.x, Bibcode: 2008MNRAS.389..869E.
- ↑ 4.0 4.1 Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series 71: 245, doi:10.1086/191373, Bibcode: 1989ApJS...71..245K.
- ↑ 5.0 5.1 5.2 Maldonado, J. et al. (June 2013), "The metallicity signature of evolved stars with planets", Astronomy & Astrophysics 554: 18, doi:10.1051/0004-6361/201321082, A84, Bibcode: 2013A&A...554A..84M.
- ↑ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode: 2012AstL...38..331A.
- ↑ 7.0 7.1 7.2 Cvetković, Z.; Novaković, B. (March 2010), "Eight new and three recalculated orbits for binaries", Astronomische Nachrichten 331 (3): 304, doi:10.1002/asna.200911250, Bibcode: 2010AN....331..304C.
- ↑ 8.0 8.1 Aurière, M.; Konstantinova-Antova, R.; Charbonnel, C.; Wade, G. A.; Tsvetkova, S.; Petit, P.; Dintrans, B.; Drake, N. A. et al. (February 2015), "The magnetic fields at the surface of active single G-K giants", Astronomy & Astrophysics 574: 30, doi:10.1051/0004-6361/201424579, A90, Bibcode: 2015A&A...574A..90A.
- ↑ "eta Psc". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=eta+Psc.
- ↑ 10.0 10.1 "Naming Stars". IAU.org. https://www.iau.org/public/themes/naming_stars/.
- ↑ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
- ↑ Allen, Richard Hinckley (1963), Star Names: Their Lore and Meaning (rep. ed.), New York City , NY: Dover Publications Inc., pp. 328–29, ISBN 0-486-21079-0, https://archive.org/details/starnamestheirlo00alle/page/328
- ↑ "IAU Working Group on Star Names (WGSN)". https://www.iau.org/science/scientific_bodies/working_groups/280/.
- ↑ "WG Triennial Report (2015-2018) - Star Names". p. 5. https://www.iau.org/static/science/scientific_bodies/working_groups/280/wg-starnames-triennial-report-2015-2018.pdf.
- ↑ (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), http://stars.astro.illinois.edu/sow/kullatnunu.html, retrieved 2017-07-30.
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