Alpha Piscium

Alpha Piscium (α Piscium) is a binary star[6] system in the equatorial constellation of Pisces. Based upon parallax measurements made by the Hipparcos spacecraft, it is about 151 light-years from the Solar System.

α Piscium
Location of α Piscium (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Pisces
Right ascension 02h 02m 02.81972s[1]
Declination +02° 45′ 49.5410″[1]
Apparent magnitude (V) 3.82 (4.33 + 5.23)[2]
Characteristics
Spectral type kA0hA7 Sr + kA2hF2mF2 (IV)[3]
Variable type α2 CVn[4]
Astrometry
Proper motion (μ) RA: +32.45[1] mas/yr
Dec.: +0.04[1] mas/yr
Parallax (π)21.66 ± 1.06 mas[1]
Distance151 ± 7 ly
(46 ± 2 pc)
Absolute magnitude (MV)+0.50[5]
Orbit[6]
Period (P)3267.4 yr
Semi-major axis (a)7.4″
Eccentricity (e)0.465
Inclination (i)113.4°
Longitude of the node (Ω)3.70°
Periastron epoch (T)2188.6
Argument of periastron (ω)
(secondary)		147.9°
Details
α Psc A
Mass2.55±0.11[7] M☉
Radius2.45[8] R☉
Luminosity55+14
−11[7] L☉
Surface gravity (log g)3.85[8] cgs
Temperature10,233+507
−483[7] K
Rotational velocity (v sin i)81[9] km/s
α Psc B
Mass2.64+0.21
−0.28[10] M☉
Radius2.66±0.45[10] R☉
Luminosity63+13
−11[10] L☉
Surface gravity (log g)4.01±0.14[10] cgs
Temperature10,000±710[10] K
Rotational velocity (v sin i)84[9] km/s
Age331+159
−153[10] Myr
Other designations
Alrischa, Kaitain, Okda, α Psc, 113 Piscium, BD+02°317, FK5 28, HIP 9487, SAO 110291, WDS J02020+0246AB[11]
α Psc A: HD 12447, HR 596[12]
α Psc B: HD 12446, HR 595[13]
Database references
SIMBADα Psc
α Psc A
α Psc B

The two components are designated Alpha Piscium A (officially named Alrescha/ælˈriːʃə/, the traditional name of the system)[14][15] and B.

Nomenclature

α Piscium (Latinised to Alpha Piscium) is the star's Bayer designation. The designations of the two components as Alpha 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).[16]

The system bore the traditional name Alrescha (alternatively Al Rescha, Alrischa, Alrisha) derived from the Arabic الرشآء al-rishā’ "the cord" and less commonly Kaitain and Okda, the latter from the Arabic عقدة ʽuqdah "knot" (see Ukdah.[17] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[18] to catalog and standardize proper names for stars. The WGSN approved the name Alrescha for the component Alpha Piscium A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[15]

In Chinese, 外屏 (Wài Píng), meaning Outer Fence, refers to an asterism consisting of Alpha Piscium, Delta Piscium, Epsilon Piscium, Zeta Piscium, Mu Piscium, Nu Piscium and Xi Piscium. Consequently, the Chinese name for Alpha Piscium itself is 外屏七 (Wài Píng qī, English: the Seventh Star of Outer Fence).[19]

Properties

Alpha Piscium comprises a close binary with angular separation of presently 1.8" between the components. The main star or primary (Alpha Piscium A) is of magnitude +4.33 and spectral type A0p, while the companion or secondary (Alpha Piscium B) is magnitude 5.23 and belongs to spectral class A3m. The two stars take more than 3,000 years to orbit one another and they will make their closest approach to each other around 2060. One or both of the stars may be a spectroscopic binary as well. The stars have masses of 2.55 and 2.64 solar masses respectively and shine with a total luminosity of 55 and 63 times that of the Sun.

A light curve for Alpha Piscium, plotted from TESS data[20]

Alpha Piscium is catalogued as an α2 Canum Venaticorum variable, a type of variable star where the brightness changes are caused by the rotation of the star. The brightness varies by about 1/100th of a magnitude, identified from Hipparcos photometry.[4] The primary component is thought to be the source of the variations, and it has a period of 0.845 days which corresponds to the rotation period of the star. Variations with a period of 6.65 days have also been identified in the variations.[21]

Long-exposure observation

Stars that can set (not in a circumpolar constellation for the viewer) culminate at midnight – where viewed away from any polar region experiencing midnight sun – when at opposition, meaning they can be viewed from dusk until dawn. This applies to α Piscium on 21 October, in the current astronomical epoch.[22]

Half of the year from this date, 22 April, the star will be at conjunction above or below, the sun – apart by the star's declination (angle set out in table, right). The nearby days and months have most of the star's risen time during daylight.

References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
  2. Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819.
  3. Gray, R. O.; Garrison, R. F. (July 1989), "The Late A-Type Stars: Refined MK Classification, Confrontation with Stroemgren Photometry, and the Effects of Rotation", Astrophysical Journal Supplement, 70: 623, Bibcode:1989ApJS...70..623G, doi:10.1086/191349.
  4. Samus, N. N.; Durlevich, O. V.; et al. (2009), "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)", VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S, 1: B/gcvs, Bibcode:2009yCat....102025S.
  5. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  6. Hartkopf, W. I.; et al. (June 30, 2006), Sixth Catalog of Orbits of Visual Binary Stars, United States Naval Observatory, archived from the original on 2017-08-01, retrieved 2017-06-02.
  7. Netopil, Martin; Paunzen, Ernst; Hümmerich, Stefan; Bernhard, Klaus (2017), "An investigation of the rotational properties of magnetic chemically peculiar stars", Monthly Notices of the Royal Astronomical Society, 468 (3): 2745, arXiv:1703.05218, Bibcode:2017MNRAS.468.2745N, doi:10.1093/mnras/stx674, S2CID 119215348.
  8. Glagolevskij, Yu. V. (2019), "On Properties of Main Sequence Magnetic Stars", Astrophysical Bulletin, 74 (1): 66, Bibcode:2019AstBu..74...66G, doi:10.1134/S1990341319010073, S2CID 149900274.
  9. Royer, F.; et al. (October 2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics, 393: 897–911, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943, S2CID 14070763.
  10. Sikora, J.; Wade, G. A.; Power, J.; Neiner, C. (2019), "A volume-limited survey of MCP stars within 100 pc - I. Fundamental parameters and chemical abundances", Monthly Notices of the Royal Astronomical Society, 483 (2): 2300, arXiv:1811.05633, Bibcode:2019MNRAS.483.2300S, doi:10.1093/mnras/sty3105, S2CID 119089236.
  11. "alf Psc", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-08-04.
  12. "alf Psc A", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-08-04.
  13. "alf Psc B", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-08-04.
  14. Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  15. "Naming Stars". IAU.org. Retrieved 2 March 2018.
  16. 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].
  17. Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, pp. 342−343.
  18. Division C WG Star Names, IAU Working Group on Star Names (WGSN), retrieved 22 May 2016.
  19. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 19 日
  20. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  21. Wraight, K. T.; Fossati, L.; Netopil, M.; Paunzen, E.; Rode-Paunzen, M.; Bewsher, D.; Norton, A. J.; White, Glenn J. (2012). "A photometric study of chemically peculiar stars with the STEREO satellites - I. Magnetic chemically peculiar stars". Monthly Notices of the Royal Astronomical Society. 420 (1): 757. arXiv:1110.6283. Bibcode:2012MNRAS.420..757W. doi:10.1111/j.1365-2966.2011.20090.x. S2CID 14811051.
  22. Ephemera table, rising and setting times In-the-Sky.org. Dominic C. Ford, 2011–2020; Cambridge UK.
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