Pi Aquarii

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Pi Aquarii
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Cercle rouge 100%.svg

Location of π Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 22h 25m 16.62285s[1]
Declination +01° 22′ 38.6346″[1]
Apparent magnitude (V) +4.66[2]
Spectral type B1 Ve[3]
U−B color index –0.98[2]
B−V color index –0.03[2]
Variable type γ Cas
Radial velocity (Rv) +4.0[4] km/s
Proper motion (μ) RA: +17.83[1] mas/yr
Dec.: +2.41[1] mas/yr
Parallax (π) 4.17 ± 0.28[1] mas
Distance 780 ± 50 ly
(240 ± 20 pc)
Mass 10.7 ± 0.7[5] M
Radius 6.2[6] R
Luminosity 7,302[7] L
Temperature 27,094[6] K
Rotational velocity (v sin i) 215[8] km/s
Age 10.0 ± 5.0[5] Myr
Other designations
52 Aquarii, BD+00 4872, FK5 1585, HD 212571, HIP 110672, HR 8539, SAO 127520.[9]
Database references

Pi Aquarii (π Aqr, π Aquarii) is the Bayer designation for a binary star in the equatorial constellation of Aquarius. It shares the traditional name Seat with Delta Aquarii, where it has long been misspelled Skat. It may be from the Arabic word ši'at, meaning "a wish". This system has an apparent visual magnitude of a mean apparent magnitude of +4.57.[2] Based upon parallax measurements, it is located at a distance of roughly 780 light-years (240 parsecs) from Earth.[1]

This is a binary star system with an orbital period of 84.1 days.[10][11] The primary component is a B-type main sequence star with a stellar classification of B1 Ve.[3] This is a large star with nearly eleven[5] times the mass and over six times the radius of the Sun.[6] Pi Aquarii shines about 7,300[7] times as brightly as the Sun. This energy is being radiated from its outer atmosphere at an effective temperature of 27,094,[6] giving it the blue-hued glow of a B-type star.[12] It is spinning rapidly with a projected rotational velocity of 215 km/s.[8]

Pi Aquarii is notable for having undergone a transition from a Be star (showing hydrogen emission lines) into an ordinary B-type star.[11] It is classified as a Gamma Cassiopeiae type[13] variable star and its brightness varies from magnitude +4.45 to +4.71; a range of 0.28. The dominant variability period, 83.8 ± 0.8 days, is nearly the same as the orbital period.[11] Pi Aquarii has a reasonable chance of becoming a supernova some day.[10]

In culture[edit]

In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of π Aquarii, γ Aquarii, ζ Aquarii, η Aquarii.[14] Consequently, π Aquarii itself is known as 墳墓四 (Fén Mù sì, English: the Fourth Star of Tomb.)[15]

In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Wasat al Achbiya (وسط الأخبية - wasath al ahbiyah), which was translated into Latin as Media Tabernaculorum, meaning the middle of luck of the homes (tents).[16] This star, along with γ Aqr (Sadachbia), ζ Aqr (Sadaltager / Achr al Achbiya) and η Aqr (Hydria), were al Aḣbiyah (الأخبية), the Tent.[17][18][19]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N. 
  3. ^ a b Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement, 17: 371, Bibcode:1968ApJS...17..371L, doi:10.1086/190179. 
  4. ^ Wielen, R.; et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions (35), Astronomisches Rechen-Institut Heidelberg, Bibcode:1999VeARI..35....1W. 
  5. ^ a b c Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x. 
  6. ^ a b c d Underhill, A. B.; et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society, 189: 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601. 
  7. ^ a b Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335Freely accessible, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355. 
  8. ^ a b Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590. 
  9. ^ "52 Aqr -- Be Star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-03. 
  10. ^ a b STARS
  11. ^ a b c Pollmann, Ernst (May 2012), "Period analysis of the Halpha line profile variation of the Be binary star pi Aqr", Information Bulletin on Variable Stars, 6023: 1, Bibcode:2012IBVS.6023....1P. 
  12. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16 
  13. ^ "pi Aqr", General Catalogue of Variable Stars, Sternberg Astronomical Institute, retrieved 2012-07-03.  Note: type = GCAS.
  14. ^ (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 978-986-7332-25-7.
  15. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日
  16. ^ Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket", Monthly Notices of the Royal Astronomical Society, 55: 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429. 
  17. ^ Davis Jr., G. A. (October 1944), "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names", Popular Astronomy, 52 (3): 12, Bibcode:1944PA.....52....8D. 
  18. ^ Allen, R. H. (1963), Star Names: Their Lore and Meaning (Reprint ed.), New York: Dover Publications Inc, p. 52, ISBN 0-486-21079-0, retrieved 2010-12-12. 
  19. ^ γ Aqr as Aoul al Achbiya or Prima Tabernaculorum (the first of luck of the homes or tents), π Aqr as Wasat al Achbiya or Media Tabernaculorum (the middle of luck of the homes or tents) and ζ Aqr as Achr al Achbiya or Postrema Tabernaculorum (the end of luck of the homes or tents). η Aqr should be designated as al Achbiya consistently, but it was not designated as the Arabic name except the name Hydria (Greek) or Deli (Hebrew)

External links[edit]