Epoch J2000 Equinox J2000
|Right ascension||22h 25m 16.62285s|
|Declination||+01° 22′ 38.6346″|
|Apparent magnitude (V)||+4.66|
|Spectral type||B1 Ve|
|U−B color index||–0.98|
|B−V color index||–0.03|
|Variable type||γ Cas|
|Radial velocity (Rv)||+4.0 km/s|
|Proper motion (μ)||RA: +17.83 mas/yr
Dec.: +2.41 mas/yr
|Parallax (π)||4.17 ± 0.28 mas|
|Distance||780 ± 50 ly
(240 ± 20 pc)
|Mass||10.7 ± 0.7 M☉|
|Rotational velocity (v sin i)||215 km/s|
|Age||10.0 ± 5.0 Myr|
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 "a wish". This system has an apparent visual magnitude of a mean apparent magnitude of +4.57. Based upon parallax measurements, it is located at a distance of roughly 780 light-years (240 parsecs) from Earth.
This is a binary star system with an orbital period of 84.1 days. The primary component is a B-type main sequence star with a stellar classification of B1 Ve. This is a large star with nearly eleven times the mass and over six times the radius of the Sun. Pi Aquarii shines about 7,300 times as brightly as the Sun. This energy is being radiated from its outer atmosphere at an effective temperature of 27,094, giving it the blue-hued glow of a B-type star. It is spinning rapidly with a projected rotational velocity of 215 km/s.
Pi Aquarii is notable for having undergone a transition from a Be star (showing hydrogen emission lines) into an ordinary B-type star. It is classified as a Gamma Cassiopeiae type 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. Pi Aquarii has a reasonable chance of becoming a supernova some day.
In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of π Aquarii, γ Aquarii, ζ Aquarii, η Aquarii. Consequently, π Aquarii itself is known as 墳墓四 (Fén Mù sì, English: the Fourth Star of Tomb.)
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). This star, along with γ Aqr (Sadachbia), ζ Aqr (Sadaltager / Achr al Achbiya) and η Aqr (Hydria), were al Aḣbiyah (الأخبية), the Tent.
- van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv: , Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
- 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.
- 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.
- 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.
- 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: , Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
- 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.
- 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: , Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355.
- 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.
- "52 Aqr -- Be Star", SIMBAD Astronomical Object Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-03.
- 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.
- "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16
- "pi Aqr", General Catalogue of Variable Stars, Sternberg Astronomical Institute, retrieved 2012-07-03. Note: type = GCAS.
- (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.
- (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日
- 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.
- 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.
- 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.
- 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)