Pi Aquarii

Pi Aquarii, Latinized from π Aquarii, is the Bayer designation for a binary star in the equatorial constellation of Aquarius. This system has an apparent visual magnitude of a mean apparent magnitude of +4.57.[4] Based upon parallax measurements, it is located at a distance of roughly 780 light-years (240 parsecs) from Earth.[1] It is drifting further away with a radial velocity of +4 km/s.[5]

A white-light light curve for Pi Aquarii, adapted from Nazé et al. (2020)[13]
π Aquarii
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) 4.42 - 4.87[2]
Characteristics
Spectral type B1III-IVe[3]
U−B color index −0.98[4]
B−V color index −0.03[4]
Variable type γ Cas[2]
Astrometry
Radial velocity (Rv)+4.0[5] km/s
Proper motion (μ) RA: +17.83[1] mas/yr
Dec.: +2.41[1] mas/yr
Parallax (π)4.17 ± 0.28 mas[1]
Distance780 ± 50 ly
(240 ± 20 pc)
Absolute magnitude (MV)−2.09[6]
Orbit[7]
Period (P)84.07±0.02 d
Semi-major axis (a)≥ 0.96 AU
Eccentricity (e)0.0 (fixed)
Periastron epoch (T)2,450,318.5±13.2 JD
Argument of periastron (ω)
(secondary)		0.0 (fixed)°
Semi-amplitude (K1)
(primary)		16.7±0.2 km/s
Semi-amplitude (K2)
(secondary)		101.4±0.2 km/s
Details
A
Mass10.7±0.7[8] M☉
Radius6.2[9] R☉
Luminosity7,302[10] L☉
Temperature27,094[9] K
Metallicity [Fe/H]−0.02[6] dex
Rotational velocity (v sin i)215[11] km/s
Age10.0±5.0[8] Myr
Other designations
π Aqr, 52 Aquarii, BD+00 4872, FK5 1585, HD 212571, HIP 110672, HR 8539, SAO 127520[12]
Database references
SIMBADdata

This is a binary star system with an orbital period of 84.1 days.[14][15] The primary component is a B1 giant or subgiant star.[3] This is a large star with nearly eleven[8] times the mass and over six times the radius of the Sun.[9] Pi Aquarii shines about 7,300[10] times as brightly as the Sun. This energy is being radiated from its outer atmosphere at an effective temperature of 27,094 K,[9] giving it the blue-hued glow of a B-type star.[16] It is spinning rapidly with a projected rotational velocity of 215 km/s.[11] The nature of the secondary is unknown; some analyses have suggested it is an A- or F-type main-sequence star,[7] but the possibility of a white dwarf has not been ruled out.[17]

Pi Aquarii is notable for having undergone a transition from a Be star (showing hydrogen emission lines) into an ordinary B-type star.[15] It is classified as a Gamma Cassiopeiae type[2] 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.[15] Pi Aquarii has a reasonable chance of becoming a supernova some day.[14]

In culture

Pi Aquarii was called Seat /ˈsiːæt/ by Grotius in the 17th century, but the name has rarely been used since.[14]

In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of π Aquarii, γ Aquarii, ζ Aquarii, η Aquarii.[18] Consequently, the Chinese name for π Aquarii itself is 墳墓四 (Fén Mù sì, English: the Fourth Star of Tomb.)[19]

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).[20] This star, along with γ Aqr (Sadachbia), ζ Aqr (Sadaltager / Achr al Achbiya) and η Aqr (Hydria), were al Aḣbiyah (الأخبية), the Tent.[21][22][23]

References
  1. van Leeuwen, F. (November 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. "pi Aqr", General Catalogue of Variable Stars, Sternberg Astronomical Institute, retrieved 2012-07-03. Note: type = GCAS.
  3. Slettebak, A (1982). "Spectral types and rotational velocities of the brighter Be stars and A-F type shell stars". Astrophysical Journal Supplement Series. 50: 55. Bibcode:1982ApJS...50...55S. doi:10.1086/190820.
  4. 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.
  5. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb, Astronomisches Rechen-Institut Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W.
  6. 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.
  7. Bjorkman, Karen S.; et al. (July 2002). "A Study of π Aquarii during a Quasi-normal Star Phase: Refined Fundamental Parameters and Evidence for Binarity". The Astrophysical Journal. 573 (2): 812–824. arXiv:astro-ph/0203357. Bibcode:2002ApJ...573..812B. doi:10.1086/340751. S2CID 14685744.
  8. 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:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x, S2CID 118629873.
  9. 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 (3): 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601.
  10. 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:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355, S2CID 111387483.
  11. 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.
  12. "pi. Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-07-03.
  13. Nazé, Yaël; Pigulski, Andrzej; Rauw, Gregor; Smith, Myron A. (May 4, 2020). "Let there be more variability in two γ Cas stars". Monthly Notices of the Royal Astronomical Society. 494 (1): 958–974. doi:10.1093/mnras/staa617. Retrieved 2 August 2022.
  14. Kaler, Jim. "Seat". Retrieved 2017-08-18.
  15. 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.
  16. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16
  17. Tsujimoto, Masahiro; Hayashi, Takayuki; Morihana, Kumiko; Moritani, Yuki (2023). "X-ray and optical spectroscopic study of a γ Cassiopeiae analog source π Aquarii". Publications of the Astronomical Society of Japan. 75 (1): 177–186. arXiv:2211.10803. Bibcode:2023PASJ...75..177T. doi:10.1093/pasj/psac099.
  18. (in 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.
  19. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日
  20. 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 (8): 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429.
  21. 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.
  22. 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.
  23. 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)
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