Delta Aquarii

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Delta Aquarii
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Cercle rouge 100%.svg
Location of δ Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 22h 54m 39.0125s[1]
Declination −15° 49′ 14.953″[1]
Apparent magnitude (V) 3.252[2]
Spectral type A3 V[3]
U−B color index +0.172[2]
B−V color index +0.068[2]
Radial velocity (Rv)+18.0[4] km/s
Proper motion (μ) RA: -42.60[1] mas/yr
Dec.: -27.89[1] mas/yr
Parallax (π)20.44 ± 2.26[1] mas
Distanceapprox. 160 ly
(approx. 49 pc)
Absolute magnitude (MV)−0.17[5]
Mass2.0[6] M
Radius2.4[6] R
Luminosity26[6] L
Surface gravity (log g)3.66[7] cgs
Temperature9,000[7] K
Metallicity [Fe/H]–0.15[7] dex
Rotational velocity (v sin i)81[8] km/s
Age0.3[9] Gyr
Other designations
Skat, Scheat, 76 Aquarii, BD-16 6173, FK5 866, HD 216627, HIP 113136, HR 8709, SAO 165375.[10]
Database references

Delta Aquarii (δ Aquarii, abbreviated Delta Aqr, δ Aqr), also named Skat,[11] is the third-brightest star in the constellation of Aquarius. The apparent visual magnitude is 3.3,[2] which can be seen with the naked eye. The distance to this star is estimated as 160 light-years (49 parsecs) from the Sun based upon parallax measurements.[1]


δ Aquarii (Latinised to Delta Aquarii) is the star's Bayer designation.

It bore the traditional name Skat (which had also been used for Beta Pegasi),[12] generally thought to derive from the Arabic الساق (as-saq), meaning "leg" or "shin"; however, the medieval forms Scheat, Seat, Sheat suggest it may instead be from the Arabic شئت (ši'at), meaning "wish".[1] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalogue and standardize proper names for stars. The WGSN approved the name Skat for this star on 21 August 2016, and it is now so included in the List of IAU-approved Star Names.[11]

In Chinese, 羽林軍 (Yǔ Lín Jūn), meaning Palace Guard, refers to an asterism consisting of Delta Aquarii, 29 Aquarii, 35 Aquarii, 41 Aquarii, 47 Aquarii, 49 Aquarii, Lambda Piscis Austrini, HD 212448, Epsilon Piscis Austrini, 21 Piscis Austrini, 20 Piscis Austrini, Upsilon Aquarii, 68 Aquarii, 66 Aquarii, 61 Aquarii, 53 Aquarii, 50 Aquarii, 56 Aquarii, 45 Aquarii, 58 Aquarii, 64 Aquarii, 65 Aquarii, 70 Aquarii, 74 Aquarii, Tau2 Aquarii, Tau1 Aquarii, 77 Aquarii, 88 Aquarii, 89 Aquarii, 86 Aquarii, 101 Aquarii, 100 Aquarii, 99 Aquarii, 98 Aquarii, 97 Aquarii, 94 Aquarii, Psi3Aquarii, Psi2Aquarii, Psi1Aquarii, 87 Aquarii, 85 Aquarii, 83 Aquarii, Chi Aquarii, Omega1 Aquarii and Omega2 Aquarii. Consequently, Delta Aquarii itself is known as 羽林軍二十六 (Yǔ Lín Jūn ershíliù, English: the Twenty Sixth Star of Palace Guard).[14]


The spectrum of Delta Aquarii matches a stellar classification of A3 V,[3] indicating this is an A-type main-sequence star that is generating energy through the nuclear fusion of hydrogen at its core. This star has double the Sun's mass and a radius 2.4 times as large.[6] It is radiating 26[6] times the luminosity of the Sun from its outer atmosphere at an effective temperature of around 9,000 K.[7] This heat gives it the characteristic white-hued glow of an A-type star.[15] It has a relatively high rate of rotation, with a projected rotational velocity of 81 km s−1.[8]

Delta Aquarii has been closely examined for a companion, but none has been discovered.[9] Nor does it display a strong signal of excess infrared emission that might indicate the presence of circumstellar matter.[16] Delta Aquarii is a probable stream star member of the Ursa Major Moving Group,[17] which has an estimated age of 500 million years.[18]


  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:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
  2. ^ a b c d Celis S., L. (October 1975), "Photoelectric photometry of late-type variable stars", Astronomy and Astrophysics Supplement Series, 22: 9–17, Bibcode:1975A&AS...22....9C
  3. ^ a b Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, 4, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan,
  4. ^ Wilson, Ralph Elmer (1953). General Catalogue of Stellar Radial Velocities. Washington: Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W.
  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.
  6. ^ a b c d e Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series, 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M
  7. ^ a b c d Hill, G. M. (February 1995), "Compositional differences among the A-type stars. 2: Spectrum synthesis up to V sin i = 110 km/s", Astronomy and Astrophysics, 294 (2): 536–546, Bibcode:1995A&A...294..536H
  8. ^ a b Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224
  9. ^ a b Ehrenreich, D.; et al. (November 2010), "Deep infrared imaging of close companions to austral A- and F-type stars", Astronomy and Astrophysics, 523: A73, arXiv:1007.0002, Bibcode:2010A&A...523A..73E, doi:10.1051/0004-6361/201014763
  10. ^ "del Aqr -- Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-30
  11. ^ a b "Naming Stars". Retrieved 18 June 2018.
  12. ^ Allen, Richard Hinkley (1963), Star Names: Their Lore and Meaning, New York: Dover Publications, ISBN 0-486-21079-0
  13. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  14. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日
  15. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-10, retrieved 2012-01-16
  16. ^ Su, K. Y. L.; et al. (December 2006), "Debris Disk Evolution around A Stars", The Astrophysical Journal, 653 (1): 675–689, arXiv:astro-ph/0608563, Bibcode:2006ApJ...653..675S, doi:10.1086/508649
  17. ^ King, Jeremy R.; et al. (April 2003), "Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group", The Astronomical Journal, 125 (4): 1980–2017, Bibcode:2003AJ....125.1980K, doi:10.1086/368241
  18. ^ Monier, R. (November 2005), "Abundances of a sample of A and F-type dwarf members of the Ursa Major Group", Astronomy and Astrophysics, 442 (2): 563–566, Bibcode:2005A&A...442..563M, doi:10.1051/0004-6361:20053222

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