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Delta Aquarii

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δ Aquarii
Location of δ Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius[1]
Right ascension 22h 54m 39.0125s[2]
Declination −15° 49′ 14.953″[2]
Apparent magnitude (V) 3.28[3]
Characteristics
Spectral type A3Vp[4]
U−B color index +0.08[5]
B−V color index +0.05[5]
Astrometry
Radial velocity (Rv)+17.4±0.9[6] km/s
Proper motion (μ) RA: −38.904 mas/yr[7]
Dec.: −33.027 mas/yr[7]
Parallax (π)28.7936±0.7289 mas[7]
Distance113 ± 3 ly
(34.7 ± 0.9 pc)
Absolute magnitude (MV)−0.17[1]
Details
Mass3.19[8] M☉
Radius4.16[8] R☉
Luminosity100[8] L☉
Surface gravity (log g)3.73[9] cgs
Temperature8,650[10] K
Metallicity [Fe/H]–0.21[11] dex
Rotational velocity (v sin i)81[12] km/s
Age300[13] Myr
Other designations
Skat, Scheat, 76 Aquarii, BD−16 6173, FK5 866, HD 216627, HIP 113136, HR 8709, SAO 165375[14]
Database references
SIMBADdata

Delta Aquarii is a binary star system in the constellation of Aquarius. Its identifier is a Bayer designation that is Latinized from δ Aquarii, and abbreviated Delta Aqr or δ Aqr, respectively. This system has the official name Skat, pronounced /ˈskæt/.[15] It is the third-brightest star in Aquarius with an apparent visual magnitude of 3.3,[16] and is readily visible to the naked eye at night. The distance to this system is about 113 light-years (35 parsecs) based upon parallax measurements. It is drifting further away from the Sun with a radial velocity of +17 km/s.[6]

Nomenclature

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δ Aquarii (Latinised to Delta Aquarii) is the star's Bayer designation. It also has the Flamsteed designation 76 Aquarii.

It bore the traditional name Skat (also rendered Scheat, Seat, Sheat, etc., which was erroneously applied to Beta Pegasi in late medieval times), from the Arabic الساق al-sāq "shin".[17]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[18] 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.[15]

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, the Chinese name for Delta Aquarii itself is 羽林軍二十六 (Yǔ Lín Jūn ershíliù, English: the Twenty Sixth Star of Palace Guard).[19]

Properties

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The spectrum of Delta Aquarii matches a stellar classification of A3 Vp, indicating this is a chemically peculiar A-type main-sequence star that is generating energy through the nuclear fusion of hydrogen at its core. This star has three times the Sun's mass and a radius 4.16 times as large. It is radiating 100 times the luminosity of the Sun[8] from its outer atmosphere at an effective temperature of around 9,000 K.[20] This heat gives it the characteristic white-hued glow of an A-type star.[21] It has a relatively high rate of rotation, with a projected rotational velocity of 81 km s−1.[12]

Delta Aquarii does not display a strong signal of excess infrared emission that might indicate the presence of circumstellar matter.[22] It is a probable stream star member of the Ursa Major Moving Group,[23] which has an estimated age of 500 million years.[24]

An analysis of Hipparcos data strongly suggested a close companion object. An orbit was derived with a 483-day period, an eccentricity of 0.12, and an inclination of 41°. When Delta Aquarii was first examined for a companion, none was found. Any possible companion beyond 100 au was constrained to be less than 0.07 M☉.[13] Infrared interferometric observations did subsequently find a companion in 2017: a likely G5 main sequence star around 2 au from the primary.[25]

References

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  1. ^ a b 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.
  2. ^ a b 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.
  3. ^ Ducati, J. R. (2002), "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system", CDS/ADC Collection of Electronic Catalogues, 2237, Bibcode:2002yCat.2237....0D.
  4. ^ Abt, Helmut A.; Morrell, Nidia I. (July 1995), "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars", Astrophysical Journal Supplement, 99: 135, Bibcode:1995ApJS...99..135A, doi:10.1086/192182.
  5. ^ a b Hoffleit, Dorrit; Jaschek, Carlos (1991), "The Bright star catalogue", New Haven, Bibcode:1991bsc..book.....H.
  6. ^ a b Gontcharov, G. A. (2006), "Pulkovo compilation of radial velocities for 35495 stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID 119231169.
  7. ^ a b Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  8. ^ a b c d Gáspár, András; et al. (August 1, 2016), "The Correlation between Metallicity and Debris Disk Mass", The Astrophysical Journal, 826 (2): 171, arXiv:1604.07403, Bibcode:2016ApJ...826..171G, doi:10.3847/0004-637X/826/2/171, ISSN 0004-637X. Skat's database entry at VizieR.
  9. ^ David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
  10. ^ Zorec, J.; Royer, F. (2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789.
  11. ^ Takeda, Yoichi; et al. (2009), "Can Sodium Abundances of A-Type Stars be Reliably Determined from Na I 5890/5896 Lines?", Publications of the Astronomical Society of Japan, 61 (5): 1165–1178, arXiv:0907.1329, Bibcode:2009PASJ...61.1165T, doi:10.1093/pasj/61.5.1165, S2CID 15454888.
  12. ^ a b Royer, F.; et al. (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, S2CID 18475298.
  13. ^ 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, S2CID 54913363.
  14. ^ "del Aqr", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2012-01-30.
  15. ^ a b Naming Stars, IAU.org, retrieved 2018-06-18.
  16. ^ 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.
  17. ^ 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.
  18. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 2016-05-22.
  19. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日 Archived 2011-05-21 at the Wayback Machine
  20. ^ 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.
  21. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on 2012-03-18, retrieved 2012-01-16.
  22. ^ 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, S2CID 14116473.
  23. ^ 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.
  24. ^ 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.
  25. ^ Borgniet, S.; et al. (2017), "Extrasolar planets and brown dwarfs around AF-type stars", Astronomy & Astrophysics, 599: A57, arXiv:1608.08257, Bibcode:2017A&A...599A..57B, doi:10.1051/0004-6361/201628805, S2CID 118723455.
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