View source for Astronomy:Delta Aquarii

{{short description|Star in the constellation Aquarius}}
{{Starbox begin
| name     = δ Aquarii
}}
{{Starbox image
 | image=
{{Location mark
|image=Aquarius constellation map.svg|alt=|float=center|width=280
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=δ Aquarii
|x=334|y=592
}}
|caption=Location of δ Aquarii (circled)
}}
{{Starbox observe
| epoch    = J2000
| ra       = {{RA|22|54|39.0125}}<ref name=aaa474_2_653/>
| dec      = {{DEC|−15|49|14.953}}<ref name=aaa474_2_653/>
| appmag_v = 3.28<ref name=ducati/>
| constell = [[Astronomy:Aquarius (constellation)|Aquarius]]
}}
{{Starbox character
| class    = A3Vp<ref name=abt/>
| b-v      = +0.05<ref name=hr/>
| u-b      = +0.08<ref name=hr/>
| variable = 
}}
{{Starbox astrometry
| radial_v = +18.0<ref name=gcsrv53/>
| prop_mo_ra  = -38.904<ref name=dr2/>
| prop_mo_dec = -33.027<ref name=dr2/>
| parallax = 28.7936
| p_error  = 0.7289
| parallax_footnote = <ref name=dr2/>
| absmag_v = −0.17<ref name=Anderson2012/>
}}
{{Starbox detail
| mass     = 2.51<ref name=borgniet/>
| radius   = 2.4<ref name=aass85_3_1015/>
| gravity  = 3.73<ref name=david/>
| luminosity  = 48<ref name=dr2/>
| temperature = 8,650<ref name=zorec/>
| metal_fe = –0.21<ref name=takeda/>
| rotational_velocity = 81<ref name=aaa463_2_671/>
| age_gyr  = 0.3<ref name=aaa523_A73/>
}}
{{Starbox catalog
| names=Skat, Scheat, 76&nbsp;Aquarii, BD-16&nbsp;6173, FK5&nbsp;866, HD&nbsp;216627, HIP&nbsp;113136, [[Astronomy:Bright Star Catalogue|HR]]&nbsp;8709, [[Astronomy:Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;165375.<ref name=SIMBAD/>
}}
{{Starbox reference
| Simbad=HD+216627
}}
{{Starbox end}}
'''Delta Aquarii''' ('''δ Aquarii''', abbreviated '''Delta Aqr''', '''δ Aqr'''), officially named '''Skat''' {{IPAc-en|ˈ|s|k|æ|t}},<ref name="IAU-LSN">{{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |access-date=18 June 2018}}</ref> is the third-brightest star in the [[Astronomy:Constellation|constellation]] of [[Astronomy:Aquarius (constellation)|Aquarius]]. The [[Astronomy:Apparent magnitude|apparent visual magnitude]] is 3.3,<ref name=aaass22_9/> which can be seen with the naked eye. The distance to this star is about {{Convert|113|ly|pc|abbr=off|lk=on}} based upon [[Astronomy:Parallax|parallax]] measurements, and it has a close [[Astronomy:Binary star|companion]].

==Nomenclature==
''δ Aquarii'' ([[Social:Latinisation of names|Latinised]] to ''Delta Aquarii'') is the star's [[Astronomy:Bayer designation|Bayer designation]].  It also has the [[Astronomy:Flamsteed designation|Flamsteed designation]] 76 Aquarii.

It bore the traditional name ''Skat'' (also rendered ''Scheat'', ''Seat'', ''Sheat'', etc., which was erroneously applied to [[Astronomy:Beta Pegasi|Beta Pegasi]] in late medieval times), from the [[Social:Arabic|Arabic]] الساق ''al-sāq'' "shin".<ref name=Kunitzsch>{{cite book
  |last1=Kunitzsch |first1=Paul
  |last2=Smart |first2=Tim
  |date = 2006  |edition = 2nd rev.
  |title = A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations
  |publisher = Sky Pub |location = Cambridge, Massachusetts
  |isbn = 978-1-931559-44-7
}}</ref>

In 2016, the [[Organization:International Astronomical Union|International Astronomical Union]] organized a [[Astronomy:IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<ref name="WGSN">{{citation
 | url=https://www.iau.org/science/scientific_bodies/working_groups/280/
 | title=IAU Working Group on Star Names (WGSN)
 | publisher=[[Organization:International Astronomical Union|International Astronomical Union]]
 | access-date=22 May 2016 | postscript=. }}</ref> to catalogue and standardize proper names for stars. The WGSN approved the name ''Skat'' for this star on 21&nbsp;August 2016, and it is now so included in the List of IAU-approved Star Names.<ref name="IAU-LSN"/>
 
In [[Astronomy:Chinese astronomy|Chinese]], {{lang|zh|羽林軍}} ({{lang|zh-Latn|Yǔ Lín Jūn}}), meaning ''[[Astronomy:Encampment (Chinese constellation)|Palace Guard]]'', refers to an [[Astronomy:Asterism|asterism]] consisting of Delta Aquarii, [[Astronomy:29 Aquarii|29 Aquarii]], [[Astronomy:35 Aquarii|35 Aquarii]], [[Astronomy:41 Aquarii|41 Aquarii]], [[Astronomy:47 Aquarii|47 Aquarii]], [[Astronomy:49 Aquarii|49 Aquarii]], [[Astronomy:Lambda Piscis Austrini|Lambda Piscis Austrini]], HD 212448, [[Astronomy:Epsilon Piscis Austrini|Epsilon Piscis Austrini]], 21 Piscis Austrini, 20 Piscis Austrini, [[Astronomy:Upsilon Aquarii|Upsilon Aquarii]], [[Astronomy:68 Aquarii|68 Aquarii]], [[Astronomy:66 Aquarii|66 Aquarii]], [[Astronomy:61 Aquarii|61 Aquarii]], [[Astronomy:53 Aquarii|53 Aquarii]], [[Astronomy:50 Aquarii|50 Aquarii]], [[Astronomy:56 Aquarii|56 Aquarii]], [[Astronomy:45 Aquarii|45 Aquarii]], [[Astronomy:58 Aquarii|58 Aquarii]], [[Astronomy:64 Aquarii|64 Aquarii]], [[Astronomy:65 Aquarii|65 Aquarii]], [[Astronomy:70 Aquarii|70 Aquarii]], [[Astronomy:74 Aquarii|74 Aquarii]], [[Astronomy:Tau2 Aquarii|Tau<sup>2</sup> Aquarii]], [[Astronomy:Tau1 Aquarii|Tau<sup>1</sup> Aquarii]], [[Astronomy:77 Aquarii|77 Aquarii]], [[Astronomy:88 Aquarii|88 Aquarii]], [[Astronomy:89 Aquarii|89 Aquarii]], [[Astronomy:86 Aquarii|86 Aquarii]], [[Astronomy:101 Aquarii|101 Aquarii]], [[Astronomy:100 Aquarii|100 Aquarii]], [[Astronomy:99 Aquarii|99 Aquarii]], [[Astronomy:98 Aquarii|98 Aquarii]], [[Astronomy:97 Aquarii|97 Aquarii]], [[Astronomy:94 Aquarii|94 Aquarii]], [[Astronomy:Psi3 Aquarii|Psi<sup>3</sup>Aquarii]], [[Astronomy:Psi2 Aquarii|Psi<sup>2</sup>Aquarii]], Psi<sup>1</sup>Aquarii, [[Astronomy:87 Aquarii|87 Aquarii]], [[Astronomy:85 Aquarii|85 Aquarii]], [[Astronomy:83 Aquarii|83 Aquarii]], [[Astronomy:Chi Aquarii|Chi Aquarii]], [[Astronomy:Omega1 Aquarii|Omega<sup>1</sup> Aquarii]] and [[Astronomy:Omega2 Aquarii|Omega<sup>2</sup> Aquarii]]. Consequently, the [[Astronomy:Chinese star names|Chinese name]] for Delta Aquarii itself is {{lang|zh|羽林軍二十六}} ({{lang|zh-Latn|Yǔ Lín Jūn ershíliù}}, {{lang-en|the Twenty Sixth Star of Palace Guard}}).<ref>{{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0607/ap060707.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日]</ref>

==Properties==

The spectrum of Delta Aquarii matches a [[Astronomy:Stellar classification|stellar classification]] of A3&nbsp;Vp, indicating this is a [[Chemistry:Chemically peculiar star|chemically peculiar]] [[Astronomy:A-type main-sequence star|A-type main-sequence star]] that is generating energy through the [[Physics:Nuclear fusion|nuclear fusion]] of hydrogen at its core. This star has double the [[Astronomy:Solar mass|Sun's mass]] and a radius 2.4 times [[Astronomy:Solar radius|as large]].<ref name=aass85_3_1015/> It is radiating 26<ref name=aass85_3_1015/> times the luminosity [[Astronomy:Solar luminosity|of the Sun]] from its outer atmosphere at an [[Astronomy:Effective temperature|effective temperature]] of around 9,000&nbsp;K.<ref name=aaa294_2_536/> This heat gives it the characteristic white-hued glow of an A-type star.<ref name=csiro/> It has a relatively high rate of rotation, with a projected rotational velocity of 81&nbsp;km s<sup>−1</sup>.<ref name=aaa463_2_671/>

Delta Aquarii does not display a strong signal of [[Astronomy:Infrared excess|excess infrared emission]] that might indicate the presence of circumstellar matter.<ref name=apj653_1_675/> Delta Aquarii is a probable stream star member of the [[Astronomy:Ursa Major Moving Group|Ursa Major Moving Group]],<ref name=aj125_4_1980/> which has an estimated age of 500 million years.<ref name=aaa442_2_563/>

==Companion==

An analysis of [[Astronomy:Hipparcos|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 the companion, it could not be seen.  Any possible companion beyond {{val|100|ul=au}} was constrained to be less than {{solar mass|0.07}}.<ref name=aaa523_A73/>  [[Physics:Infrared|Infrared]] [[Astronomy:Interferometry|interferometric]] observations did then find a companion, a likely G5 [[Astronomy:Main sequence|main sequence]] star around {{val|2|u=au}} from the primary.<ref name=borgniet/>

==References==
{{Reflist|colwidth=30em|refs=

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<ref name=aaa442_2_563>{{citation | last1=Monier | first1=R. | title=Abundances of a sample of A and F-type dwarf members of the Ursa Major Group | journal=Astronomy and Astrophysics | volume=442 | issue=2 | pages=563–566 |date=November 2005 | doi=10.1051/0004-6361:20053222 | bibcode=2005A&A...442..563M | doi-access=free }}</ref>

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<ref name=SIMBAD>{{citation | title=del Aqr -- Star | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Delta+Aquarii  | access-date=2012-01-30 }}</ref>
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<ref name=allen>{{citation | last=Allen | first=Richard Hinkley | title=Star Names: Their Lore and Meaning | publisher=[[Social:Dover Publications|Dover Publications]] | location=New York  |year=1963 | isbn=0-486-21079-0 }}</ref>
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}}

== External links ==
* [http://www.jas.org.jo/star.html Star names derived from Arabic] {{Webarchive|url=https://web.archive.org/web/20050205024411/http://www.jas.org.jo/star.html |date=2005-02-05 }}
* [http://aladin.u-strasbg.fr/AladinPreview?-c=22+54+39.0125-15+49+14.953&ident=*+del+Aqr&submit=Aladin+previewer Image Delta Aquarii]

{{Stars of Aquarius}}
<!-- Properties -->
{{DEFAULTSORT:Delta Aquarii}}
[[Category:A-type main-sequence stars]]
<!-- Identifiers -->
[[Category:Stars with proper names|Skat]]
[[Category:Aquarius (constellation)]]
[[Category:Bayer objects|Aquarii, Delta]]
[[Category:Durchmusterung objects|BD-16 6173]]
[[Category:Flamsteed objects|Aquarii, 076]]
[[Category:Henry Draper Catalogue objects|216627]]
[[Category:Hipparcos objects|113136]]
[[Category:Bright Star Catalogue objects|8709]]
[[Category:Binary stars]]

{{Sourceattribution|Delta Aquarii}}