View source for Astronomy:Delta Geminorum

{{short description|Star in the constellation Gemini}}
{{Starbox begin
| name=Delta Geminorum
}}
{{Starbox image
 | image=
{{Location mark
|image=Gemini constellation map.svg|alt=|float=center|width=280
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=δ Geminorum
|x=368|y=388
}}
|caption=Location of δ Geminorum (circled)
}}
{{Starbox observe
| epoch    = J2000
| ra       = {{RA|07|20|07.37978}}<ref name=aaa474_2_653/>
| dec      = {{DEC|+21|58|56.3377}}<ref name=aaa474_2_653/>
| appmag_v = +3.53<ref name=clpl4_99/>
| constell = [[Astronomy:Gemini (constellation)|Gemini]]
}}
{{Starbox character
| class    = F0&nbsp;IV<ref name="SIMBAD"/>
| b-v      = +0.34<ref name=clpl4_99/>
| u-b      = +0.04<ref name=clpl4_99/>
| variable = 
}}
{{Starbox astrometry
| radial_v = +4.1<ref name=rgcrv/>
| prop_mo_ra  = –15.13<ref name=aaa474_2_653/>
| prop_mo_dec = –9.79<ref name=aaa474_2_653/>
| parallax = 53.94
| p_error  = 0.66
| parallax_footnote = <ref name=aaa474_2_653/>
| absmag_v = 1.95<ref name=Reiners2006/>
}}
{{Starbox detail
| mass     = 1.57<ref name=apjss192_1_2/>
| radius   = 
| luminosity  =
| gravity  = 
| temperature = 6,900<ref name=aaa418_989/>
| metal_fe = –0.26<ref name=aaa418_989/>
| rotational_velocity = 129.7<ref name=aaa493_3_1099/>
| age_gyr  = 1.6<ref name=aaa418_989/>
}}
{{Starbox catalog
| names    = Wasat, [[Astronomy:Flamsteed designation|55]]&nbsp;Geminorum, BD+22°&nbsp;1645, FK5&nbsp;279, [[Astronomy:Gliese Catalogue of Nearby Stars|Gl]]&nbsp;271, HD&nbsp;56986, HIP&nbsp;35550, HR&nbsp;2777, [[Astronomy:Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;79294.<ref name=SIMBAD/>
}}
{{Starbox reference
|Simbad=Delta+Gem
}}
{{Starbox end}}

'''Delta Geminorum''' ('''δ Geminorum''', abbreviated '''Delta Gem''', '''δ Gem'''), formally named '''Wasat''' {{IPAc-en|'|w|ei|s|@|t}},<ref name=Kunitzsch/><ref name="IAU-CSN"/> is a [[Astronomy:Star system#Triple star systems|triple star system]] in the [[Astronomy:Constellation|constellation]] of [[Astronomy:Gemini (constellation)|Gemini]].

==Nomenclature==
''δ Geminorum'' ([[Social:Latinisation of names|Latinised]] to ''Delta Geminorum'') is the system's [[Astronomy:Bayer designation|Bayer designation]].

It bore the traditional name ''Wasat'', which derives from the [[Social:Arabic|Arabic]] word for "middle".<ref name=kaler2/><ref name=constellationsofwords/> 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"/> to catalogue and standardize proper names for stars. The WGSN approved the name ''Wasat'' for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.<ref name="IAU-CSN"/>

In [[Social:Chinese language|Chinese]], {{lang|zh|天樽}} ({{lang|zh-Latn|Tiān Zūn}}), meaning ''[[Astronomy:Well (Chinese constellation)|Celestial Wine Cup]]'', refers to an [[Astronomy:Asterism|asterism]] consisting of Delta Geminorum, [[Astronomy:57 Geminorum|57 Geminorum]] and [[Astronomy:Omega Geminorum|Omega Geminorum]].<ref>{{in lang|zh}} ''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}}.</ref> Consequently, Delta Geminorum itself is known as {{lang|zh|天樽二}} ({{lang|zh-Latn|Tiān Zūn èr}}, {{lang-en|the Second Star of Celestial Wine Cup}}.).<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_t_z.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive |url=https://web.archive.org/web/20100819122914/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_t_z.htm |date=August 19, 2010 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref>  From this Chinese name, the name ''Ta Tsun'' has appeared.<ref>[https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Gemini*.html Richard Hinckley Allen: Star Names — Their Lore and Meaning: Gemini]</ref>

==Properties==
[[File:Wasat-2013Dec10.jpg|thumb|left|180px|Wasat is the bright star next to Jupiter.<ref name="astrobob131212"/> Jupiter is ~280× brighter.]]

Delta Geminorum is a subgiant star with the [[Astronomy:Stellar classification|stellar classification]] F0&nbsp;IV.<ref name="SIMBAD"/> It is about {{Convert|60.5|ly|pc|abbr=off|lk=on}} distant.<ref name=aaa474_2_653/> This star has 1.57 times the mass of the Sun<ref name=apjss192_1_2/> and is rotating rapidly with a projected rotational velocity of {{nowrap|129.7 km s<sup>−1</sup>}}.<ref name=aaa493_3_1099/> The estimated age is 1.6 billion years.<ref name=aaa418_989/>

It has an [[Astronomy:Apparent visual magnitude|apparent visual magnitude]] of +3.53,<ref name=clpl4_99/> allowing it to be seen with the naked eye. It is 0.18 degree south of the [[Astronomy:Ecliptic|ecliptic]] so it is occasionally [[Astronomy:Occultation|occulted]] by the [[Astronomy:Sun|Sun]], [[Astronomy:Moon|Moon]] and, rarely, by a [[Astronomy:Planet|planet]]; and is eclipsed by the sun from about 10-12 July.<ref>[http://in-the-sky.org/skymap.php?year=2019&month=4&day=9 In the Sky] Earth astronomy reference utility showing the ecliptic and relevant date as at J2000 - present</ref> Thus the star can be viewed the whole night, crossing the sky, in mid-January. The last occultation by a planet was by [[Astronomy:Saturn|Saturn]] on June 30, 1857, and the next will be by [[Astronomy:Venus|Venus]] on August 12, 2420.{{citation needed|date=January 2012}} In 1930, the [[Astronomy:Dwarf planet|dwarf planet]] [[Astronomy:Pluto|Pluto]] was discovered about 0.5° to the east of this star by American astronomer [[Biography:Clyde Tombaugh|Clyde Tombaugh]].<ref name=omeara/>

Delta Geminorum is a triple star system. The inner components form a [[Astronomy:Spectroscopic binary|spectroscopic binary]] with a [[Astronomy:Orbital period|period]] of 6.1&nbsp;years (2,238.7&nbsp;days) and an [[Astronomy:Orbital eccentricity|orbital eccentricity]] of 0.3530. A cooler [[Astronomy:Stellar classification|class K]] companion is not apparent to the naked eye but clearly visible in a small telescope. It orbits the inner pair with a period of 1,200 years and an eccentricity of 0.11.<ref name=apj629_1_507/><ref name=kaler/> Although according to <ref name=rgcrv/> its [[Astronomy:Radial velocity|radial velocity]] is away from the Sun, it is actually approaching the Solar System. In about 1.1 million years, it will make its closest approach at a separation of roughly {{Convert|6.7|ly|pc|abbr=on}}.<ref name=aaa379_634/>

==References==
{{Reflist|refs=

<ref name=aaa474_2_653>{{citation | title=Validation of the new Hipparcos reduction | last=van Leeuwen | first=F. | journal=Astronomy and Astrophysics | volume=474 | issue=2 |date=November 2007 | pages=653–664 | doi=10.1051/0004-6361:20078357 | bibcode=2007A&A...474..653V |arxiv = 0708.1752 | s2cid=18759600 }}</ref>

<ref name=Reiners2006>{{citation | last1=Reiners | first1=Ansgar | title=Rotation- and temperature-dependence of stellar latitudinal differential rotation | journal=Astronomy and Astrophysics | volume=446 | issue=1 |date=January 2006 | pages=267–277 | doi=10.1051/0004-6361:20053911 | bibcode=2006A&A...446..267R |arxiv = astro-ph/0509399 | s2cid=8642707 }}</ref>

<ref name=apjss192_1_2>{{citation | last1=Shaya | first1=Ed J. | last2=Olling | first2=Rob P. | title=Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue | journal=The Astrophysical Journal Supplement | volume=192 | issue=1 | page=2 |date=January 2011 | doi=10.1088/0067-0049/192/1/2 | bibcode=2011ApJS..192....2S |arxiv = 1007.0425 | s2cid=119226823 }}</ref>

<ref name=rgcrv>{{Cite book| last=Evans | first=D. S. | date=June 20–24, 1966 | editor=Batten, Alan Henry | editor2=Heard, John Frederick | chapter=The Revision of the General Catalogue of Radial Velocities | title=Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30 | journal=Determination of Radial Velocities and Their Applications | volume=30 | page=57 | location=University of Toronto | publisher=International Astronomical Union | bibcode=1967IAUS...30...57E }}</ref>

<ref name=aaa493_3_1099>{{citation | last1=Schröder | first1=C. | last2=Reiners | first2=Ansgar | last3=Schmitt | first3=Jürgen H. M. M. | title=Ca II HK emission in rapidly rotating stars. Evidence for an onset of the solar-type dynamo | journal=Astronomy and Astrophysics | volume=493 | issue=3 | pages=1099–1107 | date=January 2009 | doi=10.1051/0004-6361:200810377 | bibcode=2009A&A...493.1099S | doi-access=free | url=http://goedoc.uni-goettingen.de/goescholar/bitstream/handle/1/9690/aa10377-08.pdf?sequence=2 }}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

<ref name=clpl4_99>{{citation | display-authors=1 | last1=Johnson | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | date=1966 | page=99 | bibcode=1966CoLPL...4...99J }}</ref>

<ref name=aaa418_989>{{citation | title=The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs | display-authors=1 | last1=Nordström | first1=B. | last2=Mayor | first2=M. | last3=Andersen | first3=J. | last4=Holmberg | first4=J. | last5=Pont | first5=F. | last6=Jørgensen | first6=B. R. | last7=Olsen | first7=E. H. | last8=Udry | first8=S. | last9=Mowlavi | first9=N. | journal=Astronomy and Astrophysics | volume=418 | pages=989–1019  |date=May 2004 | doi=10.1051/0004-6361:20035959 | bibcode=2004A&A...418..989N |arxiv = astro-ph/0405198 | s2cid=11027621 }}</ref>

<ref name=aaa379_634>{{citation | display-authors=1 | last1=García-Sánchez | first1=J. | last2=Weissman | first2=P. R. | last3=Preston | first3=R. A. | last4=Jones | first4=D. L. | last5=Lestrade | first5=J.-F. | last6=Latham | first6=D. W. | last7=Stefanik | first7=R. P. | last8=Paredes | first8=J. M. | title=Stellar encounters with the solar system | journal=Astronomy and Astrophysics | volume=379 | pages=634–659 |date=November 2001 | issue=2 | doi=10.1051/0004-6361:20011330 | bibcode=2001A&A...379..634G | doi-access=free }}</ref>

<ref name=apj629_1_507>{{citation | last1=Abt | first1=Helmut A. | title=Observed Orbital Eccentricities | journal=The Astrophysical Journal | volume=629 | issue=1 | pages=507–511 |date=August 2005 | doi=10.1086/431207 | bibcode=2005ApJ...629..507A | doi-access=free }}</ref>

<ref name="SIMBAD">{{citation | title=Delta Geminorum (Wasat) | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Delta+Geminorum | access-date=2011-06-03 }}</ref>

<ref name=omeara>{{citation | first1=Stephen James | last1=O'Meara | title=The Caldwell objects | series=Deep-sky companions | publisher={{wipe|Cambridge University Press}} | date=2002 | isbn=0-521-82796-5 | page=156 | url=https://books.google.com/books?id=3Hg6YHgx9nAC&pg=PA156 }}</ref>

<ref name=kaler>{{citation | first1=James B. | last1=Kaler | title=WASAT (Delta Geminorum) | work=Stars | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/wasat.html | access-date=2012-01-30 }}</ref>

<ref name=Kunitzsch>{{citation
  |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>

<ref name="astrobob131212">{{citation |url=http://astrobob.areavoices.com/2013/12/12/to-delta-geminorum-by-way-of-jupiter-and-pluto/ |title=To Delta Geminorum by way of Jupiter and Pluto |work=Astro Bob |publisher=Areavoices.com |first=Bob |last=King |date=12 December 2013 |access-date=13 December 2013}}</ref>

<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 }}</ref>

<ref name="IAU-CSN">{{citation | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |access-date=28 July 2016}}</ref>

<ref name=kaler2>{{citation|url=http://stars.astro.illinois.edu/sow/wasat.html|work=Stars (University of Illinois sponsored website)|title=WASAT (Delta Geminorum) |quote=The name is a mess, "Wasat" meaning "middle" in Arabic, but the middle of WHAT is not clear, whether the middle of Gemini, of the sky, or of the neighboring constellation Orion (which the Arabs referred to as the "Central One"), the star name improperly applied to our Delta. |last=Kaler|first=Jim|date=n.d.|access-date=July 29, 2014}}</ref>

<ref name=constellationsofwords>{{cite web|url=http://www.constellationsofwords.com/stars/Wasat.html |work=Constellations of Words website|title=The history of the star: Wasat, from p.234 of Star Names, Richard Hinckley Allen, 1889.|quote=Wasat and Wesat are from Al Wasat, the Middle, i.e. of the constellation; but some have referred this to the position of the star very near to the ecliptic, the central circle. |last=Allen|first=Richard|date=1889|access-date=July 29, 2014}}</ref>

}}

==External links==
* {{WikiSky}}

{{Stars of Gemini}}

{{DEFAULTSORT:Delta Geminorum}}
[[Category:Bayer objects|Geminorum, Delta]]
[[Category:Triple star systems]]
[[Category:Gemini (constellation)]]
[[Category:Stars with proper names|Wasat]]
[[Category:F-type subgiants]]
[[Category:Hipparcos objects|035550]]
[[Category:Gliese and GJ objects|0271]]
[[Category:Flamsteed objects|Geminorum, 55]]
[[Category:Bright Star Catalogue objects|2777]]
[[Category:Henry Draper Catalogue objects|056986]]
[[Category:Durchmusterung objects|BD+22 1645]]

{{Sourceattribution|Delta Geminorum}}