| absmag_v = 1.95[11]
}}{{Starbox detail
| mass = 1.57[12]
| radius =
| luminosity =
| gravity =
| temperature = 6,900[13]
| metal_fe = –0.26[13]
| rotational_velocity = 129.7[15]
| age_gyr = 1.6[13]
}}{{Starbox catalog
| names = Wasat, 55 Geminorum, BD+22° 1645, FK5 279, Gl 271, HD 56986, HIP 35550, HR 2777, SAO 79294.[4]
}}{{Starbox reference
|Simbad=Delta+Gem
}}{{Starbox end}}Delta Geminorum (δ Geminorum, abbreviated Delta Gem, δ Gem), also named Wasat,[1] is a triple star system in the constellation of Gemini.
Nomenclature
δ Geminorum (Latinised to Delta Geminorum) is the system's Bayer designation.
It bore the traditional name Wasat, which derives from the Arabic word for "middle".[2][3] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[4] 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.[1]
In Chinese, {{lang|zh|天樽}} ({{lang|zh-Latn|Tiān Zūn}}), meaning Celestial Wine Cup, refers to an asterism consisting of Delta Geminorum, 57 Geminorum and Omega Geminorum.[5] 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}}.).[6] From this Chinese name, the name Ta Tsun has appeared.[7]
Properties
Delta Geminorum is a subgiant star with the stellar classification F0 IV.[4] It is about {{Convert|60.5|ly|pc|abbr=off|lk=on}} distant.[ This star has 1.57 times the mass of the Sun[12] and is rotating rapidly with a projected rotational velocity of {{nowrap|129.7 km s−1}}.[15] The estimated age is 1.6 billion years.[13]]
It has an apparent visual magnitude of +3.53,[3] allowing it to be seen with the naked eye. It is 0.18 degree south of the ecliptic so it is occasionally occulted by the Moon and, rarely, by a planet. The last occultation by a planet was by Saturn on June 30, 1857, and the next will be by Venus on August 12, 2420.{{citation needed|date=January 2012}} In 1930, the dwarf planet Pluto was discovered about 0.5° to the east of this star by American astronomer Clyde Tombaugh.[33]
Delta Geminorum is a triple star system. The inner components form a spectroscopic binary with a period of 6.1 years (2,238.7 days) and an orbital eccentricity of 0.3530. A cooler 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.[34][35] Although according to [7] its 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}}.[37]
References
1. ^1 {{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |accessdate=28 July 2016}}
2. ^{{cite web|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.|accessdate=July 29, 2014}}
3. ^{{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|accessdate=July 29, 2014}}
4. ^{{citation | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN) | publisher=International Astronomical Union | accessdate=22 May 2016 | postscript=. }}
5. ^{{zh icon}} 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}}.
6. ^{{zh icon}} 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.
7. ^Richard Hinckley Allen: Star Names — Their Lore and Meaning: Gemini
8. ^1 {{citation | title=Rotation- and temperature-dependence of stellar latitudinal differential rotation | last=Reiners | first=A. | journal=Astronomy and Astrophysics | volume=446 | issue=1 | pages=267–277 | date=January 2006 | doi=10.1051/0004-6361:20053911 | bibcode=2006A&A...446..267R | arxiv=astro-ph/0509399 | postscript=. }}
9. ^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 }}
10. ^1 2 {{citation | last=Evans | first=D. S. | date=June 20–24, 1966 | editor=Batten, Alan Henry | editor2=Heard, John Frederick | title=The Revision of the General Catalogue of Radial Velocities | booktitle=Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30 | location=University of Toronto | publisher=International Astronomical Union | bibcode=1967IAUS...30...57E }}
11. ^1 2 {{citation | last1=Schröder | first1=C. | last2=Reiners | first2=A. | last3=Schmitt | first3=J. 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 }}
12. ^1 2 3 4 {{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 | bibcode=1966CoLPL...4...99J }}
13. ^1 2 3 4 {{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 }}
14. ^1 {{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 | doi=10.1051/0004-6361:20011330 | bibcode=2001A&A...379..634G }}
15. ^1 {{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 }}
16. ^1 2 3 {{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 | accessdate=2011-06-03 }}
17. ^1 {{citation | first1=Stephen James | last1=O'Meara | title=The Caldwell objects | series=Deep-sky companions | publisher=Cambridge University Press | date=2002 | isbn=0-521-82796-5 | page=156 | url=https://books.google.com/books?id=3Hg6YHgx9nAC&pg=PA156 }}
18. ^1 {{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 | accessdate=2012-01-30 }}
19. ^1 {{cite web |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 |accessdate=13 December 2013}}