# Epsilon Tauri

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> Markdown URL: https://mediated.wiki/source/Epsilon_Tauri.md
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> Source revision: 1344011044
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{{short description|Star in the constellation Taurus}}
{{Starbox begin|name=Epsilon Tauri / Ain}}
{{Starbox image 
| image =
   {{Location mark
     | image=Taurus constellation map.svg
     | float=center | width=250 | position=right
     | mark=Red circle.svg | mark_width=10 | mark_link=ε Tau
     | x%=54.5 | y%=47.2
   }}
| caption = Location of ε Tauri (circled)
}}
{{Starbox observe
| epoch = J2000
| constell = [Taurus](/source/Taurus_(constellation))
| ra = {{RA|04|28|37.0003}}<ref name="GaiaDR3"/>
| dec = {{DEC|+19|10|49.563}}<ref name="GaiaDR3"/>
| appmag_v = +3.53<ref name="Sato2007"/>
}}
{{Starbox character
| type = [red clump](/source/red_clump)<Ref name=Sato2007/>
| class = K0III<ref name="Sato2007"/>
| b-v = 1.014<ref name="VizieR"/>
| u-b =
| variable = 
}}
{{Starbox astrometry
| radial_v = 38.420{{±|0.0004}}<ref name="GaiaDR2"/>
| prop_mo_ra = 107.526{{±|0.193}}
| prop_mo_dec = −36.200{{±|0.126}}
| pm_footnote = <ref name="GaiaDR3"/>
| parallax = 22.3654
| p_error = 0.1721
| parallax_footnote = <ref name="GaiaDR3"/>
| absmag_v = 0.145<ref name=BohmVitense2000/>
}}
{{Starbox detail
| mass = {{val|2.458|0.073}}<ref name=Arentoft2019/>
| radius = {{val|12.46|0.26}}<ref name=Baines2025/>
| luminosity = {{val|79.4|3.4}}<ref name=Baines2025/>
| habitable_inner = {{val|8.06|0.24}}<ref name=Baines2025/> [AU](/source/Astronomical_unit)
| habitable_outer = {{val|15.82|0.47}}<ref name=Baines2025/> AU
| gravity = {{val|2.66|0.03|0.05}}<ref name="Teng2023"/>
| temperature = {{val|4880|67|fmt=commas}}<ref name=Baines2025/>
| metal_fe = {{val|+0.15|0.02}}<ref name="Arentoft2019"/>
| rotation = 141.1<ref name="Teng2023"/> days
| rotational_velocity = 3.0<ref name=BohmVitense2000/>
| age_myr = {{val|600|150|50}}<ref name="Arentoft2019"/>
 }}
{{Starbox catalog
| names = {{odlist | B=Epsilon Tau, ε Tau | F=74 Tau | name=Ain | name2=Oculus Boreus<ref name=allen/> | BD=+18°640 | CCDM=J04286+1911 | FK5=164 | GC=5430 | HD=28305 | HIP=20889 | HR=1409 | SAO=93954 | WDS=J04286+1911A }}
}}
{{Starbox reference
| Simbad = HD+28305
| NSTED = HD28305
}}
{{Starbox end}}

'''Epsilon Tauri''' or '''ε Tauri''', formally named '''Ain''' ({{IPAc-en|'|ei|n}}),<ref name="IAU-CSN">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |access-date=28 July 2016}}</ref> is an [orange giant](/source/orange_giant) [star](/source/star) located approximately {{convert|146|ly|pc|lk=on|abbr=off}} from the [Sun](/source/Sun) in the [constellation](/source/constellation) of [Taurus](/source/Taurus_(constellation)). An [exoplanet](/source/exoplanet) (designated [Epsilon Tauri b](/source/Epsilon_Tauri_b), later named Amateru) is believed to be orbiting the star.

It is a member of the [Hyades](/source/Hyades_(star_cluster)) [open cluster](/source/open_cluster). As such its age is well constrained at 625 million years.<ref name="Sato2007"/> It is claimed to be the heaviest among planet-harboring stars with reliable initial masses.<ref name="Sato2007"/> Given its large mass, this star, though presently of [spectral type](/source/stellar_classification) K0 III, was formerly of spectral type A that has now evolved off the [main sequence](/source/main_sequence) into the giant phase. It is regarded as a [red clump giant](/source/Red_clump); that is, a core-helium burning star.<ref name="Sato2007"/>

Since Epsilon Tauri lies near the plane of the [ecliptic](/source/ecliptic), it is sometimes [occulted](/source/occultation) by the [Moon](/source/Moon) and (very rarely) by [planet](/source/planet)s.

It has an 11th magnitude companion 182 [arcsecond](/source/arcsecond)s away, although this is an unrelated background star.<ref name="SIMBAD2"/>

== Nomenclature ==

''ε Tauri'' ([Latinised](/source/Latinisation_of_names) to ''Epsilon Tauri'') is the star's [Bayer designation](/source/Bayer_designation); it also bears the [Flamsteed designation](/source/Flamsteed_designation) of 74 Tauri. On discovery, the planet was designated Epsilon Tauri b (or Ain b).

The star bore the traditional name ''Ain'' ([Arabic](/source/Arabic) ''عين'' for "eye") and was given the name ''Oculus Boreus'' ([Latin](/source/Latin) for "Northern eye") by [John Flamsteed](/source/John_Flamsteed).<ref>{{cite book |first=John |last=Flamsteed |title=Historia Coelestis Britannica |url=https://archive.org/details/bub_gb_8q9FAAAAcAAJ|publisher=H. Meere |date=1725 |page=[https://archive.org/details/bub_gb_8q9FAAAAcAAJ/page/n110 47]}}</ref><ref name=allen>{{cite book |first=Richard Hickley |last=Allen |title=Star Names – Their Lore and Meaning |url=https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Taurus*.html |publisher=Dover Books|date=1963 |page=391}}</ref> In 2016, the [International Astronomical Union](/source/International_Astronomical_Union) organized a [Working Group on Star Names](/source/IAU_Working_Group_on_Star_Names) (WGSN)<ref name="WGSN">{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN) | access-date=22 May 2016 | archive-date=30 March 2019 | archive-url=https://web.archive.org/web/20190330194042/https://www.iau.org/science/scientific_bodies/working_groups/280/ | url-status=dead }}</ref> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf | title=Bulletin of the IAU Working Group on Star Names, No. 1 |access-date=28 July 2016}}</ref> included a table of the first two batches of names approved by the WGSN; which included ''Ain'' for this star.

In July 2014, the [International Astronomical Union](/source/International_Astronomical_Union) launched [NameExoWorlds](/source/NameExoWorlds), a process for giving proper names to certain exoplanets.<ref>[http://www.iau.org/news/pressreleases/detail/iau1404/ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars] {{Webarchive|url=https://web.archive.org/web/20170904221813/https://www.iau.org/news/pressreleases/detail/iau1404/ |date=2017-09-04 }}. IAU.org. 9 July 2014</ref> The process involved public nomination and voting for the new names.<ref>{{Cite web |url=http://nameexoworlds.iau.org/process |title=NameExoWorlds The Process |access-date=2015-09-05 |archive-date=2015-08-15 |archive-url=https://web.archive.org/web/20150815025117/http://nameexoworlds.iau.org/process |url-status=dead }}</ref> In December 2015, the IAU announced the winning name was ''Amateru'' for this planet.<ref>[http://www.iau.org/news/pressreleases/detail/iau1514/ Final Results of NameExoWorlds Public Vote Released] {{Webarchive|url=https://web.archive.org/web/20171202072549/http://www.iau.org/news/pressreleases/detail/iau1514/ |date=2017-12-02 }}, International Astronomical Union, 15 December 2015.</ref>

The winning name was based on that submitted by the Kamagari Astronomical Observatory of [Kure](/source/Kure%2C_Hiroshima), [Hiroshima Prefecture](/source/Hiroshima_Prefecture), [Japan](/source/Japan): namely '[Amaterasu](/source/Amaterasu)', the Shinto goddess of the Sun, born from the left eye of the god [Izanagi](/source/Izanagi). The IAU substituted 'Amateru' – which is a common Japanese appellation for [shrine](/source/shrine)s when they enshrine Amaterasu – because 'Amaterasu' is already used for an asteroid ([10385 Amaterasu](/source/List_of_minor_planets%3A_10001%E2%80%9311000)).<ref>{{Cite web |url=http://nameexoworlds.iau.org/names |title=NameExoWorlds The Approved Names |access-date=2015-12-21 |archive-date=2018-02-01 |archive-url=https://web.archive.org/web/20180201043609/http://nameexoworlds.iau.org/names |url-status=dead }}</ref>

In [Chinese](/source/Chinese_astronomy), {{lang|zh|畢宿}} ({{lang|zh-Latn|Bì Xiù}}), meaning ''[Net](/source/Net_(Chinese_constellation))'', refers to an asterism consisting ε Tauri, [δ<sup>3</sup> Tauri](/source/Delta3_Tauri), [δ<sup>1</sup> Tauri](/source/Delta1_Tauri), [γ Tauri](/source/Gamma_Tauri), [Aldebaran](/source/Aldebaran), [θ<sup>2</sup> Tauri](/source/Theta_Tauri), [71 Tauri](/source/71_Tauri) and [λ Tauri](/source/Lambda_Tauri).<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, the [Chinese name](/source/Chinese_star_names) for ε Tauri itself is {{lang|zh|畢宿一}} ({{lang|zh-Latn|Bì Xiù yī}}), "the First Star of Net".<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_ala_alz.htm 香港太空館 – 研究資源 – 亮星中英對照表] {{webarchive|url=https://web.archive.org/web/20081025110153/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_ala_alz.htm |date=2008-10-25 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref>

== Planetary system ==

In 2007, a massive [exoplanet](/source/exoplanet) was reported orbiting the star with a period of 1.6 years in a somewhat [eccentric](/source/orbital_eccentricity) orbit. It was the first planet ever discovered in an open cluster.<ref name="Sato2007"/> A 2023 study updated this planet's parameters, and detected additional [radial velocity](/source/radial_velocity) variations that are likely caused by stellar activity.<ref name="Teng2023"/>

{{OrbitboxPlanet begin
| table_ref = <ref name="Teng2023"/>
}}
{{OrbitboxPlanet
| exoplanet = [b (Amateru)](/source/Epsilon_Tauri_b)
| mass = {{val|7.190|0.056|p=≥}}
| period = {{val|585.82|0.26|0.33}}
| semimajor = {{val|1.878|0.001}}
| eccentricity = {{val|0.076|0.009|0.008}}
}}
{{Orbitbox end}}

==References==
{{Reflist|refs=

<ref name="SIMBAD2">{{cite simbad |title=UCAC2 38562433 |access-date=2 December 2023}}</ref>

<ref name="GaiaDR3">{{Cite Gaia DR3|48026706558487040}}</ref>

<ref name="GaiaDR2">{{Cite Gaia DR2|48026706557926528}}</ref>

<ref name="Sato2007">{{cite journal | title=A Planetary Companion to the Hyades Giant ε Tauri | last1=Sato | first1=Bun'ei | last2=Izumiura | first2=Hideyuki | last3=Toyota | first3=Eri | last4=Kambe | first4=Eiji | last5=Takeda | first5=Yoichi | last6=Masuda | first6=Seiji | last7=Omiya | first7=Masashi | last8=Murata | first8=Daisuke | last9=Itoh | first9=Yoichi | display-authors=1 | journal=The Astrophysical Journal | volume=661 | issue=1 | pages=527–531 | year=2007 | bibcode=2007ApJ...661..527S | doi=10.1086/513503 | doi-access=free }}</ref>

<ref name=Baines2025>{{Cite journal |last1=Baines |first1=Ellyn K. |last2=Jones |first2=Jeremy |last3=Clark |first3=James H. |last4=Schmitt |first4=Henrique R. |last5=Stone |first5=Jordan M. |date=January 2025 |title=Eighteen Exoplanet Host Stars from the NPOI Data Archive |journal=The Astronomical Journal |language=en |volume=169 |issue=2 |pages=83 |doi=10.3847/1538-3881/ad9bb1 |doi-access=free |issn=1538-3881|arxiv=2506.02934 |bibcode=2025AJ....169...83B }}</ref>

<ref name="VizieR">{{cite web | title=Entry for star HIP 20889 | work=Vizier Catalogue Service | url=http://webviz.u-strasbg.fr/viz-bin/VizieR-5?-out.add=.&-source=I/311/hip2&recno=20836 | access-date=2015-09-13}}</ref>

<ref name=BohmVitense2000>{{citation
 | title=Ultraviolet Emission Lines in BA and Non-BA Giants
 | display-authors=1 | last1=Böhm-Vitense | first1=Erika
 | last2=Carpenter | first2=Kenneth G. | last3=Robinson | first3=Richard D.
 | journal=The Astrophysical Journal | postscript=. 
 | volume=545 | issue=2 | pages=992–999 | date=December 2000
 | doi=10.1086/317850 | bibcode=2000ApJ...545..992B | doi-access=free }}</ref>

<ref name="Arentoft2019">{{cite journal |last1=Arentoft |first1=T. |last2=Grundahl |first2=F. |display-authors=etal |date=February 2019 |title=Asteroseismology of the Hyades red giant and planet host ɛ Tauri |journal=[Astronomy & Astrophysics](/source/Astronomy_%26_Astrophysics) |volume=622 |issue= |pages=A190 |doi=10.1051/0004-6361/201834690 |arxiv=1901.06187 |bibcode=2019A&A...622A.190A|s2cid=119066215 }}</ref>

<ref name="Teng2023">{{cite journal |last1=Teng |first1=Huan-Yu |last2=Sato |first2=Bun'ei |display-authors=etal |date=August 2023 |title=Revisiting planetary systems in the Okayama Planet Search Program: A new long-period planet, RV astrometry joint analysis, and a multiplicity-metallicity trend around evolved stars |journal=[Publications of the Astronomical Society of Japan](/source/Publications_of_the_Astronomical_Society_of_Japan) |volume= 75|issue= 6|pages= 1030–1071|doi=10.1093/pasj/psad056 |arxiv=2308.05343 |bibcode=2023PASJ...75.1030T}}</ref>

}}

== External links ==

* {{cite web |url=http://www.frostydrew.org/observatory/columns/essays/starnames.htm |title=Star Names |access-date=2008-06-24 |work=[Frosty Drew Observatory](/source/Frosty_Drew_Observatory)}}
* {{cite simbad|title=eps Tau}}

{{Sky|04|28|37.0|+|19|10|49|155}}
{{Stars of Taurus}}
{{Authority control}}

<!-- Properties -->

Category:K-type giants
Category:Horizontal-branch stars
Category:Planetary systems with one confirmed planet
<!-- Other -->
Category:Hyades (star cluster)
Category:Taurus (constellation)
Tauri, Epsilon
1409
BD+18 0640
Tauri, 074
028305
020889
Ain
Category:Population I stars

---
Adapted from the Wikipedia article [Epsilon Tauri](https://en.wikipedia.org/wiki/Epsilon_Tauri) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Epsilon_Tauri?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.