Editing Hyades (star cluster)

{{Short description|Open cluster in the constellation Taurus}}
{{Infobox open cluster| <!-- put name or coordinates into the following URL -->
| name = Hyades Cluster
| image = [[Image:Hyades.jpg|300px|The Hyades is a naked-eye open cluster in the constellation of Taurus. Aldebaran is bright star in bottom-middle. The "V" of Taurus is pointing to the top-right corner.]]
| caption = Photograph of the Hyades Cluster
| epoch = J2000.0
| constellation = [[Taurus (constellation)|Taurus]]
| class = II,3,m
| ra = {{RA|4|27}}
| dec = {{DEC|+15|52}}
| dist_ly = 153 [[light-year|ly]]
| dist_pc = 47 pc<ref name=Perryman/><ref name=vanleeuwen09/><ref name=majaess11/><ref name=mcarthur11/>   
| appmag_v = 0.5
| size_v = 330{{prime}}
| mass_kg = 
| mass_msol = 400
| radius_ly = 10 light-years (core radius)
| v_hb = 
| age = 625 million years
| notes = Closest [[open cluster]]
| names = [[Caldwell catalogue|Caldwell]] 41, [[Collinder catalogue|Cr]] 50, [[Philibert Jacques Melotte|Mel]] 25}}

The '''Hyades''' ({{IPAc-en|ˈ|h|aɪ|.|ə|d|iː|z}}; [[Greek language|Greek]] Ὑάδες, also known as '''Caldwell 41''', '''Collinder 50''', or '''Melotte 25''') is the nearest [[open cluster]] and one of the best-studied [[star cluster]]s. Located about {{Convert|153|ly|pc|abbr=off|lk=in}}<ref name="Perryman"/><ref name=vanleeuwen09/><ref name=majaess11/><ref name=mcarthur11/> away from the [[Sun]], it consists of a roughly spherical group of hundreds of stars sharing the same age, place of origin, chemical characteristics, and motion through space.<ref name=Perryman/><ref name="Bouvier">{{cite journal |bibcode=2008A&A...481..661B |title=Brown dwarfs and very low mass stars in the Hyades cluster: A dynamically evolved mass function |last1=Bouvier |first1=J. |last2=Kendall |first2=T. |last3=Meeus |first3=G. |last4=Testi |first4=L. |last5=Moraux |first5=E. |last6=Stauffer |first6=J. R. |last7=James |first7=D. |last8=Cuillandre |first8=J. -C. |last9=Irwin |first9=J. |last10=McCaughrean |first10=M. J. |last11=Baraffe |first11=I. |last12=Bertin |first12=E. |journal=Astronomy and Astrophysics |date=2008 |volume=481 |issue=3 |page=661 |doi=10.1051/0004-6361:20079303 |arxiv=0801.0670 }}</ref> From the perspective of observers on [[Earth]], the Hyades Cluster appears in the [[constellation]] [[Taurus (constellation)|Taurus]], where its brightest stars form a "V" shape along with the still-brighter [[Aldebaran]]. However, Aldebaran is unrelated to the Hyades, as it is located much closer to Earth (65 light-years) and merely happens to lie along the same line of sight.

The five brightest member stars of the Hyades have consumed the hydrogen fuel at their cores and have [[stellar evolution|evolved]] into [[giant star]]s.<ref name="Hyadum1">{{cite web 
  |url= http://stars.astro.illinois.edu/sow/hyadum1.html
  |title= Hyadum I
  |author= Jim Kaler
  |website= Jim Kaler's Stars
  |access-date=29 October 2013
}}</ref> Four of these stars, with [[Bayer designation]]s [[Gamma Tauri|Gamma]], [[Delta1 Tauri|Delta<sup>1</sup>]], [[Epsilon Tauri|Epsilon]], and [[Theta Tauri|Theta<sup>2</sup> Tauri]], form an [[asterism (astronomy)|asterism]] that is traditionally identified as the head of Taurus the Bull.<ref name="Hyadum1" /> The fifth of these stars is Theta<sup>1</sup> Tauri, a tight naked-eye companion to the brighter Theta<sup>2</sup> Tauri. Epsilon Tauri, known as ''Ain'' (the "Bull's Eye"), has a [[gas giant]] exoplanet candidate,<ref name="Sato"/> the first planet to be found in any open cluster.

The age of the Hyades is estimated to be about 625 million years.<ref name=Perryman/> The core of the cluster, where stars are the most densely packed, has a radius of {{Convert|2.7|pc|ly|order=flip|abbr=off}}, and the cluster's [[tidal radius (cluster)|tidal radius]] – where the stars become more strongly influenced by the gravity of the surrounding [[Milky Way]] galaxy – is {{Convert|10|pc|ly|order=flip|abbr=off}}.<ref name="Perryman" /> However, about one-third of confirmed member stars have been observed well outside the latter boundary, in the cluster's extended halo; these stars are probably in the process of escaping from its gravitational influence.<ref name="Perryman" />

== Location and motion ==
The cluster is sufficiently close to the Sun that its distance can be directly measured by observing the amount of [[stellar parallax|parallax shift]] of the member stars as the Earth orbits the Sun. This measurement has been performed with great accuracy using the [[Hipparcos]] satellite and the [[Hubble Space Telescope]]. An alternative method of computing the distance is to fit the cluster members to a standardized infrared [[Hertzsprung–Russell diagram|color–magnitude diagram]] for stars of their type, and use the resulting data to infer their intrinsic brightness. Comparing this data to the brightness of the stars as seen from Earth allows their distances to be estimated. Both methods have yielded a distance estimate of {{Convert|153|ly|pc|abbr=off}} to the cluster center.<ref name="Perryman">{{cite journal|title=The Hyades: distance, structure, dynamics, and age|author=Perryman, M.A.C.|display-authors=etal|date=1998|journal=Astronomy & Astrophysics|volume=331|pages=81–120|bibcode=1998A&A...331...81P|arxiv = astro-ph/9707253 }}</ref><ref name=vanleeuwen09>{{cite journal |bibcode=2009A&A...497..209V |title=Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue |last1=Van Leeuwen |first1=F. |journal=Astronomy and Astrophysics |date=2009 |volume=497 |issue=1 |page=209 |doi=10.1051/0004-6361/200811382 |arxiv=0902.1039 }}</ref><ref name=majaess11>{{cite journal |bibcode=2011JAVSO..39..219M |title=Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting Delta Scuti Stars |last1=Majaess |first1=D. J. |last2=Turner |first2=D. G. |last3=Lane |first3=D. J. |last4=Krajci |first4=T. |journal=Journal of the American Association of Variable Star Observers (Jaavso) |date=2011 |volume=39 |issue=2 |page=219 |arxiv=1102.1705 }}</ref><ref name=mcarthur11>{{cite journal |bibcode=2011AJ....141..172M |title=Astrometry with the Hubble Space Telescope: Trigonometric Parallaxes of Selected Hyads |last1=McArthur |first1=Barbara E. |last2=Benedict |first2=G. Fritz |last3=Harrison |first3=Thomas E. |last4=Van Altena |first4=William |journal=The Astronomical Journal |date=2011 |volume=141 |issue=5 |page=172 |doi=10.1088/0004-6256/141/5/172 |arxiv=1103.2094 }}</ref> The fact that these independent measurements agree makes the Hyades an important rung on the [[cosmic distance ladder]] method for estimating the distances of extragalactic objects.{{CN|date=November 2020}}

The stars of the Hyades are more enriched in heavier elements than the [[Sun]] and other ordinary stars in the [[solar neighborhood]], with the overall cluster [[metallicity]] measured at +0.14.<ref name="Perryman" /> The Hyades Cluster is related to other stellar groups in the Sun's vicinity. Its age, metallicity, and [[proper motion]] coincide with those of the larger and more distant [[Messier 44|Praesepe Cluster]],<ref name="Dobbie">{{cite journal | last1 = Dobbie | first1 = PD | last2 = Napiwotzki | first2 = R | last3 = Burleigh | first3 = MR | display-authors = etal | year = 2006 | title = New Praesepe white dwarfs and the initial mass-final mass relation | journal = [[Monthly Notices of the Royal Astronomical Society]] | volume = 369 | issue = 1| pages = 383–389 | doi=10.1111/j.1365-2966.2006.10311.x| doi-access = free |arxiv = astro-ph/0603314 |bibcode = 2006MNRAS.369..383D | s2cid = 17914736 }}</ref> and the trajectories of both clusters can be traced back to the same region of space, indicating a common origin.<ref>{{cite web
 | url=http://messier.seds.org/m/m044.html
 | title=Messier Object 44
 | work=SEDS
 | date=2007-08-25
 | access-date=2012-12-24 }}
</ref> Another associate is the [[Hyades Stream]], a large collection of scattered stars that also share a similar trajectory with the Hyades Cluster. Recent results have found that at least 15% of stars in the Hyades Stream share the same chemical fingerprint as the Hyades cluster stars.<ref>{{cite journal|last=De Silva|first=G|display-authors=etal|title=High-resolution elemental abundance analysis of the Hyades supercluster|journal=MNRAS|date=2011|doi=10.1111/j.1365-2966.2011.18728.x|bibcode=2011MNRAS.415..563D|arxiv = 1103.2588|volume=415|issue=1|pages=563–575|doi-access=free|s2cid=56280307}}</ref> However, about 85% of stars in the Hyades Stream have been shown to be completely unrelated to the original cluster on the grounds of dissimilar age and metallicity; their common motion is attributed to tidal effects of the massive rotating [[barred spiral galaxy|bar]] at the center of the [[Milky Way]] galaxy.<ref name="Famaey">{{cite journal |bibcode=2007A&A...461..957F |title=The Hyades stream: An evaporated cluster or an intrusion from the inner disk? |last1=Famaey |first1=B. |last2=Pont |first2=F. |last3=Luri |first3=X. |last4=Udry |first4=S. |last5=Mayor |first5=M. |last6=Jorissen |first6=A. |journal=Astronomy and Astrophysics |date=2007 |volume=461 |issue=3 |page=957 |doi=10.1051/0004-6361:20065706 |arxiv=astro-ph/0609785 }}</ref> Among the remaining members of the Hyades Stream, the [[exoplanet]] host star [[Iota Horologii]] has recently been proposed as an escaped member of the primordial Hyades Cluster.<ref name="Vauclair">{{cite journal | title=The exoplanet-host star iota Horologii: an evaporated member of the primordial Hyades cluster. | date=2008 |arxiv=0803.2029 | last1=Vauclair | first1=S. | last2=Laymand | first2=M. | last3=Bouchy | first3=F. | last4=Vauclair | first4=G. | last5=Hui Bon Hoa | first5=A. | last6=Charpinet | first6=S. | last7=Bazot | first7=M. | doi=10.1051/0004-6361:20079342 | volume=482 | journal=Astronomy and Astrophysics | issue=2 | pages=L5–L8 | bibcode=2008A&A...482L...5V| s2cid=18047352 }}, announced in {{cite web| url=http://www.astronomynow.com/Thedriftingstar.html| title=The Drifting Star| author=Emily Baldwin| access-date=2008-04-18| archive-date=2008-04-21| archive-url=https://web.archive.org/web/20080421043757/http://www.astronomynow.com/Thedriftingstar.html| url-status=dead}}</ref>

The Hyades are unrelated to two other nearby stellar groups, the [[Pleiades]] and the [[Ursa Major Moving Group|Ursa Major Stream]], which are easily visible to the [[naked eye]] under clear dark skies.<gallery mode="packed" heights="300">
File:Hyades 40°N.png|Star chart of the Hyades cluster
File:Galaxymap.com, map 100 parsecs (2022).png|Map of stars within 100 parsecs of the Sun, the Hyades is at 180° [[Galactic coordinate system|galactic longitude]].
</gallery>

== Astrometry ==
A 2018 Gaia DR1 study of the Hyades Cluster determined a (U, V, W) group velocity of (−41.92 ± 0.16, −19.35 ± 0.13, −1.11 ± 0.11) km/sec, based on the space velocities of the 138 core stars. <ref>{{Cite journal |last1=Reino |first1=Stella |last2=de Bruijne |first2=Jos |last3=Zari |first3=Eleonora |last4=d'Antona |first4=Francesca |last5=Ventura |first5=Paolo |date=2018-03-28 |title=A Gaia study of the Hyades open cluster |journal=Monthly Notices of the Royal Astronomical Society |volume=477 |issue=3 |pages=3197–3216 |doi=10.1093/mnras/sty793 |doi-access=free |issn=0035-8711|arxiv=1804.00759 }}</ref>

A 2019 Gaia DR2 study finds a (U, V, W) group velocity of (−42.24, −19.00, −1.48) km/sec, in very close agreement with the 2018 DR1 derivation. <ref>{{Cite journal |last1=Röser |first1=Siegfried |last2=Schilbach |first2=Elena |last3=Goldman |first3=Bertrand |date=2019-01-01 |title=Hyades tidal tails revealed by Gaia DR2 |url=https://www.aanda.org/articles/aa/abs/2019/01/aa34608-18/aa34608-18.html |journal=Astronomy & Astrophysics |language=en |volume=621 |pages=L2 |doi=10.1051/0004-6361/201834608 |arxiv=1811.03845 |bibcode=2019A&A...621L...2R |s2cid=118909033 |issn=0004-6361}}</ref>

Another DR2 study from 2019 focused on mapping the 3D Topology & Velocities of the Hyades main body out to 30 parsecs, and included Sub-Stellar members as well. They identified 1764 member candidates, including 10 Brown Dwarfs and 17 White Dwarfs. The White Dwarfs included 9 single stars, and 4 binary systems. <ref>{{Cite journal |last1=Lodieu |first1=N. |last2=Smart |first2=R. L. |last3=Pérez-Garrido |first3=A. |last4=Silvotti |first4=R. |date=2019-02-27 |title=A 3D view of the Hyades stellar and sub-stellar population |url=http://dx.doi.org/10.1051/0004-6361/201834045 |journal=Astronomy & Astrophysics |volume=623 |pages=A35 |doi=10.1051/0004-6361/201834045 |arxiv=1901.07534 |bibcode=2019A&A...623A..35L |s2cid=119385406 |issn=0004-6361}}</ref>

A 2022 Hyades study utilizing Gaia EDR3 derived a (U, V, W) group velocity of (-42.11±6.50, - 19.09±4.37, -1.32±0.44) km/sec, also with close agreement to DR1 and DR2 studies.<ref>{{Cite journal |last1=Elsanhoury |first1=Waleed |last2=Al-Johani |first2=Amnah |last3=Al-anzi |first3=Aneefah |last4=Al-jaber |first4=Bashayr |last5=Al-Bishi |first5=Fatmah |last6=Kanaan |first6=Nourah |last7=Al-atwi |first7=Ragwa |last8=Al-khubrani |first8=Reem |last9=Al-anzi |first9=Sarah |date=2022-03-16 |title=The Hyades Kinematical Structure with Gaia Era |url=http://op.niscpr.res.in/index.php/IJPAP/article/view/58781 |journal=Indian Journal of Pure & Applied Physics |language=en |volume=60 |issue=3 |pages=268–273 |doi=10.56042/ijpap.v60i3.58781 |s2cid=251335023 |issn=0975-1041|doi-access=free }}</ref> 

== History ==
Together with the other eye-catching open star cluster of the [[Pleiades]], the Hyades form the [[Golden Gate of the Ecliptic]], which has been known for several thousand years.

In Greek mythology, the [[Hyades (mythology)|Hyades]] were the five daughters of [[Atlas (mythology)|Atlas]] and half-sisters to the [[Pleiades (Greek mythology)|Pleiades]]. After the death of their brother, Hyas, the weeping sisters were transformed into a cluster of stars that was afterwards associated with rain.<ref name="Ridpath">{{cite web 
  |url= http://www.ianridpath.com/startales/taurus.html#hyades
  |title= The Hyades – the face of the bull
  |author= [[Ian Ridpath]]
  |website= Ian Ridpath’s Star Tales
  |access-date=20 November 2023
}}</ref>

As a naked-eye object, the Hyades cluster has been known since prehistoric times. It is mentioned by numerous Classical authors from [[Homer]] to [[Ovid]].<ref name="seds">[http://messier.seds.org/xtra/ngc/hyades.html Information on the Hyades from SEDS]</ref> In Book 18 of the ''[[Iliad]]'' the stars of the Hyades appear along with the [[Pleiades]], [[Ursa Major]], and [[Orion (constellation)|Orion]] on the shield that the god [[Hephaestus|Hephaistos]] made for [[Achilles]].<ref name="Lattimore">Homer. ''The Iliad.'' Translated by Richmond Lattimore.  University of Chicago Press, 1951.</ref>

In England the cluster was known as the "April Rainers" from an association with April showers, as recorded in the folk song "[[Green Grow the Rushes, O]]".

The cluster was probably first catalogued by [[Giovanni Battista Hodierna]] in 1654, and it subsequently appeared in many star atlases of the 17th and 18th centuries.<ref name="seds" /> However, [[Charles Messier]] did not include the Hyades in his 1781 catalog of deep sky objects.<ref name="seds" /> It therefore lacks a Messier number, unlike many other, more distant open clusters – e.g., [[Beehive Cluster|M44]] (Praesepe), M45 ([[Pleiades]]), and [[Messier 67|M67]].

In 1869, the astronomer R.A. Proctor observed that numerous stars at large distances from the Hyades share a similar motion through space.<ref name="Zuckerman">{{cite journal |bibcode=2004ARA&A..42..685Z |title=Young Stars Near the Sun |last1=Zuckerman |first1=B. |last2=Song |first2=Inseok |journal=Annual Review of Astronomy and Astrophysics |date=2004 |volume=42 |issue=1 |page=685 |doi=10.1146/annurev.astro.42.053102.134111 }}</ref> In 1908, [[Lewis Boss]] reported almost 25 years of observations to support this premise, arguing for the existence of a co-moving group of stars that he called the Taurus Stream (now generally known as the Hyades Stream or Hyades Supercluster). Boss published a chart that traced the scattered stars' movements back to a common point of convergence.<ref name="Boss">{{cite journal |bibcode=1908AJ.....26...31B |title=Convergent of a moving cluster in Taurus |last1=Boss |first1=Lewis J. |journal=The Astronomical Journal |date=1908 |volume=26 |page=31 |doi=10.1086/103802 }}</ref>

By the 1920s, the notion that the Hyades shared a common origin with the Praesepe Cluster was widespread,<ref name="Hertzprung">{{cite journal |bibcode=1922BAN.....1..150H |title=On the motions of Praesepe and of the Hyades |last1=Hertzsprung |first1=E. |journal=Bulletin of the Astronomical Institutes of the Netherlands |date=1922 |volume=1 |page=150 }}</ref> with Rudolf Klein-Wassink noting in 1927 that the two clusters are "probably cosmically related".<ref name="Klein-Wassink">{{cite journal |bibcode=1927PGro...41....1K |title=The proper motion and the distance of the Praesepe cluster |last1=Klein Wassink |first1=W. J. |journal=Publications of the Kapteyn Astronomical Laboratory Groningen |date=1927 |volume=41 |page=1 }}</ref> For much of the twentieth century, scientific study of the Hyades focused on determining its distance, modeling its evolution, confirming or rejecting candidate members, and characterizing individual stars.

== Morphology and evolution ==
All stars form in clusters, but most clusters break up less than 50 million years after star formation concludes.<ref name="LadaLada">{{cite journal | last1 = Lada | first1 = CJ | last2 = Lada | first2 = EA | year = 2003 | title = Embedded clusters in molecular clouds | journal = Annual Review of Astronomy & Astrophysics | volume = 41 | issue = 1 | pages = 57–115 |bibcode= 2003ARA&A..41...57L | doi=10.1146/annurev.astro.41.011802.094844|arxiv = astro-ph/0301540 | s2cid = 16752089 }}</ref> The astronomical term for this process is "[[Mass_segregation_(astronomy)#Evaporation|evaporation]]." Only extremely massive clusters, orbiting far from the [[Galactic Center]], can avoid evaporation over extended timescales.<ref name="PavaniBica 2007">{{cite journal | last1 = Pavani | first1 = DB | last2 = Bica | first2 = E | year = 2007 | title = Characterization of open cluster remnants | journal = Astronomy & Astrophysics | volume = 468 | issue = 1| pages = 139–150 | doi=10.1051/0004-6361:20066240|arxiv = 0704.1159 |bibcode = 2007A&A...468..139P | s2cid = 11609818 }}</ref> As one such survivor, the Hyades Cluster probably contained a much larger star population in its infancy. Estimates of its original mass range from 800 to 1,600 times the [[Solar mass|mass of the Sun]] ({{Solar mass|link=y}}), implying still larger numbers of individual stars.<ref name="Weidemann1992">Weideman V, Jordan S, Iben I, Casertano S.  (1992)  White dwarfs in the halo of the Hyades Cluster – The case of the missing white dwarfs. ''Astronomical Journal,'' 104: 1876-1891.  1992AJ....104.1876W.</ref><ref name="Kroupa">{{cite journal | last1 = Kroupa | first1 = P | last2 = Boily | first2 = CM | year = 2002 | title = On the mass function of star clusters | journal = Monthly Notices of the Royal Astronomical Society | volume = 336 | issue = 4| pages = 1188–1194 |bibcode=2002MNRAS.336.1188K | doi=10.1046/j.1365-8711.2002.05848.x| doi-access = free |arxiv = astro-ph/0207514 | s2cid = 15225436 }}</ref>

===Star populations===
Theory predicts that a young cluster of this size should give birth to stars and substellar objects of all spectral types, from huge, hot O stars down to dim [[brown dwarf]]s.<ref name="Kroupa" /> However, studies of the Hyades show that it is deficient in stars at both extremes of mass.<ref name="Bouvier" /><ref name="Bohm-Vitense2007">{{cite journal | last1 = Böhm-Vitense | first1 = E | year = 2007 | title = Hyades morphology and star formation | journal = Astronomical Journal | volume = 133 | issue = 5| pages = 1903–1910 | bibcode = 2007AJ....133.1903B | doi=10.1086/512124| doi-access = free }}</ref> At an age of 625 million years, the cluster's main sequence turn-off is about {{Solar mass|2.3|link=y}}, meaning that all heavier stars have evolved into subgiants, giants, or [[white dwarf]]s, while less massive stars continue fusing hydrogen on the main sequence.<ref name="Weidemann1992" /> Extensive surveys have revealed a total of 8 white dwarfs in the cluster core,<ref name="Bohm-Vitense1995">{{cite journal |bibcode=1995AJ....110..228B |title=White Dwarf Companions to Hyades F Stars |last1=Bohm-Vitense |first1=Erika |journal=The Astronomical Journal |date=1995 |volume=110 |page=228 |doi=10.1086/117511 }}</ref> corresponding to the final evolutionary stage of its original population of B-type stars (each about {{Solar mass|3}}).<ref name="Weidemann1992" /> The preceding evolutionary stage is currently represented by the cluster's four red clump giants. Their present spectral type is K0 III, but all are "retired A stars" of around {{Solar mass|2.5}}.<ref name="Sato" /><ref name="Torres1997">{{cite journal | last1 = Torres | first1 = G | last2 = Stefanik | first2 = RP | last3 = Latham | first3 = DW | year = 1997 | title = The Hyades binaries Theta1 Tauri and Theta2 Tauri: The distance to the cluster and the mass-luminosity relation | journal = Astrophysical Journal | volume = 485 | issue = 1| pages = 167–181 | doi=10.1086/304422|bibcode = 1997ApJ...485..167T | doi-access = free }}</ref><ref name="Johnson">{{cite journal |bibcode=2007ApJ...665..785J |title=Retired a Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants |last1=Johnson |first1=John Asher |last2=Fischer |first2=Debra A. |last3=Marcy |first3=Geoffrey W. |last4=Wright |first4=Jason T. |last5=Driscoll |first5=Peter |last6=Butler |first6=R. Paul |last7=Hekker |first7=Saskia |last8=Reffert |first8=Sabine |last9=Vogt |first9=Steven S. |journal=The Astrophysical Journal |date=2007 |volume=665 |issue=1 |page=785 |doi=10.1086/519677 |arxiv=0704.2455 }}</ref> An additional "white giant" of type A7 III is the primary of [[Theta Tauri|θ<sup>2</sup> Tauri]], a [[binary star|binary]] system that includes a less massive companion of spectral type A; this pair is visually associated with [[Theta Tauri|θ<sup>1</sup> Tauri]], one of the four red giants, which also has an A-type binary companion.<ref name="Torres1997" /><ref name="Armstrong2006">{{cite journal | last1 = Armstrong | first1 = JT | last2 = Mozurkewich | first2 = D | last3 = Hajian | first3 = AR | display-authors = etal | year = 2006 | title = The Hyades binary Theta2 Tauri: Confronting evolutionary models with optical interferometry | journal = Astronomical Journal | volume = 131 | issue = 5| pages = 2643–2651 | doi=10.1086/501429|bibcode = 2006AJ....131.2643A | citeseerx = 10.1.1.1000.4076 | s2cid = 6268214 }}</ref>

The remaining population of confirmed cluster members includes numerous bright stars of spectral types A (at least 21), F (about 60), and G (about 50).<ref name="Perryman" /><ref name="Bohm-Vitense2007" /> All these star types are concentrated much more densely within the tidal radius of the Hyades than within an equivalent 10-parsec radius of the Earth. By comparison, our local 10-parsec sphere contains only 4 A stars, 6 F stars, and 21 G stars.<ref name="RECONS">Research Consortium on Nearby Stars (RECONS). Ten-parsec census at http://joy.chara.gsu.edu/RECONS/census.posted.htm.</ref>

The Hyades' cohort of lower-mass stars – spectral types K and M – remains poorly understood, despite proximity and long observation. At least 48 K dwarfs are confirmed members, along with about a dozen [[M dwarf]]s of spectral types M0-M2.<ref name="Perryman" /><ref name="Bohm-Vitense2007" /><ref name="Endl">{{cite journal | last1 = Endl | first1 = M | last2 = Cochran | first2 = WD | last3 = Kurster | first3 = M | last4 = Paulson | first4 = DB | last5 = Wittenmyer | first5 = RA | last6 = MacQueen | first6 = PJ | last7 = Tull | first7 = RG | year = 2006 | title = Exploring the frequency of close-in Jovian planets around M dwarfs | journal = Astrophysical Journal | volume = 649 | issue = 1| pages = 436–443 | doi=10.1086/506465|arxiv = astro-ph/0606121 |bibcode = 2006ApJ...649..436E | s2cid = 14461746 }}</ref> Additional M dwarfs have been proposed in the past.<ref name="Stauffer">{{cite journal |last1=Stauffer |first1=JR |last2=Balachandran |first2=SC |last3=Krishnamurthi |first3=A |last4=Pinsonneault |first4=M |last5=Terndrup |first5=DM |last6=Stern |first6=RA |year=1997 |title=Rotational velocities and chromospheric activity of M dwarfs in the Hyades |journal=Astrophysical Journal |volume=475 |issue=2 |pages=604–622 |bibcode=1997ApJ...475..604S |doi=10.1086/303567 |doi-access=free}}</ref> This deficiency at the bottom of the mass range contrasts strongly with the distribution of stars within 10 parsecs of the Solar System, where at least 239 M dwarfs are known, comprising about 76% of all neighborhood stars.<ref name="RECONS" /> In more recent studies more low-mass members were discovered. This is due targeted searches<ref name="Bouvier" /><ref name="Hogan" /> and an improvement in [[proper motion]] searches.<ref name=":0">{{Cite journal |last1=Pérez-Garrido |first1=A. |last2=Lodieu |first2=N. |last3=Rebolo |first3=R. |date=2017-03-01 |title=A new L5 brown dwarf member of the Hyades cluster with chromospheric activity |journal=Astronomy and Astrophysics |volume=599 |pages=A78 |arxiv=1701.03398 |bibcode=2017A&A...599A..78P |doi=10.1051/0004-6361/201628778 |issn=0004-6361}}</ref><ref name=":1">{{Cite journal |last1=Schneider |first1=Adam C. |last2=Vrba |first2=Frederick J. |last3=Munn |first3=Jeffrey A. |last4=Dahm |first4=Scott E. |last5=Bruursema |first5=Justice |last6=Williams |first6=Stephen J. |last7=Dorland |first7=Bryan N. |last8=Faherty |first8=Jacqueline K. |last9=Rothermich |first9=Austin |last10=Calamari |first10=Emily |last11=Cushing |first11=Michael C. |last12=Caselden |first12=Dan |last13=Kabatnik |first13=Martin |last14=Pendrill |first14=William |last15=Sainio |first15=Arttu |date=2022-05-01 |title=Substellar Hyades Candidates from the UKIRT Hemisphere Survey |journal=The Astronomical Journal |volume=163 |issue=5 |pages=242 |arxiv=2203.11090 |bibcode=2022AJ....163..242S |doi=10.3847/1538-3881/ac5f50 |doi-access=free |issn=0004-6256}}</ref><ref name=":2">{{Cite journal |last1=Gagné |first1=Jonathan |last2=Faherty |first2=Jacqueline K. |date=2018-08-01 |title=BANYAN. XIII. A First Look at Nearby Young Associations with Gaia Data Release 2 |journal=The Astrophysical Journal |volume=862 |issue=2 |pages=138 |arxiv=1805.11715 |bibcode=2018ApJ...862..138G |doi=10.3847/1538-4357/aaca2e |doi-access=free |issn=0004-637X}}</ref> About 35 L-type (7<ref name="Hogan">{{cite journal |bibcode=2008MNRAS.388..495H |title=L dwarfs in the Hyades |last1=Hogan |first1=E. |last2=Jameson |first2=R. F. |last3=Casewell |first3=S. L. |last4=Osbourne |first4=S. L. |last5=Hambly |first5=N. C. |journal=Monthly Notices of the Royal Astronomical Society |date=2008 |volume=388 |issue=2 |page=495 |doi=10.1111/j.1365-2966.2008.13437.x |doi-access=free |arxiv=0805.1189 }}</ref><ref>{{Cite journal |last1=Lodieu |first1=N. |last2=Boudreault |first2=S. |last3=Béjar |first3=V. J. S. |date=2014-12-01 |title=Spectroscopy of Hyades L dwarf candidates★ |journal=Monthly Notices of the Royal Astronomical Society |volume=445 |issue=4 |pages=3908–3918 |arxiv=1410.0192 |bibcode=2014MNRAS.445.3908L |doi=10.1093/mnras/stu2059 |doi-access=free |issn=0035-8711}}</ref>+1<ref name=":0" />+8<ref>{{Cite journal |last1=Pérez-Garrido |first1=A. |last2=Lodieu |first2=N. |last3=Rebolo |first3=R. |last4=Chinchilla |first4=P. |date=2018-12-01 |title=Exploring the substellar population in the Hyades open cluster |journal=Astronomy and Astrophysics |volume=620 |pages=A130 |arxiv=1810.12867 |bibcode=2018A&A...620A.130P |doi=10.1051/0004-6361/201833672 |issn=0004-6361}}</ref>+6<ref name=":1" />+3<ref name=":3">{{Cite journal |last1=Schneider |first1=Adam C. |last2=Munn |first2=Jeffrey A. |last3=Vrba |first3=Frederick J. |last4=Bruursema |first4=Justice |last5=Dahm |first5=Scott E. |last6=Williams |first6=Stephen J. |last7=Liu |first7=Michael C. |last8=Dorland |first8=Bryan N. |date=2023-09-01 |title=Astrometry and Photometry for ≈1000 L, T, and Y Dwarfs from the UKIRT Hemisphere Survey |journal=The Astronomical Journal |volume=166 |issue=3 |pages=103 |arxiv=2307.11882 |bibcode=2023AJ....166..103S |doi=10.3847/1538-3881/ace9bf |doi-access=free |issn=0004-6256}}</ref>+4<ref name=":4">{{cite journal |bibcode=2024AJ....168..165S |title=Eight New Substellar Hyades Candidates from the UKIRT Hemisphere Survey |last1=Schneider |first1=Adam C. |last2=Cushing |first2=Michael C. |last3=Stiller |first3=Robert A. |last4=Munn |first4=Jeffrey A. |last5=Vrba |first5=Frederick J. |last6=Bruursema |first6=Justice |last7=Williams |first7=Stephen J. |last8=Liu |first8=Michael C. |last9=Bravo |first9=Alexia |last10=Faherty |first10=Jacqueline K. |last11=Rothermich |first11=Austin |last12=Calamari |first12=Emily |last13=Caselden |first13=Dan |last14=Kabatnik |first14=Martin |last15=Sainio |first15=Arttu |last16=Bickle |first16=Thomas P. |last17=Pendrill |first17=William |last18=Stevnbak Andersen |first18=Nikolaj |last19=Thévenot |first19=Melina |journal=The Astronomical Journal |date=2024 |volume=168 |issue=4 |page=165 |doi=10.3847/1538-3881/ad71d0 |doi-access=free |arxiv=2408.10112 }}</ref>+3<ref name=":3" /><ref>{{Cite journal |last1=Gaia Collaboration |last2=Smart |first2=R. L. |last3=Sarro |first3=L. M. |last4=Rybizki |first4=J. |last5=Reylé |first5=C. |last6=Robin |first6=A. C. |last7=Hambly |first7=N. C. |last8=Abbas |first8=U. |last9=Barstow |first9=M. A. |last10=de Bruijne |first10=J. H. J. |last11=Bucciarelli |first11=B. |last12=Carrasco |first12=J. M. |last13=Cooper |first13=W. J. |last14=Hodgkin |first14=S. T. |last15=Masana |first15=E. |date=2021-05-01 |title=Gaia Early Data Release 3. The Gaia Catalogue of Nearby Stars |journal=Astronomy and Astrophysics |volume=649 |pages=A6 |arxiv=2012.02061 |bibcode=2021A&A...649A...6G |doi=10.1051/0004-6361/202039498 |issn=0004-6361}}</ref>+3<ref name=":2" />) and 15 T-type (2<ref name="Bouvier" />+1<ref>{{Cite journal |last1=Kuzuhara |first1=Masayuki |last2=Currie |first2=Thayne |last3=Takarada |first3=Takuya |last4=Brandt |first4=Timothy D. |last5=Sato |first5=Bun'ei |last6=Uyama |first6=Taichi |last7=Janson |first7=Markus |last8=Chilcote |first8=Jeffrey |last9=Tobin |first9=Taylor |last10=Lawson |first10=Kellen |last11=Hori |first11=Yasunori |last12=Guyon |first12=Olivier |last13=Groff |first13=Tyler D. |last14=Lozi |first14=Julien |last15=Vievard |first15=Sebastien |date=2022-08-01 |title=Direct-imaging Discovery and Dynamical Mass of a Substellar Companion Orbiting an Accelerating Hyades Sun-like Star with SCExAO/CHARIS |journal=The Astrophysical Journal |volume=934 |issue=2 |pages=L18 |arxiv=2205.02729 |bibcode=2022ApJ...934L..18K |doi=10.3847/2041-8213/ac772f |doi-access=free |issn=0004-637X}}</ref>+3<ref name=":1" />+1<ref name=":3" />+4<ref name=":4" />+4<ref>{{Cite journal |last1=Zhang |first1=Zhoujian |last2=Liu |first2=Michael C. |last3=Best |first3=William M. J. |last4=Dupuy |first4=Trent J. |last5=Siverd |first5=Robert J. |date=2021-04-01 |title=The Hawaii Infrared Parallax Program. V. New T-dwarf Members and Candidate Members of Nearby Young Moving Groups |journal=The Astrophysical Journal |volume=911 |issue=1 |pages=7 |arxiv=2102.05045 |bibcode=2021ApJ...911....7Z |doi=10.3847/1538-4357/abe3fa |doi-access=free |issn=0004-637X}}</ref>) [[Brown dwarf|brown dwarfs]] are currently reported as Hyades members or candidate members. Meanwhile [[Gaia (spacecraft)|Gaia]] DR2 allowed the identification of 710 cluster members within 30 parsec, including 23 candidates with estimated masses between 60 and 80 {{Jupiter mass|link=true}}.<ref>{{Cite journal |last1=Lodieu |first1=N. |last2=Smart |first2=R. L. |last3=Pérez-Garrido |first3=A. |last4=Silvotti |first4=R. |date=2019-03-01 |title=A 3D view of the Hyades stellar and sub-stellar population |journal=Astronomy and Astrophysics |volume=623 |pages=A35 |arxiv=1901.07534 |bibcode=2019A&A...623A..35L |doi=10.1051/0004-6361/201834045 |issn=0004-6361}}</ref>

===Mass segregation===

The observed distribution of stellar types in the Hyades Cluster demonstrates a history of [[Mass segregation (astronomy)|mass segregation]]. With the exception of its white dwarfs, the cluster's central {{Convert|2|pc|abbr=off|spell=in}} contain only star systems of at least {{Solar mass|1}}.<ref name="Perryman" /> This tight concentration of heavy stars gives the Hyades its overall structure, with a core defined by bright, closely packed systems and a halo consisting of more widely separated stars in which later spectral types are common. The core radius is 2.7 parsecs (8.8 light-years, a little more than the distance between the Sun and [[Sirius]]), while the half-mass radius, within which half the cluster's mass is contained, is {{Convert|5.7|pc|abbr=off}}. The tidal radius of {{Convert|10|pc|abbr=off|spell=in}} represents the Hyades' average outer limit, beyond which a star is unlikely to remain gravitationally bound to the cluster core.<ref name="Perryman" /><ref name="Weidemann1992" />

Stellar evaporation occurs in the cluster halo as smaller stars are scattered outward by more massive insiders. From the halo they may then be lost to tides exerted by the Galactic core or to shocks generated by collisions with drifting hydrogen clouds.<ref name="PavaniBica 2007" /> In this way the Hyades probably lost much of its original population of M dwarfs, along with substantial numbers of brighter stars.

===Stellar multiplicity===
Another result of mass segregation is the concentration of binary systems in the cluster core.<ref name="Perryman" /><ref name="Bohm-Vitense2007" /> More than half of the known F and G stars are binaries, and these are preferentially located within this central region. As in the immediate Solar neighborhood, [[binary star|binarity]] increases with increasing stellar mass. The fraction of binary systems in the Hyades increases from 26% among K-type stars to 87% among A-type stars.<ref name="Bohm-Vitense2007" /> Hyades binaries tend to have small separations, with most binary pairs in shared orbits whose [[semi-major axis|semimajor axes]] are smaller than 50 [[astronomical unit]]s.<ref name="Patience1998">{{cite journal |bibcode=1998AJ....115.1972P |title=The Multiplicity of the Hyades and Its Implications for Binary Star Formation and Evolution |last1=Patience |first1=J. |last2=Ghez |first2=A. M. |last3=Reid |first3=I. N. |last4=Weinberger |first4=A. J. |last5=Matthews |first5=K. |journal=The Astronomical Journal |date=1998 |volume=115 |issue=5 |page=1972 |doi=10.1086/300321 |arxiv=astro-ph/9801216 }}</ref> Although the exact ratio of single to multiple systems in the cluster remains uncertain, this ratio has considerable implications for our understanding of its population. For example, Perryman and colleagues list about 200 high-probability Hyades members.<ref name="Perryman" /> If the binary fraction is 50%, the total cluster population would be at least 300 individual stars.

===Future evolution===
Surveys indicate that 90% of open clusters dissolve less than 1 billion years after formation, while only a tiny fraction survive for the present age of the Solar System (about 4.6 billion years).<ref name="PavaniBica 2007" /> Over the next few hundred million years, the Hyades will continue to lose both mass and membership as its brightest stars evolve off the main sequence and its dimmest stars evaporate out of the cluster halo. It may eventually be reduced to a remnant containing about a dozen star systems, most of them binary or multiple, which will remain vulnerable to ongoing dissipative forces.<ref name="PavaniBica 2007" />

==Brightest stars==
[[Image:HyadesStarMap.jpg|thumb|300px|right|Bright stars in the core of the Hyades Cluster]]
This is a list of Hyades cluster member stars that are fourth magnitude or brighter.<ref>{{cite journal
 | title=A deep all-sky census of the Hyades
 | display-authors=1
 | last1=Röser | first1=S.
 | last2=Schilbach | first2=E.
 | last3=Piskunov | first3=A. E.
 | last4=Kharchenko | first4=N. V.
 | last5=Scholz | first5=R.-D.
 | journal=Astronomy & Astrophysics
 | volume=531 | id=A92 | pages=15 | date=July 2011
 | doi=10.1051/0004-6361/201116948
 | bibcode=2011A&A...531A..92R
 | arxiv = 1105.6093 | s2cid=118630215
 }} In the Vizier catalogue, sort on Vmag using '<4.51'. See also the linked entries in the ''All-sky Compiled Catalogue of 2.5 million stars'' (Kharchenko+ 2009).</ref>

{| class="wikitable" style="text-align: center;"
|+'''Hyades brightest stars'''
|-
! [[Star designation|Designation]]
! [[Henry Draper catalogue|HD]]
! [[Apparent magnitude|Apparent<br>magnitude]]
! [[Stellar classification|Stellar<br>classification]]
|-
| style="text-align: left;" | [[Theta Tauri|Theta<sup>2</sup> Tauri]]
| 28319
| 3.398
| A7III
|-
| style="text-align: left;" | [[Epsilon Tauri]]
| 28305
| 3.529
| K0III
|-
| style="text-align: left;" | [[Gamma Tauri]]
| 27371
| 3.642
| G8III
|-
| style="text-align: left;" | [[Delta1 Tauri|Delta<sup>1</sup> Tauri]]
| 27697
| 3.753
| G8III
|-
| style="text-align: left;" | [[Theta Tauri|Theta<sup>1</sup> Tauri]]
| 28307
| 3.836
| G7III
|-
| style="text-align: left;" | [[Kappa Tauri]]
| 27934
| 4.201
| A7IV-V
|-
| style="text-align: left;" | [[90 Tauri]]
| 29388
| 4.262
| A6V
|-
| style="text-align: left;" | [[Upsilon Tauri]]
| 28024
| 4.282
| A8Vn
|-
| style="text-align: left;" | [[Delta3 Tauri|Delta<sup>3</sup> Tauri]]
| 27962
| 4.298
| A2IV
|-
| style="text-align: left;" | [[71 Tauri]]
| 28052
| 4.480
| F0V
|}

==Planets==
Five stars in the Hyades have been found to host [[exoplanet]]s. [[Epsilon Tauri]] has a [[superjovian]] planet, which was the first planet to be discovered in any open cluster.<ref name="Sato"/> [[HD 285507]] has a [[hot Jupiter]],<ref name="Quinn2014"/> [[K2-25]] has a Neptune-sized planet,<ref name="Mann2016"/> [[K2-136]] has a system of three planets,<ref name="Mann2018"/> and TOI-4364 has a [[mini-Neptune]].<ref name="Distler2025"/> Another star, HD 283869, may also host a planet, but this has not been confirmed as only one transit has been detected.<ref name="Vanderburg2018"/>

==In culture==
In the works of [[Robert W. Chambers]], [[H. P. Lovecraft]], and others, the fictional city of [[Carcosa]] is located on a planet in the Hyades.

A 2018 [[Archaeoastronomy|archaeoastronomical]] paper suggested that the Hyades may have inspired the [[Norse myth]] of [[Ragnarök]].<ref>{{Cite journal |last=Langer |first=Johnni |date=2018 |title=The Wolf's Jaw: an Astronomical Interpretation of Ragnarök |url=https://www.researchgate.net/publication/348575057 |journal=Archaeoastronomy and Ancient Technologies |volume=6 |issue=1 |via=ResearchGate}}</ref> Astronomer [[Donald Olson (astronomer)|Donald Olson]] questioned these findings, pointing out minor errors in the paper's astronomical data.<ref>{{Cite web |last=Ouellette |first=Jennifer |date=2018-11-16 |title="Wolf's jaw" star cluster may have inspired parts of Ragnarök myth |url=https://arstechnica.com/science/2018/11/wolfs-jaw-star-cluster-may-have-inspired-parts-of-ragnarok-myth/ |access-date=2022-06-09 |website=Ars Technica |language=en-us}}</ref>

== See also ==
* [[List of open clusters]]

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

<ref name="Sato">{{cite journal |last1=Sato |first1=Bun'ei |last2=Izumiura |first2=Hideyuki |last3=Toyota |first3=Eri |display-authors=etal |date=May 2007 |title=A Planetary Companion to the Hyades Giant ɛ Tauri |journal=[[The Astrophysical Journal]] |volume=661 |issue=1 |pages=527–531 |doi=10.1086/513503 |bibcode=2007ApJ...661..527S|s2cid=122683844 |doi-access=free }}</ref>

<ref name="Quinn2014">{{cite journal |last1=Quinn |first1=Samuel N. |last2=White |first2=Russel J. |display-authors=etal |date=May 2014 |title=HD 285507b: An Eccentric Hot Jupiter in the Hyades Open Cluster |journal=[[The Astrophysical Journal]] |volume=787 |issue=1 |pages=27 |doi=10.1088/0004-637X/787/1/27 |arxiv=1310.7328 |bibcode=2014ApJ...787...27Q|s2cid=118745790 }}</ref>

<ref name="Mann2016">{{cite journal |last1=Mann |first1=Andrew W. |last2=Gaidos |first2=Eric |display-authors=etal |date=February 2016 |title=Zodiacal Exoplanets in Time (ZEIT). I. A Neptune-sized Planet Orbiting an M4.5 Dwarf in the Hyades Star Cluster |journal=[[The Astrophysical Journal]] |volume=818 |issue=1 |pages=46 |doi=10.3847/0004-637X/818/1/46 |arxiv=1512.00483 |bibcode=2016ApJ...818...46M |doi-access=free }}</ref>

<ref name="Mann2018">{{cite journal |last1=Mann |first1=Andrew W. |last2=Vanderburg |first2=Andrew |display-authors=etal |date=January 2018 |title=Zodiacal Exoplanets in Time (ZEIT). VI. A Three-planet System in the Hyades Cluster Including an Earth-sized Planet |journal=[[The Astronomical Journal]] |volume=155 |issue=1 |pages=4 |doi=10.3847/1538-3881/aa9791 |arxiv=1709.10328 |bibcode=2018AJ....155....4M |doi-access=free }}</ref>

<ref name="Vanderburg2018">{{cite journal |last1=Vanderburg |first1=Andrew |last2=Mann |first2=Andrew W. |display-authors=etal |date=August 2018 |title=Zodiacal Exoplanets in Time (ZEIT). VII. A Temperate Candidate Super-Earth in the Hyades Cluster |journal=[[The Astronomical Journal]] |volume=156 |issue=2 |pages=46 |doi=10.3847/1538-3881/aac894 |arxiv=1805.11117 |bibcode=2018AJ....156...46V |doi-access=free }}</ref>

<ref name="Distler2025">{{cite journal |last1=Distler |first1=Adam |last2=Soares-Furtado |first2=Melinda |display-authors=etal |date=March 2025 |title=TESS Hunt for Young and Maturing Exoplanets (THYME). XII. A Young Mini-Neptune on the Upper Edge of the Radius Valley in the Hyades Cluster |journal=[[The Astronomical Journal]] |volume=169 |issue=3 |pages=166 |doi=10.3847/1538-3881/ada26a |doi-access=free |arxiv=2410.11990 |bibcode=2025AJ....169..166D}}</ref>

}}

== External links ==
{{Commonscat|Hyades}}
* {{cite simbad|title=Cl Melotte 25}}
* [http://messier.seds.org/xtra/ngc/hyades.html Information on the Hyades from SEDS]
* [http://antwrp.gsfc.nasa.gov/apod/ap000929.html Astronomy Picture of the Day] (2000-09-29)
* [http://www.univie.ac.at/webda/cgi-bin/ocl_page.cgi?dirname=mel025 WEBDA open cluster database website for Hyades cluster] – E. Paunzen (Univ. Vienna)
* [http://labs.physics.dur.ac.uk/level3/AP/hyades_cp.php Distance to the Hyades undergraduate lab] {{Webarchive|url=https://web.archive.org/web/20160303223748/http://labs.physics.dur.ac.uk/level3/AP/hyades_cp.php |date=2016-03-03 }} – J. Lucey (University of Durham)
* [https://iconographic.warburg.sas.ac.uk/category/vpc-taxonomy-017719 Warburg Institute Iconographic Database (medieval and early modern images of the Hyades)]
* {{WikiSky|1=Hyades|z=5}}
{{sky|04|28|17|+|15|45|40|151}}
* [http://www.constellation-guide.com/hyades/ Hyades at Constellation Guide]

{{Catalogs|C=41|Collinder=50}}
{{Caldwell catalogue}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{DEFAULTSORT:Hyades (Star Cluster)}}
[[Category:Hyades (star cluster)| ]]
[[Category:Open clusters]]
[[Category:Taurus (constellation)]]
[[Category:Caldwell objects|041b]]
[[Category:Hyades (mythology)]]