Editing Hyades (star cluster) (section)

===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>