{{Short description|Binary star in the constellation Cetus}} {{Sky|01|39|01.54|-|17|57|01.8|8.7}} {{Starbox begin}} {{Starbox image |image=frameless|upright=1.2 |caption=Gliese 65, as seen during the Digitized Sky Survey }} {{Starbox observe 2s | epoch = J2000 | constell = Cetus<ref name=constellation/> <!-- First component --> | component1 = Gliese 65 A (BL Ceti) | ra1 = {{RA|01|39|01.3773}}<ref name="Gaia3a"/> | dec1 = {{DEC|-17|57|02.587}}<ref name="Gaia3a"/> | appmag_v1 = 12.8<ref name=houdebine2019/> <!-- Second component --> | component2 = Gliese 65 B (UV Ceti) | ra2 = {{RA|01|39|01.6377}}<ref name="Gaia3b"/> | dec2 = {{DEC|-17|57|01.001}}<ref name="Gaia3b"/> | appmag_v2 = 12.8<ref name=houdebine2019/> }} {{Starbox character | component1 = Gliese 65 A (BL Ceti) | class = M5.5V<ref name=kirkpatrick1991/> | b-v = +1.87 | u-b = +1.10 | variable = UV Cet<ref name=BL/> | component2 = Gliese 65 B (UV Ceti) | class2 = M6 V<ref name=kirkpatrick1991/> | b-v2 = | u-b2 = | variable2 = UV Cet<ref name=UV/> }} {{Starbox astrometry | parallax = 371.92 | p_error = 0.42 | parallax_footnote = <ref name="GRAVITY2024"/> }} {{Starbox astrometry |no_heading=y | component1 = Gliese 65 A (BL Ceti) | radial_v = | prop_mo_ra = +3385.316<ref name="Gaia3a"/> | prop_mo_dec = +544.386<ref name="Gaia3a"/> | parallax = | p_error = | parallax_footnote = | absmag_v = 15.7<ref name=houdebine2019/> | component2 = Gliese 65 B (UV Ceti) | prop_mo_ra2 = +3178.694<ref name="Gaia3b"/> | prop_mo_dec2 = +584.061<ref name="Gaia3b"/> | parallax2 = | p_error2 = | parallax_footnote2 = | absmag_v2 = 15.7<ref name=houdebine2019/> }} {{Starbox orbit | reference = <ref name="GRAVITY2024"/> | period = {{val|26.38|0.002}} | axis = {{val|2.0584|0.0097}}<ref name=aaa593_A127/> | axis_unitless = {{val|5.459|0.002|ul=AU}} | eccentricity = {{val|0.6172|0.0001}} | inclination = {{val|128.0|0.1}} | node = {{val|325.9|0.1}} | periarg = {{val|103.2|0.1}} | periastron = {{val|41333|8|ul=MJD}}<br/>(17 January 1972) }} {{Starbox detail <!-- First component --> | component1 = Gliese 65 A | mass = {{val|0.122|0.002}}<ref name="GRAVITY2024"/> | radius = {{val|0.165|0.006}}<ref name=aaa593_A127/> | luminosity = {{val|0.00147|0.00005}}<ref name=apj860_A15/> | gravity = {{val|5.092|0.015}}<ref name=aaa593_A127/> | temperature = {{val|2784|58}}<ref name=apj860_A15/> | metal_fe = {{val|−0.03|0.20}}<ref name=aaa593_A127/> | rotation = {{val|0.2430|0.0005}}<ref name=mnras471_811/> days | rotational_velocity = {{val|28.2|2}}<ref name=aaa593_A127/> | age_myr = <!-- Second component --> | component2 = Gliese 65 B | mass2 = {{val|0.116|0.002}}<ref name="GRAVITY2024"/> | radius2 = {{val|0.159|0.006}}<ref name=aaa593_A127/> | luminosity2 = {{val|0.00125|0.00005}}<ref name=apj860_A15/> | gravity2 = {{val|5.113|0.015}}<ref name=aaa593_A127/> | temperature2 = {{val|2728|60}}<ref name=apj860_A15/> | metal_fe2 = {{val|−0.12|0.20}}<ref name=aaa593_A127/> | rotation2 = {{val|0.2268|0.0003}}<ref name=mnras471_811/> days | rotational_velocity2 = {{val|30.6|2}}<ref name=aaa593_A127/> }} {{Starbox catalog | names = {{odlist | G=272-61 | GJ=65 | L=726-8 | PLX=343.1}} | component1 = Gliese 65 A | names1 = {{odlist | V=BL Ceti | LHS=9 | LP=768-27}} | component2 = Gliese 65 B | names2 = {{odlist | V=UV Ceti | LHS=10 | LP=768-26}} }} {{Starbox reference | Simbad=GJ+65|sn=The system | Simbad2=GJ+65+A|sn2=A (BL Cet) | Simbad3=GJ+65+B|sn3=B (UV Cet) }} {{Starbox end}}
'''Gliese 65''', also known as '''Luyten 726-8''', is a binary star system that is one of Earth's nearest neighbors, at {{convert|8.8|ly|pc|lk=on|abbr=off}} from Earth in the constellation Cetus. The two component stars are both flare stars with the variable star designations '''BL Ceti''' and '''UV Ceti'''.
== Star system == The star system was discovered in 1948 by Willem Jacob Luyten in the course of compiling a catalog of stars of high proper motion; he noted its exceptionally high proper motion of 3.37 arc seconds annually and cataloged it as Luyten {{not a typo|726-8}}.<ref name=luyten1949/> The two stars are of nearly equal brightness, with visual magnitudes of 12.7 and 13.2 as seen from Earth. They orbit one another every 26.5 years. The distance between the two stars varies from {{convert|2.1|to|8.8|AU|Gm|lk=on}}. The Gliese 65 system is approximately {{convert|2.63|pc|ly|2|lk=on}} from Earth's Solar System, in the constellation Cetus, and is thus the seventh-closest star system to Earth. Its own nearest neighbor is Tau Ceti, {{convert|0.98|pc|ly|2|abbr=on}} away from it. If <math>R_v=+29</math> km/s then approximately 28,700 years ago Gliese 65 was at its minimal distance of 2.21 pc (7.2 ly) from the Sun.<ref name="SIMBAD2"/>
Gliese 65 A was later found to be a variable star and given the variable star designation BL Ceti.<ref name=BL/> It is a red dwarf of spectral type M5.5V. It is also a flare star, and classified as a UV Ceti variable type, but it is not nearly as remarkable or extreme in its behavior as its companion star UV Ceti.
[[File:UVCetLightCurve.png|thumb|left|An ultraviolet light curve for UV Ceti, adapted from Beskin ''et al.'' (2017).<ref name="Beskin"/> The main plot shows the full flare event and the inset plot shows the time around peak brightness with an expanded time scale. ]] Soon after the discovery of Gliese 65 A, the companion star Gliese 65 B was discovered. Like Gliese 65 A, this star was also found to be variable and given the variable star designation UV Ceti.<ref name=UV/> Although UV Ceti was not the first flare star discovered, it is the most prominent example of such a star, so similar flare stars are now classified as UV Ceti type variable stars. This star goes through fairly extreme changes of brightness: for instance, in 1952, its brightness increased by 75 times in only 20 seconds. UV Ceti is a red dwarf of spectral type M6V.<ref name=kirkpatrick1991/>
Both stars are listed as spectral standard stars for their respective classes, being considered typical examples of the classes.<ref name=kirkpatrick1991/>
In approximately 31,500 years, Gliese 65 will have a close encounter with Epsilon Eridani at the minimal distance of about 0.93 ly. Gliese 65 can penetrate a conjectured Oort cloud about Epsilon Eridani, which may gravitationally perturb some long-period comets. The duration of mutual transit of two star systems within 1 ly from each other is about 4,600 years.<ref name=potemine2010/>
Gliese 65 is a possible member of the Hyades Stream.<ref name=montes2001/> {{clear|left}}
== Candidate planet == In 2024, a candidate super-Neptune-mass planet was detected in the Gliese 65 system via astrometry with Very Large Telescope's GRAVITY instrument. If it exists, it would orbit one of the two stars (it is unclear which) with a period of 156 days.<ref name="GRAVITY2024"/> The planet's properties change slightly depending on which star it orbits, but in general its mass is estimated to be about {{Earth mass|sym=y|40}} and the semi-major axis is about 30% of an astronomical unit. It is estimated to be about seven times the size of Earth based on mass-radius relationships.<ref name="GRAVITY2024"/>
{{Orbitbox planet begin | name = Gliese 65 | table_ref = <ref name="GRAVITY2024"/><ref group="nb">The parameters are slightly different depending on whether the planet orbits star A (above) or star B (below).</ref> }} {{Orbitbox planet hypothetical | exoplanet = b | mass_earth = {{val|39|7|ul=Earth mass}}<br/>{{val|36|6}} | radius_earth = ~7 (estimate) | semimajor = {{val|0.283|0.002}}<br/>{{val|0.274|0.002}} | period = {{val|156|1}} | eccentricity = {{val|0.33|0.30}}<br/>{{val|0.27|0.21}} | inclination = {{val|88|6}}°<br/>{{val|89|9}} }} {{Orbitbox end}}
== Notes == {{reflist|group="nb"}}
== References == <references> <ref name="Gaia3a">{{cite Gaia DR3|5140693571158739840}}</ref>
<ref name="Gaia3b">{{cite Gaia DR3|5140693571158946048}}</ref>
<ref name="SIMBAD2">{{cite web |url=http://cdsannotations.u-strasbg.fr/annotations/simbadObject/1297613 |title=Annotations on V* UV Cet object |publisher=Centre de Données astronomiques de Strasbourg |access-date=2010-04-14 |archive-date=2014-11-23 |archive-url=https://web.archive.org/web/20141123165456/http://cdsannotations.u-strasbg.fr/annotations/simbadObject/1297613 |url-status=live }}</ref>
<ref name=constellation>{{cite constellation|Gliese 65}}</ref>
<ref name=houdebine2019>{{cite journal |bibcode=2019AJ....158...56H |title=The Mass-Activity Relationships in M and K Dwarfs. I. Stellar Parameters of Our Sample of M and K Dwarfs |last1=Houdebine |first1=Éric R. |last2=Mullan |first2=D. J. |last3=Doyle |first3=J. G. |last4=de la Vieuville |first4=Geoffroy |last5=Butler |first5=C. J. |last6=Paletou |first6=F. |journal=The Astronomical Journal |year=2019 |volume=158 |issue=2 |pages=56 |doi=10.3847/1538-3881/ab23fe |arxiv=1905.07921 |s2cid=159041104 |doi-access=free }}</ref>
<ref name=kirkpatrick1991>{{cite journal |doi=10.1086/191611 |author1=Kirkpatrick, J. Davy |author2=Henry, Todd J. |author3=McCarthy, Donald W. Jr. |title=A standard stellar spectral sequence in the red/near-infrared - Classes K5 to M9 |journal=Astrophysical Journal Supplement |date=1991 |volume=77 |pages=417 |bibcode=1991ApJS...77..417K|doi-access=free }}</ref>
<ref name="Beskin">{{cite journal |last1=Beskin |first1=G. |last2=Karpov |first2=S. |last3=Plokhotnichenko |first3=V. |last4=Stepanov |first4=A. |last5=Tsap |first5=Yu. |title=Discovery of the subsecond linearly polarized spikes of synchrotron origin in the UV Ceti giant optical flare |journal=Publications of the Astronomical Society of Australia |date=January 2017 |volume=34 |article-number=e010 |doi=10.1017/pasa.2017.3 |s2cid=125084280 |doi-access=free |arxiv=1702.06660 |bibcode=2017PASA...34...10B }}</ref>
<ref name=aaa593_A127> {{cite journal |display-authors=1 |last1=Kervella |first1=Pierre |last2=Mérand |first2=Antoine |last3=Ledoux |first3=Cédric |last4=Demory |first4=Brice-Olivier |last5=Le Bouquin |first5=Jean-Baptiste |title=The red dwarf pair GJ65 AB: inflated, spinning twins of Proxima. Fundamental parameters from PIONIER, NACO, and UVES observations |journal=Astronomy & Astrophysics |volume=593 |date=October 2016 |doi=10.1051/0004-6361/201628631 |bibcode=2016A&A...593A.127K |arxiv=1607.04351 }} </ref>
<ref name=mnras471_811> {{cite journal |display-authors=1 |last1=Barnes |first1=J. R. |last2=Jeffers |first2=S. V. |last3=Haswell |first3=Carole |last4=Jones |first4=H. R. A. |last5=Shulyak |first5=D. |last6=Pavlenko |first6=Yakiv |last7=Jenkins |first7=J. S. |title=Surprisingly different star-spot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB |journal=Monthly Notices of the Royal Astronomical Society |volume=471 |issue=1 |pages=811–823 |date=October 2017 |doi=10.1093/mnras/stx1482 |doi-access=free |bibcode=2017MNRAS.471..811B |arxiv=1706.03979 }} </ref>
<ref name=apj860_A15> {{cite journal |display-authors=1 |last1=MacDonald |first1=James |last2=Mullan |first2=Dermott J. |last3=Dieterich |first3=Sergio |title=The Magnetic Binary GJ 65: A Test of Magnetic Diffusivity Effects |journal=The Astrophysical Journal |volume=860 |issue=1 |date=June 2018 |page=15 |doi=10.3847/1538-4357/aac2c0 |bibcode=2018ApJ...860...15M |arxiv=1711.09434 |doi-access=free }} </ref>
<ref name="GRAVITY2024">{{cite journal |collaboration=GRAVITY Collaboration |last1=Abuter |first1=R. |last2=Amorim |first2=A. |last3=Benisty |first3=M. |last4=Berger |first4=J.-P. |last5=Bonnet |first5=H. |last6=Bourdarot |first6=G. |last7=Bourget |first7=P. |last8=Brandner |first8=W. |display-authors=1 |date=May 2024 |title=Astrometric detection of a Neptune-mass candidate planet in the nearest M-dwarf binary system GJ65 with VLTI/GRAVITY |journal=Astronomy & Astrophysics |volume=685 |issue= |pages=L9 |doi=10.1051/0004-6361/202449547 |arxiv=2404.08746 |bibcode=2024A&A...685L...9G}}</ref>
<ref name=luyten1949>{{cite journal | title=New stars with proper motions exceeding 0.5" annually. | author=Luyten, W. J. | journal= The Astronomical Journal | volume=55 | pages=15 | date=December 1949 | doi=10.1086/106322 | bibcode=1949AJ.....55...15L| doi-access=free }}</ref>
<ref name=BL>{{cite web | url=http://www.sai.msu.su/gcvs/cgi-bin/search.cgi?search=BL+Cet | title=Query= BL Cet | publisher=Centre de Données astronomiques de Strasbourg | work=General Catalogue of Variable Stars | access-date=2009-12-16 | archive-date=2016-03-03 | archive-url=https://web.archive.org/web/20160303232046/http://www.sai.msu.su/gcvs/cgi-bin/search.cgi?search=BL+Cet | url-status=live }}</ref>
<ref name=UV>{{cite web | url=http://www.sai.msu.su/gcvs/cgi-bin/search.cgi?search=UV+Cet | title=Query= UV Cet | publisher=Centre de Données astronomiques de Strasbourg | work=General Catalogue of Variable Stars | access-date=2009-12-16 | archive-date=2016-03-03 | archive-url=https://web.archive.org/web/20160303230041/http://www.sai.msu.su/gcvs/cgi-bin/search.cgi?search=UV+Cet | url-status=live }}</ref>
<ref name=potemine2010>{{cite arXiv |first=Igor Yu. | last=Potemine |date=April 2010 | eprint=1004.1557 |title=Transit of Luyten 726-8 within 1 ly from Epsilon Eridani | class=astro-ph.SR }}</ref>
<ref name=montes2001>{{cite journal | last1=Montes | first1=D. | last2=López-Santiago | first2=J. | last3=Gálvez | first3=M. C. | last4=Fernández-Figueroa | first4=M. J. | last5=De Castro | first5=E. | last6=Cornide | first6=M. | display-authors=1 | journal=MNRAS | title=Late-type members of young stellar kinematic groups - I. Single stars. | volume=328 | pages=45–63 | date=2001 | issue=1 | doi=10.1046/j.1365-8711.2001.04781.x | doi-access=free | arxiv=astro-ph/0106537 | bibcode=2001MNRAS.328...45M | s2cid=55727428 }}</ref> </references>
==Further reading== * {{cite journal |last=Durand |first=E. |author2=Oberly, J. J. |author3=Tousey, R. |date=1949 |title=Analysis of the First Rocket Ultraviolet Solar Spectra |journal=The Astrophysical Journal |volume=109 |pages=1 |doi=10.1086/145099 |bibcode=1949ApJ...109....1D}} * {{cite journal |last=Luyten |first=W. J. |date=1949 |title=New stars with proper motions exceeding 0.5" annually |journal=The Astronomical Journal |volume=55 |pages=15 |doi=10.1086/106322 |bibcode=1949AJ.....55...15L|doi-access=free }} * {{cite journal | last1=Geyer | first1=David W. | last2=Harrington | first2=Robert S. | last3=Worley | first3=Charles E. | title=Parallax, orbit, and mass of the visual binary L726-8 | journal=Astronomical Journal | volume=95 | pages=1841–1842 |date=June 1988 | doi=10.1086/114781 | bibcode=1988AJ.....95.1841G | doi-access=free }} * {{cite journal |bibcode=2000A&A...364..217D |display-authors=1 |last1=Delfosse |first1=Xavier |last2=Forveille |first2=Thierry |last3=Ségransan |first3=Damien |last4=Beuzit |first4=Jean-Luc |last5=Udry |first5=Stéphane |last6=Perrier |first6=Christian |last7=Mayor |first7=Michel |title=Accurate masses of very low mass stars. IV. Improved mass-luminosity relations |journal=Astronomy and Astrophysics |volume=364 |pages=217–224 |date=December 2000 |arxiv = astro-ph/0010586 }}
== External links == * http://www.aavso.org/vstar/vsots/fall03.shtml {{Webarchive|url=https://web.archive.org/web/20040305021303/http://www.aavso.org/vstar/vsots/fall03.shtml |date=2004-03-05 }} * http://www.solstation.com/stars/luy726-8.htm {{Webarchive|url=https://web.archive.org/web/20090327125818/http://www.solstation.com/stars/luy726-8.htm |date=2009-03-27 }} {{nearest systems|1}} {{Stars of Cetus}} <!-- Properties -->
Category:M-type main-sequence stars Category:BY Draconis variables Ceti, UV Category:Binary stars Category:Hyades Stream Category:Local Bubble <!-- Identifiers --> Category:Cetus 0065 Ceti, BL UV Category:Hypothetical planetary systems