View source for HD 12661

{{Short description|Star in the constellation Aries}}

{{Starbox begin
| name = [[Henry Draper catalogue|HD]] 12661
}}
{{Starbox image
| image = [[Image:HD 12661 orbit.svg|250px]]
| caption = Planetary orbits of the HD 12661 system }}
{{Starbox observe
| epoch = J2000
| constell = [[Aries (constellation)|Aries]]<ref name=constellation/>
| ra = {{RA|02|04|34.2884}}<ref name="Gaia DR2"/>
| dec = {{DEC|+25|24|51.514}}<ref name="Gaia DR2"/>
| appmag_v = 7.42<ref name=gliclas1971/>
}}
{{Starbox character
| class = G6&nbsp;V<ref name=apj551_2_1107/>
| b-v = +0.71<ref name=gliclas1971/>
| u-b = +0.33<ref name=gliclas1971/>
| variable =
}}
{{Starbox astrometry
| radial_v =
| prop_mo_ra  = {{val|−108.181|0.089}}<ref name="Gaia DR2"/>
| prop_mo_dec = {{val|−173.335|0.089}}<ref name="Gaia DR2"/>
| parallax = 26.3927
| p_error = 0.0437
| parallax_footnote = <ref name="Gaia DR2"/>
| absmag_v = 4.58<ref name=apj551_2_1107/>
}}
{{Starbox detail
| mass = 1.07<ref name=apj551_2_1107/>–1.10<ref name=apj622_2_1102/>
| radius = 1.096<ref name=apj551_2_1107/>–1.12<ref name=apj622_2_1102/>
| luminosity = 1.22<ref name=apj622_2_1102/>
| temperature = 5,754<ref name=apj551_2_1107/>
| metal_fe = {{nowrap|0.29 ± 0.05}}<ref name=apj551_2_1107/>
| rotational_velocity = 1.20<ref name=apj622_2_1102/>
| gravity = 4.43<ref name=apj551_2_1107/>
| age_gyr = 7.17<ref name=ajl741_1_L23/>
}}
{{Starbox catalog
| names = [[Durchmusterung|BD]]+24 298, [[Hipparcos Catalogue|HIP]] 9683, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]] 75125.<ref name=SIMBAD/>
}}
{{Starbox reference
| Simbad = HD+12661
}}
{{Starbox end
}}
'''HD 12661''' is a [[G-type main sequence star]] in the northern [[constellation]] of [[Aries (constellation)|Aries]]. The star is slightly larger and more massive than the Sun, with an estimated age of seven billion years. It has two known [[extrasolar planet]]s.

==Properties==
The [[apparent visual magnitude]] of this star is 7.42,<ref name=gliclas1971/> making it too faint to be viewed by the naked eye even under [[Bortle Dark-Sky Scale|ideal viewing conditions]]. However, it can be readily observed using a small [[telescope]] with an [[aperture]] of {{Convert|6|cm|in|sigfig=1|abbr=on}} or more.<ref name=sherrod_koed2003/> [[Parallax]] measurements of HD 12661 place it at a distance of about {{Convert|123.6|ly|pc|abbr=off|lk=on}} from the Earth, with a margin of error of ±0.2 light years.<ref name="Gaia DR2"/> It has a [[stellar classification]] of G6&nbsp;V, indicating that it is a [[main sequence]] star that is generating energy through the [[thermonuclear fusion]] of hydrogen at its core. The [[effective temperature]] of the star's outer envelope is about 5,754&nbsp;K,<ref name=apj551_2_1107/> giving it the characteristic yellow hue of a G-type star.<ref name=csiro/> Based on stellar models, estimates of the radius of this star range from 107% to 112% times [[solar radius|Sun's radius]], while the mass is likely in the range from 107% to 110% of the [[solar mass|Sun's mass]].<ref name=apj551_2_1107/><ref name=apj622_2_1102/>

As a star ages it slows its [[stellar rotation|rotation]] and diminishes the amount of [[stellar magnetic field|magnetic activity]] in its [[chromosphere]]. Hence the measured emission from the chromosphere can be used to estimate the age of a star, particularly for F and G-type dwarf stars with an age of less than two billion years. However, this technique becomes less accurate for ages beyond about 5.6 billion years. Based upon the chromosphere emission of HD 12661, it is older than the Sun with an estimated age of roughly seven billion years.<ref name=aaa443_2_609/> It has a low [[stellar rotation|projected rotational velocity]] of 1.20&nbsp;km/s, consistent with it being an older star.<ref name=apj622_2_1102/> The age of a star can also be estimated by the abundance of lithium, as this element is destroyed through [[thermonuclear fusion]] at the core. However, this is less accurate technique. For HD 12661, the lithium abundance gives an age estimate of 4.4 billion years.<ref name=aaa443_2_609/>

The abundance of elements other than hydrogen and helium, what astronomers term the [[metallicity]], is unusually high in this star when compared to the Sun. High metallicity has been found to be [[Correlation and dependence|statistically correlated]] with the presence of a multi-planet system around a star.<ref name=apj551_2_1107/> It is possible that a planet in this system may have been scattered and ended up being accreted by the star, which may account for the large surface metallicity.<ref name=apj690_L1/>

==Planetary system==
The first planet was discovered in 2001 from the Lick and Keck observatories using precision measurements of the star's radial velocity variations. The periodicity in this variation allowed astronomers to extract information about the planet's orbit and minimum mass.<ref name=apj551_2_1107/> A second planet was discovered by the same team two years later.<ref name=apj586_2_1394/> Both planets are greater in mass than [[Jupiter]].<ref name=apj693_2_1084/> The [[inclination]] and true mass of planet c were measured using [[astrometry]], and the results were published in 2025.<ref name=An2025/>

The system is dynamically unstable.<ref name=aaa398_3_1151/><ref name=apj628_2_1006/> "Either this system is being observed during a relatively rare state, or additional planets are affecting the observed radial velocities and/or the system’s secular eccentricity evolution."<ref name=apj690_L1/>

{{OrbitboxPlanet begin
| table_ref = <ref name=An2025/>
| period_unit = year
}}
{{OrbitboxPlanet
| exoplanet    = [[HD 12661 b|b]]
| mass         = {{val|p=>|2.382|0.080}}
| period       = {{val|0.718323|(68)}}
| semimajor    = {{val|0.843|0.014}}
| eccentricity = {{val|0.3598|0.0059|0.0060}}
}}
{{OrbitboxPlanet
| exoplanet    = [[HD 12661 c|c]]
| mass         = {{val|2.83|0.82|0.67}}
| period       = {{val|4.6535|0.0087|0.0082}}
| semimajor    = {{val|2.929|0.045|0.047}}
| eccentricity = {{val|0.0131|0.0150|0.0094}}
| inclination  = {{Val|136|11|21}}
}}
{{Orbitbox end}}

==See also==
* [[List of extrasolar planets]]

==References==
{{Reflist|refs=

<ref name=constellation>{{cite constellation|HD 12661}}</ref>

<ref name=apj551_2_1107>{{cite journal | display-authors=1 | first1=Debra A. | last1=Fischer | last2=Marcy | first2=Geoffrey W. | last3=Butler | first3=R. Paul | last4=Vogt | first4=Steven S. | last5=Frink | first5=Sabine | last6=Apps | first6=Kevin | title=Planetary Companions to HD 12661, HD 92788, and HD 38529 and Variations in Keplerian Residuals of Extrasolar Planets | journal=The Astrophysical Journal | date=2001 | volume=551 | issue=2 | pages=1107–1118 | doi=10.1086/320224 | bibcode=2001ApJ...551.1107F | doi-access=free }}</ref>

<ref name=apj586_2_1394>{{cite journal | display-authors=1 | first1=Debra A. | last1=Fischer | last2=Marcy | first2=Geoffrey W. | last3=Butler | first3=R. Paul | last4=Vogt | first4=Steven S. | last5=Henry | first5=Gregory W. | last6=Pourbaix | first6=Dimitri | last7=Walp | first7=Bernard | last8=Misch | first8=Anthony A. | last9=Wright | first9=Jason T. | title=A Planetary Companion to HD 40979 and Additional Planets Orbiting HD 12661 and HD 38529 | journal=The Astrophysical Journal | date=2003 | volume=586 | issue=2 |  pages=1394–1408  | doi=10.1086/367889 | bibcode=2003ApJ...586.1394F | doi-access=free }}</ref>

<ref name=aaa398_3_1151>{{cite journal | first1=K. | last1=Gozdziewski | title=Stability of the HD 12661 Planetary System | journal=[[Astronomy and Astrophysics]] | volume=398 | issue=3 | pages=1151–1161 | date=2003 | doi=10.1051/0004-6361:20021713 | bibcode=2003A&A...398.1151G | doi-access=free }}</ref>

<ref name=aaa443_2_609>{{cite journal | last1=Saffe | first1=C. | last2=Gómez | first2=M. | last3=Chavero | first3=C. | title=On the ages of exoplanet host stars | journal=Astronomy and Astrophysics | volume=443 | issue=2 | pages=609–626 |date=November 2005 | doi=10.1051/0004-6361:20053452 | bibcode=2005A&A...443..609S |arxiv = astro-ph/0510092 | s2cid=11616693 }}</ref>

<ref name=apj628_2_1006>{{cite journal | last1=Rodríguez | first1=Adrián | last2=Gallardo | first2=Tabaré | title=The Dynamics of the HD 12661 Extrasolar Planetary System | journal=[[The Astrophysical Journal]] | volume=628 | issue=2 | pages=1006–11013 | date=2005 | doi=10.1086/430816 | bibcode=2005ApJ...628.1006R  | s2cid=31278031 | doi-access=free }}</ref>

<ref name=apj690_L1>{{cite journal | title=Secular evolution of HD 12661: a system caught at an unlikely time | date=2008 | first1=Dimitri | last1=Veras | last2=Ford | first2=Eric B. | journal=The Astrophysical Journal | volume=690 | issue=1 | pages=L1–L4 | arxiv=0811.0001v1 | bibcode = 2009ApJ...690L...1V | doi=10.1088/0004-637X/690/1/L1 | s2cid=17386482 }}</ref>

<ref name=apj693_2_1084>{{cite journal | display-authors=1 | last1=Wright | first1=J. T. | last2=Upadhyay | first2=S. | last3=Marcy | first3=G. W. | last4=Fischer | first4=D. A. | last5=Ford | first5=Eric B. | last6=Johnson | first6=John Asher | title=Ten New and Updated Multi-planet Systems, and a Survey of Exoplanetary Systems| journal=The Astrophysical Journal | volume=693 | issue=2 | date=2009 | pages=1084–1099 | type=abstract | doi=10.1088/0004-637X/693/2/1084 | bibcode=2009ApJ...693.1084W | arxiv=0812.1582 | s2cid=18169921 }}</ref>

<ref name=apj622_2_1102>{{cite journal | last1=Fischer | first1=Debra A. | last2=Valenti | first2=Jeff | title=The Planet-Metallicity Correlation | journal=The Astrophysical Journal | volume=622 | issue=2 | pages=1102–1117 |date=April 2005 | doi=10.1086/428383 | bibcode=2005ApJ...622.1102F | doi-access=free }}</ref>

<ref name=sherrod_koed2003>{{cite book | first1=P. Clay | last1=Sherrod | first2=Thomas L. | last2=Koed | title=A Complete Manual of Amateur Astronomy: Tools and Techniques for Astronomical Observations | series=Astronomy Series | publisher=[[Courier Dover Publications]] | date=2003 | isbn=0-486-42820-6 | page=9 | url=https://books.google.com/books?id=4zjv84hHNPcC&pg=PA9 }}</ref>

<ref name=SIMBAD>{{cite journal | title=G 72-54 -- High proper-motion Star  | work=SIMBAD | publisher=[[Centre de Données astronomiques de Strasbourg]] | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HD+12661 }}</ref>

<ref name=gliclas1971>{{cite book| last1=Giclas | first1=H. L. | last2=Burnham | first2=R. | last3=Thomas | first3=N. G. | title=Lowell proper motion survey Northern Hemisphere. The G numbered stars. 8991 stars fainter than magnitude 8 with motions > 0".26/year | location=Flagstaff, Arizona | publisher=Lowell Observatory | date=1971 | bibcode=1971lpms.book.....G }}</ref>

<ref name=ajl741_1_L23>{{cite journal | last1=Koriski | first1=Shuki | last2=Zucker | first2=Shay | title=On the Ages of Planetary Systems with Mean-motion Resonances | journal=The Astrophysical Journal Letters | volume=741 | issue=1 | page=L23 |date=November 2011 | doi=10.1088/2041-8205/741/1/L23 | bibcode=2011ApJ...741L..23K |arxiv = 1109.6671 | s2cid=118553051 }}</ref>

<ref name=csiro>{{cite journal | title=The Colour of Stars | date=December 21, 2004 | work=Australia Telescope, Outreach and Education | publisher=[[Commonwealth Scientific and Industrial Research Organisation]] | url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html | access-date=2012-01-16 | archive-url=https://web.archive.org/web/20120318151427/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html | archive-date=March 18, 2012 | url-status=dead }}</ref>

<ref name="Gaia DR2">{{Cite Gaia DR2|105332908999068032}}</ref>

<ref name=An2025>{{cite journal |last=An |first=Qier |last2=Brandt |first2=Timothy D. |last3=Brandt |first3=G. Mirek |last4=Venner |first4=Alexander |title=Orbits and Masses for 156 Companions from Combined Astrometry and Radial Velocities, and A Validation of Gaia Non-Single Star Solutions |date=2025-08-11 |journal=[[The Astrophysical Journal Supplement Series]] |arxiv=2508.08374}}</ref>

}}

==External links==
* {{cite encyclopedia|url=http://exoplanet.eu/star.php?st=HD+12661|title=Notes for star HD 12661|access-date=2006-04-14|url-status=dead|archive-url=https://web.archive.org/web/20120505100541/http://exoplanet.eu/star.php?st=HD+12661|encyclopedia=[[Extrasolar Planets Encyclopaedia]]|archive-date=2012-05-05}}
* {{cite web|url=http://exoplanets.org/esp/hd12661/hd12661.shtml|title=Two Planets Around HD 12661|work=California & Carnegie Planet Search| access-date = 2006-04-14}}
* [http://www.lpl.arizona.edu/~rory/research/xsp/dynamics/ Extrasolar Planet Interactions] {{Webarchive|url=https://web.archive.org/web/20160505160348/http://www.lpl.arizona.edu/~rory/research/xsp/dynamics/ |date=2016-05-05 }} by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona
* [https://web.archive.org/web/20120213202113/http://planetquest1.jpl.nasa.gov/atlas/atlas_skymap.cfm?Star=137 Local Sky Map]

{{Sky|02|04|34.36|+|25|24|53|121.202668153}}

{{HD 12661}}
{{Stars of Aries}}

{{DEFAULTSORT:HD 12661}}
[[Category:Hipparcos objects|009683]]
[[Category:Aries (constellation)]]
[[Category:Henry Draper Catalogue objects|012661]]
[[Category:G-type main-sequence stars]]
[[Category:Planetary systems with two confirmed planets]]
[[Category:Durchmusterung objects]]