Sigma Boötis

{{Short description|Star in the constellation Boötes}} {{distinguish|S Boötis}} __NOTOC__ {{Starbox begin | name=σ Boötis }} {{Starbox image | image = {{Location mark | image=Boötes IAU.svg | alt= | float=center | width=200 | label= | position=right | mark=Red circle.svg | mark_width=10 | mark_link=σ Boötis | x%=48.9 | y%=47.9 }} | caption = Location of σ Boötes (circled) }} {{Starbox observe | epoch = J2000 | ra = {{RA|14|34|40.817}}<ref name=GaiaDR3/> | dec = {{DEC|+29|44|42.48}}<ref name=GaiaDR3/> | appmag_v = 4.46<ref name=Elliott1974/> | constell = [[Boötes (constellation)|Boötes]] }} {{Starbox character | type = [[main sequence]]<ref name=GaiaDR3/> | class = F4VkF2mF1<ref name=Gray2001/> | b-v = +0.366<ref name=Elliott1974/> | u-b = −0.084<ref name=Elliott1974/> | variable = Suspected<ref name=Samus_et_al_2017/> }} {{Starbox astrometry | radial_v = {{Val|+0.37|0.09}}<ref name=Nidever2002/> | prop_mo_ra = +188.574 | prop_mo_dec = +131.580 | pm_footnote = <ref name=GaiaDR3/> | parallax = 63.4679 | p_error = 0.1173 | parallax_footnote = <ref name=GaiaDR3/> | absmag_v = 3.52<ref name=Paunzen2014/> }} {{Starbox detail | mass = {{val|1.48|u=solar mass}}<ref name=David2015/> 1.18<ref name=Luck2018/> | radius = {{Val|1.431|0.023}}<ref name=apj746_1_101/> | luminosity = {{Val|3.461|0.042}}<ref name=apj746_1_101/> | temperature = {{Val|6594|55|fmt=commas}}<ref name=apj746_1_101/> | metal_fe = −0.24<ref name=Bensby2014/> | gravity = 4.30<ref name=Paunzen2014/> | age_gyr = 1.7 Gyr<ref name=apj598_1_636/> 2.42 Gyr<ref name=Luck2018/> 3.1<ref name=Rachford_Foight_2009/> | rotational_velocity = 7.32<ref name=Arnaiz2010/> }} {{Starbox catalog | names = {{odlist | name=Genghe | B=σ Boo | F=28 Boötis | BD=+30°2536 | FK5= | GJ=557 | HD=128167 | HIP=71284 | HR=5447 | SAO=83416 | GC=19659 | CCDM=14347+2945 | WDS=J14347+2945A | PPM=103421 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad=sig+Boo  | ARICNS = }} {{Starbox end}}

'''Sigma Boötis''', also named '''Genghe''',<ref name=IAU-CSN/> is a single,<ref name=Eggleton_Tokovinin_2008/><ref name=Rodriguez_et_al_2015/> yellow-hued [[star]] in the northern [[constellation]] of [[Boötes]]. This star is visible to the [[naked eye]] with an [[apparent visual magnitude]] of 4.46.<ref name=Elliott1974/> Located to the southeast of [[Rho Boötis]], the dwarf Sigma may at first appear as a naked-eye double, but the angular proximity with Rho is merely line-of-sight. Sigma Boötis is located at a distance of {{convert|51.4|ly|pc|0|abbr=out|lk=on}} from the [[Sun]] based on [[stellar parallax|parallax]].<ref name=GaiaDR2/> The star has a relatively high [[proper motion]] and is traversing the sky at the rate of {{val|0.230|ul=arcsecond}} yr−1.<ref name=Lepine_Shara_2005/>

==Nomenclature== ''Sigma Boötis'' is a [[Bayer designation]] that is [[Romanization of Greek|Latinized]] from σ Boötis, and abbreviated Sigma Boo or σ Boo. It is known by several other catalog designations, including 28 Boötis, BD+30°2536, GC 19659, GJ 557, HD 128167, HIP 71284, HR 5447, SAO 83416, and CCDM 14347+2945.<ref name=SIMBAD/>

In [[Chinese astronomy]], {{lang|zh|梗河}} ({{lang|zh-Latn|Gěng Hé}}), meaning ''[[Root (Chinese constellation)|Celestial Lance]]'', refers to an asterism consisting of σ Boötis, [[Epsilon Boötis|ε Boötis]] and [[Rho Boötis|ρ Boötis]].<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 star names|Chinese name]] for σ Boötis itself is {{lang|zh|梗河二}} ({{lang|zh-Latn|Gěng Hé èr}}, {{langx|en|the Second Star of Celestial Lance}}).<ref>{{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0606/ap060629.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 29 日] {{Webarchive|url=https://web.archive.org/web/20210605100121/http://aeea.nmns.edu.tw/2006/0606/ap060629.html |date=2021-06-05 }}</ref> The [[IAU Working Group on Star Names]] approved the name Genghe for this star on 15 April 2026, after the Chinese asterism.<ref name=IAU-CSN/>

==Properties== The [[stellar classification]] of Sigma Boötis is F4VkF2mF1.<ref name=Gray2001/> This notation is used for so-called "metal-weak" stars; [[Am star]]s with [[absorption line]]s of some metals weaker than expected in comparison with other [[stellar spectrum|spectral]] features. The 'F4V', indicating an [[F-type main-sequence star]], is derived from the hydrogen spectral lines and the shape of the metallic lines, the 'kF2' means it has the [[Calcium K line]] strength of a hotter F2 star and 'mF1' showing it has the [[metallic-line star|metallic line]] strength of an F1 star.<ref name=Gray_Corbally_2009/> It is around twice as luminous as a comparable [[zero age main sequence]] star, which may indicate it is near the end of its [[main sequence]] lifetime.<ref name=Rachford_Foight_2009/>

Sigma Boötis is a solar-type star but is larger and more massive than the Sun. It has an estimated age of around two<ref name=apj598_1_636/> to three<ref name=Rachford_Foight_2009/> billion years and is spinning with a [[projected rotational velocity]] of 7 km/s.<ref name=Arnaiz2010/> There is some evidence of variation in [[radial velocity]] as well as rotational modulation of active latitudes.<ref name=Rachford_Foight_2009/> Even though the outer convective zone of the star only occupies a few percent of the stellar radius, a surface [[stellar magnetic field|magnetic field]] has been detected with a strength of {{val|1.4|0.4|ul=Gauss}}.<ref name=Seach_et_al_2020/> This surface field forms a relatively simple [[Magnetic dipole|dipole]] topology.<ref name=Seach_et_al_2022/> The star is radiating 3.5<ref name=apj746_1_101/> times the luminosity of the Sun from its [[photosphere]] at an [[effective temperature]] of 6,594 K.<ref name=apj746_1_101/> It appears to be a source for [[Astrophysical X-ray source|X-ray emission]].<ref name=Haakonsen_Rutledge_2009/>

Infrared surveys with the [[Spitzer Space Telescope|Spitzer]] and [[Herschel Space Observatory|Herschel]] [[space telescope]]s failed to detect an [[infrared excess]] around this star at [[wavelength]]s up to {{Val|160|u=micrometre}}. However, the HOSTS Survey with the [[Large Binocular Telescope]] reported a detection of an excess in the [[far infrared]], indicating the presence of exozodiacal dust near the [[habitable zone]] of the star.<ref name=Ertel2018/>

==References== <references> <ref name=SIMBAD>{{cite simbad | title=sig Boo | access-date=2021-01-26 | postscript=. | mode=cs2 }}</ref>

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<ref name=apj746_1_101>{{citation | postscript=. | last1=Boyajian | first1=Tabetha S. | last2=McAlister | first2=Harold A. | last3=van Belle | first3=Gerard | last4=Gies | first4=Douglas R. | last5=ten Brummelaar | first5=Theo A. | last6=von Braun | first6=Kaspar | last7=Farrington | first7=Chris | last8=Goldfinger | first8=P. J. | last9=O'Brien | first9=David | last10=Parks | first10=J. Robert | last11=Richardson | first11=Noel D. | last12=Ridgway | first12=Stephen | last13=Schaefer | first13=Gail | last14=Sturmann | first14=Laszlo | last15=Sturmann | first15=Judit | last16=Touhami | first16=Yamina | last17=Turner | first17=Nils H. | last18=White | first18=Russel | title=Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars | display-authors=1 | journal=The Astrophysical Journal | volume=746 | issue=1 | page=101 | date=February 2012 | doi=10.1088/0004-637X/746/1/101 | arxiv=1112.3316 | bibcode=2012ApJ...746..101B | s2cid=18993744 }}. See Table 10.</ref>

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<ref name=Seach_et_al_2022>{{citation | postscript=. | title=The magnetic fields of β Coronae Borealis and the early F-star σ Bootis | display-authors=1 | last1=Seach | first1=J. M. | last2=Marsden | first2=S. C. | last3=Carter | first3=B. D. | last4=Neiner | first4=C. | last5=Folsom | first5=C. P. | journal=Monthly Notices of the Royal Astronomical Society | volume=513 | issue=3 | pages=4278–4294 | date=July 2022 | doi=10.1093/mnras/stac1173 | doi-access=free | bibcode=2022MNRAS.513.4278S }}</ref>

<ref name=IAU-CSN>{{cite web |title=IAU Catalog of Star Names |url=https://exopla.net/star-names/modern-iau-star-names/ |access-date=20 April 2026}}</ref> </references>

==External links== * [http://webviz.u-strasbg.fr/viz-bin/VizieR-S?HR%205447 HR 5447] * [http://webviz.u-strasbg.fr/viz-bin/VizieR-S?CCDM%20J14347%2b2945A CCDM J14347+2945] * [http://aladin.u-strasbg.fr/AladinPreview?-c=14+34+40.8171%2B29+44+42.468&ident=NSV++6717&submit=Aladin+previewer Image Sigma Boötis]

[[Category:F-type main-sequence stars]] [[Category:Am stars]] [[Category:Suspected variables]]  [[Category:Boötes]] [[Category:Bayer objects|Bootis, Sigma]] [[Category:Bright Star Catalogue objects|5447]] [[Category:Durchmusterung objects|BD+30 2536]] [[Category:Flamsteed objects|Bootis, 28]] [[Category:Gliese and GJ objects|0557]] [[Category:Henry Draper Catalogue objects|128167]] [[Category:Hipparcos objects|071284]] [[Category:Stars with proper names|Genghe]]