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{{Short description|Star in the constellation Corona Borealis}}{{distinguish|S Coronae Borealis}}
{{Starbox begin
| name=Sigma Coronae Borealis {{Starbox begin|title=Sigma Coronae Borealis}}
{{Starbox image
| image = ]
| caption = A ] for TZ Coronae Borealis, plotted from ] data<ref name=MAST/>
}} }}
{{Starbox observe {{Starbox observe 3s
| epoch=J2000 |epoch=]
|constell=]
| ra={{RA|16|14|40.85557}}<ref name="SIMBAD">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Sigma+Coronae+Borealis&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id |title = Sigma Coronae Borealis - Variable of RS CVn type|work = SIMBAD Astronomical Database|publisher=Centre de Données astronomiques de Strasbourg|accessdate = 23 November 2014}}</ref>
|component1=σ CrB A (σ<sup>2</sup>)
| dec={{DEC|+33|51|30.9497}}<ref name="SIMBAD"/>
|ra1={{RA|16|14|40.854}}<ref name=TYC2>{{cite journal|title=The Tycho-2 catalogue of the 2.5 million brightest stars|author=Høg, E.|display-authors=etal|date=2000|journal=Astronomy and Astrophysics|volume=355|pages=L27–L30|bibcode=2000A&A...355L..27H}}</ref>
| appmag_v=5.64<ref name="SIMBAD"/>
|dec1={{DEC|+33|51|31.02}}<ref name=TYC2/>
| constell=]
|appmag_v1=5.55<ref name=TYC2/>
|component2=σ CrB B (σ<sup>1</sup>)
|ra2={{RA|16|14|40.394}}<ref name=TYC2/>
|dec2={{DEC|+33|51|27.05}}<ref name=TYC2/>
|appmag_v2=6.419<ref name=TYC2/>
|component3=σ CrB C
|ra3={{RA|16|13|56.26666}}<ref name=HIP>{{cite journal|title=Validation of the new Hipparcos reduction|url=http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2007A%2526A...474..653VFUL|author=van Leeuwen, F.|display-authors=etal|journal=Astronomy and Astrophysics|volume=474|issue=2|pages=653–664|date=2007|arxiv=0708.1752|bibcode=2007A&A...474..653V|doi=10.1051/0004-6361:20078357|s2cid = 18759600}}</ref>
|dec3={{DEC|+33|46|24.2953}}<ref name=HIP/>
|appmag_v3=12.229<ref name=UCAC4>{{cite journal|author=Zacharias, N.|display-authors=etal|title=The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)|journal=VizieR On-line Data Catalog|volume=1322|date=2012|bibcode=2012yCat.1322....0Z}}</ref>
}}
{{Starbox character
|component1=σ CrB
|class=F6V (A)<ref name=Strassmeier>{{cite journal|title=Chromospheric activity in G and K giants: the spectroscopic data base|author=Strassmeier, K. G.|journal=Astronomy and Astrophysics Supplement|volume=103|number=103|pages=413–425|bibcode=1994A&AS..103..413S|date=1994}}</ref> + G1V (B)<ref name=Gray>{{cite journal|bibcode=2003AJ....126.2048G|doi=10.1086/378365|arxiv=astro-ph/0308182|title=Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I|journal=The Astronomical Journal|volume=126|issue=4|pages=2048|year=2003|last1=Gray|first1=R. O.|last2=Corbally|first2=C. J.|last3=Garrison|first3=R. F.|last4=McFadden|first4=M. T.|last5=Robinson|first5=P. E.|s2cid=119417105}}</ref>
|b-v=+0.599<ref name=UBV>{{cite journal|title=Photometric and astrometric observations of close visual binaries|author1=Rakos, K. D.|author2=Albrecht, R.|author3=Jenkner, H.|author4=Kreidl, T.|author5=Michalke, R.|author6=Oberlerchner, D.|author7=Santos, E.|author8=Schermann, A.|author9=Schnell, A.|author10=Weiss, W.|journal=Astronomy and Astrophysics Supplement Series|volume=47|issue=221–235|pages=221|date=1982|bibcode=1982A&AS...47..221R}}</ref>
|u-b=+0.045<ref name=UBV/>
|variable=]<ref name=SimbadAB/>
|component2=σ CrB C
|class2=M2.5V<ref name=Reid>{{cite journal|doi=10.1086/117655|bibcode=1995AJ....110.1838R|title=The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics|journal=The Astronomical Journal|volume=110|pages=1838|year=1995|last1=Reid|first1=I. Neill|last2=Hawley|first2=Suzanne L.|last3=Gizis|first3=John E.|doi-access=free}}</ref>
}}
{{Starbox astrometry
|component1=σ CrB A
|radial_v=−12.30 ± 0.06<ref name=Karatas>{{cite journal |doi=10.1111/j.1365-2966.2004.07588.x
| title=Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution | journal=Monthly Notices of the Royal Astronomical Society
| volume=349 | issue=3 | pages=1069–1092
| bibcode=2004MNRAS.349.1069K |arxiv = astro-ph/0404219 | last1=Karataș
| first1=Yüksel
| last2=Bilir |first2=Selçuk
| last3=Eker |first3=Zeki
| last4=Demircan |first4=Osman
| last5=Liebert |first5=James
| last6=Hawley |first6=Suzanne L.
| last7=Fraser |first7=Oliver J.
| last8=Covey |first8=Kevin R.
| last9=Lowrance |first9=Patrick
| last10=Kirkpatrick |first10=J. Davy
| last11=Burgasser |first11=Adam J.
| year=2004
| doi-access=free | s2cid=15290475
}}</ref>
|prop_mo_ra=−268.325<ref name=dr2a/>
|prop_mo_dec=−86.925<ref name=dr2a/>
|parallax=44.1346
|p_error=0.0644
|parallax_footnote=<ref name=dr2a>{{cite DR2|1328866562170960512}}</ref>
|component2=σ CrB B
|radial_v2=−12.30 ± 0.06<ref name=Karatas/>
|prop_mo_ra2=−291.118<ref name=dr2b/>
|prop_mo_dec2=−78.651<ref name=dr2b/>
|parallax2=44.1475
|p_error2=0.0237
|parallax_footnote2=<ref name=dr2b>{{cite DR2|1328866562170960384}}</ref>
<!--|absmag_v=4.64 ± 0.01 (σ<sup>1</sup> CrB)<br/>4.35 ± 0.02 (σ<sup>2</sup> CrB primary)<br/>4.74 ± 0.02 (σ<sup>2</sup> CrB secondary)-->
}}
{{Starbox astrometry|no_heading=y
|component1=σ CrB C
|radial_v=−16.30 ± 10<ref name=Hawley>{{cite journal|bibcode=1996AJ....112.2799H|doi=10.1086/118222|title=The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity|journal=The Astronomical Journal|volume=112|pages=2799|year=1996|last1=Hawley|first1=Suzanne L.|last2=Gizis|first2=John E.|last3=Reid|first3=I. Neill}}</ref>
|prop_mo_ra=−265.92<ref name=HIP/>
|prop_mo_dec=−83.63<ref name=HIP/>
|parallax=42.8557
|p_error=0.3965
|parallax_footnote=<ref name=dr2c>{{cite DR2|1322906861255829376}}</ref>
|absmag_v=
}}
{{Starbox orbit
|reference=<ref name=Raghavan>{{cite journal|bibcode=2009ApJ...690..394R|doi=10.1088/0004-637X/690/1/394|arxiv=0808.4015|title=The Visual Orbit of the 1.1-day Spectroscopic Binary σ<sup>2</sup> Coronae Borealis from Interferometry at the CHARA Array|journal=The Astrophysical Journal|volume=690|issue=1|pages=394–406|year=2009|last1=Raghavan|first1=Deepak|last2=McAlister|first2=Harold A.|last3=Torres|first3=Guillermo|last4=Latham|first4=David W.|last5=Mason|first5=Brian D.|last6=Boyajian|first6=Tabetha S.|last7=Baines|first7=Ellyn K.|last8=Williams|first8=Stephen J.|last9=Brummelaar|first9=Theo A. ten|last10=Farrington|first10=Chris D.|last11=Ridgway|first11=Stephen T.|last12=Sturmann|first12=Laszlo|last13=Sturmann|first13=Judit|last14=Turner|first14=Nils H.|s2cid=14638405}}</ref>
|primary=σ<sup>2</sup> CrB primary
|name=σ<sup>2</sup> CrB secondary
|period_unitless=1.139791423(80)
|axis_unitless=1.225 ± 0.013 mas
|eccentricity=0.0
|inclination=28.08 ± 0.34
|node=207.93 ± 0.67
|periastron=''T''<sub>node</sub>&nbsp;{{=}}&nbsp;2450127.04855(20)
|periarg=0.0
}}
{{Starbox orbit
|reference=<ref name=Raghavan/>
|primary=σ<sup>2</sup> CrB
|name=σ<sup>1</sup> CrB
|period=726 ± 62
|axis=5.26 ± 0.35
|eccentricity=0.72 ± 0.01
|inclination=32.3 ± 4.1
|node=28.0 ± 0.5
|periastron=] 1825.2 ± 1.5
|periarg_primary=237.3 ± 6.8
}}
{{Starbox orbit
|reference=<ref name=Heintz/>
|primary=σ CrB Ca
|name=σ CrB Cb
|period=52
|axis=0.111
|eccentricity=0.36
|inclination=59
|node=30
|periastron=B 1963.0
|periarg=127
}}
{{Starbox detail
|component1=σ<sup>1</sup> CrB
|mass=1.0<ref name=Raghavan/>
|radius=
|temperature=5950 ± 100<ref name=Raghavan/>
|rotational_velocity=3 ± 2<ref name=Raghavan/>
|metal_fe=
|gravity=4.5<ref name=Raghavan/>
|luminosity=
|age_myr=1 to 3<ref name=Raghavan/>
}}
{{Starbox detail|no_heading=y
|component1=σ<sup>2</sup> CrB primary
|mass=1.137 ± 0.037<ref name=Raghavan/>
|radius=1.244 ± 0.050<ref name=Raghavan/>
|temperature=6050 ± 150<ref name=Raghavan/>
|rotational_velocity=26 ± 1<ref name=Raghavan/>
|metal_fe=0.0<ref name=Raghavan/>
|gravity=4.5<ref name=Raghavan/>
|luminosity=
|age_gyr=0.5 to 1.5<ref name=Raghavan/>
|component2=σ<sup>2</sup> CrB secondary
|mass2=1.090 ± 0.036<ref name=Raghavan/>
|radius2=1.244 ± 0.050<ref name=Raghavan/>
|temperature2=5870 ± 150<ref name=Raghavan/>
|rotational_velocity2=26 ± 1<ref name=Raghavan/>
|metal_fe2=0.0<ref name=Raghavan/>
|gravity2=4.5<ref name=Raghavan/>
|luminosity2=
|age_gyr2=0.5 to 1.5<ref name=Raghavan/>
}}
{{Starbox detail|no_heading=y
|component1=σ CrB C
|mass=0.423 ± 0.042<ref name=Mann>{{cite journal|bibcode=2015ApJ...804...64M|arxiv=1501.01635|doi=10.1088/0004-637X/804/1/64|title=How to Constrain Your M Dwarf: Measuring Effective Temperature, Bolometric Luminosity, Mass, and Radius|author1=Mann, Andrew W.|author2=Feiden, Gregory A.|author3=Gaidos, Eric|author4=Boyajian, Tabetha|author5=von Braun, Kaspar|journal=The Astrophysical Journal|volume=804|issue=1|pages=38|date=2015|s2cid=19269312}}</ref><!-- not the theoretical values -->
|radius=0.437 ± 0.020<ref name=Mann/>
|temperature=3454 ± 63<ref name=Mann/>
|metal_fe=−0.06 ± 0.03<ref name=Mann/>
|gravity=5.0<ref name=Lepine>{{cite journal|title=A Spectroscopic Catalog of the Brightest (J < 9) M Dwarfs in the Northern Sky|author=Lépine, S.|display-authors=etal|date=2013|journal=The Astronomical Journal|volume=145|issue=4|pages=102|bibcode=2013AJ....145..102L|doi=10.1088/0004-6256/145/4/102|arxiv=1206.5991|s2cid=117144290}}</ref>
|age_gyr=2.95<ref name=Mann/><!-- 10^(9.47 ± 0.58) -->
}} }}
{{Starbox catalog {{Starbox catalog
|names={{odlist|ADS=9979|B=σ CrB|F=17 CrB|BD=+34° 2750|HIP=79607 (only AB)|SAO=65165}}<ref name=SimbadAB>{{cite simbad|title=* sig CrB|access-date=20 April 2017}}</ref>
| names= Sigma Coronae Borealis, TZ Coronae Borealis, ] 146361, ]+34° 2750, ] 79607, ] 21863, ] 65165.
|component1=σ CrB A
|names1={{odlist|B=σ<sup>2</sup> CrB|V=TZ CrB|HR=6064|HD=146361|GJ=9550B|TYC=2583-1846-1|WDS=J16147+3352A|CCDM=J16147+3352A}}<ref name=Simbad2>{{cite simbad|title=* sig02 CrB|access-date=20 April 2017}}</ref>
|component2=σ CrB B
|names2={{odlist|B=σ<sup>1</sup> CrB|HR=6063|HD=146362|GJ=9550A|TYC=2583-1846-2|WDS=J16147+3352B|CCDM=J16147+3352B}}<ref name=Simbad1>{{cite simbad|title=* sig01 CrB|access-date=20 April 2017}}</ref>
|component3=σ CrB C
|names3={{odlist|GJ=9549|G=180-42|HIP=79551|WDS=J16147+3352E}}<ref name=SimbadC>{{cite simbad|title=* sig CrB C|access-date=20 April 2017}}</ref>
}}
{{Starbox reference
|Simbad=sig+CrB|sn=σ CrB
|Simbad2=HD+146361A|sn2=σ<sup>1</sup> CrB
|Simbad3=HD+146362|sn3=σ<sup>2</sup> CrB
|Simbad4=sig+CrB+C|sn4=σ CrB C
|ARICNS=01274|an=σ<sup>1</sup> CrB
|ARICNS2=01275|an2=σ<sup>2</sup> CrB
|ARICNS3=01276|an3=σ CrB C
}} }}
{{Starbox end}} {{Starbox end}}

'''Sigma Coronae Borealis''' is a multiple star system in the constellation ], the main components of which are three sunlike stars.<ref name=kalersigma>{{cite web| first1=James B. | last1=Kaler | title=Sigma Coronae Borealis | work=Stars | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/sigmacrb.html | accessdate=23 November 2014}}</ref> Appearing as a single star of apparent magnitude 5.64 to the unaided eye, Sigma can be separated into Sigma<sup>1</sup> and Sigma<sup>2</sup> when observed with a telescope. The two take 726 years to orbit each other. Sigma<sup>1</sup> is a yellow main sequence star of spectral type G1V and weighing around 1 ]. Sigma<sup>2</sup> is a spectroscopic binary system composed of two stars very close (6 solar radii) together that orbit each other every 1.14 days.
'''Sigma Coronae Borealis''' ('''σ CrB''') is a ] in the ] of ]. It is a quintuple ] containing three sunlike ]s and two other low-mass stars. The combined ] is 5.3 and the system lies 74 light years from Earth. σ CrB A is the ] '''TZ Coronae Borealis'''.

==System components==
The brightest components of Sigma Coronae Borealis form a visual ] with an angular separation of 7 arcsecond first resolved in the 19th century,<ref name=wds>{{cite journal|bibcode=2001AJ....122.3466M|title=The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog|journal=The Astronomical Journal|volume=122|issue=6|pages=3466|last1=Mason|first1=Brian D.|last2=Wycoff|first2=Gary L.|last3=Hartkopf|first3=William I.|last4=Douglass|first4=Geoffrey G.|last5=Worley|first5=Charles E.|year=2001|doi=10.1086/323920|doi-access=free}}</ref> and are designated σ Corona Borealis A and B. More recently, the designations σ<sup>2</sup> and σ<sup>1</sup> Corona Borealis have come into use. Somewhat confusingly, the brighter component A is referred to as σ<sup>2</sup> because it has the higher ]. A third component, while being separated by {{val|635|ul="}} (translating to a minimum distance of 14,000 au), has a similar parallax and ] to the brighter stars and is physically associated. It is known in the ] (WDS), a compilation of observations of double stars, as component E,<ref name=wds/> but it is usually called Sigma Coronae Borealis C.<ref name=Raghavan/>

Sigma<sup>1</sup> Corona Borealis is a ] like the ], and has similar parameters: a mass roughly equal to that of the Sun, and an ] of 5950 ].<ref name=Raghavan/> A visual ] has been calculated, with a ] of about 730 years and a high ] of 0.72.<ref name=Raghavan/>

Sigma<sup>2</sup> Corona Borealis itself is a close binary. Here, the two stars are extremely close and orbit fairly quickly, every 1.14 days.<ref name=Raghavan/> This tiny separation of only 0.0279 ]<ref name=Raghavan/> has allowed the two stars to exert ]s on each other, leading to synchronization of their rotation. They have also been classified as ]s (RS CVn)—young, active stars that show variability in their apparent magnitude due to ]s on their surfaces.<ref name=SimbadAB/>

Despite Sigma<sup>2</sup> Corona Borealis's two stars being separated only by about the diameter of each star, they were ] using the ] ] at the ]. As of 2006, it is the shortest-period binary ever to be resolved. The primary is 13.7% more massive than the Sun, while the secondary is 9.0% more massive than the Sun, and both are 24.4% wider than the Sun.<ref name=Raghavan/>

σ Coronae Borealis C, also known as HIP 79551, appears as a ] with a ] of M2.5V.<ref name=Reid/> It too is a binary star, with a companion in a 52-year orbit. The companion has a mass of {{solar mass|0.10}} and has been detected through ].<ref name=Heintz>{{cite journal|doi=10.1086/115340|bibcode=1990AJ.....99..420H|title=Photographic astrometry of binary and proper-motion stars|journal=The Astronomical Journal|volume=99|pages=420|year=1990|last1=Heintz|first1=W. D.}}</ref><ref name=Raghavan/>

==Optical companions==
The ] (WDS), a compilation of observations of double stars, lists several components to the main system. Two of those are listed in the WDS as components C, and D. As of 1984, component C was separated from the primary by {{val|18|u="}} along a ] of 103° and as of 1996, component D was separated from the primary by {{val|88|u="}} along a ] of 82°. However, both of them have different ]s through space and are not related, just optical alignments.<ref name=wds/>

==Variability==
The spectroscopic binary σ<sup>2</sup> CrB is an ]. It varies in brightness by 0.05 magnitudes every 1.139789 days, the same as the orbital period. The brightness changes are caused by variations in surface brightness on the stars, effectively giant sunspots. ]s are not given to stars with ]s, but in this case only one component of σ Coronae Borealis is identified as variable, so it has the designation TZ Coronae Borealis.<ref name=ibvs>{{cite journal|bibcode=1981IBVS.1921....1K|title=65th Name-List of Variable Stars|journal=Information Bulletin on Variable Stars|volume=1921|pages=1|last1=Kholopov|first1=P. N.|last2=Samus'|first2=N. N.|last3=Kukarkina|first3=N. P.|last4=Medvedeva|first4=G. I.|last5=Perova|first5=N. B.|year=1981}}</ref>

==See also==
*], another quintuple containing an RS CVn binary


==References== ==References==
{{reflist}} {{reflist|refs=

<ref name=MAST>{{cite web |title=MAST: Barbara A. Mikulski Archive for Space Telescopes |url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html |publisher=Space Telescope Science Institute |access-date=8 December 2021}}</ref>

}}

==External links==
*{{cite web|first1=James B.|last1=Kaler|title=Sigma Coronae Borealis|work=Stars|publisher=University of Illinois|url=http://stars.astro.illinois.edu/sow/sigmacrb.html}}


{{Stars of Corona Borealis}} {{Stars of Corona Borealis}}


{{DEFAULTSORT:Sigma Coronae Borealis}}
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Latest revision as of 20:59, 22 August 2024

Star in the constellation Corona BorealisNot to be confused with S Coronae Borealis.
Sigma Coronae Borealis

A light curve for TZ Coronae Borealis, plotted from TESS data
Observation data
Epoch J2000      Equinox J2000
Constellation Corona Borealis
σ CrB A (σ)
Right ascension 16 14 40.854
Declination +33° 51′ 31.02″
Apparent magnitude (V) 5.55
σ CrB B (σ)
Right ascension 16 14 40.394
Declination +33° 51′ 27.05″
Apparent magnitude (V) 6.419
σ CrB C
Right ascension 16 13 56.26666
Declination +33° 46′ 24.2953″
Apparent magnitude (V) 12.229
Characteristics
σ CrB
Spectral type F6V (A) + G1V (B)
U−B color index +0.045
B−V color index +0.599
Variable type RS CVn
σ CrB C
Spectral type M2.5V
Astrometry
σ CrB A
Radial velocity (Rv)−12.30 ± 0.06 km/s
Proper motion (μ) RA: −268.325 mas/yr
Dec.: −86.925 mas/yr
Parallax (π)44.1346 ± 0.0644 mas
Distance73.9 ± 0.1 ly
(22.66 ± 0.03 pc)
σ CrB B
Radial velocity (Rv)−12.30 ± 0.06 km/s
Proper motion (μ) RA: −291.118 mas/yr
Dec.: −78.651 mas/yr
Parallax (π)44.1475 ± 0.0237 mas
Distance73.88 ± 0.04 ly
(22.65 ± 0.01 pc)
σ CrB C
Radial velocity (Rv)−16.30 ± 10 km/s
Proper motion (μ) RA: −265.92 mas/yr
Dec.: −83.63 mas/yr
Parallax (π)42.8557 ± 0.3965 mas
Distance76.1 ± 0.7 ly
(23.3 ± 0.2 pc)
Orbit
Primaryσ CrB primary
Companionσ CrB secondary
Period (P)1.139791423(80)
Semi-major axis (a)1.225 ± 0.013 mas
Eccentricity (e)0.0
Inclination (i)28.08 ± 0.34°
Longitude of the node (Ω)207.93 ± 0.67°
Periastron epoch (T)Tnode = 2450127.04855(20)
Argument of periastron (ω)
(secondary)		0.0°
Orbit
Primaryσ CrB
Companionσ CrB
Period (P)726 ± 62 yr
Semi-major axis (a)5.26 ± 0.35″
Eccentricity (e)0.72 ± 0.01
Inclination (i)32.3 ± 4.1°
Longitude of the node (Ω)28.0 ± 0.5°
Periastron epoch (T)B 1825.2 ± 1.5
Argument of periastron (ω)
(primary)		237.3 ± 6.8°
Orbit
Primaryσ CrB Ca
Companionσ CrB Cb
Period (P)52 yr
Semi-major axis (a)0.111″
Eccentricity (e)0.36
Inclination (i)59°
Longitude of the node (Ω)30°
Periastron epoch (T)B 1963.0
Argument of periastron (ω)
(secondary)		127°
Details
σ CrB
Mass1.0 M☉
Surface gravity (log g)4.5 cgs
Temperature5950 ± 100 K
Rotational velocity (v sin i)3 ± 2 km/s
Age1 to 3 Myr
σ CrB primary
Mass1.137 ± 0.037 M☉
Radius1.244 ± 0.050 R☉
Surface gravity (log g)4.5 cgs
Temperature6050 ± 150 K
Metallicity 0.0 dex
Rotational velocity (v sin i)26 ± 1 km/s
Age0.5 to 1.5 Gyr
σ CrB secondary
Mass1.090 ± 0.036 M☉
Radius1.244 ± 0.050 R☉
Surface gravity (log g)4.5 cgs
Temperature5870 ± 150 K
Metallicity 0.0 dex
Rotational velocity (v sin i)26 ± 1 km/s
Age0.5 to 1.5 Gyr
σ CrB C
Mass0.423 ± 0.042 M☉
Radius0.437 ± 0.020 R☉
Surface gravity (log g)5.0 cgs
Temperature3454 ± 63 K
Metallicity −0.06 ± 0.03 dex
Age2.95 Gyr
Other designations
σ CrB, 17 CrB, BD+34° 2750, HIP 79607 (only AB), SAO 65165, ADS 9979
σ CrB A: σ CrB, TZ CrB, GJ 9550B, HD 146361, HR 6064, CCDM J16147+3352A, WDS J16147+3352A, TYC 2583-1846-1
σ CrB B: σ CrB, GJ 9550A, HD 146362, HR 6063, CCDM J16147+3352B, WDS J16147+3352B, TYC 2583-1846-2
σ CrB C: GJ 9549, HIP 79551, WDS J16147+3352E, G 180-42
Database references
SIMBADσ CrB
σ CrB
σ CrB
σ CrB C
ARICNSσ CrB
σ CrB
σ CrB C

Sigma Coronae Borealis (σ CrB) is a star system in the constellation of Corona Borealis. It is a quintuple star system containing three sunlike main-sequence stars and two other low-mass stars. The combined visual magnitude is 5.3 and the system lies 74 light years from Earth. σ CrB A is the variable star TZ Coronae Borealis.

System components

The brightest components of Sigma Coronae Borealis form a visual binary with an angular separation of 7 arcsecond first resolved in the 19th century, and are designated σ Corona Borealis A and B. More recently, the designations σ and σ Corona Borealis have come into use. Somewhat confusingly, the brighter component A is referred to as σ because it has the higher right ascension. A third component, while being separated by 635″ (translating to a minimum distance of 14,000 au), has a similar parallax and proper motion to the brighter stars and is physically associated. It is known in the Washington Double Star Catalog (WDS), a compilation of observations of double stars, as component E, but it is usually called Sigma Coronae Borealis C.

Sigma Corona Borealis is a G-type main-sequence star like the Sun, and has similar parameters: a mass roughly equal to that of the Sun, and an effective temperature of 5950 K. A visual orbit has been calculated, with a period of about 730 years and a high eccentricity of 0.72.

Sigma Corona Borealis itself is a close binary. Here, the two stars are extremely close and orbit fairly quickly, every 1.14 days. This tiny separation of only 0.0279 au has allowed the two stars to exert tidal forces on each other, leading to synchronization of their rotation. They have also been classified as RS Canum Venaticorum variables (RS CVn)—young, active stars that show variability in their apparent magnitude due to starspots on their surfaces.

Despite Sigma Corona Borealis's two stars being separated only by about the diameter of each star, they were resolved using the CHARA optical interferometer at the Mount Wilson Observatory. As of 2006, it is the shortest-period binary ever to be resolved. The primary is 13.7% more massive than the Sun, while the secondary is 9.0% more massive than the Sun, and both are 24.4% wider than the Sun.

σ Coronae Borealis C, also known as HIP 79551, appears as a red dwarf with a spectral type of M2.5V. It too is a binary star, with a companion in a 52-year orbit. The companion has a mass of 0.10 M☉ and has been detected through astrometry.

Optical companions

The Washington Double Star Catalog (WDS), a compilation of observations of double stars, lists several components to the main system. Two of those are listed in the WDS as components C, and D. As of 1984, component C was separated from the primary by 18″ along a position angle of 103° and as of 1996, component D was separated from the primary by 88″ along a position angle of 82°. However, both of them have different proper motions through space and are not related, just optical alignments.

Variability

The spectroscopic binary σ CrB is an RS Canum Venaticorum variable. It varies in brightness by 0.05 magnitudes every 1.139789 days, the same as the orbital period. The brightness changes are caused by variations in surface brightness on the stars, effectively giant sunspots. Variable star designations are not given to stars with Bayer designations, but in this case only one component of σ Coronae Borealis is identified as variable, so it has the designation TZ Coronae Borealis.

See also

References

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