Sigma Coronae Borealis

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Sigma Coronae Borealis
Observation data
Epoch J2000      Equinox J2000
Constellation Corona Borealis
σ CrB A (σ2)
Right ascension 16h 14m 40.854s[1]
Declination +33° 51′ 31.02″[1]
Apparent magnitude (V) 5.55[1]
σ CrB B (σ1)
Right ascension 16h 14m 40.394s[1]
Declination +33° 51′ 27.05″[1]
Apparent magnitude (V) 6.419[1]
σ CrB C
Right ascension 16h 13m 56.26666s[2]
Declination +33° 46′ 24.2953″[2]
Apparent magnitude (V) 12.229[3]
σ CrB
Spectral type F6V (A)[4] + G1V (B)[5]
U−B color index +0.045[6]
B−V color index +0.599[6]
Variable type RS CVn[7]
σ CrB C
Spectral type M2.5V[8]
σ CrB AB
Radial velocity (Rv) −12.30 ± 0.06[9] km/s
Proper motion (μ) RA: −263.39[2] mas/yr
Dec.: −92.67[2] mas/yr
Parallax (π) 43.93 ± 0.10[10] mas
Distance 74.2 ± 0.2 ly
(22.76 ± 0.05 pc)
Absolute magnitude (MV) 4.64 ± 0.01 (σ1 CrB)
4.35 ± 0.02 (σ2 CrB primary)
4.74 ± 0.02 (σ2 CrB secondary)
σ CrB C
Radial velocity (Rv) −16.30 ± 10[11] km/s
Proper motion (μ) RA: −265.92[2] mas/yr
Dec.: −83.63[2] mas/yr
Parallax (π) 45.40 ± 3.71[2] mas
Distance 72 ± 6 ly
(22 ± 2 pc)
Primary σ2 CrB primary
Companion σ2 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)
Primary σ2 CrB
Companion σ1 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)
237.3 ± 6.8°
Primary σ CrB Ca
Companion σ 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)
σ1 CrB
Mass 1.0[12] M
Surface gravity (log g) 4.5[12] cgs
Temperature 5950 ± 100[12] K
Rotational velocity (v sin i) 3 ± 2[12] km/s
Age 1 to 3[12] Myr
σ2 CrB primary
Mass 1.137 ± 0.037[12] M
Radius 1.244 ± 0.050[12] R
Surface gravity (log g) 4.5[12] cgs
Temperature 6050 ± 150[12] K
Metallicity [Fe/H] 0.0[12] dex
Rotational velocity (v sin i) 26 ± 1[12] km/s
Age 0.5 to 1.5[12] Gyr
σ2 CrB secondary
Mass 1.090 ± 0.036[12] M
Radius 1.244 ± 0.050[12] R
Surface gravity (log g) 4.5[12] cgs
Temperature 5870 ± 150[12] K
Rotational velocity (v sin i) 26 ± 1[12] km/s
Age 0.5 to 1.5[12] Gyr
σ CrB C
Mass 0.423 ± 0.042[14] M
Radius 0.437 ± 0.020[14] R
Surface gravity (log g) 5.0[15] cgs
Temperature 3454 ± 63[14] K
Metallicity [Fe/H] −0.06 ± 0.03[14] dex
Age 2.95[14] Gyr
Other designations
σ CrB, 17 CrB, BD+34° 2750, HIP 79607 (only AB), SAO 65165, ADS 9979[7]
σ CrB A: σ2 CrB, TZ CrB, GJ 9550B, HD 146361, HR 6064, CCDM J16147+3352A, WDS J16147+3352A, TYC 2583-1846-1[16]
σ CrB B: σ1 CrB, GJ 9550A, HD 146362, HR 6063, CCDM J16147+3352B, WDS J16147+3352B, TYC 2583-1846-2[17]
σ CrB C: GJ 9549, HIP 79551, WDS J16147+3352E, G 180-42[18]
Database references
σ1 CrB
σ2 CrB
σ CrB C
σ2 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 72 light years from Earth. σ CrB A is the variable star TZ Coronae Borealis.

System components[edit]

The brightest components of Sigma Coronae Borealis form a visual binary first resolved in the 19th century,[19] and are designated σ Corona Borealis A and B. More recently, the designations σ2 and σ1 Corona Borealis have come into use. Somewhat confusingly, the brighter component A is referred to as σ2 because it has the higher right ascension. A third component, while being separated 635&Prime (translating to a minimum distance of 14,000 au), has a similar proper motion to the main system and is physically associated. It is known in the Washington Double Star Catalog (WDS), a compilation of observations of double stars, as component E,[19] but it is usually called Sigma Coronae Borealis C.[12]

Sigma1 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.[12] A visual orbit has been calculated, with a period of about 730 years and a high eccentricity of 0.72.[12]

Sigma2 Corona Borealis itself is a close binary. Here, the two stars are extremely close and orbit fairly quickly, every 1.14 days.[12] This tiny separation of only 0.0279 au[12] 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.[7]

Despite Sigma2 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.[12]

σ Coronae Borealis C, also known as HIP 79551, appears as a red dwarf with a spectral type of M2.5V.[8] 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.[13][12]

Optical companions[edit]

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.[19]


The spectroscopic binary σ2 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.[20]


  1. ^ a b c d e f Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H. 
  2. ^ a b c d e f g van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  3. ^ Zacharias, N.; et al. (2012). "The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)". VizieR On-line Data Catalog. 1322. Bibcode:2012yCat.1322....0Z. 
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  5. ^ Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Robinson, P. E. (2003). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I". The Astronomical Journal. 126 (4): 2048. arXiv:astro-ph/0308182Freely accessible. Bibcode:2003AJ....126.2048G. doi:10.1086/378365. 
  6. ^ a b Rakos, K. D.; Albrecht, R.; Jenkner, H.; Kreidl, T.; Michalke, R.; Oberlerchner, D.; Santos, E.; Schermann, A.; Schnell, A.; Weiss, W. (1982). "Photometric and astrometric observations of close visual binaries". Astronomy and Astrophysics Supplement Series. 47 (221–235): 221. Bibcode:1982A&AS...47..221R. 
  7. ^ a b c "* sig CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 April 2017. 
  8. ^ a b Reid, I. Neill; Hawley, Suzanne L.; Gizis, John E. (1995). "The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics". The Astronomical Journal. 110: 1838. Bibcode:1995AJ....110.1838R. doi:10.1086/117655. 
  9. ^ Karataş, Y.; Bilir, S.; Eker, Z.; Demircan, O. (2004). "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution". Monthly Notices of the Royal Astronomical Society. 349 (3): 1069. arXiv:astro-ph/0404219Freely accessible. Bibcode:2004MNRAS.349.1069K. doi:10.1111/j.1365-2966.2004.07588.x. 
  10. ^ Lestrade, J.-F.; Preston, R. A.; Jones, D. L.; Phillips, R. B.; Rogers, A. E. E.; Titus, M. A.; Rioja, M. J.; Gabuzda, D. C. (1999). "High-precision VLBI astrometry of radio-emitting stars". Astronomy and Astrophysics. 344: 1014. Bibcode:1999A&A...344.1014L. 
  11. ^ Hawley, Suzanne L.; Gizis, John E.; Reid, I. Neill (1996). "The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity". The Astronomical Journal. 112: 2799. Bibcode:1996AJ....112.2799H. doi:10.1086/118222. 
  12. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa Raghavan, Deepak; McAlister, Harold A.; Torres, Guillermo; Latham, David W.; Mason, Brian D.; Boyajian, Tabetha S.; Baines, Ellyn K.; Williams, Stephen J.; Brummelaar, Theo A. ten; Farrington, Chris D.; Ridgway, Stephen T.; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H. (2009). "The Visual Orbit of the 1.1-day Spectroscopic Binary σ2 Coronae Borealis from Interferometry at the CHARA Array". The Astrophysical Journal. 690: 394. arXiv:0808.4015Freely accessible. Bibcode:2009ApJ...690..394R. doi:10.1088/0004-637X/690/1/394. 
  13. ^ a b Heintz, W. D. (1990). "Photographic astrometry of binary and proper-motion stars". The Astronomical Journal. 99: 420. Bibcode:1990AJ.....99..420H. doi:10.1086/115340. 
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  17. ^ "* sig01 CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 April 2017. 
  18. ^ "* sig CrB C". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 April 2017. 
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External links[edit]