Sigma Coronae Borealis

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.

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]
Characteristics
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]
Astrometry
σ CrB A
Radial velocity (Rv)−12.30 ± 0.06[9] km/s
Proper motion (μ) RA: −268.325[10] mas/yr
Dec.: −86.925[10] mas/yr
Parallax (π)44.1346 ± 0.0644[10] mas
Distance73.9 ± 0.1 ly
(22.66 ± 0.03 pc)
σ CrB B
Radial velocity (Rv)−12.30 ± 0.06[9] km/s
Proper motion (μ) RA: −291.118[11] mas/yr
Dec.: −78.651[11] mas/yr
Parallax (π)44.1475 ± 0.0237[11] mas
Distance73.88 ± 0.04 ly
(22.65 ± 0.01 pc)
σ CrB C
Radial velocity (Rv)−16.30 ± 10[12] km/s
Proper motion (μ) RA: −265.92[2] mas/yr
Dec.: −83.63[2] mas/yr
Parallax (π)42.8557 ± 0.3965[13] mas
Distance76.1 ± 0.7 ly
(23.3 ± 0.2 pc)
Orbit[14]
Primaryσ2 CrB primary
Companionσ2 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[14]
Primaryσ2 CrB
Companionσ1 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[15]
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
σ1 CrB
Mass1.0[14] M☉
Surface gravity (log g)4.5[14] cgs
Temperature5950 ± 100[14] K
Rotational velocity (v sin i)3 ± 2[14] km/s
Age1 to 3[14] Myr
σ2 CrB primary
Mass1.137 ± 0.037[14] M☉
Radius1.244 ± 0.050[14] R☉
Surface gravity (log g)4.5[14] cgs
Temperature6050 ± 150[14] K
Metallicity [Fe/H]0.0[14] dex
Rotational velocity (v sin i)26 ± 1[14] km/s
Age0.5 to 1.5[14] Gyr
σ2 CrB secondary
Mass1.090 ± 0.036[14] M☉
Radius1.244 ± 0.050[14] R☉
Surface gravity (log g)4.5[14] cgs
Temperature5870 ± 150[14] K
Rotational velocity (v sin i)26 ± 1[14] km/s
Age0.5 to 1.5[14] Gyr
σ CrB C
Mass0.423 ± 0.042[16] M☉
Radius0.437 ± 0.020[16] R☉
Surface gravity (log g)5.0[17] cgs
Temperature3454 ± 63[16] K
Metallicity [Fe/H]−0.06 ± 0.03[16] dex
Age2.95[16] 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[18]
σ CrB B: σ1 CrB, GJ 9550A, HD 146362, HR 6063, CCDM J16147+3352B, WDS J16147+3352B, TYC 2583-1846-2[19]
σ CrB C: GJ 9549, HIP 79551, WDS J16147+3352E, G 180-42[20]
Database references
SIMBADσ CrB
σ1 CrB
σ2 CrB
σ CrB C
ARICNSσ1 CrB
σ2 CrB
σ CrB C

System components

The brightest components of Sigma Coronae Borealis form a visual binary first resolved in the 19th century,[21] 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 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,[21] but it is usually called Sigma Coronae Borealis C.[14]

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.[14] A visual orbit has been calculated, with a period of about 730 years and a high eccentricity of 0.72.[14]

Sigma2 Corona Borealis itself is a close binary. Here, the two stars are extremely close and orbit fairly quickly, every 1.14 days.[14] This tiny separation of only 0.0279 au[14] 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.[14]

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.[15][14]

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.[21]

Variability

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.[22]

See also

References
  1. 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. van Leeuwen, F.; et al. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  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.
  4. Strassmeier, K. G. (1994). "Chromospheric activity in G and K giants: the spectroscopic data base". Astronomy and Astrophysics Supplement. 103 (103): 413–425. Bibcode:1994A&AS..103..413S.
  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/0308182. Bibcode:2003AJ....126.2048G. doi:10.1086/378365. S2CID 119417105.
  6. 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. "* sig CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 April 2017.
  8. 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/0404219. Bibcode:2004MNRAS.349.1069K. doi:10.1111/j.1365-2966.2004.07588.x. S2CID 15290475.
  10. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  11. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  12. 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.
  13. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  14. 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 (1): 394–406. arXiv:0808.4015. Bibcode:2009ApJ...690..394R. doi:10.1088/0004-637X/690/1/394. S2CID 14638405.
  15. 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.
  16. Mann, Andrew W.; Feiden, Gregory A.; Gaidos, Eric; Boyajian, Tabetha; von Braun, Kaspar (2015). "How to Constrain Your M Dwarf: Measuring Effective Temperature, Bolometric Luminosity, Mass, and Radius". The Astrophysical Journal. 804 (1): 38. arXiv:1501.01635. Bibcode:2015ApJ...804...64M. doi:10.1088/0004-637X/804/1/64. S2CID 19269312.
  17. Lépine, S.; et al. (2013). "A Spectroscopic Catalog of the Brightest (J < 9) M Dwarfs in the Northern Sky". The Astronomical Journal. 145 (4): 102. arXiv:1206.5991. Bibcode:2013AJ....145..102L. doi:10.1088/0004-6256/145/4/102. S2CID 117144290.
  18. "* sig02 CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 April 2017.
  19. "* sig01 CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 April 2017.
  20. "* sig CrB C". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 April 2017.
  21. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  22. Kholopov, P. N.; Samus', N. N.; Kukarkina, N. P.; Medvedeva, G. I.; Perova, N. B. (1981). "65th Name-List of Variable Stars". Information Bulletin on Variable Stars. 1921: 1. Bibcode:1981IBVS.1921....1K.
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