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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.

Components

The brightest components of Sigma Coronae Borealis form a visual binary and are designated Sigma Corona Borealis and Sigma Corona Borealis, also known as Sigma Corona Borealis B and Sigma Corona Borealis A, respectively. (Sigma Corona Borealis received the designation A because it is the brighter component.) 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 for Sigma and Sigma Corona Borealis has been calculated, with an orbital 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. For that reason they bear the variable star designation TZ Coronae Borealis.

Despite Sigma Corona Borealis's two stars being extremely close and difficult to resolve, this was done successfully 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.

Sigma Coronae Borealis has one common proper motion companion: a star or star system that shares the same motion throughout space and must be physically related. That companion is called Sigma Coronae Borealis C, also known as HIP 79551. It is a red dwarf with a spectral type of M2.5V. It too is thought to be a binary star itself, 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 cas 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. A third component, while being separated 635″ (translating to a minimum distance of 14,000 au), has a similar proper motion to the main system: while it is known in the WDS as component E, it is also called Sigma Coronae Borealis C.

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.
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.
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.{{cite journal}}: CS1 maint: unflagged free DOI (link)
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. ^ 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 σ Coronae Borealis from Interferometry at the CHARA Array". The Astrophysical Journal. 690: 394. arXiv:0808.4015. Bibcode:2009ApJ...690..394R. doi:10.1088/0004-637X/690/1/394.
13. ^ 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.
14. ^ . arXiv:1501.01635. Bibcode:2015ApJ...804...64M. doi:10.1088/0004-637X/804/1/64. {{cite journal}}: Cite journal requires |journal= (help); Missing or empty |title= (help)
15. Lépine, S.; et al. (2013). "A Spectroscopic Catalog of the Brightest (J < 9) M Dwarfs in the Northern Sky". The Astronomical Journal. 145 (4). arXiv:1206.5991. Bibcode:2013AJ....145..102L. doi:10.1088/0004-6256/145/4/102.
16. ^ "* sig01 CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 April 2017.
17. ^ "* sig02 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.

See also

• Xi Ursae Majoris, a quintuple containing an RS CVn binary

External links

• Kaler, James B. "Sigma Coronae Borealis". Stars. University of Illinois.

• Corona Borealis (constellation)
• Henry Draper Catalogue objects
• Bayer objects
• Objects named with variable star designations
• Flamsteed objects
• HR objects
• F-type main-sequence stars
• G-type main-sequence stars
• Hipparcos objects
• Multiple star systems
• RS Canum Venaticorum variables