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Sigma Coronae Borealis is a multiple star system in the constellation Corona Borealis, the main components of which are three sunlike stars. Appearing as a single star of apparent magnitude 5.3 to the unaided eye, Sigma can be separated into 6.6-magnitude Sigma and 5.64-magnitude Sigma when observed with a telescope. The two take 726 years to orbit each other. The orbit of Sigma is eccentric, with an average distance of 128 AU, and a minimum of 31 AU and maximum of 225 AU. Sigma is a yellow main sequence star of spectral type G1V and weighing around 1 solar mass. Sigma is a spectroscopic binary system composed of two stars very close (6 solar radii) together that orbit each other every 1.14 days. These stars are 1.14 and 1.09 times as massive as the Sun, with spectral types F9V and G0V respectively. Each has a diameter around 1.2 times that of the Sun. They rotate each other very rapidly, and are very active as a result, with prominent star spots and are classed as RS Canum Venaticorum variables. The system emits radio waves. Much further away, at a distance of 14,000 astronomical units (AU), are a pair of red dwarf stars that take 52 years to rotate each other. This pair has an combined apparent magnitude of 12.24. Another pair of faint stars that appear nearby were found to be unrelated.

The system is thought to be anywhere from 100 million to 3 billion years old, from measurement of lithium in its spectrum. Its parallax was measured in 1999, yielding a distance of 74.2 light-years.

References

1. ^ "Sigma Coronae Borealis - Variable of RS CVn type". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Retrieved 23 November 2014.
2. ^ 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: 1014–26. Bibcode:1999A&A...344.1014L.{{cite journal}}: CS1 maint: multiple names: authors list (link)
3. ^ Kaler, James B. "Sigma Coronae Borealis". Stars. University of Illinois. Retrieved 23 November 2014.
4. ^ Raghavan, Deepak; McAlister, Harold A.; Torres, Guillermo; Latham, David W.; Mason, Brian D.; Boyajian, Tabetha S.; Baines, Ellyn K.; Williams, Stephen J.; ten Brummelaar, Theo A.; 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. Bibcode:2009ApJ...690..394R. doi:10.1088/0004-637X/690/1/394.{{cite journal}}: CS1 maint: multiple names: authors list (link)

• 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