Epsilon Coronae Borealis

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Epsilon Coronae Borealis
Observation data
Epoch J2000      Equinox
Constellation Corona Borealis
Right ascension 15h 57m 35.25147s [1]
Declination +26° 52′ 40.3635″ [1]
Apparent magnitude (V) 4.13
Evolutionary stage giant
Spectral type K2III [1]
Radial velocity (Rv) –30.92 km/s
Proper motion (μ) RA: -77.07 mas/yr
Dec.: -60.61 mas/yr
Parallax (π) 13.97 ± 0.68 mas
Distance 230 ± 10 ly
(72 ± 3 pc)
Mass 1.7±0.1 M
Radius 21 R
Luminosity (bolometric) 151 L
Temperature 4406 ± 15 K
Metallicity [Fe/H] –0.094 ± 0.001 dex
Age 1.74±0.37 Gyr
Other designations
HD 143107, HR 5947, HIP 78159

Epsilon Coronae Borealis (ε CrB) is a multiple star system in the constellation Corona Borealis located around 230 light-years from the Solar System. It shines with a combined apparent magnitude of 4.13,[1] meaning it is visible to the unaided eye in all night skies except those brightly lit in inner city locations.[2] It is an orange giant around 1.7 times as massive as the Sun of spectral type K2III,[3] which has exhausted its core fuel supply of hydrogen and swollen to 21 times the Sun's diameter and 151 times its luminosity.[4] That is, Epsilon Coronae Borealis's diameter is about one-quarter of Mercury's orbit.[5] Its surface temperature has been calculated to be 4365 ± 9 K,[4] or 4406 ± 15 K.[3] It is thought to be around 1.74 billion years old.[3]

Epsilon Coronae Borealis B is a companion star thought to be an orange dwarf of spectral types K3V to K9V that orbits at a distance of 135 astronomical units, completing one orbit every 900 years.[5]

A faint (magnitude 11.5) star, 1.5 arc minutes away, has been called Epsilon Coronae Borealis C although it is only close by line of sight and is unrelated to the system.[5][6]

The ε CrB star system's radial velocity was observed over seven years from January 2005 to January 2012, during which time a 'wobble' with a period of around 418 days was recorded. This has been calculated to be a planet around 6.7 times as massive as Jupiter orbiting at a distance of 1.3 astronomical units with an eccentricity of 0.11.[3]

Epsilon Coronae Borealis lies one degree north of (and is used as a guide for) the variable T Coronae Borealis.[5]


  1. ^ a b c d SIMBAD, Epsilon Coronae Borealis (accessed 9 September 2012)
  2. ^ Bortle, John E. (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Retrieved 2013-02-20. 
  3. ^ a b c d Lee, B.-C.; Han, I.; Park, M.-G.; Mkrtichian, D. E.; Kim, K.-M. (2012). "A planetary companion around the K giant ɛ Corona Borealis". Astronomy & Astrophysics 546: 5. arXiv:1209.1187. Bibcode:2012A&A...546A...5L. doi:10.1051/0004-6361/201219347. A5. 
  4. ^ a b Massarotti, Alessandro; Latham, David W.; Stefanik, Robert P.; Fogel, Jeffrey (January 2008). "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity". The Astronomical Journal 135 (1): 209–31. Bibcode:2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209. 
  5. ^ a b c d Kaler, James B. (19 August 2011). "Epsilon and T Coronae Borealis". Stars. University of Illinois. Retrieved 16 November 2014. 
  6. ^ SIMBAD, CCDM J15576+2652C -- Star in double system (accessed 16 November 2014)