Epsilon Coronae Borealis

Epsilon Coronae Borealis, Latinized from ε Coronae Borealis, 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,[7] meaning it is visible to the unaided eye in all night skies except those brightly lit in inner city locations.[8] It is an orange giant around 1.7 times as massive as the Sun of spectral type K2III,[9] which has exhausted its core fuel supply of hydrogen and swollen to 21 times the Sun's diameter and 151 times its luminosity.[10] That is, Epsilon Coronae Borealis's diameter is about one-quarter of Mercury's orbit.[11] Its surface temperature has been calculated to be 4365 ± 9 K,[10] or 4406 ± 15 K.[9] It is thought to be around 1.74 billion years old.[9]

ε Coronae Borealis
Location of ε Coronae Borealis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Corona Borealis
Right ascension  15h 57m 35.25147s[1]
Declination +26° 52′ 40.3635″[1]
Apparent magnitude (V) 4.13[2]
Characteristics
Spectral type K2 III[2]
U−B color index +1.28[3]
B−V color index +1.235[3]
Astrometry
Radial velocity (Rv)–32.42[2] km/s
Proper motion (μ) RA: –77.07[1] mas/yr
Dec.: –60.61[1] mas/yr
Parallax (π)14.73 ± 0.21[1] mas
Distance221 ± 3 ly
(67.9 ± 1.0 pc)
Absolute magnitude (MV)−0.02[4]
Details
Mass1.44±0.18[5] M☉
Radius21[6] R☉
Luminosity (bolometric)151[2] L☉
Surface gravity (log g)1.94±0.15[5] cgs
Temperature4,365±28[2] K
Metallicity [Fe/H]−0.22±0.03[5] dex
Rotational velocity (v sin i)2.4[6] km/s
Age4.13[2] Gyr
Other designations
13 Coronae Borealis, BD+27° 2558, HD 143107, HIP 78159, HR 5947, SAO 84098[7]
Database references
SIMBADdata

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.[11]

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.[11][12]

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.[9]

Epsilon Coronae Borealis lies one degree north of (and is used as a guide for) the variable T Coronae Borealis.[11]

The Epsilon Coronae Borealis planetary system[13]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥6.7 ± 0.3 MJ 1.3 417.9 ± 0.5 0.11 ± 0.03 — —

References
  1. van Leeuwen, F. (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.
  2. Luck, R. Earle (2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 88, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88.
  3. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Bibcode:1986EgUBV........0M. Cite journal requires |journal= (help)
  4. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  5. Mortier, A.; et al. (September 2013), "New and updated stellar parameters for 71 evolved planet hosts. On the metallicity-giant planet connection", Astronomy & Astrophysics, 557: 19, arXiv:1307.7870, Bibcode:2013A&A...557A..70M, doi:10.1051/0004-6361/201321641, A70.
  6. Massarotti, Alessandro; et al. (January 2008), "Rotational and radial velocities for a sample of 761 HIPPARCOS giants and the role of binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
  7. "eps CrB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-03-17.
  8. Bortle, John E. (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Retrieved 2013-02-20.
  9. 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.
  10. 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.
  11. Kaler, James B. (19 August 2011). "Epsilon and T Coronae Borealis". Stars. University of Illinois. Retrieved 16 November 2014.
  12. SIMBAD, CCDM J15576+2652C -- Star in double system (accessed 16 November 2014)
  13. Jean Schneider (2003). "Planet eps CrB b". Extrasolar Planets Encyclopaedia. Retrieved 4 February 2017.
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