Epsilon Coronae Borealis
  | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Corona Borealis[1] |
| Right ascension | 15h 57m 35.25147s[2] |
| Declination | +26° 52′ 40.3635″[2] |
| Apparent magnitude (V) | 4.13[3] |
| Characteristics | |
| Spectral type | K2 III[3] |
| U−B color index | +1.28[4] |
| B−V color index | +1.231±0.001[1] |
| Astrometry | |
| Radial velocity (Rv) | −32.42±0.07[3] km/s |
| Proper motion (μ) | RA: −77.716 mas/yr[2] Dec.: −60.971 mas/yr[2] |
| Parallax (π) | 13.4922±0.1023 mas[2] |
| Distance | 242 ± 2 ly (74.1 ± 0.6 pc) |
| Absolute magnitude (MV) | −0.02[1] |
| Details[5] | |
| ε CrB A | |
| Mass | 1.69+0.29 −0.30 M☉ |
| Radius | 23.87±1.04 R☉ |
| Luminosity | 194±5 L☉ |
| Surface gravity (log g) | 1.94±0.15[6] cgs |
| Temperature | 4,408±96 K |
| Metallicity [Fe/H] | −0.22±0.03[6] dex |
| Rotational velocity (v sin i) | 2.4[7] km/s |
| Age | 1,600+1,420 −447 Gyr |
| Other designations | |
| ε CrB, 13 Coronae Borealis, BD+27°2558, FK5 593, GC 21440, HD 143107, HIP 78159, HR 5947, SAO 84098, WDS J15576+2653A, 2MASS J15573523+2652400[8] | |
| Database references | |
| SIMBAD | data |
Epsilon Coronae Borealis is a binary star system in the northern constellation of Corona Borealis. Its name is a Bayer designation that is Latinized from ε Coronae Borealis, and abbreviated Epsilon CrB or ε CrB. This system shines with a combined apparent magnitude of 4.13,[8] meaning it is visible to the unaided eye in all night skies except those brightly lit in inner city locations.[9] Based on parallax measurements, it is located at a distance of around 242 light-years (74 pc) light-years from the Sun. The system is drifting closer with a line of sight velocity component of −32 km/s.[3]
The primary component has a spectrum matching the stellar classification K2III, which suggests it is a giant star that exhausted its hydrogen supply at its core and evolved off the main sequence.[10] Being 70% more massive than the Sun and 1.6 billion years old, it expanded to nearly 24 times the Sun's size and cooled to an effective temperature of 4,408 K.[5] That is, Epsilon Coronae Borealis's diameter is about one-quarter of Mercury's orbit.[11] The star radiates with 194 times the Sun's luminosity.[5]
Epsilon Coronae Borealis B is a companion star thought to be an orange dwarf of spectral type in the range 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, at an angular separation of 1.5′, is designated Epsilon Coronae Borealis C, although it is only close by line of sight and is unrelated to the system.[11][12]
Epsilon Coronae Borealis lies one degree north of (and is used as a guide for) the variable T Coronae Borealis.[11]
Planetary system
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 is inferred to be due to an orbiting exoplanetary companion, calculated as at least 6.7 times as massive as Jupiter orbiting at a distance of 1.3 astronomical units with an eccentricity of 0.11.[10]
| 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 2 3 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 XHIP record for this object at VizieR.
- 1 2 3 4 5 Vallenari, A.; et al. (Gaia collaboration) (2023), "Gaia Data Release 3. Summary of the content and survey properties", Astronomy and Astrophysics, 674: A1, arXiv:2208.00211, Bibcode:2023A&A...674A...1G, doi:10.1051/0004-6361/202243940, S2CID 244398875 Gaia DR3 record for this source at VizieR.
- 1 2 3 4 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, S2CID 118505114.
- ↑ Mermilliod, J.-C. (1986), Compilation of Eggen's UBV data, transformed to UBV (unpublished), SIMBAD, Bibcode:1986EgUBV........0M.
- 1 2 3 Baines, Ellyn K.; et al. (February 2025), "Eighteen Exoplanet Host Stars from the NPOI Data Archive", The Astronomical Journal, 169 (2), id. 83, arXiv:2506.02934, Bibcode:2025AJ....169...83B, doi:10.3847/1538-3881/ad9bb1.
- 1 2 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, S2CID 55027519, A70.
- ↑ 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.
- 1 2 "eps CrB", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-03-17.
- ↑ Bortle, John E. (February 2001), "The Bortle Dark-Sky Scale", Sky & Telescope, Sky Publishing Corporation, archived from the original on 2014-03-31, retrieved 2013-02-20.
- 1 2 Lee, B.-C.; et al. (2012), "A planetary companion around the K giant ɛ Corona Borealis", Astronomy & Astrophysics, 546, arXiv:1209.1187, Bibcode:2012A&A...546A...5L, doi:10.1051/0004-6361/201219347, S2CID 55260442, A5.
- 1 2 3 4 Kaler, James B. (19 August 2011). "Epsilon and T Coronae Borealis". Stars. University of Illinois. Retrieved 16 November 2014.
- ↑ "CCDM J15576+2652C", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2014-11-16.
- ↑ Schneider, Jean (2003), "Planet eps CrB b", Extrasolar Planets Encyclopaedia, retrieved 4 February 2017.
