Epsilon Coronae Borealis
Multiple star system in the constellation Corona Borealis
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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,[9] meaning it is visible to the unaided eye in all night skies except those brightly lit in inner city locations.[10]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Corona Borealis |
| Right ascension | 15h 57m 35.25147s[1] |
| Declination | +26° 52â² 40.3635â³[1] |
| Apparent magnitude (V) | 4.13[2] |
| Characteristics | |
| Spectral type | K2 III[2] |
| UâB color index | +1.28[3] |
| BâV color index | +1.235[3] |
| Astrometry | |
| Radial velocity (Rv) | â32.42[2] km/s |
| Proper motion (μ) | RA: â77.07[1] mas/yr Dec.: â60.61[1] mas/yr |
| Parallax (Ï) | 13.4922±0.1023 mas[4] |
| Distance | 242 ± 2 ly (74.1 ± 0.6 pc) |
| Absolute magnitude (MV) | â0.02[5] |
| Details[6] | |
| Mass | 1.37±0.24 Mâ |
| Radius | 21.87+0.98 â0.99 Râ |
| Luminosity (bolometric) | 162.9±9.4 Lâ |
| Surface gravity (log g) | 1.94±0.15[7] cgs |
| Temperature | 4,408±109 K |
| Metallicity [Fe/H] | â0.22±0.03[7] dex |
| Rotational velocity (v sin i) | 2.4[8] km/s |
| Age | 3.24±1.81 Gyr |
| Other designations | |
| 13 Coronae Borealis, BD+27°2558, HD 143107, HIP 78159, HR 5947, SAO 84098, 2MASS J15573523+2652400[9] | |
| Database references | |
| SIMBAD | data |
This star has a stellar spectrum matching the class K2III, which indicate it is a giant star that exhausted its hydrogen supply at its core and evolved.[11] Being 40% more massive than the Sun and 3.2 billion years old, it expanded to over 20 times the Sun's size and cooled to an effective temperature of 4,408 K.[6] That is, Epsilon Coronae Borealis's diameter is about one-quarter of Mercury's orbit.[12] The star radiates with 160 times the Sun's luminosity.[6]
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.[12]
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.[12][13]
Epsilon Coronae Borealis lies one degree north of (and is used as a guide for) the variable T Coronae Borealis.[12]
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 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.[11]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination (°) |
Radius |
|---|---|---|---|---|---|---|
| b | â¥6.7 ± 0.3 MJ | 1.3 | 417.9 ± 0.5 | 0.11 ± 0.03 | â | â |