Eta Coronae Borealis
Binary star in the constellation Corona Boeralis
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Eta Coronae Borealis is a stellar system in the northern constellation of Corona Borealis. Its name is a Bayer designation that is Latinized from η Coronae Borealis, and abbreviated Eta CrB or η CrB. The system has a combined apparent visual magnitude of 4.98,[2] which means it is faintly visible to the naked eye as a point of light. Based on parallax measurements, it lies at a distance of approximately 55 light-years. The primary component is a mid-wide binary, while a brown dwarf component is located at a wide separation.
 | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Corona Borealis |
| Right ascension | 15h 23m 12.305s[1] |
| Declination | +30° 17′ 16.17″[1] |
| Apparent magnitude (V) | 4.98[2] |
| Characteristics | |
| Spectral type | G1V[3] + G3V[3] + L8 [4] |
| U−B color index | +0.04[2] |
| B−V color index | +0.58[2] |
| Astrometry | |
| Radial velocity (Rv) | −7.410±0.054[5] km/s |
| Proper motion (μ) | RA: +116.83 mas/yr[1] Dec.: −171.37 mas/yr[1] |
| Parallax (π) | 58.786±0.084 mas[6] |
| Distance | 55.48 ± 0.08 ly (17.01 ± 0.02 pc) |
| Orbit[7] | |
| Primary | Eta Coronae Borealis A |
| Name | Eta Coronae Borealis B |
| Period (P) | 15,204.9(1.4) days |
| Semi-major axis (a) | 0.86226(33) mas (15.79±0.27 AU)[6] |
| Eccentricity (e) | 0.27907(26) |
| Inclination (i) | 58.084±0.026° |
| Longitude of the node (Ω) | 202.827±0.024° |
| Periastron epoch (T) | 42,612.9±3.4 |
| Argument of periastron (ω) (secondary) | 39.24±0.37[5]° |
| Argument of periastron (ω) (primary) | 219.2±0.37[5]° |
| Semi-amplitude (K1) (primary) | 4.709±0.095[5] km/s |
| Semi-amplitude (K2) (secondary) | 5.276±0.054[5] km/s |
| Position (relative to Eta Coronae Borealis AB)[8] | |
| Component | Eta Coronae Borealis C |
| Angular distance | 195.3″ |
| Position angle | 136° |
| Projected separation | 3,635 AU |
| Details[9] | |
| A | |
| Mass | 1.243±0.054[7] M☉ |
| Radius | 0.99[a] R☉ |
| Luminosity | 1.2 L☉ |
| Surface gravity (log g) | 4.45 cgs |
| Temperature | 6,060±53 K |
| Metallicity [Fe/H] | −0.03 dex |
| Rotational velocity (v sin i) | 6.6 km/s |
| Age | 2.62+0.50 −0.93 Gyr |
| B | |
| Mass | 1.100±0.039[7] M☉ |
| Radius | 0.89[b] R☉ |
| Luminosity | 0.89 L☉ |
| Surface gravity (log g) | 4.51 cgs |
| Temperature | 5,948±36 K |
| Metallicity [Fe/H] | -0.04 dex |
| Rotational velocity (v sin i) | 7.0 km/s |
| Age | 3.11+1.30 −1.13 Gyr |
| C | |
| Mass | 44±6[10] MJup |
| Radius | 0.95±0.03[10] RJup |
| Luminosity | 1.91+0.28 −0.25×10−5[10] L☉ |
| Surface gravity (log g) | 5.11±0.09[10] cgs |
| Temperature | 1,237±24[10] K |
| Age | 3 to 5[8] Gyr |
| Other designations | |
| 2 Coronae Borealis, BD+30 2653, GJ 584, HIP 75312, HR 5727 | |
| A: HD 137107 | |
| B: HD 137108 | |
| Database references | |
| SIMBAD | data |
| A | |
| B | |
Components
Eta Coronae Borealis has been known since the late 18th century to be a moderate-separation binary. The orbit of the two components takes approximately 42 years, which when combined with the distance to the system makes the two stars fairly easily resolvable with a larger telescope. Possible stable planetary orbits in the habitable zone were calculated for the system in 1996.[11]
This system consists of two G-dwarfs[3] that have similar properties to the Sun.[9] At present the angular separation between both stars is 0.5 arcseconds, so a telescope with a diameter of over 25 centimetres is required to resolve it.[12]
The estimated age of the system is around three billion years. Component A has 1.2 times the mass of the Sun and is radiating 1.2 times the Sun's luminosity from its photosphere at an effective temperature of 6,060 K. Component B has 1.1 times the Sun's mass and radiates nearly double the Sun's luminosity at an effective temperature of 5,948 K.[9]
A brown dwarf companion was detected in 2001. The source 2MASSW J1523226+301456 in the 2MASS working database was identified as having a similar proper motion to the AB binary, and subsequent observations confirmed its relationship to the system. The new component, Eta Coronae Borealis C, was found to have a spectral type of L8. The brown dwarf has a minimum separation of 3600 AU, and considering a cooling age of 1–2.5 gigayears, the brown dwarf has a mass of 0.060 ± 0.015 M☉, or 63 ± 16 MJ.[4]
See also
Notes
- Calculated, using the Stefan-Boltzmann law and the star's effective temperature and luminosity, with respect to the solar nominal effective temperature of 5,772 K:
- Calculated, using the Stefan-Boltzmann law and the star's effective temperature and luminosity, with respect to the solar nominal effective temperature of 5,772 K:
