Eta Coronae Borealis

Eta Coronae Borealis (η Coronae Borealis, η CrB) is a stellar system that lies approximately 58 light-years away. The primary component is a mid-wide binary, while a brown dwarf component is located at a wide separation.

η Coronae Borealis

Location of η Corona Borealis (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Corona Borealis
Right ascension	15^h 23^m 12.31^s[1]
Declination	+30° 17′ 16.17″[1]
Apparent magnitude (V)	5.02
Characteristics
Spectral type	G1V[2] / G3V[2] / L8 [3]
B−V color index	0.56
Astrometry
Radial velocity (Rv)	-7.410 ± 0.054[4] km/s
Proper motion (μ)	RA: 116.83 ± 0.40[1] mas/yr Dec.: -171.37 ± 0.49[1] mas/yr
Parallax (π)	55.98 ± 0.78[1] mas
Distance	58.3 ± 0.8 ly (17.9 ± 0.2 pc)
Orbit[4]
Primary	Eta Coronae Borealis A
Companion	Eta Coronae Borealis B
Period (P)	15189.1 ± 2.9 days
Semi-major axis (a)	0.860 ± 0.003″
Eccentricity (e)	0.277 ± 0.001
Inclination (i)	58.7 ± 0.16°
Longitude of the node (Ω)	22.9 ± 0.19°
Periastron epoch (T)	1892.317 ± 0.031
Argument of periastron (ω) (secondary)	39.24 ± 0.37°
Argument of periastron (ω) (primary)	219.2 ± 0.37°
Semi-amplitude (K1) (primary)	4.709 ± 0.095 km/s
Semi-amplitude (K2) (secondary)	5.276 ± 0.054 km/s
Position (relative to Eta Coronae Borealis AB)[3]
Component	Eta Coronae Borealis C
Angular distance	194″
Position angle	136°
Observed separation (projected)	~3600 AU
Details
Mass	1.19 ± 0.071[4] / 1.05 ± 0.05[4] / 0.060 ± 0.015[3] M☉
Metallicity [Fe/H]	-0.20[5] dex
Age	1-2.5[3] Gyr
Other designations
2 Coronae Borealis, HD 137107/137108, HIP 75312, Gliese 584, HR 5727
Database references
SIMBAD	data

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. The two stars have similar physical parameters, though the secondary is slightly cooler than the primary and has approximately 90% of the primary's mass. Possible stable planetary orbits in the habitable zone were calculated for the system in 1996.[6]

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 M_J.[3]

See also

• 81 Cancri

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. Edwards, T. W. (1976). "MK classification for visual binary components". The Astronomical Journal. 81: 245. Bibcode:1976AJ.....81..245E. doi:10.1086/111879.
3. Kirkpatrick, J. Davy; Dahn, Conard C.; Monet, David G.; Reid, I. Neill; et al. (2001). "Brown Dwarf Companions to G-Type Stars. I. Gliese 417B and Gliese 584C". The Astronomical Journal. 121 (6): 3235. arXiv:astro-ph/0103218. Bibcode:2001AJ....121.3235K. doi:10.1086/321085.
4. Pourbaix, D. (2000). "Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar masses". Astronomy and Astrophysics Supplement Series. 145 (2): 215. Bibcode:2000A&AS..145..215P. doi:10.1051/aas:2000237.
5. Soderblom, D. R. (1983). "Rotational studies of late-type stars. II - Ages of solar-type stars and the rotational history of the sun". The Astrophysical Journal Supplement Series. 53: 1. Bibcode:1983ApJS...53....1S. doi:10.1086/190880.
6. Benest, D. (1996). "Planetary orbits in the elliptic restricted problem. III. The η Coronae Borealis system". Astronomy and Astrophysics. 314: 983–88. Bibcode:1996A&A...314..983B.