Epsilon Librae

Epsilon Librae is a binary star system in the zodiac constellation Libra. Its name is a Bayer designation that is Latinized from ε Librae, and abbreviated Epsilon Lib or ε Lib. With an apparent visual magnitude of 4.922,^[2] it is bright enough to be seen with the naked eye. Based upon an annual parallax shift of 32.02 mas,^[1] it is located about 102 light years away from the Sun.

Epsilon Librae

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Libra
Right ascension	15h 24m 11.89101s[1]
Declination	−10° 19′ 20.1740″[1]
Apparent magnitude (V)	4.922[2]
Characteristics
Spectral type	F3 V[3] or F5 IV[4]
U−B color index	+0.080[2]
B−V color index	+0.451[2]
Astrometry
Proper motion (μ)	RA: −66.52[1] mas/yr Dec.: −154.24[1] mas/yr
Parallax (π)	32.02±0.72 mas[1]
Distance	102 ± 2 ly (31.2 ± 0.7 pc)
Absolute magnitude (MV)	2.37[5]
Orbit[6]
Period (P)	226.9437±0.0025 d
Semi-major axis (a)	0.85192±0.00359 au
Eccentricity (e)	0.6649±0.0014
Inclination (i)	52.6±9.4[7]°
Periastron epoch (T)	2453593.022 ± 0.041 HJD[8]
Argument of periastron (ω) (secondary)	339.84±0.15°
Details
ε Lib A
Mass	1.17±0.02[6] M☉
Radius	2.159[9] R☉
Luminosity	9.3[10] L☉
Surface gravity (log g)	4.13[10] cgs
Temperature	6,552±80[6] K
Metallicity [Fe/H]	+0.09[10] dex
Rotational velocity (v sin i)	10[5] km/s
Age	1.5[10] Gyr
ε Lib B
Mass	0.410±0.004[6] M☉
Other designations
ε Lib, 31 Lib, BD−09°4138, HD 137052, HIP 75379, HR 5723, SAO 159234[11]
Database references
SIMBAD	data

This is a single-lined spectroscopic binary star system. The pair orbit each other with a period of 226.9 days and an eccentricity of 0.66.^[6] The semimajor axis of their orbit is estimated to be 0.85 AU, or 85% of the distance from the Earth to the Sun. The primary, component A, has been catalogued with stellar classifications of F3 V^[3] and F5 IV,^[4] suggesting that it is an F-type star that either belongs to the main sequence or has evolved into a subgiant as the hydrogen at its core nears exhaustion.

The primary has 1.17 times the mass of the Sun^[6] and 2.16 times the Sun's radius.^[9] It is around 1.5 billion years old^[10] and is spinning with a projected rotational velocity of 10^[5] km/s. The star radiates 9.3 times the solar luminosity^[10] from its outer atmosphere at an effective temperature of 6,552 K.^[6] The secondary, component B, has 41% of the Sun's mass.^[6]