Tau Librae

Tau Librae, Latinized from τ Librae, is a binary star system at the southern edge of the zodiac constellation of Libra. It can be seen with the naked eye, having an apparent visual magnitude of 3.68.^[2] The distance to this system is around 367 light years, as determined from an annual parallax shift of 8.89 mas.^[1]

Tau Librae

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Libra
Right ascension	15h 38m 39.36950s[1]
Declination	−29° 46′ 39.8956″[1]
Apparent magnitude (V)	3.68[2]
Characteristics
Spectral type	B2.5 V[3]
U−B color index	−0.717[2]
B−V color index	−0.179[2]
Astrometry
Radial velocity (Rv)	+33.3±2.3[4] km/s
Proper motion (μ)	RA: −22.08[1] mas/yr Dec.: −24.46[1] mas/yr
Parallax (π)	8.89±0.20 mas[1]
Distance	367 ± 8 ly (112 ± 3 pc)
Absolute magnitude (MV)	−1.59[5]
Orbit[6]
Period (P)	3.2907 d
Eccentricity (e)	0.28
Longitude of the node (Ω)	114°
Periastron epoch (T)	2439272.312 JD
Semi-amplitude (K1) (primary)	75 km/s
Semi-amplitude (K2) (secondary)	167 km/s
Details
τ Lib A
Mass	7.25±0.49[7] M☉
Radius	3.2[8] R☉
Luminosity (bolometric)	2,705[7] L☉
Surface gravity (log g)	4.33[9] cgs
Temperature	17,990[9] K
Metallicity [Fe/H]	+0.17[9] dex
Rotational velocity (v sin i)	134[4] km/s
Age	31.5±5.6[10] Myr
Other designations
τ Lib, 40 Lib, CD−29°11837, HD 139365, HIP 76600, HR 5812, SAO 183649[11]
Database references
SIMBAD	data

Judging by its motion through space and physical properties, this system is a member of the Upper Centaurus–Lupus group of the Scorpius–Centaurus association.^[4] It is a double-lined spectroscopic binary^[12] with an orbital period of just 3.3 days and an eccentricity of 0.28.^[6] The primary, component A, is a B-type main sequence star with a stellar classification of B2.5 V.^[3] It is estimated to hold more than seven times the mass of the Sun^[7] and have over three times the Sun's radius.^[8] It is only 31.5 million years old^[10] and is spinning relatively rapidly with a projected rotational velocity of 134 km/s.^[4] It is a heartbeat star system, with pulsations caused by tidal forces.^[13]

The system is emitting an infrared excess, suggesting the presence of a circumstellar disk of material.^[9]