Theta Antliae

Theta Antliae is a binary star system in the southern constellation of Antlia. Its identifier is a Bayer designation that was Latinized from θ Antliae, and is abbreviated Tet Ant or θ Ant, respectively. The pair have a combined apparent visual magnitude of +4.78,^[3] which is bright enough to be faintly visible to the naked eye. The brighter component is magnitude +5.30 while the secondary is +6.18.^[8] Based upon parallax measurements, it is located at a distance of around 340 light-years (104 parsecs) from Earth. The system is receding with a heliocentric radial velocity of +24 km/s.^[5]

θ Antliae

Location of θ Antliae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Antlia[1]
Right ascension	09h 44m 12.09512s[2]
Declination	−27° 46′ 10.1011″[2]
Apparent magnitude (V)	4.79[3]
Characteristics
Spectral type	A8 Vm + G7 III[4]
U−B color index	+0.35[3]
B−V color index	+0.50[3]
Astrometry
Radial velocity (Rv)	+24.0[5] km/s
Proper motion (μ)	RA: −53.23[2] mas/yr Dec.: +37.24[2] mas/yr
Parallax (π)	9.61±0.46 mas[2]
Distance	340 ± 20 ly (104 ± 5 pc)
Absolute magnitude (MV)	−0.30[1]
Orbit[6]
Companion	θ Ant B
Period (P)	18.266±0.185 yr
Semi-major axis (a)	0.110±0.002″
Eccentricity (e)	0.404±0.005
Inclination (i)	123.6±1.0°
Longitude of the node (Ω)	3.5±1.0°
Periastron epoch (T)	2020.143±0.200
Argument of periastron (ω) (secondary)	141.2±3.0°
Details[6]
θ Ant A
Mass	1.8±0.1 M☉
θ Ant B
Mass	2.1±0.5 M☉
Other designations
θ Antliae, Tet Ant, θ Ant, CD−27 6881, FK5 366, HD 84367, HIP 47758, HR 3871, SAO 177908, PPM 256646[7]
Database references
SIMBAD	data

The binary nature of this system was discovered by W. S. Finsen in 1952.^[6] The primary component of this system, θ Antliae A, has a stellar classification of A8 Vm,^[4] indicating that it is an A-type main sequence star with enhanced metallic lines in its spectrum. The companion, θ Antliae B, is a giant star with a classification of G7 III.^[4] The pair have an orbital period of 18.3 years, a significant eccentricity of 0.4, and an angular separation of 0.1 arcseconds.^[6]