Theta Piscis Austrini

Theta Piscis Austrini, Latinized as θ Piscis Austrini, is a binary star^[8] system in the southern constellation of Piscis Austrinus. It is faintly visible to the naked eye with a combined apparent visual magnitude of +5.01.^[2] Based upon an annual parallax shift of 10.16 mas as seen from the Earth,^[1] the system is located around 320 light years from the Sun. The system is drifting further away with a radial velocity of +13 km/s.^[4]

Theta Piscis Austrini

Location of θ Piscis Austrini (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Piscis Austrinus
Right ascension	21h 47m 44.14993s[1]
Declination	−30° 53′ 53.9027″[1]
Apparent magnitude (V)	+5.01[2]
Characteristics
Spectral type	A1 V + A1 V[3]
B−V color index	+0.04[2]
Astrometry
Radial velocity (Rv)	+12.80±1.8[4] km/s
Proper motion (μ)	RA: −34.40[1] mas/yr Dec.: −0.08[1] mas/yr
Parallax (π)	10.16±0.40 mas[1]
Distance	320 ± 10 ly (98 ± 4 pc)
Absolute magnitude (MV)	+0.06[5]
Orbit[3]
Period (P)	19.957±0.050 yr
Semi-major axis (a)	0.137±0.004″
Eccentricity (e)	0.256±0.030
Inclination (i)	103±2°
Longitude of the node (Ω)	29.1±2.0°
Periastron epoch (T)	2006.00±0.07
Argument of periastron (ω) (secondary)	199±6°
Details
θ PsA A
Mass	2.32±0.33[3] M☉
Luminosity	86[5] L☉
Surface gravity (log g)	4.05[6] cgs
Temperature	9,716±330[6] K
Rotational velocity (v sin i)	150[6] km/s
Age	281[6] Myr
θ PsA B
Mass	2.32±0.33[3] M☉
Other designations
θ PsA, 10 Piscis Austrini, CPD−31°6596, HD 207155, HIP 107608, HR 8326, SAO 213292, WDS J21477-3054AB[7]
Database references
SIMBAD	data

The binary nature of this system was discovered in 1951 by South African astronomer W. S. Finsen. Both components A and B have the same apparent magnitude. They orbit each other with a period of 20 years and an eccentricity of 0.256. The pair are A-type main sequence stars with stellar classifications of A1 V.^[3] A magnitude 11.3 visual companion star, labelled component C, is located at an angular separation of 33.2 arc seconds along a position angle of 342°, as of 1999.^[9]

Theta Piscis Austrini is moving through the Galaxy at a speed of 21.3 km/s relative to the Sun. Its projected Galactic orbit carries it between 22,629 and 38,431 light-years from the center of the Galaxy. Theta Piscis Austrini came closest to the Sun 2.7 million years ago at a distance of 256 light-years.^[5]

Naming

In Chinese, 天錢 (Tiān Qián), meaning Celestial Money, refers to an asterism consisting of refers to an asterism consisting of θ Piscis Austrini, 13 Piscis Austrini, ι Piscis Austrini, μ Piscis Austrini and τ Piscis Austrini. Consequently, the Chinese name for θ Piscis Austrini itself is 天錢二 (Tiān Qián èr, English: the Second Star of Celestial Money.)^[10]