Theta Piscis Austrini
Star in the constellation Piscis Austrinus
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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]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Piscis Austrinus |
| Right ascension | 21h 47m 44.14993s[1] |
| Declination | â30° 53â² 53.9027â³[1] |
| Apparent magnitude (V) | +5.01[2] |
| Characteristics | |
| Spectral type | A1 V + A1 V[3] |
| BâV color index | +0.04[2] |
| Astrometry | |
| Radial velocity (Rv) | +12.80±1.8[4] km/s |
| Proper motion (μ) | RA: â34.40[1] mas/yr Dec.: â0.08[1] mas/yr |
| Parallax (Ï) | 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±0.004Ⳡ|
| 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 (Ï) (secondary) | 199±6° |
| Details | |
| θ PsA A | |
| Mass | 2.32±0.33[3] Mâ |
| Luminosity | 86[5] Lâ |
| 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] Mâ |
| Other designations | |
| θ PsA, 10 Piscis Austrini, CPDâ31°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, å¤©é¢ (TiÄn 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 Ï Piscis Austrini. Consequently, the Chinese name for θ Piscis Austrini itself is 天é¢äº (TiÄn Qián èr, English: the Second Star of Celestial Money.)[10]