Zeta Trianguli Australis
Binary star system in the constellation Triangulum Australe
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Zeta Trianguli Australis is a spectroscopic binary star system in the southern constellation Triangulum Australe. The pair have a combined apparent visual magnitude of 4.90,[4] which is bright enough to be visible to the naked eye. Based on parallax measurements, the system is located at a distance of approximately 39.4 light years from Earth.[7] After closing to within 31.3 ly (9.59 pc) some 436,600 years ago,[17] it is now drifting farther away with a radial velocity of +8.3 km/s.[6]
 | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Triangulum Australe |
| Right ascension | 16h 28m 28.14362s[1] |
| Declination | −70° 05′ 03.8419″[1] |
| Apparent magnitude (V) | 4.91[2] |
| Characteristics | |
| Spectral type | F9V + M4V[2][3] |
| U−B color index | +0.02[4] |
| B−V color index | +0.55[5] |
| Astrometry | |
| Radial velocity (Rv) | +8.3[6] km/s |
| Proper motion (μ) | RA: 200.742 mas/yr[7] Dec.: 109.341 mas/yr[7] |
| Parallax (π) | 82.8699±0.1627 mas[7] |
| Distance | 39.36 ± 0.08 ly (12.07 ± 0.02 pc) |
| Absolute magnitude (MV) | 4.49[8] |
| Orbit[9] | |
| Period (P) | 12.97662±0.00017 d |
| Eccentricity (e) | 0.01442±0.00021 |
| Inclination (i) | 35±19[10]° |
| Periastron epoch (T) | JD 2452752.31955 |
| Argument of periastron (ω) (secondary) | 252.98°±0.80° |
| Semi-amplitude (K1) (primary) | 7.4988±0.0016 km/s |
| Details | |
| ζ TrA A | |
| Mass | 1.12[11] M☉ |
| Radius | 1.02±0.02[12] R☉ |
| Luminosity | 1.41+0.15 −0.09[12] L☉ |
| Surface gravity (log g) | 4.42+0.04 −0.05[12] cgs |
| Temperature | 6,210+180 −120[12] K |
| Metallicity [Fe/H] | −0.09±0.06[13] dex |
| Rotation | 13 days[5] |
| Rotational velocity (v sin i) | 3.23[14] km/s |
| Age | 600–900[15] Myr |
| ζ TrA B | |
| Mass | 0.30[10] M☉ |
| Temperature | 3,327[10] K |
| Other designations | |
| CPD−69°2558, FK5 610, GJ 624, HD 147584, HIP 80686, HR 6098, SAO 253554, LTT 6558[16] | |
| Database references | |
| SIMBAD | data |
| ARICNS | data |
The pair orbit each other once every 13 days, and the orbital eccentricity is a low 0.014, making their orbit nearly circular.[9] The primary component has a stellar classification of F9V, matching an F-type main-sequence star. It has a mass equal to 1.12 times the mass of the Sun,[11] a radius 1.06 times the radius of the Sun, and irradiated at an effective temperature of 6,032 K, slightly hotter than the Sun as well.[13] The companion is a small red dwarf star with a class in the range of M1–7V[2] and 40% of the Sun's mass.[11] The age of the system is estimated at 600–900 million years.[15]
Any objects orbiting the pair in a circumbinary orbit should have an orbital separation of 0.217 AU or higher; otherwise its orbit would be unstable due to gravitational interactions.[12]
Somewhat surprisingly for a star located at a declination of 70° S, it is a candidate swarm member of the Ursa Major moving group.[18] However, there is some evidence to the contrary.[5]