Tau Octantis, Latinized from τ Octantis, is a solitary[11] star in the southern circumpolar constellation Octans. It has an apparent magnitude of 5.50,[2] allowing it to be faintly seen with the naked eye. The object is located at a distance of 480 light years[1] but is receding with a heliocentric radial velocity of 31 km/s.[5]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Octans |
| Right ascension | 23h 28m 03.7855s[1] |
| Declination | −87° 28′ 55.967″[1] |
| Apparent magnitude (V) | 5.50[2] |
| Characteristics | |
| Spectral type | K2 III[3] |
| U−B color index | +1.43[4] |
| B−V color index | +1.27[4] |
| Astrometry | |
| Radial velocity (Rv) | 31.0±1.4[5] km/s |
| Proper motion (μ) | RA: +16.782 mas/yr[1] Dec.: +11.957 mas/yr[1] |
| Parallax (π) | 6.8009 ± 0.0574 mas[1] |
| Distance | 480 ± 4 ly (147 ± 1 pc) |
| Absolute magnitude (MV) | −0.36[2] |
| Details | |
| Mass | 1.14[6] M☉ |
| Radius | 24[7] R☉ |
| Luminosity | 223[8] L☉ |
| Surface gravity (log g) | 1.63[6] cgs |
| Temperature | 4,422[8] K |
| Metallicity [Fe/H] | +0.12[9] dex |
| Rotational velocity (v sin i) | <1[10] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Tau Octantis has a stellar classification of K2 III, indicating that the object is a red giant. It has 114% the mass of the Sun[6] but is 223 times as luminous.[8] However, an enlarged radius of 24 R☉ yields an effective temperature of 4,422 K,[8] giving it an orange glow. Tau Octantis has an iron abundance 132% that of the Sun and is believed to be a member of the old disk population.[9] Currently, it spins with a projected rotational velocity less than 1 km/s.[10]