Tau Octantis

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]

τ Octantis

Location of τ Octantis (circled)
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
τ Oct, 81 G. Octantis, CPD−88°204, FK5 925, GC 32558, HD 219765, HIP 115836, HR 8862, SAO 258970
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]