Theta Octantis

θ Octantis, Latinized as Theta Octantis, is a single^[10] star in the southern circumpolar constellation of Octans, near the constellation border with Hydrus. It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.78.^[1] The star is located approximately 217 light years from the Sun based on parallax,^[2] and is drifting further away with a radial velocity of +22.5 km/s.^[6]

Theta Octantis

Location of θ Octantis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Octans[1]
Right ascension	00h 01m 35.70158s[2]
Declination	−77° 03′ 56.6092″[2]
Apparent magnitude (V)	4.78[1]
Characteristics
Evolutionary stage	red clump[3]
Spectral type	K3III[4]
U−B color index	+1.41[5]
B−V color index	+1.27[5]
Astrometry
Radial velocity (Rv)	+22.48±0.17[6] km/s
Proper motion (μ)	RA: −57.30[2] mas/yr Dec.: −177.06[2] mas/yr
Parallax (π)	15.02±0.18 mas[2]
Distance	217 ± 3 ly (66.6 ± 0.8 pc)
Absolute magnitude (MV)	0.66[1]
Details
Mass	1.20[7] M☉
Radius	15.84+0.42 −1.02[6] R☉
Luminosity	79.2±1.5[6] L☉
Surface gravity (log g)	2.16[7] cgs
Temperature	4,325+147 −55[6] K
Rotational velocity (v sin i)	< 1.0[8] km/s
Other designations
θ Oct, CPD−77°1596, FK5 904, GC 33321, HD 224889, HIP 122, HR 9084, SAO 258207[9]
Database references
SIMBAD	data

This is an aging giant star with a stellar classification of K3III,^[4] having exhausted the supply of hydrogen at its core then cooled and expanded. It has been catalogued as a red clump giant,^[3] which would indicate it is on the horizontal branch and is undergoing core helium fusion. At present it has 16^[6] times the radius of the Sun. This star has 1.20^[7] times the mass of the Sun and is radiating 79^[6] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,325 K.^[6]