Gamma3 Octantis

Gamma³ Octantis, Latinized from γ³ Octantis, is a solitary star^[12] located in the southern circumpolar constellation Octans. It is faintly visible to the naked eye as an orange-hued star with an apparent magnitude of 5.28.^[2] The object is located relatively close at a distance of 264 light years but is receding with a heliocentric radial velocity of 15 km/s. At its current distance, Gamma³ Octantis' brightness is diminished by two tenths of a magnitude due to interstellar dust^[13] and Eggen (1993) lists it as a member of the old disk population.^[14] It has an absolute magnitude of +0.83.^[7]

For other stars with this Bayer designation, see γ Octantis.

γ³ Octantis

Location of γ3 Octantis (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Octans
Right ascension	00h 10m 02.17249s[1]
Declination	−82° 13′ 26.5695″[1]
Apparent magnitude (V)	5.28±0.01[2]
Characteristics
Evolutionary stage	Horizontal branch[3]
Spectral type	K1/2 III[4]
U−B color index	+0.92[5]
B−V color index	+1.05[5]
Astrometry
Radial velocity (Rv)	15±2.8[6] km/s
Proper motion (μ)	RA: −22.050 mas/yr[1] Dec.: −20.218 mas/yr[1]
Parallax (π)	12.3535±0.0517 mas[1]
Distance	264 ± 1 ly (80.9 ± 0.3 pc)
Absolute magnitude (MV)	+0.83[7]
Details[8]
Mass	2.23±0.09 M☉
Radius	9.94±0.24 R☉
Luminosity	50.5±1.2 L☉
Surface gravity (log g)	2.78±0.15 cgs
Temperature	4,879±51 K
Metallicity [Fe/H]	+0.19±0.04 dex
Rotational velocity (v sin i)	<1[9] km/s
Other designations
γ3 Octantis, 1 G. Octantis[10], CPD−82°4, FK5 3971, GC 173, HD 636, HIP 814, HR 30, SAO 258215[11]
Database references
SIMBAD	data

Gamma³ Octantis has a stellar classification of K1/2 III,^[4] indicating that it is an evolved K-type star with the characteristics of a K1 and K2 giant star. It is a red clump star that is currently on the horizontal branch,^[3] fusing helium at its core. At present it has 2.23 times the mass of the Sun but has expanded to almost 10 times its girth.^[8] It radiates 50.5 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,879 K, which gives it a yellowish-orange glow.^[8] Gamma³ Octantis is metal enriched with an iron abundance 1.55^[8] times that of the Sun and common for giant stars, spins slowly with a projected rotational velocity less than 1 km/s.^[9]

Stars sharing the Gamma designation

The stars Gamma¹, Gamma² Octantis, and Gamma³ Octantis all lie within a degree of each other and all are red clump giants with luminosities of 50 to 60 L_☉.^[8][15] Based on parallax measurements from Gaia Data Release 3, the magnitude 5 Gamma¹ Octantis and Gamma³ Octantis are at very similar distances of 268 and 264 light years respectively.^[1][16] Gamma² Octantis is considerably further away at 320 light years^[17] and consequently is about half a magnitude fainter than the other two stars.^[2]