  | |
| 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, 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]
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]
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]
