Gamma3 Octantis
{{Short description|Star in the constellation Octans}}
{{DISPLAYTITLE:Gamma3 Octantis}}
{{other stars by Bayer designation|Gamma Octantis{{!}}γ Octantis}}
{{Starbox begin
| name = γ3 Octantis
}}
{{Starbox image
| image ={{Location mark
| image=Octans IAU.svg | alt= | float=center | width=250
| label= | position=right
| mark=Red circle.svg | mark_width=7 | mark_link=Gamma3 Oct
| x%=48 | y%=32
}}
| caption = Location of γ3 Octantis (circled)
}}
{{Starbox observe
| constell = Octans
| dec = {{DEC|-82|13|26.5695}}
}}
{{Starbox character
| type = Horizontal branch
}}
{{Starbox astrometry
| parallax = 12.3535
| p_error = 0.0517
| prop_mo_ra = −22.050
| prop_mo_dec = −20.218
}}
{{Starbox detail
| mass = 2.23{{±|0.09}}
| radius = 9.94{{±|0.24}}
| luminosity = 50.5{{±|1.2}}
| temperature = 4,879{{±|51}}
| gravity = 2.78{{±|0.15}}
| metal_fe = +0.19{{±|0.04}}
| age_myr =
}}
{{Starbox catalog
| names = {{odlist|Gould = 1 G. Octantis|HD = 636|B = γ3 Octantis|CPD = −82°4|FK5 = 3971|GC = 173|HIP = 814|HR = 30|SAO = 258215}}
}}
{{Starbox reference
| Simbad = gam03+Oct
}}
{{Starbox end}}
Gamma3 Octantis, Latinized from γ3 Octantis, is a solitary star 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. The object is located relatively close at a distance of 264 light years but is receding with a heliocentric radial velocity of {{val|15|ul=km/s}}. At its current distance, Gamma3 Octantis' brightness is diminished by two tenths of a magnitude due to interstellar dust and Eggen (1993) lists it as a member of the old disk population. It has an absolute magnitude of +0.83.
Gamma3 Octantis has a stellar classification of K1/2 III, 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, 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. 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. Gamma3 Octantis is metal enriched with an iron abundance 1.55 times that of the Sun and common for giant stars, spins slowly with a projected rotational velocity less than {{val|1|ul=km/s}}.
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 {{solar luminosity|60}}. 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. Gamma2 Octantis is considerably further away at 320 light years and consequently is about half a magnitude fainter than the other two stars.