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Star in the constellation Octans From Wikipedia, the free encyclopedia
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]
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 | |
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]
The very similar brightness and potentially close stars of Gamma2, 3 have been examined by the Gaia space telescope/observatory. Gamma2 is much more distant than the other two whose margins of error overlap when parallaxes are considered — they may thus be close enough to be in loose mutual orbital. These distances from our star system per Gaia's second Data Release (DR2) are, respectively, around 319 ± 5 ly and 259 ± 3 ly. The observation refines Gamma1 as being 262 ± 4 ly away.
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