Zeta Octantis

Zeta Octantis, Latinized from ζ Octantis, is a solitary,^[16] yellowish-white hued star located in the southern circumpolar constellation Octans. It has an apparent magnitude of 5.42,^[2] making it faintly visible to the naked eye under ideal conditions. The star is located relatively close at a distance of only 156 light-years based on Gaia DR3 parallax measurements,^[1] but is drifting closer with a radial velocity of −3.6 km/s.^[6] At its current distance, Zeta Octantis' brightness is diminished by 0.25 magnitudes due to interstellar dust.^[17]

ζ Octantis

Location of ζ Octantis (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Octans
Right ascension	08h 56m 40.97572s[1]
Declination	−85° 39′ 47.3476″[1]
Apparent magnitude (V)	5.42±0.01[2]
Characteristics
Spectral type	A8/9 IV[3] or F0 III[4]
U−B color index	+0.07[5]
B−V color index	+0.31[5]
Astrometry
Radial velocity (Rv)	−3.6±2[6] km/s
Proper motion (μ)	RA: −117.699 mas/yr[1] Dec.: +33.964 mas/yr[1]
Parallax (π)	20.9964±0.0776 mas[1]
Distance	155.3 ± 0.6 ly (47.6 ± 0.2 pc)
Absolute magnitude (MV)	+1.95[7]
Details
Mass	2.06±0.40[8] M☉
Radius	2.25±0.11[9] R☉
Luminosity	12.63±0.09[1] L☉
Surface gravity (log g)	4.04±0.28[8] cgs
Temperature	7,063±325[10] K
Metallicity [Fe/H]	−0.36[11] dex
Rotational velocity (v sin i)	115[12] km/s
Age	1.25[13] Gyr
Other designations
ζ Oct, 9 G. Octantis[14], CPD−85°183, FK5 918, GC 12580, HD 79837, HIP 43908, HR 3678, SAO 258515[15]
Database references
SIMBAD	data

This is an evolved A-type star with a stellar classification of A8/9 IV.^[3] David S. Evans and colleagues, however, give it a classification of F0 III,^[4] which suggests it is already an evolved giant star. It has double the Sun's mass,^[8] and 2.25 times the Sun's radius.^[9] It radiates around 13 times the luminosity of the Sun^[1] from its photosphere at an effective temperature of 7,063 K.^[10] Zeta Octantis is estimated to be 1.25 billion years olds based on stellar evolution models by Trevor J. David and Lynne A. Hillenbrand.^[13] It has a low metallicity, having only 44% the abundance of heavy metals compared to the Sun.^[11] Despite its advanced age, the object spins rapidly with a projected rotational velocity of 115 km/s,^[12] resulting in an oblate shape with an equatorial bulge 11% larger than the polar radius.^[18]