Epsilon Octantis

Epsilon Octantis, Latinized from ε Octantis, is a star in the southern circumpolar constellation of Octans. It is a faintly visible to the naked eye with an apparent visual magnitude of about 5. The annual parallax shift of 11.22^[1] mas yields a distance estimate of around 291 light years. It is moving further from the Sun with a radial velocity of +11.7 km/s.^[5]

A light curve for Epsilon Octantis, plotted from Hipparcos data^[9]

ε Octantis

Location of ε Octantis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Octans
Right ascension	22h 20m 01.67970s[1]
Declination	−80° 26′ 23.0947″[1]
Apparent magnitude (V)	4.58 - 5.30[2]
Characteristics
Spectral type	M5III[3]
U−B color index	+1.18[4]
B−V color index	+1.47[4]
Variable type	SRb[2]
Astrometry
Radial velocity (Rv)	+11.70[5] km/s
Proper motion (μ)	RA: +56.81[1] mas/yr Dec.: −43.47[1] mas/yr
Parallax (π)	11.22±0.23 mas[1]
Distance	291 ± 6 ly (89 ± 2 pc)
Absolute magnitude (MV)	+0.34[6]
Details
Mass	1.34[7] M☉
Radius	112±15[8] R☉
Luminosity	1,819[8] L☉
Surface gravity (log g)	2.15[7] cgs
Temperature	3,560±264[8] K
Other designations
BO Oct, ε Oct, CD−81°831, FK5 839, GC 31166, HD 210967, HIP 110256, HR 8481, SAO 258928
Database references
SIMBAD	data

This is an evolved, cool red giant star with a stellar classification of class M5III.^[3] It is a semiregular variable with a magnitude range of 4.58 to 5.30 and a (poorly defined) period around 55 days.^[2] The star has 1.34^[7] times the mass of the Sun and has expanded to around 112^[8] times the Sun's radius. It is radiating 1,819^[8] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,560 K.^[8]

Epsilon Octantis was found to be variable on a survey of the southern sky conducted by the Bamberg observatory, which was reported in 1966.^[10] In 1972, it was assigned the variable star designation BO Octantis,^[11] although this is now recognised as a mistake since stars with Bayer designations are not given a separate variable star designation.^[2]