Epsilon Octantis

ε Octantis
	Location of ε Octantis (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Octans
Right ascension	22h 20m 01.67970s
Declination	−80° 26′ 23.0947″
Apparent magnitude (V)	4.58 - 5.30
Characteristics
Spectral type	M5III
U−B color index	+1.18
B−V color index	+1.47
Variable type	SRb
Astrometry
Radial velocity (Rv)	+11.70 km/s
Proper motion (μ)	RA: +56.81 mas/yr ; Dec.: −43.47 mas/yr
Parallax (π)	11.22±0.23 mas
Distance	291 ± 6 ly ; (89 ± 2 pc)
Absolute magnitude (MV)	+0.34
Details
Mass	1.34 M☉
Radius	112±15 R☉
Luminosity	1,819 L☉
Surface gravity (log g)	2.15 cgs
Temperature	3,560±264 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

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]

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]

References

^ ^a ^b ^c ^d ^e ^f Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Vizier catalog entry
^ ^a ^b ^c ^d Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
^ ^a ^b Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.
^ ^a ^b Mermilliod, J. C. (2006). "VizieR Online Data Catalog: Homogeneous Means in the UBV System (Mermilliod 1991)". VizieR On-line Data Catalog: II/168. Originally Published in: Institut d'Astronomie. 2168. Bibcode:2006yCat.2168....0M.Vizier catalog entry
^ ^a ^b Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
^ Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644. Vizier catalog entry
^ ^a ^b ^c Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555–562. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A. Vizier catalog entry
^ ^a ^b ^c ^d ^e ^f Arroyo-Torres, B.; et al. (June 2014), "VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters", Astronomy & Astrophysics, 566: 11, arXiv:1404.7384, Bibcode:2014A&A...566A..88A, doi:10.1051/0004-6361/201323264, S2CID 16778588, A88
^ "/ftp/cats/more/HIP/cdroms/cats". Centre de Données astronomiques de Strasbourg. Strasbourg astronomical Data Center. Retrieved 15 October 2022.
^ Strohmeier, W.; Fischer, H.; Ott, H. (1966). "Bright Southern BV-Stars". Information Bulletin on Variable Stars. 120: 1. Bibcode:1966IBVS..120....1S.
^ Kukarkin, B. V.; Kholopov, P. N.; Kukarkina, N. P.; Perova, N. B. (1 September 1972). "58th Name-List of Variable Stars". Information Bulletin on Variable Stars. 717: 1. Bibcode:1972IBVS..717....1K. ISSN 0374-0676.

[vanLeeuwen2007-1] ^ ^a ^b ^c ^d ^e ^f Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600. Vizier catalog entry

[gcvs-2] Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.

[Hoffleit1991-3] Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H. 5050. Bibcode:1995yCat.5050....0H.

[MermiliodUBV-4] Mermilliod, J. C. (2006). "VizieR Online Data Catalog: Homogeneous Means in the UBV System (Mermilliod 1991)". VizieR On-line Data Catalog: II/168. Originally Published in: Institut d'Astronomie. 2168. Bibcode:2006yCat.2168....0M.Vizier catalog entry

[Gontcharov2006-5] Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.

[XHIP-6] Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644. Vizier catalog entry

[AllendePrieto-7] Allende Prieto, C.; Lambert, D. L. (1999). "Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures". Astronomy and Astrophysics. 352: 555–562. arXiv:astro-ph/9911002. Bibcode:1999A&A...352..555A. Vizier catalog entry

[ArroyoTorres2014-8] ^ ^a ^b ^c ^d ^e ^f Arroyo-Torres, B.; et al. (June 2014), "VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters", Astronomy & Astrophysics, 566: 11, arXiv:1404.7384, Bibcode:2014A&A...566A..88A, doi:10.1051/0004-6361/201323264, S2CID 16778588, A88

[CDS-9] "/ftp/cats/more/HIP/cdroms/cats". Centre de Données astronomiques de Strasbourg. Strasbourg astronomical Data Center. Retrieved 15 October 2022.

[bamberg-10] Strohmeier, W.; Fischer, H.; Ott, H. (1966). "Bright Southern BV-Stars". Information Bulletin on Variable Stars. 120: 1. Bibcode:1966IBVS..120....1S.

[11] Kukarkin, B. V.; Kholopov, P. N.; Kukarkina, N. P.; Perova, N. B. (1 September 1972). "58th Name-List of Variable Stars". Information Bulletin on Variable Stars. 717: 1. Bibcode:1972IBVS..717....1K. ISSN 0374-0676.

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Observation data Epoch J2000 Equinox J2000
Location of ε Octantis (circled)
Constellation	Octans
Right ascension	22^h 20^m 01.67970^s^[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 (R_v)	+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 (M_V)	+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

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