Astronomy:Epsilon Octantis

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ε Octantis
Octans constellation map.svg
Red circle.svg
Location of ε Octantis (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Octans
Right ascension  22h 20m 01.67970s[1]
Declination −80° 26′ 23.0947″[1]
Apparent magnitude (V) 5.09[2]
Spectral type M5III[3]
U−B color index +1.18[4]
B−V color index +1.47[4]
Variable type SRb[5]
Radial velocity (Rv)+11.70[6] km/s
Proper motion (μ) RA: +56.81[1] mas/yr
Dec.: −43.47[1] mas/yr
Parallax (π)11.22 ± 0.23[1] mas
Distance291 ± 6 ly
(89 ± 2 pc)
Absolute magnitude (MV)0.34[2]
Mass1.34[7] M
Radius112±15[8] R
Luminosity1,819[8] L
Surface gravity (log g)2.15[7] cgs
Temperature3,560±264[8] K
Other designations
Database references

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 5.09.[2] 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.[6]

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 5.3 and a (poorly defined) period around 55 days.[5] 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]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653. doi:10.1051/0004-6361:20078357. Bibcode2007A&A...474..653V.  Vizier catalog entry
  2. 2.0 2.1 2.2 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode2012AstL...38..331A.  Vizier catalog entry
  3. 3.0 3.1 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. Bibcode1995yCat.5050....0H. 
  4. 4.0 4.1 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. Bibcode2006yCat.2168....0M. Vizier catalog entry
  5. 5.0 5.1 Samus, N. N. 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. Bibcode2009yCat....1.2025S. 
  6. 6.0 6.1 Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters 32 (11): 759. doi:10.1134/S1063773706110065. Bibcode2006AstL...32..759G. 
  7. 7.0 7.1 7.2 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. Bibcode1999A&A...352..555A.  Vizier catalog entry
  8. 8.0 8.1 8.2 8.3 8.4 8.5 Arroyo-Torres, B. et al. (June 2014), "VLTI/AMBER observations of cold giant stars: atmospheric structures and fundamental parameters", Astronomy & Astrophysics 566: 11, doi:10.1051/0004-6361/201323264, A88, Bibcode2014A&A...566A..88A