66 Eridani

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66 Eridani
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
Right ascension  05h 06m 45.65314s[1]
Declination −04° 39′ 18.5939″[1]
Apparent magnitude (V) 5.12[2]
Spectral type B9V[3]
U−B color index -0.16[4]
B−V color index -0.06[4]
Variable type α2 CVn
Radial velocity (Rv)32.28 ± 0.10[5] km/s
Proper motion (μ) RA: 10.70[1] mas/yr
Dec.: -0.78[1] mas/yr
Parallax (π)10.56 ± 0.34[1] mas
Distance309 ± 10 ly
(95 ± 3 pc)
Absolute magnitude (MV)0.37[6]
Period (P)5.5226013 ± 0.0000020 d
Eccentricity (e)0.0844 ± 0.0013
Periastron epoch (T)2441356.499 ± 0.017
Argument of periastron (ω)
160.9 ± 1.1°
Semi-amplitude (K1)
102.83 ± 0.20 km/s
Semi-amplitude (K2)
100.35 ± 0.19 km/s
66 Eri A
Mass2.629 ± 0.032 M
Radius1.948 ± 0.063 R
Luminosity51.3 ± 3.3 L
Surface gravity (log g)4.28 ± 0.03 cgs
Temperature11077 K
Rotational velocity (v sin i)17.1 ± 0.2 km/s
Age30 Myr
66 Eri B
Mass2.566 ± 0.032 M
Radius1.919 ± 0.061 R
Luminosity46.9 ± 3.0 L
Surface gravity (log g)4.28 ± 0.03 cgs
Temperature10914 K
Rotational velocity (v sin i)16.9 ± 0.2 km/s
Other designations
EN Eri, BD−04° 1044, HD 32964, HIP 23794, HR 1657, SAO 131777[7]
Database references

66 Eridani is a binary star in the constellation of Eridanus. The combined apparent magnitude of the system is 5.12 on average.[2] Parallax measurements by Hipparcos put the system at some 309 light-years (95 parsecs) away.[1]

This is a spectroscopic binary: the two stars cannot be individually resolved, but periodic Doppler shifts in its spectrum mean there must be orbital motion. The two stars orbit each other every 5.5226013 days.[5] Their orbit is fairly eccentric, at 0.0844.[5]

The combined spectrum of 66 Eridani matches that of a B-type main-sequence star,[3] and the two stars have similar masses.[5] The spectrum also shows excess of mercury and manganese, as it is a type of chemically peculiar star called a mercury-manganese star.[5] 66 Eridani is a Alpha2 Canum Venaticorum variable. For this reason, it has been given the designation EN Eridani.[7]


  1. ^ a b c d e f van Leeuwen, F.; et al. (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.
  2. ^ a b Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  3. ^ a b Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars, Vol. 5". Michigan Spectral Survey. 5: 0. Bibcode:1999MSS...C05....0H.
  4. ^ a b Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  5. ^ a b c d e f g Makaganiuk, V.; Kochukhov, O.; Piskunov, N.; Jeffers, S. V.; Johns-Krull, C. M.; Keller, C. U.; Rodenhuis, M.; Snik, F.; Stempels, H. C.; Valenti, J. A. (2011). "Chemical spots in the absence of magnetic field in the binary Hg Mn star 66 Eridani". Astronomy & Astrophysics. 529: A160. arXiv:1102.4661. Bibcode:2011A&A...529A.160M. doi:10.1051/0004-6361/201016302.
  6. ^ Hubrig, S.; et al. (June 2001), "Search for low-mass PMS companions around X-ray selected late B stars", Astronomy and Astrophysics, 372: 152–164, arXiv:astro-ph/0103201, Bibcode:2001A&A...372..152H, doi:10.1051/0004-6361:20010452.
  7. ^ a b "* 66 Eri". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 13 August 2017.