Mu Eridani

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μ Eridani
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Eridanus
Right ascension 04h 45m 30.15038s[1]
Declination −03° 15′ 16.7765″[1]
Apparent magnitude (V) 4.00[2]
Spectral type B5 IV[3]
U−B color index −0.60[2]
B−V color index −0.15[2]
Proper motion (μ) RA: +0.25[1] mas/yr
Dec.: −1.97[1] mas/yr
Parallax (π) 6.25 ± 0.19[1] mas
Distance 520 ± 20 ly
(160 ± 5 pc)
Absolute magnitude (MV) −2.06±0.07[4]
Period (P) 7.38090 d
Eccentricity (e) 0.344±0.021
Periastron epoch (T) 2455143.254±0.067 HJD
Argument of periastron (ω)
Semi-amplitude (K1)
0.344±0.021 km/s
μ Eri A
Mass 6.2±0.2[4] M
Radius 6.1[5] R
Luminosity 1,905[5] L
Surface gravity (log g) 3.5[4] cgs
Temperature 15,668[5] K
Metallicity [Fe/H] 0[4] dex
Rotational velocity (v sin i) 130±3[5] km/s
Other designations
μ Eri, BD-03° 876, 57 Eridani, FK5 176, HD 30211, HIP 22109, HR 1520, SAO 131468.[6]
Database references

Mu Eridani (μ Eri) is a binary star system in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude of 4.00.[2] Based upon an annual parallax shift of 0.00625 arcseconds,[1] it is located roughly 520 light years from the Sun.

In 1910, this was determined to be a single-lined spectroscopic binary star system. The pair orbit each other with a period of 7.38 days and an eccentricity of 0.344, during which they undergo Algol-like eclipses.[4] The primary is a slowly pulsating B-type star[5] with a stellar classification of B5 IV.[3] It has a relatively high rate of rotation with a projected rotational velocity of 130 km/s, which is at least 30% of the star's break-up velocity.[5] The star has about six times the Sun's mass and radius, and it shines with 1,905 times the solar luminosity from its outer atmosphere at an effective temperature of 15,668 K.[4][5]


  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:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Crawford, D. L.; et al. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal, 76: 1058, Bibcode:1971AJ.....76.1058C, doi:10.1086/111220. 
  3. ^ a b Levato, H. (January 1975), "Rotational velocities and spectral types for a sample of binary systems", Astronomy and Astrophysics Supplement Series, 19: 91–99, Bibcode:1975A&AS...19...91L. 
  4. ^ a b c d e f g Jerzykiewicz, M.; et al. (June 2013), "μ Eridani from MOST and from the ground: an orbit, the SPB component's fundamental parameters and the SPB frequencies", Monthly Notices of the Royal Astronomical Society, 432 (2): 1032–1045, arXiv:1303.6812Freely accessible, Bibcode:2013MNRAS.432.1032J, doi:10.1093/mnras/stt522. 
  5. ^ a b c d e f g Daszyńska-Daszkiewicz, J.; et al. (January 2015), "Oscillation modes in the rapidly rotating slowly pulsating B-type star μ Eridani", Monthly Notices of the Royal Astronomical Society, 446 (2): 1438–1448, arXiv:1410.6283Freely accessible, Bibcode:2015MNRAS.446.1438D, doi:10.1093/mnras/stu2216. 
  6. ^ "mu. Eri -- Eclipsing binary of Algol type (detached)", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2016-11-01.