51 Eridani

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51 Eridani
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
Right ascension 04h 37m 36.13234s[1]
Declination −02° 28′ 24.7749″[1]
Apparent magnitude (V) 5.22[2]
Spectral type F0 V[2]
Radial velocity (Rv)12.60 ± 0.3[3] km/s
Proper motion (μ) RA: 44.22 ± 0.34[1] mas/yr
Dec.: -64.39 ± 0.27[1] mas/yr
Parallax (π)33.98 ± 0.34[1] mas
Distance96.0 ± 1.0 ly
(29.4 ± 0.3 pc)
Absolute magnitude (MV)2.87[4]
51 Eri A
Mass1.75 ± 0.05[2] M
Radius1.45±0.02 R
Luminosity6.7[6] L
Surface gravity (log g)3.95±0.04 cgs
Temperature7,331±30 K
Metallicity [Fe/H]−0.12±0.06 dex
Rotational velocity (v sin i)77.9[7] km/s
Other designations
51 Eridani, c Eridani, BD−02° 963, HD 29391, HIP 21547, HR 1474, SAO 131358
Database references

51 Eridani is a star in the constellation Eridanus. It has an apparent magnitude of 5.22,[2] meaning it is just visible to the unaided eye in suburban and rural skies.[8] The primary star's absolute magnitude is 2.87.[4] There is also a binary star named GJ 3305 which shares the same proper motion through space with it.[9]

General information[edit]

Johann Bayer gave the star its Bayer designation of c Eridani,[10] using lower-case letters once he had exhausted all the letters of the Greek alphabet, in his 1603 star chart Uranometria.[11] It was catalogued as 51 Eridani by John Flamsteed in 1725.[12]

Located around 97 light-years distant, it shines with a luminosity approximately 5.38 times that of the Sun and has a surface temperature of 7199 K.[13] A cold debris disk has been detected with a likely inner border of 82 astronomical units (AU).[14] A yellow-white main sequence star of spectral type F0V, 51 Eridani is a member of the Beta Pictoris moving group and hence thought to be around 23 million years old.[4] Somewhat more luminous than it should be for its surface temperature, 51 Eridani has also been classified as spectral type F0IV—a type corresponding to ageing stars that have used up their core hydrogen fuel and become subgiants—however in this case it is a phenomenon of very young stars 5 to 30 million years old that have yet to settle on the main sequence.[15]

51 Eridani has a companion, known as GJ 3305. The system has a common proper motion with 51 Eridani, and hence it is gravitationally bound, although it is separated by 66″ corresponding to 2,000 AU. It is a binary star system with two M-type red dwarfs. The primary has a mass of 0.67 ± 0.05 M while the secondary has a mass of 0.44 ± 0.05 M. The two red dwarfs themselves are separated by a semimajor axis of 9.78 ± 0.14 AU and have an eccentricity of 0.19 ± 0.02.[9]

The star is significant as the host sun to one of the first planets to have been directly imaged in wide-orbit, and the first detected by the Gemini Planet Imager.[16]

Planetary system[edit]

51 Eridani b is a young Jupiter-like planet and was photographed, in near-infrared light, on December 21, 2014.[17] The study, led by Bruce Macintosh, a professor of physics at Stanford University and confirmed by Christian Marois found that methane and water were abundant in the atmosphere of the planet and its mass was only slightly larger than Jupiter’s.[16] It is the smallest exoplanet directly imaged to date.[18]


  1. ^ a b c d e van Leeuwen, F. (November 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 c d Simon, M.; Schaefer, G. H. (2011). "MEASURED DIAMETERS OF TWO F STARS IN THE β PIC MOVING GROUP". The Astrophysical Journal. 743 (2): 158. arXiv:1109.3483. Bibcode:2011ApJ...743..158S. doi:10.1088/0004-637X/743/2/158.
  3. ^ 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.
  4. ^ a b c Mamajek, Eric E.; Bell, Cameron P. M. (2014). "On the age of the β Pictoris moving group". Monthly Notices of the Royal Astronomical Society. 445 (3): 2169–80. arXiv:1409.2737. Bibcode:2014MNRAS.445.2169M. doi:10.1093/mnras/stu1894.
  5. ^ Rajan, Abhijith; et al. (May 2017), "Characterizing 51 Eri b from 1 to 5μm: a partly-cloudy exoplanet", The Astronomical Journal, 154 (1), arXiv:1705.03887, Bibcode:2017AJ....154...10R, doi:10.3847/1538-3881/aa74db.
  6. ^ McCarthy, Kyle; White, Russel J. (June 2012), "The Sizes of the Nearest Young Stars", The Astronomical Journal, 143 (6): 14, arXiv:1201.6600, Bibcode:2012AJ....143..134M, doi:10.1088/0004-6256/143/6/134, 134.
  7. ^ Paunzen, E.; et al. (July 2014), "Investigating the possible connection between λ Bootis stars and intermediate Population II type stars", Astronomy & Astrophysics, 567: 8, arXiv:1406.3936, Bibcode:2014A&A...567A..67P, doi:10.1051/0004-6361/201423817, A67.
  8. ^ Bortle, John E. (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Retrieved 15 August 2015.
  9. ^ a b Montet, Benjamin T.; Bowler, Brendan P.; Shkolnik, Evgenya L.; Deck, Katherine M.; Wang, Ji; Horch, Elliott P.; Liu, Michael C.; Hillenbrand, Lynne A.; Kraus, Adam L.; Charbonneau, David (2015). "Dynamical Masses of Young M Dwarfs: Masses and Orbital Parameters of Gj 3305 Ab, the Wide Binary Companion to the Imaged Exoplanet Host 51 Eri". The Astrophysical Journal. 813: L11. arXiv:1508.05945. Bibcode:2015ApJ...813L..11M. doi:10.1088/2041-8205/813/1/L11.
  10. ^ Wagman 2003, p. 144.
  11. ^ Wagman 2003, pp. 6–7.
  12. ^ Wagman 2003, p. 403.
  13. ^ McDonald, I.; Zijlstra, A. A.; Boyer, M. L. (2012). "Fundamental Parameters and Infrared Excesses of Hipparcos Stars". Monthly Notices of the Royal Astronomical Society. 427 (1): 343–57. arXiv:1208.2037. Bibcode:2012MNRAS.427..343M. doi:10.1111/j.1365-2966.2012.21873.x.
  14. ^ Riviere-Marichalar, P.; Barrado, D.; Montesinos, B.; Duchêne, G.; Bouy, H.; Pinte, C.; et al. (2014). "Gas and dust in the beta Pictoris moving group as seen by the Herschel Space Observatory". Astronomy & Astrophysics. 565: 11. arXiv:1404.1815. Bibcode:2014A&A...565A..68R. doi:10.1051/0004-6361/201322901. A68.
  15. ^ Pecaut, Mark J.; Mamajek, Eric E. (2013). "Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-main-sequence Stars". The Astrophysical Journal Supplement. 208 (1): 22. arXiv:1307.2657. Bibcode:2013ApJS..208....9P. doi:10.1088/0067-0049/208/1/9.
  16. ^ a b "Hot Jupiter-esque Discovery Hints at Planet Formation". W. M. Keck Observatory. Kamuela, Hawaii. 13 August 2015. Archived from the original on 2015-12-26. Retrieved 14 August 2015.
  17. ^ Feltman, Rachel (August 13, 2015). "Newly discovered, Jupiter-like planet may sit in a solar system much like our own". Speaking of Science. Washington Post. Retrieved 14 August 2015.
  18. ^ Gary, Stuart (14 August 2015). "Small alien world most Jupiter-like planet ever seen". ABC Science. ABC. Retrieved 14 August 2015.
Cited text
  • Wagman, Morton (2003). Lost Stars: Lost, Missing and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas Louis de Lacaille, John Flamsteed, and Sundry Others. Blacksburg, Virginia: The McDonald & Woodward Publishing Company. ISBN 978-0-939923-78-6.