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51 Pegasi

51 Pegasi
51 Pegasi is located in 100x100

51 Peg (circled) in the constellation Pegasus.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Pegasus
Right ascension 22h 57m 27.98004s[1]
Declination +20° 46′ 07.7912″[1]
Apparent magnitude (V) 5.49[2]
Spectral type G5V[3]
Apparent magnitude (B) 6.16[4]
Apparent magnitude (R) 5.0[4]
Apparent magnitude (I) 4.7[4]
Apparent magnitude (J) 4.66[4]
Apparent magnitude (H) 4.23[4]
Apparent magnitude (K) 3.91[2]
U−B color index +0.20[5]
B−V color index +0.67[5]
V−R color index 0.37
R−I color index 0.32
Radial velocity (Rv) −33.7 km/s
Proper motion (μ) RA: 207.25 ± 0.31[1] mas/yr
Dec.: 60.34 ± 0.30[1] mas/yr
Parallax (π) 64.07 ± 0.38[1] mas
Distance 50.9 ± 0.3 ly
(15.61 ± 0.09 pc)
Absolute magnitude (MV) 4.51
Mass 1.11[3] M
Radius 1.237 ± 0.047[2] R
Luminosity 1.30 L
Surface gravity (log g) 4.33[6] cgs
Temperature 5571 ± 102[2] K
Metallicity [Fe/H] 0.20[6] dex
Rotation 21.9 ± 0.4 days[7]
Age 6.1–8.1[8] Gyr
Other designations
51 Peg, GJ 882, HR 8729, BD +19°5036, HD 217014, LTT 16750, GCTP 5568.00, SAO 90896, HIP 113357.[9]
Database references
Exoplanet Archive data
Extrasolar Planets

51 Pegasi (abbreviated 51 Peg) is a Sun-like star located 50.9 light-years (15.6 parsecs)[1] from Earth in the constellation Pegasus. It was the first extrasolar Sun-like star found to have a planet orbiting it.[10]


  • Properties 1
  • Planetary system 2
  • See also 3
  • References 4
  • External links 5


51 Pegasi

The star is of apparent magnitude 5.49, and so is visible with the naked eye under suitable viewing conditions. The Flamsteed designation for this star, 51 Pegasi, was assigned by John Flamsteed in his star atlas published in 1712.

51 Pegasi has a stellar classification of G5V,[3] indicating that it is a main-sequence star that is generating energy through the thermonuclear fusion of hydrogen at its core. The effective temperature of the chromosphere is about 5571 K, giving 51 Pegasi the characteristic yellow hue of a G-type star.[11] It is estimated to be 6.1–8.1 billion years old, somewhat older than the Sun, with a radius 24% larger and 11% more massive. The star has a higher proportion of elements other than hydrogen/helium compared to the Sun; a quantity astronomers term a star's metallicity. Stars with higher metallicity such as this are more likely to host planets.[3] In 1996 astronomers Baliunas, Sokoloff, and Soon measured a rotational period of 37 days for 51 Pegasi.[12]

Although the star was suspected of being variable during a 1981 study,[13] subsequent observation showed there was almost no chromospheric activity between 1977 and 1989. Further examination between 1994 and 2007 showed a similar low or flat level of activity. This, along with its relatively low X-ray emission, suggests that the star may be in a Maunder minimum period[3] during which a star produces a reduced number of star spots.

The star rotates at an inclination of 79+11
degrees relative to Earth.[7]

Planetary system

Artist impression of the exoplanet 51 Pegasi b.[14]

On October 6, 1995, Swiss astronomers Michel Mayor and Didier Queloz announced the discovery of an exoplanet orbiting 51 Pegasi.[10] The discovery was made with the radial velocity method on a telescope at Observatoire de Haute-Provence in France and using the ELODIE spectrograph. On October 12, 1995, confirmation came from Geoffrey Marcy from San Francisco State University and Paul Butler from the University of California, Berkeley using the Hamilton Spectrograph at the Lick Observatory near San Jose in California.

51 Pegasi b (51 Peg b) is the first discovered planetary-mass companion of its parent star. The planet has been informally named Bellerophon. After its discovery, many teams confirmed its existence and obtained more observations of its properties, including the fact that it orbits very close to the star, experiences estimated temperatures around 1200 °C, and has a minimum mass about half that of Jupiter. At the time, this close distance was not compatible with theories of planet formation and resulted in discussions of planetary migration. It has been assumed that the planet shares the star's inclination of 79 degrees.[15] However, several "hot Jupiters" are now known to be oblique relative to the stellar axis.[16]

The 51 Pegasi planetary system[17]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b ≥ 0.472 ± 0.039 MJ 0.0527 ± 0.0030 4.230785 ± 0.000036 0.013 ± 0.012

The planet and its host star is one of the planetary systems selected by the International Astronomical Union as part of their public process for giving proper names to exoplanets and their host star (where no proper name already exists).[18][19] The process involves public nomination and voting for the new names, and the IAU plans to announce the new names in mid-November 2015.[20]

See also


  1. ^ a b c d e f van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664.  
  2. ^ a b c d van Belle, Gerard T.; von Braun, Kaspar (2009). "Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars". The  
  3. ^ a b c d e Poppenhäger, K.; et al. (December 2009), "51 Pegasi – a planet-bearing Maunder minimum candidate", Astronomy and Astrophysics 508 (3): 1417–1421,  
  4. ^ a b c d e Monet, David G.; et al. (February 2003). "The USNO-B Catalog". The Astronomical Journal 125 (2): 984–993.  
  5. ^ a b Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory 4 (99).  
  6. ^ a b Frasca, A.; et al. (December 2009). "REM near-IR and optical photometric monitoring of pre-main sequence stars in Orion. Rotation periods and starspot parameters". Astronomy and Astrophysics 508 (3): 1313–1330.  
  7. ^ a b Simpson, E. K.; et al. (November 2010), "Rotation periods of exoplanet host stars",   [as "HD 217014"]
  8. ^ Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008). "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics". The Astrophysical Journal 687 (2): 1264–1293.  
  9. ^ "51 Peg – Star suspected of Variability". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2011-12-17. 
  10. ^ a b Mayor, Michael; Queloz, Didier (1995). "A Jupiter-mass companion to a solar-type star".  
  11. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  12. ^ Baliunas, Sallie; Sokoloff, Dmitry; Soon, Willie (1996). "Magnetic Field and Rotation in Lower Main-Sequence Stars: An Empirical Time-Dependent Magnetic Bode's Relation?". The  .
  13. ^ Kukarkin, B. V.; et al. (1981). Nachrichtenblatt der Vereinigung der Sternfreunde e.V. (Catalogue of suspected variable stars). Moscow: Academy of Sciences USSR Shternberg.  
  14. ^ "First Exoplanet Visible Light Spectrum". ESO Press Release. Retrieved 22 April 2015. 
  15. ^ "51_peg_b". Extrasolar Planet Encyclopaedia. Retrieved November 12, 2012. 
  16. ^ Roberto Sanchis-Ojeda; Josh N. Winn; Daniel C. Fabrycky (2012). "Starspots and spin-orbit alignment for Kepler cool host stars".  
  17. ^ Butler, R. P.; et al. (2006). "Catalog of Nearby Exoplanets". The  
  18. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. 9 July 2014
  19. ^ NameExoWorlds.
  20. ^ NameExoWorlds.

External links

  • Jean Schneider (2011). "Notes for star 51 Peg".  
  • 51 Pegasi at
  • nStars database entry
  • David Darling's encyclopedia

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