51 Pegasi

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51 Pegasi
51 Pegasi is located in 100x100
51 Pegasi

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]
Characteristics
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
Astrometry
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
Details
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
Helvetios, 51 Peg, GJ 882, HR 8729, BD +19°5036, HD 217014, LTT 16750, GCTP 5568.00, SAO 90896, HIP 113357.[9]
Database references
SIMBAD data
Exoplanet Archive data
ARICNS data
Extrasolar Planets
Encyclopaedia
data

51 Pegasi (abbreviated 51 Peg), also named Helvetios, is a Sun-like star located 50.9 light-years (15.6 parsecs)[1] from Earth in the constellation of Pegasus. It was the first main-sequence star found to have an exoplanet (designated 51 Pegasi b, unofficially dubbed Bellerophon, later named Dimidium) orbiting it.[10]

Properties

The star is of apparent magnitude 5.49, and so is visible with the naked eye under suitable viewing conditions.

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
−30
degrees relative to Earth.[7]

Nomenclature

51 Pegasi is the Flamsteed designation. On its discovery, the planet was designated 51 Pegasi b by its discoverers and unofficially dubbed Bellerophon by the astronomer Geoffrey Marcy, in keeping with the convention of naming planets after Greek and Roman mythological figures (Bellerophon was a figure from Greek mythology who rode the winged horse Pegasus).[14] In July 2014 the International Astronomical Union launched a process for giving proper names to certain exoplanets and their host stars.[15] The process involved public nomination and voting for the new names.[16] In December 2015, the IAU announced the winning names were Helvetios for this star and Dimidium for its planet.[17]

The winning names were those submitted by the Astronomische Gesellschaft Luzern, Switzerland. 'Helvetios' is Latin for 'the Helvetian' and refers to the Celtic tribe that lived in Switzerland during the Middle Ages; 'Dimidium' is Latin for 'half', referring to the planet's mass of at least half the mass of Jupiter.[18]

Planetary system

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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. 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.[19] However, several "hot Jupiters" are now known to be oblique relative to the stellar axis.[20]

The 51 Pegasi planetary system[22]
Companion
(in order from star)
Mass Semimajor axis
(AU)
Orbital period
(days)
Eccentricity Inclination Radius
b (Dimidium) ≥ 0.472 ± 0.039 MJ 0.0527 ± 0.0030 4.230785 ± 0.000036 0.013 ± 0.012

See also

References

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  14. University of California at Berkeley News Release 1996-17-01
  15. NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
  16. NameExoWorlds The Process
  17. Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
  18. NameExoWorlds The Approved Names
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External links

Coordinates: Sky map 22h 57m 28.0s, +20° 46′ 08″