51 Pegasi
| 51 Pegasi | |
| Stellar characteristics | |
|---|---|
| Constellation | Pegasus |
| Right ascension (Epoch J2000) | 22h 57m 28s |
| Declination (Epoch J2000) | +20° 46' 7.8" |
| Spectral type | G4-5 Va |
| Distance from Sol | 50.1 ly |
| Other designations | 51 Peg, NSV 14374, HR 8729, Gl 882, Hip 113357, HD 217014, BD+19 5036, SAO 90896, LTT 16750 |
51 Pegasi is a yellow-orange main sequence dwarf star of spectral and luminosity type G4-5 Va, but it had been previously classified as G2-2.5 and sometimes as a subgiant (IV). The star has about 1.06 times the mass of Sol (51 Peg at exoplanets.org), 1.15 to 1.4 times its diameter (Henry et al, 2000; and Guillot et al, 1996), and 1.30 times its visual luminosity (51 Pegasi at the Observatoire de Genève). Relatively bright and large for its spectral type and mass, it appears to be running low on core hydrogen and may be as old as 8.5 billion years old or more (Henry et al, 1997), but one analysis of isochrones suggests that the star could be a billion years younger -- at 7.5 billion years old (Guinan et al, 1999). 51 Pegasi is 1.6 times more enriched than Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (51 Peg at exoplanets.org).
In 1995, astronomers (Michel Mayor and Didier Queloz) announced the discovery of a Jupiter-class planet around 51 Pegasi using radial-velocity methods (Mayor and Queloz, 1995; and 51 Pegasi at the Observatoire de Genève). Planet "b" has at least 46 percent of Jupiter's mass. It moves around 51 Pegasi at an average distance of only 0.05 AUs (a semi-major axis well within Mercury's orbital distance) in a highly circular orbit (e=0.03) that takes only 4.2 days to complete. Its orbit may be inclined by less than 85° from the perspective of an observer on Earth (Henry et al, 1997). Assuming a Jupiter-like composition, its radius may be about 1.2 times that of Jupiter, enlarged relative to Jupiter because of greater absorbed stellar radiation in its inner ("torch") orbit. However, the planet may be too hot to hold onto a thick hydrogen atmosphere
(Boilerplate from SolStation.com)
Known Places Around 51 Pegasi
- 51 Pegasi I
