Gamma Cephei Ab
|Extrasolar planet||List of extrasolar planets|
|Star||Gamma Cephei A|
|Right ascension||(α)||23h 39m 20.8s|
|Declination||(δ)||+77° 37′ 56″|
|Distance||44.9 ± 0.3 ly
(13.76 ± 0.08 pc)
|Semimajor axis||(a)||2.044 ± 0.057 AU
|Eccentricity||(e)||0.115 ± 0.058|
|Orbital period||(P)||902.9 ± 3.5 d
(2.472 ± 0.010 y)
|Orbital speed||(υ)||24.71 km/s|
|(ω)||63 ± 27°|
|Time of periastron||(T0)||2,453,156.8
± 52.4 JD
|Semi-amplitude||(K)||27.5 ± 1.5 m/s|
|Minimum mass||(m sin i)||1.60 ± 0.13 MJ|
|Discovery date||13 July 1988 (suspected)
24 September 2002 (confirmed)
|Discoverer(s)||Hatzes et al.|
|Discovery method||Doppler spectroscopy|
|Discovery site||United States|
Gamma Cephei Ab is an extrasolar planet approximately 45 light-years away in the constellation of Cepheus (the King). The planet was confirmed to be in orbit around Gamma Cephei in 2002, but was first suspected to exist around 1988 (making this planet arguably the first true extrasolar planet discovered).
Detection and discovery
The first indications of Gamma Cephei Ab were reported in July 1988. The planet was tentatively identified by a Canadian team of astronomers, which was led by Bruce Campbell, Gordon Walker, and Stephenson Yang, while its existence was also announced by Anthony Lawton and P. Wright in 1989. Though not confirmed, this would have been the first true extrasolar planet, and it was hypothesized based on the same radial velocity technique later used successfully by others. However, the claim was retracted in 1992 due to the quality of the data not being good enough to make a solid discovery.
On September 24, 2002, Gamma Cephei Ab was finally confirmed. The team of astronomers (including William D. Cochran, Artie P. Hatzes, et al.) at the Planetary Systems and their Formation Workshop announced the preliminary confirmation of a long-suspected planet Gamma Cephei Ab with a minimum mass of 1.59 MJ (1.59 times that of Jupiter). The parameters were later recalculated when direct detection of the secondary star Gamma Cephei B allowed astronomers to better constrain the properties of the system. Gamma Cephei Ab moves in an elliptical orbit with a semimajor axis of 2.044 AU which takes almost two and a half years to complete. The eccentricity is 0.115, which means it moves between 1.81 and 2.28 AUs in orbital distance around Gamma Cephei A, which would place it from slightly beyond the orbit of Mars, to the inner Asteroid belt in the solar system.
Hipparcos data taken in 2006 constrains its mass below "13.3 MJ at the 95% confidence level, and 16.9 MJ at the 99.73% (3 σ) confidence level". This is not much to go on, but it is enough to verify that it is not another unseen brown or red dwarf.
- Neuhäuser, R.; Mugrauer, M.; Fukagawa, M.; Torres, G.; Schmidt, T. (2007). "Direct detection of exoplanet host star companion γ Cep B and revised masses for both stars and the sub-stellar object". Astronomy and Astrophysics 462 (2): 777–780. arXiv:astro-ph/0611427. Bibcode:2007A&A...462..777N. doi:10.1051/0004-6361:20066581.
- Boss, Alan (2009). The Crowded Universe: The Search for Living Planets. Basic Books. ISBN 978-0-465-00936-7.
- Hatzes et al.; Cochran, William D.; Endl, Michael; McArthur, Barbara; Paulson, Diane B.; Walker, Gordon A. H.; Campbell, Bruce; Yang, Stephenson (2003). "A Planetary Companion to Gamma Cephei A". The Astrophysical Journal 599 (2): 1383–1394. arXiv:astro-ph/0305110. Bibcode:2003ApJ...599.1383H. doi:10.1086/379281.
- Guillermo Torres (2007). "The Planet Host Star γ Cephei: Physical Properties, the Binary Orbit, and the Mass of the Substellar Companion". The Astrophysical Journal 654 (2): 1095–1109. arXiv:astro-ph/0609638. Bibcode:2007ApJ...654.1095T. doi:10.1086/509715.
- "A Planetary Companion to the Binary Star Gamma Cephei". McDonald Observatory. Retrieved 2008-06-23.
- "Errai 2". SolStation. Retrieved 2008-06-23.