Upsilon Andromedae A Planetary System
The innermost planet of the Upsilon Andromedae A system was discovered in 1996 and announced in January 1997, together with the planet of Tau Boötis and the innermost planet of 55 Cancri. The discovery was made by Geoffrey Marcy and R. Paul Butler, both astronomers at San Francisco State University. The planet, designated Upsilon Andromedae b, was discovered by measuring changes in the star's radial velocity induced by the planet's gravity. Because of its closeness to the parent star, it induced a large wobble which was detected relatively easily. The planet appears to be responsible for enhanced activity in the chromosphere of its star.
Image : Upsilon Andromedae A Planetary System (Ups And A System)
Image credit : Ricnun
Licensed under CC-BY-SA-0.3
Even when the first planet was taken into account, there still remained significant residuals in the radial velocity measurements, and it was suggested there might be a second planet in orbit. In 1999, astronomers at both San Francisco State University and the Harvard-Smithsonian Center for Astrophysics independently concluded that a three-planet model best fit the data. The two outer planets were designated Upsilon Andromedae c and Upsilon Andromedae d in order of increasing distance from the star. Both of these planets are in more eccentric orbits than any of the planets in the Solar System (including Pluto). Upsilon Andromedae d resides in the system's habitable zone.
Image: Upsilon Andromedae b planet
Image : Upsilon Andromedae c planet
Image credit: Harbingerdawn
Licensed under CC BY-SA 0.3
The orbital parameters of this three planet system have been fully determined. The system is not coplanar, with each other or with the stellar rotation, as in our solar system. Simulations shows that the measured configuration of the planets produces indeed stable orbits for at least 100 million years, where planets b and d remain roughly coplanar. General relativity is expected to have strong effects on planet b, because it orbits at a distance of just ~0.05 AU from the parent star. The apsides of planet c and d, instead, oscillates with time; the orbit of Upsilon Andromedae c thus returns to a nearly circular state every 9,000 years. The eccentricity of those planets may have arisen from a close encounter between the outer planet and a fourth planet, with the result that the third planet was ejected from the system or destroyed. Such a mechanism could have been triggered by perturbations on the orbit of the companion star, which arise from close encounters with other stars and from the tidal field of the Milky Way. The orbits of the two inner planets seems to be shaped by tidal interactions, while the evolution of c and d orbits is secular.
Image : Upsilon Andromedae d moon
Image credit : Lucianomendez
Licensed under CC BY-SA 3.0
The existence of further planets too small or distant to detect has not been ruled out, though the presence of Jupiter-mass planets as close as 5 AU from Upsilon Andromedae A would make the system unstable. However, a fourth planet (Upsilon Andromedae e) was discovered in 2010. This planet seems to be in a 3:1 resonance with Upsilon Andromedae d; other authors, while confirming evidence for a fourth planet, challenge the values found, since they use a data set inconsistent with the others.
Upsilon Andromedae does not appear to have a circumstellar dust disk similar to the Kuiper belt in the Solar System. This may be the result of perturbations from the companion star removing material from the outer regions of the Upsilon Andromedae A system.
Host Star
Upsilon Andromedae (υ Andromedae, abbreviated Upsilon And, υ And) is a binary star located approximately 44 light-years from Earth in the constellation of Andromeda. The system consists of an F-type main-sequence star (designated υ Andromedae A, officially named Titawin in the Amazigh language /tɪtəˈwiːn/) and a smaller red dwarf.
As of 2010, four extrasolar planets (designated Upsilon Andromedae b, c, d and e; the first three named Saffar, Samh and Majriti, respectively) are believed to orbit υ Andromedae A. All four are likely to be jovian planets that are comparable in size to Jupiter. This was both the first multiple-planet system to be discovered around a main-sequence star, and the first multiple-planet system known in a multiple star system.
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