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Upsilon Andromedae c

2007 Schools Wikipedia Selection. Related subjects: Space (Astronomy)

   CAPTION: Upsilon Andromedae c

     Extrasolar planet    Lists of extrasolar planets
                      Parent star
   Star                   Upsilon Andromedae A
   Constellation          Andromeda
   Right ascension    (α) 01^h 36^m 47.8^s
   Declination        (δ) +41° 24′ 20″
   Spectral type          F8V
                   Orbital elements
   Semimajor axis     (a) 0.830 ± 0.048 AU
   Eccentricity       (e) 0.262 ± 0.021
   Orbital period     (P) 241.23 ± 0.30 d
   Inclination        (i)  ?°
   Longitude of
   periastron         (ω) 245.5 ± 5.3°
   Time of periastron (τ) 2,450,158.1 ± 4.5 JD
               Physical characteristics
   Mass               (m) >1.97 ± 0.17 M[J]
   Radius             (r)  ? R[J]
   Density            (ρ)  ? kg/ m^3
   Temperature        (T)  ? K
                 Discovery information
   Discovery date         1999
   Discoverer(s)          Marcy et al.
   Detection method       Radial velocity
   Discovery status       Confirmed
                  Other designations
   50 Andromedae c

   Upsilon Andromedae c is an extrasolar planet orbiting the Sun-like star
   Upsilon Andromedae A every 241.5 days. Its discovery in 1999 by
   Geoffrey Marcy and R. Paul Butler made Upsilon Andromedae the first
   known star (excluding the pulsar PSR 1257+12) to host a multiple-planet
   planetary system. Upsilon Andromedae c is the second known planet in
   order of distance from its star.

Discovery

   Like the majority of known extrasolar planets, Upsilon Andromedae c was
   detected by measuring variations in its star's radial velocity as a
   result of the planet's gravity. This was done by making precise
   measurements of the Doppler shift of the spectrum of Upsilon Andromedae
   A. At the time of discovery, Upsilon Andromedae A was already known to
   host one extrasolar planet, the hot Jupiter Upsilon Andromedae b,
   however by 1999 it was clear that the inner planet could not explain
   the velocity curve.

   In 1999, astronomers at both San Francisco State University and the
   Harvard-Smithsonian Centre for Astrophysics independently concluded
   that a three-planet model best fit the data. The two new planets were
   designated Upsilon Andromedae c and Upsilon Andromedae d.

Orbit and mass

   Like the majority of long- period extrasolar planets, the orbit of
   Upsilon Andromedae c is eccentric, more so than any of the major
   planets in our solar system (including Pluto). If placed in our solar
   system, Upsilon Andromedae c would lie between the orbits of Earth and
   Venus.

   The high orbital eccentricity may be the result of gravitational
   perturbations from the planet Upsilon Andromedae d. It is thought that
   interactions between Upsilon Andromedae d and a (now lost) outer planet
   moved Upsilon Andromedae d into an orbit closer to the star, where it
   gradually caused the orbit of Upsilon Andromedae c to become eccentric.
   Simulations suggest that the orbit of Upsilon Andromedae c returns to
   its original circular state roughly once every 6,700 years.

   A limitation of the radial velocity method used to detect Upsilon
   Andromedae c is that only a lower limit on the planet's mass can be
   obtained. For Upsilon Andromedae c, this lower limit is 1.97 times the
   mass of Jupiter, though depending on the inclination of the planet's
   orbit, the true mass may be much greater.

Characteristics

   Given the planet's high mass, it is likely that Upsilon Andromedae c is
   a gas giant with no solid surface. Since the planet has only been
   detected indirectly through observations of its star, properties such
   as its radius, composition and temperature are unknown. Assuming a
   composition similar to that of Jupiter and that its environment is
   close to chemical equilibrium, it is predicted that the upper
   atmosphere of Upsilon Andromedae c is cloudless.
   Retrieved from " http://en.wikipedia.org/wiki/Upsilon_Andromedae_c"
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