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Upsilon Andromedae b

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

   CAPTION: Upsilon Andromedae b

     Extrasolar planet       Lists of extrasolar planets

                 Artist's impression of Upsilon Andromedae b

                         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) 0.0595 ± 0.0034 AU
   Eccentricity       (e) 0.023 ± 0.018
   Orbital period     (P) 4.617113 ± 0.000082 d
   Inclination        (i)  ?°
   Longitude of
   periastron         (ω) 63.4°
   Time of periastron (τ) 2,451,802.64 ± 0.71 JD
                   Physical characteristics
   Mass               (m) >0.687 ± 0.058 M[J]
   Radius             (r)  ? R[J]
   Density            (ρ)  ? kg/ m^3
   Temperature        (T) ~150 to ~1800 K
                    Discovery information
   Discovery date         1996
   Discoverer(s)          Butler, Marcy et al.
   Detection method       Radial velocity
   Discovery status       Confirmed
                      Other designations
   Upsilon Andromedae Ab, 50 Andromedae b

   Upsilon Andromedae b (occasionally referred to as Upsilon Andromedae Ab
   to distinguish it from the red dwarf star Upsilon Andromedae B) is an
   extrasolar planet orbiting the Sun-like star Upsilon Andromedae A every
   4.62 days. Discovered in 1996 by Geoffrey Marcy and R. Paul Butler, it
   was one of the first hot Jupiters to be discovered. Upsilon Andromedae
   b is the innermost known planet in its planetary system.

Discovery

   Like the majority of known extrasolar planets, Upsilon Andromedae b was
   detected by the variations in its star's radial velocity caused by the
   planet's gravity. The variations were detected by making sensitive
   measurements of the Doppler shift of Upsilon Andromedae's spectrum. The
   planet was announced in 1996, together with 55 Cancri b and the planet
   orbiting Tau Boötis.

Orbit and mass

   Like 51 Pegasi b, the first extrasolar planet discovered around a
   normal star, Upsilon Andromedae b orbits very close to its star, closer
   than Mercury does to our Sun. The planet takes 4.617 days to complete
   an orbit, with a semimajor axis of 0.0595 AU.

   A limitation of the radial velocity method used to detect Upsilon
   Andromedae b is that only a lower limit on the mass can be found. In
   the case of Upsilon Andromedae b, this lower limit is 68.7% of the mass
   of Jupiter, though depending on the inclination of the orbit, the true
   mass may be much greater.

Characteristics

   Given the planet's high mass, it is likely that Upsilon Andromedae b is
   a gas giant with no solid surface. Since the planet has only been
   detected indirectly, properties such as its radius and composition are
   unknown. Assuming that the planet is similar to Jupiter in composition
   and that its environment is close to chemical equilibrium, Upsilon
   Andromedae b is predicted to have clouds of silicates and iron in its
   upper atmosphere.

   The Spitzer Space Telescope measured the planet temperature, and found
   that the difference between the two sides of Upsilon Andromedae b of
   about 1,400 degrees Celsius, ranging from minus 20 to 230 degrees to
   about 1,400 to 1,650 degrees Celsius.

   Upsilon Andromedae b appears to be responsible for increased
   chromospheric activity on its parent star. Observations suggest that
   there is a "hot spot" on the star around 169° away from the
   sub-planetary point. This may be the result of interactions between the
   magnetic fields of the planet and the star. The mechanism may be
   similar to that responsible for the activity of RS Canum Venaticorum
   variable stars, or the interaction between Jupiter and its moon Io.

   The planet is unlikely to have large moons, since tidal forces would
   either eject them from orbit or destroy them on short timescales
   compared to the age of the system.
   Retrieved from " http://en.wikipedia.org/wiki/Upsilon_Andromedae_b"
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