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Upsilon Andromedae

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

   CAPTION: Upsilon Andromedae A

                         Observation data
   Epoch J2000.0
   Constellation             Andromeda
   Right ascension           01^h 36^m 47.8^s
   Declination               +41° 24' 20"
   Apparent magnitude (V)    +4.09
                          Characteristics
   Spectral type             F8V
   B-V colour index          0.54
   U-B colour index          0.06
   Variable type             none
                            Astrometry
   Radial velocity (R[v])    -28.9 km/s
   Proper motion (μ)         RA: -172.57 mas/ yr
                             Dec.: -381.03 mas/ yr
   Parallax (π)              74.25 ± 0.72 mas
   Distance                  43.9 ± 0.4 ly
                             (13.5 ± 0.1 pc)
   Absolute magnitude (M[V]) 3.96
                              Details
   Mass                      1.28 M[☉]
   Radius                    1.6 R[☉]
   Luminosity                3.4 L[☉]
   Temperature               6,095 K
   Metallicity               100%
   Rotation                  ~8 km/s
   Age                       3.3 × 10^9 years
                        Other designations
   50 Andromedae, Gl 61, HR 458, BD +40°332, HD 9826, LTT 10561,
   GCTP 331.00, SAO 37362, FK5 1045, GC 1948, CCDM 01367+4125,
   WDS 01368+4124A, HIP 7513

   Upsilon Andromedae (υ Andromedae / Ups And) is a binary star,
   approximately 44 light-years away in the constellation Andromeda. The
   system contains a yellow-white dwarf star (Upsilon Andromedae A)
   similar to the Sun and a dim red dwarf (Upsilon Andromedae B). The two
   stars are separated by around 750 times the distance from the Earth to
   the Sun.

   As of 1999, three extrasolar planets are known in orbit around Upsilon
   Andromedae A. All three are comparable to Jupiter in mass. Upsilon
   Andromedae was both the first multiple-planet planetary system to be
   discovered around a main sequence star, and the first multiple-planet
   system known in a multiple star system.

   Upsilon Andromedae A is ranked 12th in the list of top 100 target stars
   for the NASA Terrestrial Planet Finder mission.

Distance and visibility

   Upsilon Andromedae is located fairly close to our solar system: the
   parallax of Upsilon Andromedae A was measured by the Hipparcos
   astrometry satellite as 74.25 milliarcseconds, corresponding to a
   distance of 13.5 parsecs. Upsilon Andromedae A has an apparent
   magnitude of +4.09, making it visible to the naked eye even under
   moderately light-polluted skies, about 10 degrees east of the Andromeda
   Galaxy. The dimmer star Upsilon Andromedae B is only visible with a
   telescope.

System components

   Upsilon Andromedae A is a yellow-white dwarf of spectral type F8V,
   similar to our Sun but rather younger, more massive and luminous.
   According to its entry in the Geneva-Copenhagen survey, the star is
   around 3.3 thousand million years old, and has a similar proportion of
   iron relative to hydrogen as the Sun. At around 1.3 solar masses, it
   will have a shorter lifetime than our Sun. The amount of ultraviolet
   radiation received by any planets in the star's habitable zone would be
   similar to the ultraviolet flux the Earth receives from the Sun.

   Upsilon Andromedae B is a red dwarf of spectral type M4.5V located at a
   projected distance of 750 AU from the primary star. It was discovered
   in 2002 in data collected as part of the Two Micron All Sky Survey. The
   star is less massive and far less luminous than our Sun.

   The Washington Double Star Catalog lists two optical components,
   however these do not share the system's proper motion and only appear
   close to Upsilon Andromedae because they happen to lie near the same
   line of sight.

Planetary system

   Upsilon Andromedae system planets
   Enlarge
   Upsilon Andromedae system planets

   The innermost planet of the Upsilon Andromedae A system was discovered
   in 1996 and announced in January of 1997, together with the planet of
   Tau Boötis and the innermost planet of 55 Cancri A. 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.

   Even when this 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
   Centre for Astrophysics independently concluded that, in fact, a
   three-planet model best fit the data. The two outer planets were
   designated Upsilon Andromedae c and d in order of increasing distance
   from the star. Both of the two outer planets are in more eccentric
   orbits than any of the planets in our solar system (including Pluto).
   The outermost planet resides in the system's habitable zone. In 2001,
   preliminary astrometric measurements suggested the orbit of the
   outermost planet is inclined at 155.5° to the plane of the sky,
   implying its true mass may lie between 9 and 10 Jupiter masses.

   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.
   Simulations show that the eccentricity of the system's planets may have
   arisen from a close encounter between the outer planet and a fourth
   planet, with the result that the fourth planet was ejected from the
   system or destroyed. As a result, the orbit of Upsilon Andromedae c
   gradually oscillates between circular and eccentric states every 6,700
   years.

   Upsilon Andromedae A does not appear to have a circumstellar dust disk
   similar to the Kuiper belt in our 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.

                                  Companion
                          (In order from star) Mass
                           ( M[J]) Orbital period
                            (days) Semimajor axis
                             ( AU) Eccentricity
   b >0.687 ± 0.058 4.617113 ± 0.000082 0.0595 ± 0.0034 0.023 ± 0.018
        c >1.97 ± 0.17 241.23 ± 0.30 0.830 ± 0.048 0.262 ± 0.021
          d >3.93 ± 0.33 1290.1 ± 8.4 2.54 ± 0.15 0.258 ± 0.032

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