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47 Ursae Majoris

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

   CAPTION: 47 Ursae Majoris

                             Observation data
   Epoch J2000.0
   Constellation             Ursa Major
   Right ascension           10^h 59^m 28.0^s
   Declination               +40° 25′ 49″
   Apparent magnitude (V)    +5.03
                             Characteristics
   Spectral type             G1V
   B-V colour index          0.61
   U-B colour index          0.13
   Variable type             none
                                Astrometry
   Radial velocity (R[v])    +12.6 km/s
   Proper motion (μ)         RA: -315.92 mas/ yr
                             Dec.: 55.15 mas/ yr
   Parallax (π)              71.04 ± 0.66 mas
   Distance                  45.9 ± 0.4 ly
                             (14.1 ± 0.1 pc)
   Absolute magnitude (M[V]) 4.29
                                 Details
   Mass                      1.03 M[☉]
   Radius                    1.26 R[☉]
   Luminosity                1.54 L[☉]
   Temperature               5,740 K
   Metallicity               110%
   Rotation                  ~3 km/s.
   Age                       6.03 × 10^9 years
                            Other designations
   Gl 407, HR 4277, BD +41°2147, HD 95128, LTT 12934, GCTP 2556.00, SAO
   43557, FK5 1282, GC 15087, HIP 53721.

   47 Ursae Majoris (abbreviated 47 UMa) is a yellow dwarf star similar to
   our Sun located approximately 46 light-years away in the constellation
   Ursa Major. As of 2002, 47 Ursae Majoris is known to have two
   extrasolar planets orbiting it. 47 Ursae Majoris is ranked 72nd in the
   list of top 100 target stars for the NASA Terrestrial Planet Finder
   mission.

Distance and visibility

   47 Ursae Majoris is located fairly close to our solar system: according
   to astrometric measurements made by the Hipparcos astrometry satellite,
   the star exhibits a parallax of 71.04 milliarcseconds, corresponding to
   a distance of 14.1 parsecs. With an apparent magnitude of +5.03, it is
   visible to the naked eye under good conditions.

Stellar characteristics

   47 Ursae Majoris has a similar mass to that of our Sun. It is slightly
   more metal-rich than the Sun, having around 110% of the solar abundance
   of iron. With a spectral type of G1V, it is also slightly hotter than
   the Sun, at around 5,855 K. 47 Ursae Majoris has an absolute magnitude
   of +4.29, implying it has a visual luminosity around 60% greater than
   the Sun.

   Like the Sun, 47 Ursae Majoris is on the main sequence, converting
   hydrogen to helium in its core by nuclear fusion. Based on its
   chromospheric activity, the star may be around 6,000 million years old,
   though evolutionary models suggest an older age of around 8,700 million
   years.

Planetary system

   Orbits of the 47 Ursae Majoris system (black) compared to the planets
   of our solar system (blue)
   Enlarge
   Orbits of the 47 Ursae Majoris system (black) compared to the planets
   of our solar system (blue)

   In 1996 an extrasolar planet was announced in orbit around 47 Ursae
   Majoris by Geoffrey Marcy and R. Paul Butler. The discovery was made by
   observing the change in the star's radial velocity as the planet's
   gravity pulled it around. The measurements were made by observing the
   Doppler shift of the star's spectrum. The planet, designated 47 Ursae
   Majoris b was the first long- period extrasolar planet discovered.
   Unlike the majority of known long-period extrasolar planets, 47 Ursae
   Majoris b has a low- eccentricity orbit. The planet is at least 2.63
   times the mass of Jupiter and takes 1,089 days to orbit its star. If
   located in our solar system, it would lie between the orbits of Mars
   and Jupiter.

   In 2001, preliminary astrometric measurements suggest the orbit of 47
   Ursae Majoris b is inclined at an angle of 63.1° to the plane of the
   sky. If these measurements are confirmed, this implies the planet's
   true mass is around 2.9 times that of Jupiter.

   A second planet, designated 47 Ursae Majoris c was announced in 2002 by
   Debra Fischer, Geoffrey Marcy and R. Paul Butler. The discovery was
   made using the same radial velocity method used to detect the first
   planet. 47 Ursae Majoris c is also in a long-period orbit, taking
   around 2,594 days to complete. The eccentricity of the orbit is not as
   well known as that of the inner planet, though it is likely to be low.

   The two known planets are in a similar configuration to Jupiter and
   Saturn in our solar system: the ratio of orbital periods in both cases
   is close to 5:2, and the mass ratios are similar. The smaller scale and
   higher masses of the 47 Ursae Majoris system implies that the planets
   experience stronger mutual perturbations than Jupiter and Saturn do,
   which suggests the true masses of the planets are not much greater than
   the lower limits obtained by the radial velocity method.

   Simulations suggest that the inner part of the habitable zone of 47
   Ursae Majoris could host a terrestrial planet on a stable orbit, though
   the outer regions of the habitable zone would be disrupted by the
   gravitational influence of the planet 47 Ursae Majoris b. However, the
   presence of a giant planet within 2.5 AU of the star may have disrupted
   planet formation in the inner system, and reduced the amount of water
   delivered to inner planets during accretion. This may mean any
   terrestrial planets orbiting in the habitable zone of 47 Ursae Majoris
   are likely to be small and dry.

        Companion
   (In order from star)     Mass
                          ( M[J])    Orbital period
                                         (days)    Semimajor axis
                                                       ( AU)     Eccentricity
            b           >2.63 ± 0.23  1089.0 ± 2.9  2.13 ± 0.12  0.061 ± 0.014
            c           >0.79 ± 0.13   2594 ± 90    3.79 ± 0.24   0.00 ± 0.12

47 Ursae Majoris in fiction

   47 Ursae Majoris is the setting of the Coyote series by Allen Steele:
   much of the action takes place on Coyote, a fictional habitable moon of
   47 Ursae Majoris b, which is named Bear in the books.

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