47 Ursae Majoris is a sunlike star of magnitude 5.10, lying 46 light years away near the feet of Ursa Major, the Great Bear. It is a yellow class G1 V hydrogen-fusing star with a temperature almost exactly the same as the Sun's, 5780 K. Though the star's mass is about the same as the Sun's, it is 1.5 times as luminous as a result of greater age, estimated to be around 7 billion years. 47 UMa rotates with a period of 24 days, just slightly faster than the Sun, and has very solar metal content. On the other hand, the star shows no trace of solar-like sunspot activity.
Planetary System
In 1996, Geoffrey Marcy and R. Paul Butler announced the discovery of an extrasolar planet in orbit around 47 UMa. The discovery was made by observing the change in the Doppler shift of the star's spectrum, and hence its radial velocity, as the planet's gravity pulls it around. The planet, designated 47 UMa b, was the first long-period extrasolar planet discovered. A second planet, designated 47 UMa c, was announced in 2002, but is parameters have a much greater uncertainty.
The planetary system of 47 UMa is similar to the configuration of Jupiter and Saturn in our solar system, with same the orbital period ratio (close to 5:2), and a similar mass ratio. The innermost of the two planets averages 2.1 AU from the star, has a slightly elliptical orbit (e=0.06) with a period of 2.98 years, and contains a minimum mass of 2.4 times Jupiter's. The outer planet orbits nearly twice as far away, at a distance of 3.73 AU, with a somewhat more eccentric orbit (e=0.1), a period of 7.1 years, and a mass at least 0.76 times Jupiter's.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]