THE UPSILON ANDROMEDAE AND SOLAR PLANETARY SYSTEMS COMPARED

This figure compares the position of the planets orbiting Upsilon Andromedae with those orbiting the Sun, on April 16, 1999. The Upsilon Andromedae positions are determined from data obtained by two groups of scientists working at the Lick Observatory of the University of California, and at the Whipple Observatory of the Smithsonian Astrophysical Observatory. Each of these groups obtained completely independent data, which when analyzed yielded essentially the same characteristics of the planets. The plots show the positions as calculated from the combined data set.

The lower left panel shows that three planets orbit the star Upsilon Andromedae. The innermost planet is so close to the star that its orbit cannot be seen in this picture; it lies only about 0.06 AU from the star, where one AU, or Astronomical Unit, is the distance from the Sun to the Earth. The planet has a minimum mass of about 0.7 Jupiter Masses. The second planet, at 0.83 AU from the star, has minimum mass of about 2.1 Jupiter masses, and the third, at 2.5 AU from the star, has minimum mass of about 4.6 Jupiter masses. The orbits of the two outer planets are significantly elliptical.

The lower right panel shows our own solar system out as far as the planet Jupiter, plotted to the same scale as the Upsilon Andromedae system. This illustrates that if Upsilon Andromedae were laid on top of our solar system, its middle planet would lie between Venus and Earth, and its outer planet would lie between Mars and Jupiter.

The upper left panel shows how the speed of Upsilon Andromedae in the direction toward or away from the Earth has varied over the past dozen years. This pattern is due to the "wobble" of the star induced by each of the three massive planets orbiting it. The wobble caused by the inner planet, orbiting with a 4.6 day period, is so fast that it appears as only a blur in the figure. The middle planet, with a 242 day period, causes a variation with about 20 peaks across the figure. The outer planet, with about a 3.5 year period, causes a slower variation with about 4 peaks across the figure. Because of the ellipticity of its orbit, this last wobble makes a sawtooth pattern.

The upper right panel shows the corresponding wobble of the Sun as might be seen from a distant star. Only the influence of the planet Jupiter, with its 11-year period, is seen. The size of the wobble is only about 12 m/s (25 mph), similar to the speed of the fastest human sprinter.

This figure and other material about Upsilon Andromedae planetary system, plus an animation of the orbits, may be found on the web at

http://cfa-www.harvard.edu/afoe/

Other material about this planetary system may be found at

http://www.physics.sfsu.edu/~gmarcy/planetsearch/

This work has been submitted for publication to the Astrophysical Journal by the authors: R. Paul Butler (Anglo-Australian Observatory), Geoffrey W. Marcy and Debra A. Fischer (San Francisco State University and University of California, Berkeley), Timothy W. Brown (High Altitude Observatory, National Center for Atmospheric Research), Adam R. Contos, Sylvain G. Korzennik, Peter Nisenson, and Robert W. Noyes (Harvard-Smithsonian Center for Astrophysics).

The work of the Lick Observatory team is supported by NASA, NSF, and Sun Microsystems. The work of the Whipple Observatory team is supported by the Smithsonian Institution, NASA, and NSF.

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Adam Contos (acontos@cfa.harvard.edu)

Last modified: Wed Apr 14 17:37:31 1999