AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 14. Extra-Solar Planets
Display, Monday, May 31, 1999, 9:20am-6:30pm, Southeast Exhibit Hall

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[14.02] Three Jupiter-Mass Companions Orbiting Upsilon Andromedae

G.W. Marcy (SFSU \& U.C. Berkeley), R.P. Butler (Anglo-Australian Obs.), D.A. Fischer (SFSU)

The F8 main-sequence star Upsilon Andromedae has a known Jupiter-mass companion residing in a 4.6-day circular orbit of radius 0.06 AU (Butler et al. 1997). Follow-up observations by us and by the ``AFOE'' team (R.Noyes, S.Korzennik, T.Brown et al.) have revealed two additional velocity periodicities which are superimposed on the 4.6-day wobble. These new velocity periodicities are consistent with two elliptical orbits, with periods of 0.65 yr and 3.5 yr, and imply two additional companions orbiting at 0.82 AU and 2.5 AU, with minimum masses (M sin i) of 2.0 and 4.1 Jupiter-masses, respectively.

Non-Keplerian explanations for the new Doppler variations are examined, including radial and nonradial pulsations, rotational modulation of surface features, and stellar magnetic cycles. These explanations seem unlikely based on the observed photometric and chromospheric stability of the star, and the lack of stellar interior time scales at 0.65 or 3.5 yr.

Such a system of three Jupiter-mass planets is dynamically stable, as shown by analytic and numerical tests. The outer two companions both reside in elliptical, rather than circular, orbits (e = 0.23 and 0.36 respectively), as do all 9 known extrasolar planet candidates in distant orbits. If real, this planetary system is the first found around a main-sequence star, and offers insights into planet formation, planet--planet interactions, and the eccentricities of planetary orbits.

This work was supported by NASA, NSF, and Sun Microsystems.

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