DDA 36th Meeting, 10-14 April 2005
Session 7 Planets: Orbits and Tides
Oral, Tuesday, April 12, 2005, 9:35am-12:15pm

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[7.03] On the 2:1 Orbital Resonance in the HD 82943 Planetary System

M.H. Lee (UCSB), R.P. Butler (Carnegie Inst. of Washington), D.A. Fischer (SFSU), G.W. Marcy (UC Berkeley), S.S. Vogt (UCO/Lick)

We present an analysis of the HD 82943 planetary system based on a radial velocity data set that combines new measurements obtained with the Keck telescope and the published CORALIE measurements. We examine simultaneously the goodness of fit and the dynamical properties of the best-fit double-Keplerian model as a function of the poorly constrained eccentricity and argument of periapse of the outer planet's orbit. The fit with the minimum \chi\nu2 is dynamically unstable if the orbits are assumed to be coplanar. However, the minimum is relatively shallow, and there is a wide range of fits outside the minimum with reasonable \chi\nu2. For an assumed coplanar inclination i = 30\circ (\sin i = 0.5), only the good fits with both of the lowest order, eccentricity-type mean-motion resonance variables at the 2:1 commensurability, \theta1 and \theta2, librating about 0\circ are stable. For \sin i = 1, there are also some good fits with only \theta1 librating that are stable for at least 107 years. The libration semiamplitudes are about 6\circ for \theta1 and 10\circ for \theta2 for the stable good fit with the smallest libration amplitudes of both \theta1 and \theta2. We do not find any good fits that are non-resonant and stable. Thus the two planets in the HD 82943 system are almost certainly in 2:1 mean-motion resonance, with at least \theta1 librating, and the observations may even be consistent with small-amplitude librations of both \theta1 and \theta2.

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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.