Short-Term Dynamical Interactions among Extrasolar Planets

We show that short-term perturbations among massive planets in multipleplanet systems can result in radial velocity variations of the central starwhich differ substantially from velocity variations derived assuming theplanets are executing independent Keplerian motions. We discuss two alternatefitting methods which can lead to an improved dynamical description of multipleplanet systems. In the first method, the osculating orbital elements aredetermined via a Levenberg-Marquardt minimization scheme driving an N-bodyintegrator. The second method is an improved analytic model in which orbitalelements are allowed to vary according to a simple model for resonantinteractions between the planets. Both of these methods can determine the truemasses for the planets by eliminating the sin(i) degeneracy inherent in fitsthat assume independent Keplerian motions. We apply our fitting methods to theGJ876 radial velocity data (Marcy et al. 2001), and argue that the mass factorsfor the two planets are likely in the 1.25-2.0 rangeComment: 13 pages, including 4 figures and 3 tables Accepted by Astrophyiscal Journal Letter