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Published online by Cambridge University Press: 01 December 2005
The orbital fits of multi-planetary systems from radial velocity data has proved to be a complex task. In some cases, different orbital solutions provide similarly good fits, especially when two planets are near mean-motion resonances. Ferraz-Mello et al (2005) and Goździewski et al (2005) showed that the published best fits of systems HD82932 and HD160691 are dynamically unstable, and re-determined their orbital parameters with Monte Carlo and genetic algorithms. In both cases dynamically stable orbits were found with RMS similar to the published orbits. It was also shown that uncertainties in the stellar mass Ferraz Mello et al (2005) and the stellar jitter Gozdziewski et al (2005) can significantly affect the orbital determination. Ford (2005) used a Markov chain Monte Carlo technique to quantify the orbit uncertainties. For some planetary systems he found a strong correlation between the orbital elements and/or significant non-Gaussian error distribution in the parameter space. As a consequence, the actual uncertainties in the orbital fits can be much larger (or smaller) than those published.