37th DPS Meeting, 4-9 September 2005
Session 28 Extrasolar Planets
Oral, Tuesday, September 6, 2005, 4:20-6:00pm, Law LG19

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[28.06] Capture of the 55 Cancri planets b and c into a 3:1 orbital resonance by migration

H. Scholl (Observatoire de la Cote d'Azur), F. Marzari (University of Padova), P. Tricarico (Washington State University)

Four planets are known to orbit the main-sequence star 55 Cancri. Planets b and c have respective semimajor axes of 0.115 and 0.240 AU. They are locked in a 3:1 orbital resonance. The eccentricity of planet b oscillates between almost zero and 0.22 while it oscillates between 0.25 and 0.44 for planet c. This suggests that the system has dynamically evolved: Originally, the two planetary orbits were farther apart and converged due to a migration process which resulted in a capture into the 3:1 resonance. We simulate a type II migration scenario by a 3-D N-Body model. The semimajor axis, eccentricity and periastron precession rate of each planet are parameters. In order to compare the simulated migrating planetary systems in phase space with the observed one, we project the resulting evolutionary tracks on diagrams obtained by a Frequency Map Analysis for the 55 CnC planetary system. Most simulations yield resonant systems which are quite different from the observed one. The present system can be obtained if the eccentricities of at least one of the planets planets b or c are in the range 0.05 to 0.06 just before capture into the 3:1 resonance. Mutual perturbations of the two planets b and c on originally almost cirular orbits do not produce such comparatively large eccentricities before capture. An additional excitation mechanism appears to be necessary.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.