Dynamical Properties of the Multiplanet System around HD 169830

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Abstract
The new 2-planetary system around HD169830 has been announced during the XIX-th IAP Colloquium "Extrasolar Planets: Today & Tomorrow" (Paris, June 30 - July 4, 2003) by the Geneva Extrasolar Planet Search team. We study the orbital dynamics of this system in the framework of the $N$-body problem. The analysis of its orbital stability is performed using the long-term integrations and the fast indicators, the Mean Exponential Growth factor of Nearby Orbits and the Frequency Map Analysis. The HD169830 appears to be located in a wide stable region of the phase space. The ratio of the mean motions of the planets HD169830b and c is between low-order mean motion resonances, 9:1 and 10:1. The long-term integration of the coplanar configurations, conducted over 1Gyr, reveals that the eccentricities of the companions vary with a large amplitude about 0.4-0.5 but there is no sign of instability. The orbital parameters of the planets resemble those of another 2-planetary system, around HD12661. Both of them can be classified as hierarchical planetary systems. We investigate whether these two exosystems are dynamically similar. Such similarities may be important for finding out if the formation and subsequent orbital evolution of exoplanetary systems obey common rules.Comment: 24 pages, 13 figures, 3 tables, submitted to ApJ. The preprint with high resolution figures is available from http://www.astri.uni.torun.pl/~chris/ms.ps.g