Secular dynamics of coplanar, non-resonant planetary system under the   general relativity and quadrupole moment perturbations
  We construct a secular theory of a coplanar system of N-planets not involved in strong mean motion resonances, and which are far from collision zones. Besides the point-to-point Newtonian mutual interactions, we consider the general relativity corrections to the gravitational potential of the star and the innermost planet, and also a modification of this potential by the quadrupole moment and tidal distortion of the star. We focus on hierarchical planetary systems. A survey regarding model parameters (the masses, semi-major axes, spin rate of the star) reveals a rich and non-trivial dynamics of the secular system. Our study is focused on its equilibria. Such solutions predicted by the classic secular theory, which correspond to aligned (mode I) or anti-aligned (mode II) apsides, may be strongly affected by the gravitational corrections. The so called true secular resonance, which is a new feature of the classic two-planet problem discovered by Michtchenko & Malhotra (2004), may appear in other, different regions of the phase space of the generalized model. We found bifurcations of mode II which emerge new, yet unknown in the literature, secularly unstable equilibria and a complex structure of the phase space. These equilibria may imply secularly unstable orbital configurations even for nitially moderate eccentricities. The point mass gravity corrections can affect the long term-stability in the secular time scale, which may directly depend on the age of the host star through its spin rate. We also analyze the secular dynamics of the upsilon Andromede system in the realm of the generalized model. Also in this case of the three-planet system, new secular equilibria may appear. 
Cezary Migaszewski, Krzysztof Gozdziewski