  A number of multiplanet systems are observed to contain planets very close to
mean motion resonances, although there is no significant pileup of precise
resonance pairs. We present theoretical and numerical studies on the outcome of
capture into first-order mean motion resonances (MMRs) using a parametrized
planet migration model that takes into account nonlinear eccentricity damping
due to planet-disk interaction. This parametrization is based on numerical
hydrodynamical simulations and is more realistic than the simple linear
parametrization widely used in previous analytic studies. We find that
nonlinear eccentricity damping can significantly influence the stability and
outcome of resonance capture. In particular, the equilibrium eccentricity of
the planet captured into MMRs become larger, and the captured MMR state tends
to be more stable compared to the prediction based on the simple migration
model. In addition, when the migration is sufficiently fast or/and the planet
mass ratio is sufficiently small, we observe a novel phenomenon of eccentricity
overshoot, where the planet's eccentricity becomes very large before settling
down to the lower equilibrium value. This can lead to the ejection of the
smaller planet if its eccentricity approaches unity during the overshoot. This
may help explain the lack of low-mass planet companion of hot Jupiters when
compared to warm Jupiters.
