  The Kepler mission has released ~4229 transiting planet candidates. There are
approximately 222 candidate systems with three planets. Among them, the period
ratios of planet pairs near 1.5 and 2.0 reveal that two peaks exist for which
the proportions of the candidate systems are ~7.0% and 18.0%, respectively. In
this work, we study the formation of mean motion resonance (MMR) systems,
particularly for the planetary configurations near 3:2 and 2:1 MMRs, and we
concentrate on the interplay between the resonant configuration and the
combination of stellar accretion rate, stellar magnetic field, speed of
migration and additional planets. We perform more than 1000 runs by assuming a
system with a solar-like star and three surrounding planets. From the
statistical results, we find that under the formation scenario, the proportions
near 1.5 and 2.0 can reach 14.5% and 26.0%, respectively. In addition, $\dot
M=0.1\times 10^{-8} ~M_\odot ~{\rm yr^{-1}}$ is propitious toward the formation
of 3:2 resonance, whereas $\dot M=2\times 10^{-8} ~M_\odot ~{\rm yr^{-1}}$
contributes to the formation of 2:1 resonance. The speed-reduction factor of
type I migration $f_1\geq 0.3$ facilitates 3:2 MMRs, whereas $f_1\geq 0.1$
facilitates 2:1 MMRs. If additional planets are present in orbits within the
innermost or beyond the outermost planet in a three-planet system, 3:2:1 MMRs
can be formed, but the original systems trapped in 4:2:1 MMRs are not affected
by the supposed planets. In summary, we conclude that this formation scenario
will provide a likely explanation for Kepler candidates involved in 2:1 and 3:2
MMRs.
