  Earth-sized planets were observed in close-in orbits around M dwarfs. While
more and more planets are expected to be uncovered around M dwarfs, theories of
their formation and dynamical evolution are still in their infancy. We
investigate the giant impact growth of protoplanets, which includes strong
scattering around low-mass stars. The aim is to clarify whether strong
scattering around low-mass stars affects the orbital and mass distributions of
the planets. We perform $N$-body simulation of protoplanets by systematically
surveying the parameter space of the stellar mass and surface density of
protoplanets. We find that protoplanets are often ejected after twice or three
times close-scattering around late M dwarfs. The ejection sets the upper limit
of the largest planet mass. Adopting the surface density scaling linearly with
the stellar mass, we find that as the stellar mass decreases less massive
planets are formed in orbits with higher eccentricities and inclinations. Under
this scaling, we also find that a few close-in protoplanets are generally
ejected. The ejection of protoplanets plays an important role in the mass
distribution of super-Earths around late M dwarfs. The mass relation of
observed close-in super-Earths and their central star mass is well reproduced
by ejection.

Earth and Planetary Astrophysics;Solar and Stellar Astrophysics