  In the environments where the abundance of heavy elements is low, rare events
are expected to impact the chemical enrichment. Dwarf galaxies have small
masses, low average metallicities and in general low star formation rates, and
thus investigating the chemical enrichment provides understanding on the impact
of each source of elements on the chemical abundance. Using a chemical
evolution model in which the rarity is introduced, we investigate the impact of
rare events on the chemical enrichment for Local Group dwarf galaxies. In the
model, the occurrence of individual sources of elements is estimated with the
star formation history derived by the colour-magnitude diagram. The abundance
ratios of trans-iron elements to iron predicted by the model show the
oscillation at the lowest metallicities because of the r-process events. In the
case of a galaxy of a lower mass, the oscillation caused by neutron star
mergers is also seen at higher metallicities, which suggests that the rarity
can be important in lower-mass systems. Regarding the source of the chemical
enrichment, we observe that the r-process sites seem to contribute more to the
production of trans-iron elements at low metallicities, but massive stars of
different rotating velocities also contribute to create part of the dispersion
of the abundance ratios through the s-process. Both observational and
theoretical data, including nucleosynthesis calculations and the chemical
abundance of metal-poor stars, are needed to obtain deeper insights into the
sources of the chemical enrichment at low metallicities.
