  We present computer simulations of a system of purely repulsive soft
colloidal particles interacting via the Hertz potential and constrained to a
two-dimensional plane. This potential describes the elastic interaction of
weakly deformable bodies and can be a reliable model for qualitative
description of behavior of soft macromolecules, like globular micelles and star
polymers. We find a large number of ordered phases, including the dodecagonal
quasicrystal, and analyze the melting scenarios of low density triangle and
square phases. It is interesting that depending on the position on the phase
diagram the system can melt both through the first order transition and in
accordance with the Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young
(BKTHNY) scenario (two continuous transitions with the intermediate hexatic
phase) and also in accordance with recently proposed two-stage melting with the
first order hexatic-isotropic liquid transition and continuous solid-hexatic
transition. We also demonstrate the possibility of the tricritical point on the
melting line.
