  The phase diagram of star polymer solutions in a good solvent is obtained
over a wide range of densities and arm numbers by Monte Carlo simulations. The
effective interaction between the stars is modeled by an ultrasoft pair
potential which is logarithmic in the core-core distance. Among the stable
phases are a fluid as well as body-centered cubic, face-centered cubic,
body-centered orthogonal, and diamond crystals. In a limited range of arm
numbers, reentrant melting and reentrant freezing transitions occur for
increasing density.
