  We investigate the dependence of stellar properties on the initial mean
density of the molecular cloud in which stellar clusters form using radiation
hydrodynamical simulations that resolve the opacity limit for fragmentation. We
have simulated the formation of three star clusters from the gravitational
collapse of molecular clouds whose densities vary by a factor of a hundred. As
with previous calculations including radiative feedback, we find that the
dependence of the characteristic stellar mass, $M_{\rm c}$, on the initial mean
density of the cloud, $\rho$, is weaker than the dependence of the thermal
Jeans mass. However, unlike previous calculations, which found no statistically
significant variation in the median mass with density, we find a weak
dependence approximately of the form $M_{\rm c} \propto \rho^{-1/5}$. The
distributions of properties of multiple systems do not vary significantly
between the calculations. We compare our results to the result of observational
surveys of star-forming regions, and suggest that the similarities between the
properties of our lowest density calculation and the nearby Taurus-Auriga
region indicate that the apparent excess of solar-type stars observed may be
due to the region's low density.
