1 INTRODUCTION
2 DATA
3 SOURCE SELECTION AND MODELLING
3.1 Source Sample
3.2 Distances
3.3 Radiative Transfer Modelling
4 RESULTS
4.1 Masses
4.2 Temperatures
4.3 Central Densities
4.4 The Interstellar Radiation Field
4.5 Asymmetry Factor
4.6 Mean Core Properties
5 SUMMARY