Top row: evolution of the central temperature (a) and entropy (b) as a function of density for all 143 runs. The lines have been colour-coded according to the cloud’s initial temperature T₀ (see legend in panel b)). Bottom row: c) evolution of the central temperature as a function of density for runs 30, 3, and 140 (see legend). d) Optical depth of the systems as a function of radius for runs 30, 3, and 140 (same colours as in panel c)), when the central density has just reached log (ρ_c) = −12.75 g cm^-3 (solid), and when the central temperature has reached log (T_c) = 1.2 K (dashed).