Abstract
We present the observations of ammonia emission lines toward the interstellar filament WB 673 hosting the dense clumps WB 673, WB 668, S233-IR, and G173.57+2.43. LTE analysis of the lines allows us to estimate gas kinetic temperature (less than or similar to 30K in all the clumps), number density (7-17 x 10(3) cm(-3)), and ammonia column density (approximate to 1-1.5 x 10(15) cm(-2)) in the dense clumps. We find signatures of collapse in WB 673 and presence of compact spatially unresolved dense clumps in S233-IR. We reconstruct 1D density and temperature distributions in the clumps and estimate their ages using astrochemical modelling. Considering CO, CS, NH3, and N2H+ molecules (plus HCN and HNC for WB 673), we find a chemical age of t(chem )= 1-3 x 10(5) yrs, providing the best agreement between the simulated and observed column densities in all the clumps. Therefore, we consider t(chem) as the chemical age of the entire filament. A long preceding low-density stage of gas accumulation in the astrochemical model would break the agreement between the simulated and observed column densities. We suggest that rapid star formation over a similar to 10(5) yrs time-scale take place in the filament.