On the history of the interplay between HD 56925 and NGC 2359

NGC 2359 is an optical nebula excited by the powerful wind and the radiatio n of the Wolf-Rayet star HD56925. We have investigated the interaction betw een this massive star and the surrounding neutral gas by analyzing the larg e-scale 21 cm-HI emission and by mapping the nebula in the J = 1 --> 0 and the J = 2 --> 1 lines of CO. We found a conspicuous (70 x 37 pc) HI shell, expanding at 12 km s(-1), likely produced during the main-sequence phase of the star. The molecular gas towards NGC 2359 shows three velocity componen ts. Two of these components, A1 and A2, have narrow linewidths (1-2 km s(-1 )) and radial velocities of 35-38 and 64-68 km s(-1) respectively. The thir d component is detected at radial velocities between 50 and 58 km s(-1) and has a broader profile (up to 5.5 km s(-1)). Furthermore, this component is morphologicaly related with the nebula and has a velocity gradient of a fe w km s(-1). We have also estimated the physical parameters of the molecular gas by means of a LVG modelling of the CO emission. The gas projected onto the southern HII region of the nebula has low CO column density and is rat her hot, probably up to 80K. Several profiles of the (CO)-C-13 J = 1 --> 0 line near the peak of the emission, together with a weak emission bridge be tween the broad and one of the narrow components (component A2), suggest th e presence of a shock front acting in the southern part of the nebula. This shock was likely produced in a previous RSG/LBV phase of HD56925.