Context. The coalescence of two white dwarfs is the final outcome of a sizeable fraction of binary stellar systems. Moreover, this process has been proposed to explain several interesting astrophysical phenomena. Aims. We present the results of a set of high-resolution simulations of the merging process of two white dwarfs. Methods. We use an up-to-date Smoothed Particle Hydrodynamics code which incorporates very detailed input physics and an improved treatment of the artificial viscosity. Our simulations have been done using a large number of particles (~ 4 × 105 ) and cover the full range of masses and chemical compositions of the coalescing white dwarfs. We also compare the time evolution of the system during the first phases of the coalescence with that obtained using a simplified treatment of mass transfer, we discuss in detail the characteristics of the final configuration, we assess the possible observational signatures of the merger, like the associated gravitational waveforms and the fallback X-ray flares, and we study the long-term evolution of the coalescence. Results. The mass transfer rates obtained during the first phases of the merger episode are in agreement the theoretical expectations. In all the cases studied the merged configuration is a central compact object surrounded by a self-gravitating keplerian disk, except in the case in which two equal-mass white dwarfs coalesce. Conclusions. We find that the overall evolution the system and the main characteristics of the of the final object are in agreement with other previous studies in which smaller resolutions were used. We also find the the fallback X-ray luminosities are of the order of 1047 erg/s. The gravitational waveforms are characterized by the sudden dissapearance of the signal in a few orbital periods.

Peer Reviewed