Sputtering of grains in C-type shocks

Sputtering yields are reported for the release of Mg, Fe, Si and O under im pact of He, C, O, Si and Fe on grain material composed of Mg- and Fe-bearin g silicates. The yields were derived using the trim code, which simulates t he results of the transport of ions in matter by means of classical Monte C arlo techniques. The energetics of the sputtering process are a key factor in the sputtering calculations, and so detailed determinations have been ma de of the energy with which atoms are bound to the lattice, using solid-sta te simulation programs. The probability of ejection of an atom is computed at a given energy, for a number of angles of incidence, and integrated to o btain the mean yield at that energy. These numerical results are then fitte d with a simple function of energy for convenience in subsequent applicatio ns. A grid of C-type shock models has been computed, using our new sputtering y ields, for pre-shock densities in the range 10(4)less than or equal ton(H)n (H)+2n(H-2)less than or equal to 10(6) cm(-3) and shock speeds 20 less than or equal tov(s)less than or equal to 45 km s(-1). Sputtered fractions can be high, exceeding 50 per cent for shock speeds in excess of approximately 40 km s(-1). The column densities of Si and SiO were also computed, for com parison with observations.