The Water D/H Ratio in Molecular Outflows in Orion BN/KL Shiya Wang Astronomy Department, University of Michigan Edwin A. Bergin (U. of Michigan) René Plume (U. of Calgary) Midwest Astrochemistry Meeting, Nov. 7-8, 2008

Interstellar and Cometary Ices H 2 O CO CO 2 CH 3 OH CH 4 OCS ISM(ices)Comets(1AU) Langer et al 1999, PPIV

Deuterium Fractionation of Water OHH2OH2OH3O+H3O+ O O H2H2 e-e- e-e- H3+H3+ HD H2H2 H2D+H2D+ cosmic ray H 2 DO + OOD HDO e-e- O e-e- e-e- HD High T Low T HDO/H 2 O > HD/H 2 ~ 3 x 10 -5

Water Origin in Molecular Outflows Orion BN/KLHigh-T shock chemistry Supersonic flows compress and heat the surrounding material and change the chemistry shocks with velocities between 15 and 30 km/s will produce large amounts of water vapor (Kaufmann & Neufeld 1996) O + H 2 OH + H OH + H 2 H 2 O + H Grain surface evaporation Grain-grain collisions and sputtering in shocks can vaporize mantles

CSO HDO 464 GHz Emission in Orion BN/KL T A * (K) V LSR (km/s) Offset in Arc-Seconds Plateau (18km/s flow): X(H 2 O) ~ 4 x (Persson et al. 2007) HDO/H 2 O ~ 0.005

3 Stage Chemical Model Pre-Shock T gas = T dust = K 10 6 years Shock v s = km/s T gas = K T dust = 10, 500 K 100 years Post-Shock T gas = T dust = 30 K 10 6 years Stage 1Stage 2 Stage 3 Bergin, Neufeld, & Melnick 1998 Kaufmann & Neufeld 1996 constant density visual extinction

shock post-shock Outflow age ~ 3000 years with 20 km/s, 0.04pc

shock post-shock Outflow age ~ 3000 years with 20 km/s, 0.04pc

Enhanced water abundance will persist for ~10 5 yrs, whereupon water freezes onto grain surfaces Two cases: (1) all the shocked water is produced by shock chemistry via gas-phase reactions of O and OH with H 2 (2) all atomic oxygen is locked on grains in the form of H 2 O, which then evaporates from the grain surfaces when shocked. Observed water abundance in Orion BN/KL low-velocity outflows can be produced in shocks (with shock velocity ~20 km/s and preshock gas temperature ~ 20 K), without grain evaporation contributions Summary