The Water D/H Ratio in Molecular Outflows in Orion BN/KL
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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
description
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. ISM(ices). Comets(1AU). 100 2 - 20 4 - 24 3 - 10 2 0.4. 100 - PowerPoint PPT Presentation
Transcript of The Water D/H Ratio in Molecular Outflows in Orion BN/KL
The Water D/H Ratio in Molecular Outflows in Orion
BN/KL
Shiya WangAstronomy 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
H2OCOCO2
CH3OHCH4
OCS
1002 - 204 - 243 - 1020.4
1005 - 73 - 200.3 - 50.2 - 1.20.2
ISM(ices) Comets(1AU)
Langer et al 1999, PPIV
Deuterium Fractionation of Water
OH
H2O
H3O+
O
O
H2
e-
e-H3
+
HD
H2
H2D+
cosmic ray
H2DO+
O
OD
HDO
e-
O
e-
e-
HD
High TLow T
HDO/H2O > HD/H2 ~ 3 x 10-5
Water Origin in Molecular Outflows
Orion BN/KL High-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 + H2 OH + H OH + H2 H2O + 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)
VLSR (km/s)
Offset in Arc-Seconds
Plateau (18km/s flow): X(H2O) ~ 4 x 10-6
(Persson et al. 2007) HDO/H2O ~ 0.005
3 Stage Chemical Model3 Stage Chemical Model
Pre-Shock
Tgas = Tdust
= 10 - 30 K106 years
Shock
vs = 10 - 40 km/sTgas= 500 - 3000 KTdust = 10, 500 K100 years
Post-Shock
Tgas = Tdust = 30 K
106 years
Stage 1 Stage 2 Stage 3Stage 3
Bergin, Neufeld, & Melnick 1998Kaufmann & 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 ~105 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 H2
(2) all atomic oxygen is locked on grains in the form of H2O, 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
