Transcript O2talk.ppt

Chemical Modeling of O2 in
Cold Interstellar Cores
Donghui Quan
Eric Herbst
George Hassel
The Ohio State University
Outline
• O2 Mystery
• Modeling Method
• Key Reaction
• Results and Discussion
• Conclusion
O2 observations VS Steady State Estimation
• O2 is lack of detection towards cold
interstellar cores
L134N: XO2 ≤1.7E-7
TMC-1: XO2 ≤7.7E-8
• Steady state estimation gives much bigger
values exceeding upper limits
Modeling method – pseudo time
dependant gas phase model: osu2007
• Chemical species abundances evolve with
time under fixed physical conditions
• Contains 452 species, 4462 reactions
• Good overall agreement with L134N and
TMC-1 observations
O2 chemistry in gas phase
O2H+
O
H2
CO
OH
CH
CRP
H3+
C+
O
OH
O2
O
CO+
O+
CO
H+
C2H
CO
C
HCO
O2+
CO
O
H
Key formation reaction and estimated rates
O + OH
k1
O2 + H
Modeling method – physical conditions and
initial abundances
Modeling results – O2 in L134N
Modeling results – O2 in TMC-1
Modeling results - high Sulfur abundance
L134N
TMC-1
Warm cores - a gas-grain approach
Conclusions
• For L134N, all k1 values lead to good agreement
of O2 observation only at early time
• For TMC-1, all four k1 values lead to reasonable
agreement of O2 observation
• Using OH as criteria, experimental and highorder theoretical values of k1 are preferred
• Dust grains’ role may be important
Thank you!