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Circumstellar Chemistry:
The Effects of High Density Shells on the Distribution of Molecules in IRC+10216
Joanna Brown
CW Leo: IRC+10216Part of Asymptotic Giant Branch
Why is CW Leo chemically interesting?
During helium flashes, convection zones form which bring C & O from the core to the surface.
The C & O is then pushed outwards in the star’s wind
Rings around CW Leo
From Mauron & Huggins (1999). Astron. Astrophys. 349, 204.
How does the model work?
UV light
Abundances of molecules
Experimental and theoretical rates of reaction
Differential rate equations
Parent abundances
Effects of density rings on distribution
No enhanced density shells
Density enhancement of 6 times normal 1/r2 distribution
With shells at positions in agreement with observations
Mass loss of 3.0E-5 M/yr
Observational agreement
From Guélin et al. (2000). IAU Symposium, 197, 369.
Actual distribution in IRC+10216 using 3mm lines
Conclusions
•Density shells have a significant effect on chemical abundances and need included in the models
•Peak abundances are aligned in agreement with observations
•High abundance range is narrower than previous models in agreement with observations
Acknowledgments
Dr. Tom Millar for providing such an interesting project and supervising my research
Dr. David Cohen for advising on my thesis and this presentation
My family for their support