Transcript ppt

Circumstellar Chemistry:
The Effects of High Density Shells on the
Distribution of Molecules in IRC+10216
Joanna Brown
CW Leo: IRC+10216
Part 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?
Experimental
and theoretical
rates of reaction
UV light
Parent
abundances
Differential rate
equations
Abundances
of molecules
Effects of density rings on distribution
Density enhancement of 6
times normal 1/r2 distribution
No enhanced density shells
Mass loss of 3.0E-5 M/yr
With shells at positions in
agreement with observations
Observational agreement
Actual distribution in IRC+10216 using 3mm lines
From Guélin et al. (2000). IAU Symposium, 197, 369.
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