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