Asymptotic giant branch (AGB) stars contribute significant amounts of gas and dust to the interstellar medium. These stars lose their outer envelope through a stellar wind, which creates an extended circumstellar envelope (CSE). An active chemistry takes place within these CSEs, forming both molecules and dust. The chemistry in the outflow of an AGB star is dominated by its C/O abundance ratio. For C-rich stars, no O-rich species are expected in the inner wind since oxygen is locked up in CO, and vice versa for O-rich stars. However, several of these unexpected molecules have been detected. Non-equilibrium chemistry in the inner wind, caused by shocks due to the pulsating AGB star, can in most cases explain their existence and abundance. An alternative mechanism is the penetration of harsh UV photons in a non-uniform outflow. In a non-uniform or "clumpy" outflow, interstellar UV photons can reach the formerly shielded inner wind and break up CO. Using a porosity formalism, we have taken a clumpy density distribution into account by modifying the optical depth of the outflow. The formalism also allows us to include the effects of the relative overdensity of the clumps, making the model unique. I will talk about the results of our parameter study on effects of a clumpy outflow on its chemistry. We find that our results can explain the existence of certain species in the inner wind and add to the results of the non-equilibrium models.
Unless announced otherwise, the lunch talks start at 12:30 sharp. The approximate duration of the lunch talk is given above, and additional time will be given for questions and discussion following the presentation. Please make sure that you take ample time to pick up your lunch beforehand.
Information for Speakers and Hosts: Talks by internal speakers are limited to 20 minutes, with additional time for questions. Visiting speakers can have up to 30 minutes, with additional time for questions. Hosts are responsible for bringing the speaker to the correct room in ample time to set up laptops etc., and for ensuring the speaker also has time for lunch.
For questions and/or suggestions concerning the lunch talks, please contact Themiya Nanayakkara () or Alvaro Hacar ()).