Light in the Darkness: The Role of UV Photons in the Circumstellar Envelopes of AGB Stars

Abstract: As well as forming silicates and carbonaceous dust grains, the circumstellar envelopes (CSEs) of AGB stars are host to nearly 100 molecular species. The traditional paradigm – that these result from the interaction of a spherically-symmetric expanding wind with interstellar photons – is under strain from recent observations that show ‘unexpected’ molecules in the hot, inner layers of the CSE.  I will discuss some recent observations that indicate mass-loss outflows are clumpy and that CSEs may also be irradiated by internally-generated UV photons and will present the results of new models that take these two factors into account.