Properties of AGB star progenitors

In this paper, two separate topics are discussed. Firstly, shells around AGB stars are considered. The highly spherical shells seen in microwave lines around some AGE stars are readily explained in terms of helium shell flash behaviour. On the other hand, deep images of AGE and post-AGE stars show that in some of them, the almost spherically symmetric AGE wind is modulated on a timescale of a few hundred years, much shorter than the helium shell flash timescale. Some single star explanations for this modulated are investigated: no single star mechanism appears satisfactory, although merging of mass shells produced near the AGE star by pulsation and dust formation needs further investigation. Secondly, binarity in AGE stars is discussed. In particular, it is noted that observations of variable AGE stars in the LMC indicate that similar to 25% of them show long secondary periods consistent with that expected for the orbital period of a close companion. If it turns out that the long secondary periods are indeed the result of a close orbiting companion, then it is almost certain that these companions will lead to the axially symmetric mass ejection observed in many planetary nebulae.