Circumstellar emission and absorption from post-AGB stars

We present the results of multi-wavelength observations, involving IUE, ground-based observations, and ISO, to study the circumstellar environment of two binary post-AGB stars, HR 4049 and HD 213985, at different orbital phases. These objects offer a unique opportunity to probe the nature of dust in absorption as well as in emission. Some conclusions can be drawn concerning the carriers of the 220nm bump and the far-UV extinction rise. Progress for this research has heavily relied on the flexibility of IUE to carry out regular observations in a crucial wavelength range.status: publishe