Abstract

OH/IR stars are evolved stars exhibiting large infrared excess as well its prominent OH maser emission. The vast majority of this heterogeneous object class are highly-evolved low- and intermediate-mass stars ascending the upper part of the asymptotic giant branch (AGB). Thus, these stars are in the final phase of their AGB evolution which is characterized by intensive mass loss with mass-loss rates that can reach up to 10(-4) M-circle dot. This high mass loss leads to the development of an extended, usually optically thick dusty circumstellar envelope which can be well studied with infrared-interferometric observations.