Near-IR/optical monitoring programme of the 'Arecibo sample of OH/IR stars'

We performed a near-IR/optical monitoring programme from 1999 to 2005 in order to study the variability properties of the 'Arecibo sample of OH/IR stars' (periods, amplitudes, and colour variations). Here we describe this multi-wavelength long-term monitoring programme. Data analysis is still in process. Our ultimate goal is to study in particular the oxygen-rich AGB stars with masses larger than 2 Solar Mass, which are probably rare among AGB stars discovered optically and/or in the near-IR, but are common in samples discovered in the mid- to far-IR.