We analyse public domain time-series photometric observations of 30 known and candidate binary post-AGB stars for measuring pulsation and orbital periods .
We derive periodicities for 17 stars for the first time in the literature .
Besides identifying five new RV Tauri type pulsating variables ( three with the RVb phenomenon , i.e .
long-term changes of the mean brightness ) , we find multiply periodic ( or possibly irregular ) post-AGB stars on the two edges of the instability strip .
The temperature dependence of the peak-to-peak light curve amplitudes clearly indicates the changes in excitation as post-AGB stars evolve through the strip .
One object , the peculiar Type II Cepheid ST Pup , showed a period increase from 18.5 to 19.2 d , which is consistent with the known period fluctuations in the past .
In HD 44179 , the central star of the Red Rectangle nebula , we see very similar asymmetric light curve than was measured 10–15 years ago , suggesting a very stable circumstellar environment .
In contrast to this , HD 213985 shows coherent but highly non-repetitive brightness modulation , indicating changes in the circumstellar cloud on a similar time-scale to the orbital period .