RV Tauri stars are variable yellow supergiants and they display anomalous excesses in infrared radiation indicating the presence of cool and extended dust thermospheres, presumbly formed from the matter ejected by them (Gehrz 1972). AR Pup, recognised as a member of RV Tauri stars, shows strong CH and CN bands in the optical spectrum and is considered to be carbon-rich (Lloyd Evans 1974). During a programme of broad band polarimetric observations of carbon variables, AR Pup was found to exhibit a large and highly time-dependent linear polarisation (Raveendran & Kameswara Rao 1987).

During the period from 1987 January 20 to April 6, AR Pup was observed on 33 nights through standard B and V filters with the 34-cm reflector of the Vainu Bappu Observatory, Kavalur. We also obtained UBVRI polarimetry of AR Pup with the PRL - Polarimeter (Deshpande et al. 1985) attached to the 102-cm reflector on six nights during the same period. Present observations clearly indicate that the large time dependent variations in polarisation, both in the amount and wavelength dependence, observed at earlier epochs by us were not isolated events but were segments of a continuous variation which is cyclic and related to the light curve.