| Abstract
| - We present optical broad-band ( UBVRI) aperture polarimetry of 52 post-AGB stars, selected from De Ruyter et al. (2006) and the Torun Catalog, based on the shape of their SED and near-infrared excess. We find 10 (19%) of the stars in our sample to have high polarization ( P> 5%), 30 (56%) intermediate/low polarization (1% < P< 5%) and 13 (25%) very low (or non-polarized) polarization ( P< 1%). Our observations show clear evidence of asymmetric circumstellar envelopes or equatorial density enhancement around post-AGB stars, probably formed at the beginning of the AGB phase. Some stars exhibit wavelength-independent polarization suggesting scattered light by large dust grains or free electrons (Thomson scattering), while others show wavelength-dependent polarization originated from scattering by small dust grains (Rayleigh scattering). Finally, we conclude that highly polarized sources ( P> 3%), show systematically [12] − [25] > 1.5, J − H> 0.5 and J − K> 0.5, clearly separated from the group of RV Tauri stars, which are found to have very low polarization ( P< 3%).
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