2002A&A...386..916Y

We present broadband optical polarimetry of 3 RS CVn stars and 3 Mira variables, including the symbiotic star R Aqr, which contains a Mira component. Polarimetric variability has been studied on time-scales from hours to years. Our programme objects at the time of our observations showed different forms of P(λ) dependence, P∝~λ^–4 for most of the RSCVn-type stars, and P∝~λ^–2 for the RSCVn-type star UV Psc and the Mira Ceti-type variables, and a significant increase of polarization to the red for the Mira RCet. Combining our data with previously published data, we conclude that most of RS CVn-type and Mira Ceti-type objects show evidence of large polarimetric variability at wavelengths shorter than 0.5µm, whereas the level of polarization is more stable in the red. This behaviour is consistent with episodic mass ejection and formation of small dust particles in the circumstellar environment. Although all targets showed polarimetric variability on different time scales, only for IM Peg might these variations be possibly linked with the photometric period.