Polarimetry of evolved stars

I. RS CVn and Mira variables

¹ Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, 196140 Saint-Petersburg, Russia
² Isaac Newton Institute of Chile, St.-Petersburg Branch, Russia
³ Department of Physics, Keele University, Keele, Staffordshire, ST5 5BG, UK e-mail: ae@astro.keele.ac.uk

Corresponding author: R. V. Yudin, ruslan61@hotmail.com

Received: 15 January 2002
Accepted: 25 February 2002

Abstract

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  dependence, for most of the RS CVn-type stars, and for the RS CVn-type star UV Psc and the Mira Ceti-type variables, and a significant increase of polarization to the red for the Mira R Cet. 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 0.5, 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.