We have reported an attempt to observe polarization effects in the wind of 
Cas.
Though we have not attained our goal to detect such effects, we have resolved
the circumstellar envelope of 
Cas for the first time in the continuum. From this
result we have estimated the extent of this envelope as 8-10 times the diameter of
the central star, comparable to the value found from interferometric observations in the
H
emission line (Thom et al. 1986; Quirrenbach et al. 1993;
Stee et al. 1995).
From an instrumental point of view, we think that interfero-polarimetric accuracies could significantly be improved by recording simultaneously the fringe signal in different polarizations so as to minimize the dispersion of measured visibilities due to atmospheric turbulence and instrumental residuals. Such a differential scheme will be implemented as an observational mode of the future beam-combiner REGAIN of the GI2T to be operated by the end of 1997 (Rousselet-Perraut 1996). Interferometric polarimetry could therefore be extended to other classes of stars such as evolved red supergiants, magnetic stars, semi-contact binaries where the mutual reflection effect is at play. In fine, such observations could directly be interpreted in terms of physical parameters of the star being observed if adequate models built for interferometry become available. Such models should compute intensity maps and corresponding spatial power spectra in linear polarizations for a direct comparison with interferometric visibilities (Vakili et al. 1994).
Acknowledgements
We are grateful to Emeric Le Floch for his assistance during the observing runs. This work was partially supported by the PNHRAA french organisation from CNRS-INSU.