\chapter*{Appendix}
\addcontentsline{toc}{chapter}{Appendix}
\markboth{}{}
\pagenumbering{roman} 
\normalsize
\noindent

{\Large \bf The detached shells around S~Sct \& TT~Cyg}\\
\\
 Polarimetry imaging done towards S~Sct and TT~Cyg has yielded
 tentative detections of stellar light scattered by their CSEs. The
 structure of the circumstellar medium in these objects, the large
 number of field stars, the crude instrumental setups and the use of
 an inadequate telescope (Wollaston prism, alt-az telescope, see
 Sect.~2.1), and/or the shortage of useful observing time during the
 runs, limited the possibility of detection.
 
 In the case of S~Sct, polarised scattered light of circumstellar
 origin is clearly present in the images that show the Stokes
 parameters (see Fig.1).  However, the very low S/N-ratios of the
 observations hinder a quantitative study.  The detected scattered
 stellar light is only marginally above the readout noise in the
 images.  Thus, no net polarised and total fluxes were detected.
 Therefore, awaiting the reduction and analysis of the higher quality
 polarimetry data obtained recently (see Fig.2), we restrict here to a
 description of the tentative detection.
 
 The images showing the Stokes parameters exhibit, in the F77 and F59
 filters, a circular pattern of alternating bright and dark bands
 centred on the star at $\approx$70\arcsec (5.7$\times$10$^{17}$ cm)
 (Fig.2).  This distance is in very good agreement with the CO radio
 line maps towards this star, which show the presence of CO emission
 from a detached shell with a radius of 66\arcsec.  This reinforces
 our tentative detection of scattered stellar light.
 
 In the case of TT~Cyg only observations done in the F59 filter
 produced positive results due to the poor opaqueness of the
 coronographic mask.  Furthermore, there is only evidence of polarised
 scattered light in the image that shows the Stokes~U parameter.  The
 image that shows the Stoke~Q parameter is useless due to the poor
 weather conditions under which these observations were performed and
 the unfavourable orientation of the NOT's spider in the image.  As a
 result, no net polarised flux was detected. New polarimetry data
 obtained recently (see observations taken with four different filters
 in Fig.4) are expected to result in images which show the polarised
 scattered stellar light with higher S/N-ratio.
 
 The total intensity image reveals scattered light of circumstellar
 origin around this star (see Fig.3).  The image show a brightness
 distribution in the form of a uniform disk with an outer radius of
 $\approx$36\arcsec (2.8$\times$10$^{17}$ cm).  This radius is
 consistent with the gas shell (34\arcsec radius) seen in the
 remarkable interferometric CO radio line observations presented by
 Olofsson et al.  (2000, see Fig.~\ref{ttcygshell}).  This strongly
 supports our tentative detection of scattered stellar light towards
 this star.

\pagebreak


\begin{figure*} \centering \vspace{9.1 cm}
\special{psfile=mosssctboth.eps hoffset=-70 voffset=-540 hscale=130 vscale=130 angle=0}
\end{figure*}
\vspace{1cm}
{\bf Figure 1}. Images showing the polarimetric information of the
light scattered in the circumstellar medium around S~Sct.
\textit{Left upper panel:} measured Stokes $Q$ in the F77 filter. The
frame has been derotated 45 degrees to correct for the rotation of the
instrument during the exposure. \textit{Right upper panel:} measured
Stokes $U$ in the F77 filter. \textit{Left lower panel:} measured
Stokes $Q$ in the F59 filter. \textit{Right lower panel:} measured
Stokes $U$ in the F59 filter. The effects of the Wollaston prism
method are clearly seen.
\vspace{2.5cm}
\pagebreak

\begin{figure*} \centering \vspace{12.1 cm}
\special{psfile=ssctnew.eps hoffset=10 voffset=-20 hscale=70 vscale=70 angle=0}
\end{figure*}


{\bf Figure 2}. New data showing the Stokes parameters of the stellar light scattered in the CSE around S~Sct in the F77 filter.

\vspace{7.8cm}

\pagebreak

\begin{figure*} \centering \vspace{12.1 cm}
\special{psfile=ttcyg.eps hoffset=20 voffset=-100 hscale=65 vscale=65 angle=0}
\end{figure*}
\vspace{4.5cm}

{\bf Figure 3}. Images showing the polarimetric information in the F59
filter of the light scattered in the circumstellar medium around
TT~Cyg. \textit{Upper left panel:} Total intensity. 
\textit{Upper right
panel:} Azimuthally averaged radial profile (AARP) of the total
intensity derived from a smoothed image with the field stars removed.
A fit of a step function, convolved with the seeing Gaussian, to the
total intensity is shown (dotted line).  The AARP of the
CO($J$=1$\rightarrow$0) emission seen towards this star is included
for comparison (triangles; Olofsson et al. 1996).  The CO peak value
has been normalized to the plateau value of the fit to the total
scattered intensity. \textit{Lower left panel:} Stokes $U$ parameter.
\textit{Lower right panel:} Radially averaged azimuthal profile of the
Stokes $Q$ and $U$ parameters.  The averages have been done over
intervals of 3$\arcsec$ centered at the radii of maximum circumstellar
scattered light.  Fits of sinusoidal functions have been added to the
profiles.

\pagebreak

\begin{figure*} \centering \vspace{12.1 cm}
\special{psfile=ttcygallhr.eps hoffset=40 voffset=-75 hscale=70 vscale=70 angle=0}
\end{figure*}


{\bf Figure 4}. New data showing the intensity of the stellar light
scattered in the CSE around TT~Cyg in four different filters.
\textit{Upper left panel:} Observations done with the F59 filter (see
Sect. 2.1.3).
\textit{Upper right panel:} Observations done with the F77 filter (see
Sect. 2.1.3).
\textit{Lower left panel:} Observations done with a 1300\AA~wide
Bessel \textit{R} filter centred on 6500\AA.  \textit{Lower right
panel:} Observations done with a 1570\AA~wide interference \textit{i}
filter centred on 7970\AA. The stellar PSF has not been subtracted
from the images.

\vspace{3.5cm}
\pagebreak

{\Large \bf Unpublished data on the scattered stellar light of U~Ant}\\

New polarimetry data towards U~Ant is shown in Fig.4 and Fig.5. The
new observations provide images of the scattered stellar light with a
much higher S/N-ratio. Fig.4 shows an image of the total intensity of
scattered stellar light taken the F59 filter. Already in this
unreduced image it is clearly discernible the multi-shell structute of
the CSEs around U~Ant. The new data also evidences the polarisation of
the scattered light. 

The polarimetry images shown in Fig.5 are taken in a continuum filter
in which strong resonance lines (like those of Na~I and K~I) are not
present. Therefore, these new images confirm the occurrence of
scattering by dust particles. In these raw frames, it can be seen
ellipsoidal CSEs rather than circular brightness distributions, with
the axis in different directions for each polarisation
angle. This is a clear sign of polarised scattered light. The
reduced images are expected to allow a better quantitative analysis of
the scattering of the stellar light in terms of resonance and/or dust
scattering.

\vspace{13cm}

\pagebreak

\vspace{14.cm}
\begin{figure*} \centering 
\special{psfile=uantdirnew.eps hoffset=90 voffset=-350 hscale=90 vscale=90 angle=0}
\end{figure*}

{\bf Figure 5}. High S/N-ratio image of the CSE around U~Ant as seen in
total intensity scattered stellar light. The stellar PSF has not been
subtracted from the image.
\vspace{7.6cm}

\pagebreak

\begin{figure*} \centering \vspace{15cm}
\special{psfile=uantpolnew.eps hoffset=20 voffset=-20 hscale=65 vscale=65 angle=0}
\end{figure*}
%\vspace{1cm}
{\bf Figure 6}. High S/N-ratio polarimetry images at four different
polarisation angles, of the CSE around U~Ant seen in scattered stellar
light. The images were taken with a 182\AA Str\"omgren y filter
centred on 5482 \AA. The stellar PSF has not been subtracted from the
images.
\vspace{2.cm}