\begin{table}%t2 \caption{\label{tb:observations}Summary of the new spectropolarimetry observations obtained with TBL/MuSiCoS. \object{HD~163472} or \object{V2052 Oph} (B2IV/V = 5.834 mag, $(B-V)$ = 0.05 mag, \Ebv\ $\sim$ 0.29 mag) and \object{HD~174638} or \mbox{\object{* bet Lyr A}} (B7Ve, $V = 3.52$ mag, $(B-V)$ = 0.00 mag, \Ebv\ $\sim$ 0.135 mag) are the two reddened lines of sight not previously studied in this context. All spectra cover the wavelength range from 4480 to 6620~\AA. $\tau_V/p_{\rm max}$ gives the ratio of the continuum optical depth over the continuum polarisation; see Eq.~(\ref{eq:2}). For optimal alignment the maximum polarisation efficiency is $p_{\rm max} / \tau_V \sim\ 0.032$ or $\tau_V / p_{\rm max} \sim\ 31.25$ (\citealt{1975ApJ...196..261S}). $S/N_{\rm I}$ is the signal-to-noise of the total transmittance spectrum at about 5800~\AA. $^{(1)}$ PDLP is the 1$\sigma$ Polarisation Detection Limit per Pixel (1 pixel = 0.06~\AA), measured across 1~\AA\ at 5800~\AA. $^{(2)}$ PDLA is the 1$\sigma$ Polarisation Detection Limit per 0.8~\AA\ ($\approx$16~pixels), which is equal to the resolution obtained by \citet{1995ApJ...448L..49A}.} \small%\begin{center} { \begin{tabular}{llllllllll}\hline\hline\noalign{\smallskip} Targets & \Ebv & $A_V$ & $\tau_V/p_{\rm max}$ & Stokes & Date of observation & Exp. &$S/N_{\rm I}$ &PDLP$^{(1)}$ & PDLA$^{(2)}$ \\ Reddened: & (mag)& (mag) & & & & (min) & & (\%) & (\%) \\\hline\noalign{\smallskip} \object{HD~183143} & 1.28 & 3.72$^1$ & 58.2 & $U, Q$ & October 2004 & 360 & 270 & 0.4 & 0.12 \\ & & & & & June 2004 & 540 & 400 &$\sim$0.2 & \\ \object{HD~197770} & 0.58 & 1.61 $\pm$ 0.14$^2$ & 35.7 & $U, Q$ & October 2003 & 360 & 528 & 0.2 & 0.08 \\ & & & & & June 2004 & 120 & 260 & & \\ & & & & $V$ & October 2003 & 60 & 305 & 0.9 & 0.3--0.7 \\ \object{HD~21291} & 0.43 & 1.48$^1$ & 41.5 &$U, Q$ & October 2003 & 360 & 1487 & 0.06 & 0.04 \\ \object{HD~198478} & 0.54 & 1.48 $\pm$ 0.19$^2$ & 47.4 & $U, Q$ & June 2004 & 520 & 1160 & 0.08 & 0.05 \\ \object{HD~163472} & 0.29 & 0.9$^3$ & & $V$ & June/July 2000, 2001, 2002 & 1242 & 2000 &$\sim$0.1 & 0.04 \\ \object{HD~174638} & 0.135& 0.4$^3$ & 46.0 & $U, Q$ & June 2004 & 312 & 1500 & & \\ Standard: & & & & & & & & & \\ \object{HD~109387} & 0.04 & & & $U, Q$ & June 2004 & 232 & 1500 & & \\ \hline \end{tabular}} \parbox{16.5cm}{ References: [1] \citet{2003ApJ...588..344D}; [2] \citet{2004ApJ...616..912V}; [3] average ISM value adopted: $R_V = 3.1$.} %\end{center} \par \end{table}