All Figures

$\begin{figure} \par\includegraphics[width=15.3cm,clip]{7740fig1.eps}\end{figure}$ Figure 1: Example plots of the UV variability for three stars of our sample. Plots for all stars of our sample for which IUE observations are available can be found in Figs. 9-11 of the online edition. Top panels: UV spectra near the C IV and S IV resonance lines as observed with the IUE satellite. Bottom panels: ratio of observed to the expected variance, which is a measure for the significance of the variability. The horizontal velocity scales are with respect of the rest wavelength of the principal member of the C IV doublet, corrected for the radial velocity of the star as listed in Table 2. Vertical dashed lines denote the positions of the rest wavelengths of the doublet members.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{7740fig2.eps}\end{figure}$ Figure 2: Timeseries of 20 days in August 1995 of the N V UV resonance lines of the slowly-rotating O9V star 10 Lac, showing the appearance and development of the Discrete Absorption Components in both doublet members. The horizontal scale and the two panels at the top are similar to Fig. 1. Third panel: overplot of quotient spectra (see text); Bottom panel: gray-scale representation of the quotient spectra. Arrows indicate the mid epochs of the observations.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{7740fig3.eps}\end{figure}$ Figure 3: Comparison between C IV profiles of the magnetic oblique rotators $\beta$ Cep ( top) and $\xi ^1$ CMa ( bottom). The panels are similar to Fig. 1. To appreciate the excess emission in $\xi ^1$ CMa, we overplot the scaled profile of the B0.5IV star 1 Cas, which has a typical C IV profile for this spectral type.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{7740fig4.ps}\end{figure}$ Figure 4: Longitudinal magnetic-field measurements as a function of phase for $\alpha ^2$ CVn (full circles), one of our magnetic calibrator stars, compared with measurements of Wade et al. (2000, open squares). The line is a second-order Fourier fit to the points of Wade et al. (2000).
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{7740fig5.ps}\end{figure}$ Figure 5: Same as Fig. 4, but for 53 Cam.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{7740fig6.eps}\end{figure}$ Figure 6: Results for $\delta$ Cet of 2003/10/24. Average intensity profile ( bottom) and the Stokes N ( middle) and V profile ( top). No magnetic signature is present.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{7740fig7.eps}\end{figure}$ Figure 7: Weighted average of the three $\eta$ Hya LSD profiles. The average intensity profile ( bottom) and the Stokes V ( top) and N profiles before the fringe correction, and the Stokes V profile after the fringe correction ( third panel) are shown. A marginal magnetic signature is present without correction for the fringes, which disappears, however, after the correction has been applied.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{7740fig8.eps}\end{figure}$ Figure 8: The LSD intensity profile ( bottom) and the Stokes V ( top) and N ( second panel) profiles of 10 Lac on 2004/11/05 (number 10 in Table 3). The Stokes V profile after fringe correction is shown in the third panel. The integration limits for the calculation of the magnetic field were [-83, 83] km s^-1.
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In the text

$\begin{figure} \par\includegraphics[width=15.5cm,clip]{7740fig9.eps}\end{figure}$ Figure 9: Top panels: UV spectra near the C IV resonance lines as observed with the IUE satellite of the first part of the B stars of our sample. Bottom panels: ratio of observed to the expected variance, which is a measure for the significance of the variability. The horizontal velocity scales are with respect of the rest wavelength of the principal member of the C IV doublet, corrected for the radial velocity of the star as listed in Table 2. Vertical dashed lines denote the positions of the rest wavelengths of the doublet members.
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In the text

$\begin{figure} \par\includegraphics[width=15.5cm,clip]{7740fi10.eps}\end{figure}$ Figure 10: Same as Fig. 9, but for the second part of the B stars, for which the Si IV doublet is also shown.
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In the text

$\begin{figure} \par\includegraphics[width=15.5cm,clip]{7740fi11.eps}\end{figure}$ Figure 11: Same as Figs. 9 and 10, but for the O stars in our sample.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{7740fig3.eps}\end{figure}$	Figure 3: Comparison between C IV profiles of the magnetic oblique rotators $\beta$ Cep ( top) and $\xi ^1$ CMa ( bottom). The panels are similar to Fig. 1. To appreciate the excess emission in $\xi ^1$ CMa, we overplot the scaled profile of the B0.5IV star 1 Cas, which has a typical C IV profile for this spectral type.
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$\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{7740fig4.ps}\end{figure}$	Figure 4: Longitudinal magnetic-field measurements as a function of phase for $\alpha ^2$ CVn (full circles), one of our magnetic calibrator stars, compared with measurements of Wade et al. (2000, open squares). The line is a second-order Fourier fit to the points of Wade et al. (2000).
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$\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{7740fig5.ps}\end{figure}$	Figure 5: Same as Fig. 4, but for 53 Cam.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{7740fig6.eps}\end{figure}$	Figure 6: Results for $\delta$ Cet of 2003/10/24. Average intensity profile ( bottom) and the Stokes N ( middle) and V profile ( top). No magnetic signature is present.
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$\begin{figure} \par\includegraphics[width=7.8cm,clip]{7740fig8.eps}\end{figure}$	Figure 8: The LSD intensity profile ( bottom) and the Stokes V ( top) and N ( second panel) profiles of 10 Lac on 2004/11/05 (number 10 in Table 3). The Stokes V profile after fringe correction is shown in the third panel. The integration limits for the calculation of the magnetic field were [-83, 83] km s^-1.
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$\begin{figure} \par\includegraphics[width=15.5cm,clip]{7740fi10.eps}\end{figure}$	Figure 10: Same as Fig. 9, but for the second part of the B stars, for which the Si IV doublet is also shown.
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$\begin{figure} \par\includegraphics[width=15.5cm,clip]{7740fi11.eps}\end{figure}$	Figure 11: Same as Figs. 9 and 10, but for the O stars in our sample.
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