All Figures

$\begin{figure} \par\includegraphics[angle=-90,width=14cm,clip]{9225fig1.ps} \end{figure}$ Figure 1: The low-resolution spectrum of comet C/2004 Q2 (Machholz) taken with the EFOSC2 instrument taken with the ESO 3.6 m at La Silla on 9 december 2004. See the text for the line identification. The passbands of the three photometric filters of the Merope instrument used in this paper are shown in red. It is obvious that these broad filters cover a mix of continuum and emission features, with the I filter having the most emission-free passband. The two spectra are ESO archive data, and are taken under programme 274.C-5020 (Weiler).
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{9225fig2.eps} \end{figure}$ Figure 2: Three observations, one in each band, taken on January 11, 2005. The frames are shown here to give an idea of the type of data. They are taken consecutively, and hence under very similar ambient conditions. In the U filter, the very clear signature of the ion tail is visible, in B this tail is only marginally visible, and in I it is absent. The field of view of these images is $3\hbox {$.\mkern -4mu^\prime $ }6\times 5\hbox {$.\mkern -4mu^\prime $ }0$ of the total square 6 $.\mkern -4mu^\prime$ 5 of the CCD; the scale is shown in the lower left corner. Note that on these images, the core of the coma seems to be saturated, which is obviously not the case, but solely a consequence of the chosen colour scale.
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In the text

$\begin{figure} \par\resizebox{9cm}{!}{\includegraphics{9225fig3a1.ps}\includegra... ...{!}{\includegraphics{9225fig3a3.ps}\includegraphics{9225fig3b3.ps}} \end{figure}$ Figure 3: Correction for the seeing effect for a frame taken in optimal conditions ( left column of figures), and for a frame taken in less favourable conditions ( right column). The upper row shows the optocentres of the reduced frames (but not yet seeing-corrected). To degrade these frames to the same seeing, the left one has to be convolved with a broad Gaussian kernel ( middle left panel), while the right one with a very narrow Gaussian kernel ( middle right panel). The resulting optocentres are show in the bottom panels.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=7.8cm,clip]{9225fig4.ps} \end{figure}$ Figure 4: The evolution of the seeing during our observational run as recorded by the RoboDIMM telescope (O'Mahony 2003; Augusteijn 2001), interpolated to the times of our comet observations.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{9225fig5.ps} \end{figure}$ Figure 5: Overview of the magnitudes for the extracted optocentre of the comet in the three different bands. Shown here are the results for an aperture radius of 1 and 6 pixels (0 $.\!\!^{\prime\prime}$ 19 and 1 $.\!\!^{\prime\prime}$ 14).
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In the text

$\begin{figure} \par\includegraphics[width=4.2cm,clip]{9225fig6a.ps}\hspace*{4mm}\includegraphics[width=4.2cm,clip]{9225fig6b.ps} \end{figure}$ Figure 6: Jurkevich-Stellingwerf PDM ( left panels) $\theta$ -statistic and Lomb-Scargle ( right panels) periodogram for the I magnitudes of 1 pixel aperture. In the two upper panels, the diagrams for the original data are shown, while in the lower panels, the diagrams for the magnitudes prewhitened with f₁ = 0.20 c d^-1 (P = 5 d) are shown (method #1 in Table 3). On each figure, the frequency f = 2.64 c d^-1 (P = 9.1 h) is shown with a red line.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9225fig7.ps} \end{figure}$ Figure 7: Phase diagrams of the comet's optocentre magnitudes in the I filter with an aperture radius of 1 pixel. upper panel: phase plot with f₁ = 0.20 c d^-1 (P = 5 d); lower panel: phase plot with f₂=2.64 c d^-1 (P = 9.1 h) on the magnitudes prewhitened with f₁ (method #1 in Table 3).
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9225fig8.ps} \end{figure}$ Figure 8: Coma profiles of three representative observations for the three filters used in our programme. Crosses represent the profile in the sunward direction, while the $\times$ es show the profile in the direction of the ion tail. The coma in the I filter shows a clean m = -1 profile for $\rho$ < 10⁴ km and m = -1.5 for $\rho$ > 10⁴ km, the profiles in the U and B filter have smaller values for |m|, indicating the influence of gas emissions in these spectral bands.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9225fig9.ps} \end{figure}$ Figure 9: Temporal evolution (in function of the heliocentric distance $r_{\rm h}$ ) of the inner and outer coma profiles represented by their m-values, and of the terminal ejection velocity determined with formula (3). The terminal ejection velocity is related to the heliocentric distance $r_{\rm h}$ of the comet, but the difference of $\Delta r_{\rm h}$ $\simeq$ 0.02 AU between the beginning and ending of our observational run is too small to establish global trends.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=7.8cm,clip]{9225fig4.ps} \end{figure}$	Figure 4: The evolution of the seeing during our observational run as recorded by the RoboDIMM telescope (O'Mahony 2003; Augusteijn 2001), interpolated to the times of our comet observations.
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$\begin{figure} \par\includegraphics[width=8.4cm,clip]{9225fig5.ps} \end{figure}$	Figure 5: Overview of the magnitudes for the extracted optocentre of the comet in the three different bands. Shown here are the results for an aperture radius of 1 and 6 pixels (0 $.\!\!^{\prime\prime}$ 19 and 1 $.\!\!^{\prime\prime}$ 14).
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$\begin{figure} \par\includegraphics[width=8.5cm,clip]{9225fig7.ps} \end{figure}$	Figure 7: Phase diagrams of the comet's optocentre magnitudes in the I filter with an aperture radius of 1 pixel. upper panel: phase plot with f₁ = 0.20 c d^-1 (P = 5 d); lower panel: phase plot with f₂=2.64 c d^-1 (P = 9.1 h) on the magnitudes prewhitened with f₁ (method #1 in Table 3).
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