Astronomy & Astrophysics

All Figures

$\begin{figure} \par\begin{turn}{0} \mbox{\epsfig{file=notations.eps,width=8.7cm} } \end{turn} \end{figure}$ Figure 1: Notations: The source is located in the (x₂,y₂) plane, the screen contains the diffusive structure, and the observer is located in the (x₀,y₀) plane. A₁(x₁,y₁) and A'₁(x₁,y₁) are the amplitudes before and after screen crossing.
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In the text

$\begin{figure} \par\begin{turn}{0} {\epsfig{file=franges-point.eps,width=8.0cm}\... ....0cm}\par\epsfig{file=contraste-point.eps,width=8.0cm} } \end{turn} \end{figure}$ Figure 2: Top: Diffraction pattern produced in the observer's plane, perpendicularly to a step of optical path $\delta =\lambda /4$ . The $X_0-{\rm axis}$ origin is the intercept of the source-step line with the observer's plane. X₀=1 corresponds to $x_0=\sqrt {\pi }R_{\rm F}$ . Middle: Diffraction pattern as a function of the step size $\delta$ (in depth, from 0 to 0.5 in $\lambda$ units). Bottom: Contrast of the diffraction pattern as a function of the step size $\delta$ .
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In the text

$\begin{figure} \par\begin{turn}{0} {\epsfig{file=point-coin.eps,width=8.0cm} } \end{turn} \end{figure}$ Figure 3: Diffraction pattern produced perpendicularly to a prism of optical path with $\delta =X_0\times \lambda /2$ for X₀>0. The X₀-axis origin is the intercept of the source-corner line with the observer's plane. X₀=1 corresponds to $x_0=\sqrt {\pi }R_{\rm F}$ .
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In the text

$\begin{figure} \par\begin{turn}{0} \mbox{\epsfig{file=taille-source.eps,width=8.7cm} } \end{turn} \end{figure}$ Figure 4: Diffraction pattern produced perpendicularly to a step of optical path of $\delta =\lambda /2$ , for extended disk-sources of reduced radius $R_{\rm S}=1$ (top), 2 (middle) and 4 (bottom). The size of the central depression corresponds to the reduced source size. Notice that the vertical scales are very different because the contrast is much lower for $R_{\rm S}=4$ .
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In the text

$\begin{figure} \par\begin{turn}{0} \mbox{\epsfig{file=hcontrast.eps,width=8.8cm} } \end{turn} \end{figure}$ Figure 5: Fringe contrast as a function of the reduced star radius $R_{\rm S}$ ( $\sim$ $\theta _{\rm S}/\sqrt {\pi }\theta _{\rm F}$ when the source is much farther from the observer than the screen), for 2 values of the step size: $\delta =\lambda /4$ (thin line) and $\delta =\lambda /2$ (thick line). For a large source radius, the contrast varies like $1/R_{\rm S}$ .
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In the text

$\begin{figure} \par\begin{turn}{0} \mbox{\epsfig{file=diffusions-highres.eps,width=8.7cm} } \end{turn} \end{figure}$ Figure 6: The two scintillation regimes: sections of the wavefront after screen crossing. - Top panel: $R_{\rm diff}\gg R_{\rm F}$ . The weakly distorted wavefront produces a weak scintillation at scale $R_{\rm F}$ in the observer's plane. - Bottom panel: $R_{\rm diff}\ll R_{\rm F}$ . The strongly distorted wavefront produces strong scintillation at scales $R_{\rm diff}$ (diffractive mode) and $R_{\rm ref}$ (refractive mode) in the observer's plane.
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In the text

$\begin{figure} \par\begin{turn}{0} \mbox{\epsfig{file=angles.eps,width=8.8cm} } \end{turn} \end{figure}$ Figure 7: Apparent stellar angular radius $\theta _{\rm S}$ for a solar-like star ( $r_{\rm S}=r_{\odot }$ ) and for a star with $r_{\rm S}=10~r_{\odot}$ as a function of the distance. The lower line gives the Fresnel radius $R_{\rm F}$ as a function of the screen's distance, illustrating the fact that the source has to be much farther than the screen to give contrasted diffractive scintillation.
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In the text

$\begin{figure} \par\begin{turn}{0} \mbox{\epsfig{file=isocontraste.eps,width=8.8cm} } \end{turn} \end{figure}$ Figure 8: Lines of equal diffractive scintillation modulation index at $\lambda=500~{\rm nm}$ in the source/screen distances plane. The modulation index is 100% (thick line), 50%, 10%, 5% and 1% (from top to bottom lines), assuming that the product $\left[\frac{R_{\rm diff}}{R_{\rm F}}\right]\left[\frac{r_{\rm S}}{r_{\odot}}\right]^{-1}$ is unity. This happens only for very small sources, and when $R_{\rm diff}$ is not too small compared to $R_{\rm F}$ . Otherwise, the modulation index has to be multiplied by this product. Typical distances of disks and halo clouds are indicated, as well as the distances of the two most promising targets.
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In the text

$\begin{figure} \par\begin{turn}{0} \mbox{\epsfig{file=notations.eps,width=8.7cm} } \end{turn} \end{figure}$	Figure 1: Notations: The source is located in the (x₂,y₂) plane, the screen contains the diffusive structure, and the observer is located in the (x₀,y₀) plane. A₁(x₁,y₁) and A'₁(x₁,y₁) are the amplitudes before and after screen crossing.
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$\begin{figure} \par\begin{turn}{0} {\epsfig{file=point-coin.eps,width=8.0cm} } \end{turn} \end{figure}$	Figure 3: Diffraction pattern produced perpendicularly to a prism of optical path with $\delta =X_0\times \lambda /2$ for X₀>0. The X₀-axis origin is the intercept of the source-corner line with the observer's plane. X₀=1 corresponds to $x_0=\sqrt {\pi }R_{\rm F}$ .
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$\begin{figure} \par\begin{turn}{0} \mbox{\epsfig{file=taille-source.eps,width=8.7cm} } \end{turn} \end{figure}$	Figure 4: Diffraction pattern produced perpendicularly to a step of optical path of $\delta =\lambda /2$ , for extended disk-sources of reduced radius $R_{\rm S}=1$ (top), 2 (middle) and 4 (bottom). The size of the central depression corresponds to the reduced source size. Notice that the vertical scales are very different because the contrast is much lower for $R_{\rm S}=4$ .
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$\begin{figure} \par\begin{turn}{0} \mbox{\epsfig{file=hcontrast.eps,width=8.8cm} } \end{turn} \end{figure}$	Figure 5: Fringe contrast as a function of the reduced star radius $R_{\rm S}$ ( $\sim$ $\theta _{\rm S}/\sqrt {\pi }\theta _{\rm F}$ when the source is much farther from the observer than the screen), for 2 values of the step size: $\delta =\lambda /4$ (thin line) and $\delta =\lambda /2$ (thick line). For a large source radius, the contrast varies like $1/R_{\rm S}$ .
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