All Figures

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{5194fig1.eps}} \end{figure}$ Figure 1: An overview of the chosen definition of band passes for continuum and features. The top figure shows the overall spectrum for a typical OH/IR stars. The dotted lines indicate the central positions of the features. The other 4 figures show for each line the selected passband for the feature (dotted lines) and the selected passband for the continuum (dashed lines). (For the ¹²CO(2, 0) the feature's first dotted line overlaps with the last dashed line from the continuum.)
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In the text

$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fig2.eps}} \end{figure}$ Figure 2: RGB stars in common with Schultheis et al. (2003); black line: this work, gray line: Schultheis et al. (2003). The features between 1.8 and 1.9 $\mu$ m and around 2 $\mu$ m are due to the atmosphere.
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In the text

$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fig3.eps}} \end{figure}$ Figure 3: Equivalent line width measurements for the candidate RGB stars in common with Schultheis et al. (2003). The plus-signs are taken from Schultheis et al. (2003), the diamonds from this work.
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In the text

$\begin{figure} \par\resizebox{7cm}{!}{\includegraphics{5194fig4.eps}} \end{figure}$ Figure 4: Equivalent line width measurements for the stars in common with Ramírez et al. (1997) and Ramírez et al. (2000). The plus-signs are taken from Ramírez et al. (1997), the stars are from Ramírez et al. (2000) and the diamonds are from this work.
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In the text

$\begin{figure} \par\resizebox{7.5cm}{!}{\includegraphics{5194fig5.eps}}\end{figure}$ Figure 5: Variations in the equivalent widths for stars in common with Lançon & Wood (2000). The plus-signs indicate values taken from Lançon & Wood (2000), the diamonds those from this work.
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In the text

$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{5194fig6.eps}}\end{figure}$ Figure 6: Equivalent line-width measurements for the OH/IR stars in common with Schultheis et al. (2003). The plus-signs indicate values taken from Schultheis et al. (2003), the diamonds those from this work.
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In the text

$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fig7.eps}}\end{figure}$ Figure 7: Histograms for EW(Ca), EW(Na), EW(CO) and the water absorption for the OH/IR stars from this work (full line) and the OH/IR stars from Schultheis et al. (2003) (dotted line). All x-axes are in the same unit Å.
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In the text

$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{5194fig8.eps}}\end{figure}$ Figure 8: OH/IR star for which the Na I and Ca I lines could not be measured. The dotted lines indicate the Na I feature and the dashed lines the selected continuum points. The dashed-dotted lines indicate the Ca I feature with its corresponding continuum (dashed-triple-dotted).
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In the text

$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fig9.eps}}\end{figure}$ Figure 9: Equivalent line widths for the different models. The x-axis indicates the mass-loss rate, and the y-axis the equivalent line widths for Na I ( left) and Ca I ( right). The different symbols indicate the different dust temperatures. Crosses: $T_{\rm dust} = 1500$ K, diamonds: $T_{\rm dust} = 1000$ K and triangles: $T_{\rm dust} = 750$ K. The dotted line indicates the equivalent line width for the reference line. The line disappears when the equivalent width is below the dashed line.
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In the text

$\begin{figure} \par\resizebox{7cm}{!}{\includegraphics{5194fi10.eps}}\vspace*{7mm} \resizebox{7cm}{!}{\includegraphics{5194fi11.eps}}\end{figure}$ Figure 10: Upper panel: EW(Ca) vs. EW(H₂O), lower panel: EW(Na) vs. EW(H₂O). The OH/IR in this work are the crosses, RGB (Schultheis et al. 2003): stars, OH/IR (Schultheis et al. 2003): diamonds, LPV (Schultheis et al. 2003): triangles. All equivalent line widths are given in the same unit Å.
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In the text

$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fi12.eps}}\end{figure}$ Figure 11: Determination of the phase $\phi$ . The dotted horizontal line gives $\langle K\rangle$ .
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In the text

$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fi13.eps}}\end{figure}$ Figure 12: The phase at time of observation versus the equivalent line width of water absorption.
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In the text

$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fi14.eps}}\end{figure}$ Figure 13: Comparison of the expansion velocities with the equivalent line widths of Na I, Ca I, ¹²CO(2, 0), and the water absorption. The dotted vertical line separates the 2 groups of OH/IR stars.
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In the text

$\begin{figure}\par\resizebox{17cm}{!}{\includegraphics{5194fi15.eps}}\end{figure}$ Figure B.1: OH/IR stars. OH 359.437-0.051 is possibly a mismatch.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics{5194fi16.eps}}\end{figure}$ Figure B.2: OH/IR stars - continued. OH 359.803-0.248 is possibly a mismatch.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics{5194fi17.eps}}\end{figure}$ Figure B.3: OH/IR stars - continued. OH 359.943-0.055 is possibly a mismatch.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics{5194fi18.eps}}\end{figure}$ Figure B.4: OH/IR stars - continued. OH 0.452+0.046 is possibly a mismatch.

In the text

$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics{5194fi19.eps}}\end{figure}$ Figure B.5: High-velocity OH/IR stars (van Langevelde et al. 1992).

In the text

$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics{5194fi20.eps}}\end{figure}$ Figure B.6: Stars in common with Ramírez et al. (1997).

In the text

$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics{5194fi21.eps}}\end{figure}$ Figure B.7: Stars in common with Ramírez et al. (2000).

In the text

$\begin{figure} \par\resizebox{17cm}{!}{\includegraphics{5194fi22.eps}}\end{figure}$ Figure B.8: Stars in common with Lançon & Wood (2000).

In the text

$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fig2.eps}} \end{figure}$	Figure 2: RGB stars in common with Schultheis et al. (2003); black line: this work, gray line: Schultheis et al. (2003). The features between 1.8 and 1.9 $\mu$ m and around 2 $\mu$ m are due to the atmosphere.
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$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fig3.eps}} \end{figure}$	Figure 3: Equivalent line width measurements for the candidate RGB stars in common with Schultheis et al. (2003). The plus-signs are taken from Schultheis et al. (2003), the diamonds from this work.
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$\begin{figure} \par\resizebox{7cm}{!}{\includegraphics{5194fig4.eps}} \end{figure}$	Figure 4: Equivalent line width measurements for the stars in common with Ramírez et al. (1997) and Ramírez et al. (2000). The plus-signs are taken from Ramírez et al. (1997), the stars are from Ramírez et al. (2000) and the diamonds are from this work.
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$\begin{figure} \par\resizebox{7.5cm}{!}{\includegraphics{5194fig5.eps}}\end{figure}$	Figure 5: Variations in the equivalent widths for stars in common with Lançon & Wood (2000). The plus-signs indicate values taken from Lançon & Wood (2000), the diamonds those from this work.
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$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{5194fig6.eps}}\end{figure}$	Figure 6: Equivalent line-width measurements for the OH/IR stars in common with Schultheis et al. (2003). The plus-signs indicate values taken from Schultheis et al. (2003), the diamonds those from this work.
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$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fig7.eps}}\end{figure}$	Figure 7: Histograms for EW(Ca), EW(Na), EW(CO) and the water absorption for the OH/IR stars from this work (full line) and the OH/IR stars from Schultheis et al. (2003) (dotted line). All x-axes are in the same unit Å.
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$\begin{figure} \par\resizebox{8cm}{!}{\includegraphics{5194fig8.eps}}\end{figure}$	Figure 8: OH/IR star for which the Na I and Ca I lines could not be measured. The dotted lines indicate the Na I feature and the dashed lines the selected continuum points. The dashed-dotted lines indicate the Ca I feature with its corresponding continuum (dashed-triple-dotted).
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$\begin{figure} \par\resizebox{7cm}{!}{\includegraphics{5194fi10.eps}}\vspace*{7mm} \resizebox{7cm}{!}{\includegraphics{5194fi11.eps}}\end{figure}$	Figure 10: Upper panel: EW(Ca) vs. EW(H₂O), lower panel: EW(Na) vs. EW(H₂O). The OH/IR in this work are the crosses, RGB (Schultheis et al. 2003): stars, OH/IR (Schultheis et al. 2003): diamonds, LPV (Schultheis et al. 2003): triangles. All equivalent line widths are given in the same unit Å.
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$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fi12.eps}}\end{figure}$	Figure 11: Determination of the phase $\phi$ . The dotted horizontal line gives $\langle K\rangle$ .
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$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fi13.eps}}\end{figure}$	Figure 12: The phase at time of observation versus the equivalent line width of water absorption.
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$\begin{figure} \par\resizebox{7.8cm}{!}{\includegraphics{5194fi14.eps}}\end{figure}$	Figure 13: Comparison of the expansion velocities with the equivalent line widths of Na I, Ca I, ¹²CO(2, 0), and the water absorption. The dotted vertical line separates the 2 groups of OH/IR stars.
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