All Figures

$\begin{figure} \includegraphics[width=11.3cm,clip]{1709fig1.eps} \end{figure}$ Figure 1: The position in the IRAS two-colour diagram of the stars in the "Arecibo sample'', where the IRAS colours are defined as: $[12]-[25]=-2.5\log\frac{F_{\nu}(12)}{F_{\nu}(25)}$ and $[25]-[60]=-2.5\log\frac{F_{\nu}(25)}{F_{\nu}(60)}$ . The continuous line is what we call the "O-rich AGB sequence'' (see text).
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In the text

$\begin{figure} \par\includegraphics[width=12.6cm,clip]{1709fig2.ps} \end{figure}$ Figure 2: Atlas images for IRAS 19323+1952. The upper row gives the optical DSS2 R band and the Calar Alto J band images, and the lower row the H- and K-band images. The adopted counterpart is marked by a big circle, the reference stars by small circles surrounded by squares.
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In the text

$\begin{figure} \par {\includegraphics[width=7.9cm,clip]{1709fig3.eps} } \par\end{figure}$ Figure 3: Angular separation between Calar Alto and MSX coordinates for the 243 OH/IR stars in common for which an optical/near-infrared counterpart was found.
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In the text

$\begin{figure} \par {\includegraphics[width=7.7cm,clip]{1709fi4a.eps} } \par\vsp... ...4mm} \par {\includegraphics[width=7.9cm,clip]{1709fi4b.eps} } \par\end{figure}$ Figure 4: Absolute coordinate differences in right ascension ( upper panel) and declination ( lower panel) between Calar Alto and IRAS coordinates for the 363 OH/IR stars for which an optical/near-infrared counterpart was found. Not included are six sources with $30\hbox{$^{\prime\prime}$ }$ < $\vert$ $\Delta \alpha$ $\vert$ < $61\hbox{$^{\prime\prime}$ }$ .
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In the text

$\begin{figure} \par\includegraphics[width=11.5cm]{1709fig5.eps} \end{figure}$ Figure 5: J band ( dotted line), H band ( dashed line), and K band ( solid line) magnitude distribution of the sources included in the "Arecibo sample''.
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In the text

$\begin{figure} \par {\includegraphics[width=11cm,clip]{1709fig6.eps} } \end{figure}$ Figure 6: Near-infrared J-H vs. H-K colour-colour diagram of all Arecibo sources with photometry at least in the H and K bands. J-H lower limits are indicated by arrows. The solid line shows the location of black-bodies of different temperatures and the dashed lines show the location of the combination of a 2500 K black-body with dust shells of temperatures 200, 400 and 800 K following Whitelock (1985). In addition we also indicate the reddening vector corresponding to $A_{\rm V} = 10$ $^{\rm m}$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{1709fig7.eps} % \par \end{figure}$ Figure 7: The total number of sources in the sample ( solid line) is compared with the number of sources with an optical counterpart on the DSS2 images ( broken line) as a function of the H-K colour. The numbers on top of each bin indicate the percentage of opticaldetections.
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In the text

$\begin{figure} {\includegraphics[width=11.65cm,clip]{1709fig8.eps} } \end{figure}$ Figure 8: IRAS two-colour diagram with the Arecibo sources distinguished according to the H-K colours of their near-infrared counterparts. Diamonds ( $\diamondsuit$ ) are sources with $H-K\le1.0$ , crosses (+) are those with $1.0< H - K \le 2.0$ , and triangles ( $\triangle$ ) those with 2.0<H -K. Circles ( $\circ$ ) correspond to sources with H brightness below the detection limit. The solid line is the "O-rich AGB sequence''.
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In the text

$\begin{figure} \includegraphics[width=11.4cm,clip]{1709fig9.eps} %\end{figure}$ Figure 9: K-[12] vs. [12]-[25] colour-colour diagram, where the K-[12] colour is defined as $K-[12]=-2.5\log\frac{F_{\nu}(2.2)}{F_{\nu}(12)}$ , and the [12]-[25] colour is defined as in Fig. 1. The dashed lines indicate the dispersion expected from the intrinsic variability of these sources. Candidate post-AGB stars are marked with open symbols. The dotted box delimits the region occupied by the type of Mira variables studied by Whitelock et al. (1994). For details, see text.
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In the text

$\begin{figure} \includegraphics[width=11.3cm,clip]{1709fig1.eps} \end{figure}$	Figure 1: The position in the IRAS two-colour diagram of the stars in the "Arecibo sample'', where the IRAS colours are defined as: $[12]-[25]=-2.5\log\frac{F_{\nu}(12)}{F_{\nu}(25)}$ and $[25]-[60]=-2.5\log\frac{F_{\nu}(25)}{F_{\nu}(60)}$ . The continuous line is what we call the "O-rich AGB sequence'' (see text).
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$\begin{figure} \par\includegraphics[width=12.6cm,clip]{1709fig2.ps} \end{figure}$	Figure 2: Atlas images for IRAS 19323+1952. The upper row gives the optical DSS2 R band and the Calar Alto J band images, and the lower row the H- and K-band images. The adopted counterpart is marked by a big circle, the reference stars by small circles surrounded by squares.
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$\begin{figure} \par {\includegraphics[width=7.9cm,clip]{1709fig3.eps} } \par\end{figure}$	Figure 3: Angular separation between Calar Alto and MSX coordinates for the 243 OH/IR stars in common for which an optical/near-infrared counterpart was found.
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$\begin{figure} \par {\includegraphics[width=7.7cm,clip]{1709fi4a.eps} } \par\vsp... ...4mm} \par {\includegraphics[width=7.9cm,clip]{1709fi4b.eps} } \par\end{figure}$	Figure 4: Absolute coordinate differences in right ascension ( upper panel) and declination ( lower panel) between Calar Alto and IRAS coordinates for the 363 OH/IR stars for which an optical/near-infrared counterpart was found. Not included are six sources with $30\hbox{$^{\prime\prime}$ }$ < $\vert$ $\Delta \alpha$ $\vert$ < $61\hbox{$^{\prime\prime}$ }$ .
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$\begin{figure} \par\includegraphics[width=11.5cm]{1709fig5.eps} \end{figure}$	Figure 5: J band ( dotted line), H band ( dashed line), and K band ( solid line) magnitude distribution of the sources included in the "Arecibo sample''.
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$\begin{figure} \par\includegraphics[width=7.7cm,clip]{1709fig7.eps} % \par \end{figure}$	Figure 7: The total number of sources in the sample ( solid line) is compared with the number of sources with an optical counterpart on the DSS2 images ( broken line) as a function of the H-K colour. The numbers on top of each bin indicate the percentage of opticaldetections.
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