All Figures

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{2484fig01.ps} \end{figure}$ Figure 1: Classification diagram, based on van Boekel et al. (2003). Objects in the upper left corner are classified as group II sources (open diamonds), sources on the lower right side are either group I (filled diamonds) or group III (squares) members. The dashed line represents the empirical separation between group I and II: $L({\rm NIR})/L({\rm IR}) = ([12]-[60])+0.9$ (AV04). The quantities $L({\rm NIR})/L({\rm IR})$ and IRAS [12]-[60] are listed in Table 2.
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In the text

$\begin{figure} \par\includegraphics[width=17cm,clip]{2484fig02.ps} \end{figure}$ Figure 2: The detected [O I]6300 Å emission line spectra. Along the x-axis, the velocity in ${\rm km}~{\rm s}^{-1}$ is given, on the y-axis the normalized intensity. The horizontal dotted line indicates the continuum level, the vertical line the stellar radial velocity ( $v_{\rm rad} = 0$ ). The source's name and group (in parentheses) are indicated in the upper left corner of each frame. When more than one spectrum is available, the type of spectrum is included as well.
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In the text

$\begin{figure} \par\includegraphics[width=18cm,clip]{2484fig03.ps} \end{figure}$ Figure 3: The 6300 Å spectra of the sample stars for which the detection of [O I]emission is confused by photospheric absorption lines. Legend see Fig. 2.
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In the text

$\begin{figure} \par\includegraphics[width=18cm,clip]{2484fig04.ps} \end{figure}$ Figure 4: The 6300 Å spectra of the sample stars with undetected [O I] emission. Legend see Fig. 2.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2484fig05.ps} \end{figure}$ Figure 5: Comparison between published values for the equivalent width of the [O I]6300 Å line and our determinations. The different plotting symbols refer to data obtained by different authors. The typical error bar is plotted in the upper left corner. The error bar on the literature values is expected to be larger than the indicated error, which is equal to our estimate for the error bar. The dashed line represents $\Delta ~ {\it EW} = 0$ .
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In the text

$\begin{figure} \par\includegraphics[width=17.7cm,clip]{2484fig06.ps} \end{figure}$ Figure 6: The EWs of the [O I]emission lines versus the effective temperature of the central star. Filled diamonds refer to group I sources, open diamonds to group II. Squares are group III sources, with the $\times$ -marks indicating the three sources with an extended highly-blueshifted wing. On the y-axis, | EW| is plotted, on the x-axis the logarithm of the effective temperature. The typical error bar is indicated in the upper right corner. The right panel contains the 10 sample stars for which the 6300 Å region is rich in photospheric lines. The EWs are positive due to dominance of the absorption spectrum. The y-axis is flipped to make clear that increasing EW designates an increasing contribution of the absorption features. The other 39 sample sources (of which 29 with detected [O I]6300 Å emission) are plotted in the left panel. These objects have earlier spectral types.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2484fig07.ps} %\end{figure}$ Figure 7: The EW of the detected [O I]emission lines versus the FWHM. Filled diamonds represent group I, open diamonds group II and squares group III sources. The $\times$ -marked squares represent PV Cep, V645 Cyg and Z CMa. The dash-dotted line indicates the mean FWHM (47 ${\rm km}~{\rm s}^{-1}$ ). The dotted and dashed lines indicate the mean values of group I (34 ${\rm km}~{\rm s}^{-1}$ ) and group II (67 ${\rm km}~{\rm s}^{-1}$ ) respectively. The typical error bar is represented on the right side of the plot.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig08.ps} \end{figure}$ Figure 8: The EW of the detected [O I]emission lines versus the centroid position of the feature. The plotting symbols are as in Fig. 7. The vast majority of the features is centered around the stellar radial velocity within the error bars. The dashed line represents the average centroid position (-4 ${\rm km}~{\rm s}^{-1}$ ). The typical error bar is represented in the lower left corner.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig09.ps} \end{figure}$ Figure 9: The histogram of the centroid positions of the 12 group I and 12 group II sample sources with a detected [O I]6300 Å feature. The bin size is 10 ${\rm km}~{\rm s}^{-1}$ . The dashed line represents distribution $D_{{\rm exp}}$ , the full line is the Gaussian fit to the observed distribution. The cross-hatched part of the bars indicate group I sources, the open parts group II members.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig10.ps} \end{figure}$ Figure 10: The FWHM of the detected [O I]emission lines versus the asymmetry parameter of the feature. The plotting symbols are as in Fig. 7. The dashed horizontal line represents the mean value (1.04) for $\mathcal{A}$ , the vertical line indicates the mean FWHM (47 ${\rm km}~{\rm s}^{-1}$ ). The typical error bar is represented in the upper right corner.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2484fig11.ps} \end{figure}$ Figure 11: The [O I]-versus-H $\alpha$ luminosity. The sources with a negative H $\alpha$ EW have been included. The typical error bar is presented in the upper left corner. Plotting symbols are as in Fig. 7. The dotted line represents the median luminosity ratio L([O I]) $/L({\rm H}\alpha ) = 6.3 \times 10^{-3}$ .
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2484fig12.ps} \end{figure}$ Figure 12: The [O I]6300 Å luminosity versus the stellar UV luminosity. The plotting symbols are as in Fig. 7. The typical error bar is indicated in the upper left corner. The dotted line represents the median luminosity ratio L([O I]) $/L_{{\rm uv}} = 1.5 \times 10^{-5}$ .
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2484fig13.ps} \end{figure}$ Figure 13: Histogram of the EWs containing the 13 group I and 24 group II members for which we have a measurement of, or an upper limit to the EW of the [O I]6300 Å emission line. The filled part of the bars represents group I sources, the open part group II members. The bin size is 0.05 Å. The group I sources have slightly higher EW values than their group II counterparts.
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2484fig14.ps} \end{figure}$ Figure 14: The average [O I]6300 Å profiles for group I and group II. The horizontal dotted lines are plotted at 0 and 0.5, while the vertical dotted line represents the centroid position of the feature. The 12 group I and 12 group II sources which display [O I] emission are included. The profile of each source was shifted to its centroid position, continuum-subtracted and normalized by dividing by its peak-flux. The group II profile (dashed line) is $\sim$ 20 ${\rm km}~{\rm s}^{-1}$ broader than the group I profile (full line).
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2484fig15.ps} \end{figure}$ Figure 15: The PAH luminosity versus the [O I]6300 Å luminosity. The plot includes the 12 group I, 14 group II and 5 group III sources for which (an upper limit of) both measurements was available. The dotted line represents the median PAH-over-[O I]luminosity ratio L(PAH)/L([O I]) = 130. Plotting symbols are as in Fig. 7. The typical error bar is indicated in the upper left corner.
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig16.ps} \end{figure}$ Figure 16: The luminosity of the amorphous 10 micron silicate feature versus the [O I]6300 Å luminosity. The plot includes the 12 group I and 15 group II sources for which (an upper limit of) both measurements was available. The group III sources are left out since they display silicate absorption at 10 $\mu$ m. Plotting symbols are as in Fig. 7. The typical error bar is indicated in the lower right corner.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{2484fig17.ps} \end{figure}$ Figure 17: The [O I]6300 Å emission line in the spectra of HD 100546. The double-peaked profile is clearly seen in the ESO 3.6 m and CAT spectrum. Due to the lower spectral resolution, the profile remains unresolved in the FEROS spectrum. The horizontal dotted lines represent the continuum levels of the three spectra. The vertical line is the mean centroid position of the feature at 3 ${\rm km}~{\rm s}^{-1}$ .
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2484fig18color.ps} \end{figure}$ Figure 18: The temperature structure of a flared-disk model. On the x-axis the radial distance R to the star is plotted, on the y-axis the ratio of the height above the midplane z over R. The color scale is linear and ranges from 0 to 3500 K. The dashed line represents the disk surface height $H_{\rm cg}$ . (This figure is available in color in the electronic version.)
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2484fig19color.ps} \end{figure}$ Figure 19: The [O I]6300 Å emissivity in the flared-disk model. The x-axis gives the radial distance R to the central star in AU, the y-axis plots z/R, the ratio of the vertical height and the radial distance. The colors represent the local [O I]6300 Å emissivity on a log-scale which covers 10 orders of magnitude. On the color bar, the emissivity is given in [erg s^-1 cm^-3 sr^-1]. The disk region sampled by the model ranges from roughly 0.6 to 1.5 times the disk surface height $H_{\rm cg}$ . The latter is indicated by the dashed line. The geometrical full width at half maximum of the [O I] emission region in the vertical direction is 5-10% of $H_{\rm cg}$ . (This figure is available in color in the electronic version.)
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{2484fig20.ps} \end{figure}$ Figure 20: Pictogram of a flat rotating circumstellar disk, seen under an inclination of $i=45^\circ$ . The location of the central star is indicated by the asterisk. The light-grey band represents a circular orbit. In this orbit, the rotational velocity as well as the [O I]intensity (I₀) are constant due to the assumption of axisymmetry. The narrow dark-grey band represents the region where the projected rotational velocity is equal to a certain value $v_{\rm p}$ . At the cross-section of both surfaces the projected velocity is equal to $v_{\rm p}$ and the intensity is equal to I₀. The insertion shows the intensity-versus-velocity profile of the light-grey band. The dark-grey part represents the contribution of the cross section of the dark-grey band and the orbit in the disk.
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2484fig21color.ps} \end{figure}$ Figure 21: The intensity-versus-radius distribution I(R) for four template models, with different values for the surface-density parameters. From top to bottom, $\beta$ is 1.0, 2.0, 2.5 and 3.0 respectively. The value of $\Sigma _0$ is chosen such that the disk masses of the four models are the same. The intensity function is multiplied by the total surface S(R) of the ring at radius R. In this way the fluxes from the inner and outer parts of the disk can be compared directly. The vertical dashed lines mark the radii where the Keplerian velocity is 5, 10, 50 and 100 ${\rm km}~{\rm s}^{-1}$ . The shoulder of the intensity distribution shifts closer to the star with increasing $\beta$ . Furthermore, the total emission is smaller when the power-law describing $\Sigma$ has a steeper slope. (This figure is available in color in the electronic version.)
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In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2484fig22color.ps} \end{figure}$ Figure 22: The line profiles I(v) corresponding to the intensity-versus-radius distribution in Fig. 21. From top to bottom, $\beta$ is 1.0, 2.0, 2.5 and 3.0 respectively. Since the intensity-versus-radius distribution falls off rapidly in the models with large $\beta$ values, the corresponding profiles have peaks at higher velocities than the profiles belonging to low- $\beta$ models. (This figure is available in color in the electronic version.)
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig23color.ps} \end{figure}$ Figure 23: The line profiles I(v) of the template model seen under different inclinations. From top to bottom, the inclination is $18^\circ , 30^\circ , 45^\circ$ and $70^\circ$ respectively. Note the decrease in integrated intensity and the shift of the peaks with increasing i. (This figure is available in color in the electronic version.)
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig24.ps} \end{figure}$ Figure 24: Similar plot as Fig. 12. The filled diamonds are the observed [O I]intensities for the group I sources. The open circles represent model results. The typical error bar for the observations is given in the upper left corner. The models differ from each other in stellar parameters; from the lower left to the upper right, the model [O I]-versus-UV luminosity for a typical F0V, A3V, A0V, B8V, B5V and B0V star are plotted respectively. The error bars on the model determinations represent the spread in results when simultaneously varying the surface density $\Sigma$ and inclination i in the ranges described in Figs. 22 and 23. The dotted lines represent the model results when altering the fractional OH abundance $\epsilon \rm (OH)$ and using the average [O I]-versus-UV luminosity ratio of the models. The abundance is indicated next to each line, with a(-b) representing $a \times 10^{-b}$ . The fractional OH abundance of the models is $1 \times 10^{-6}$ .
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In the text

$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig25.ps} \end{figure}$ Figure 25: The [O I]6300 Å luminosity versus the effective temperature of the group I sources (filled diamonds). The open circles and dotted lines plotted in this figure represent the same models as in Fig. 24.
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In the text

$\begin{figure} \par\includegraphics[width=17cm,clip]{2484fig26color.ps} \end{figure}$ Figure 26: The observed spectra of group I sources AB Aur, HD 97048, HD 100546 and T CrA overplotted with the model results. The parameters of the model are adapted to the stellar parameters of each source combined with the template parameters, unless otherwise indicated in the upper right corner. We have shifted the theoretical profile to the centroid position of the observed feature. For HD 100546 two models with different parameter sets have been displayed to illustrate the difficulty to distinguish between models. The theoretical profiles extracted from our flared-disk model fit the observed features strikingly well for a range of reasonable model parameters. a(-b) represents $a \times 10^{-b}$ . (This figure is available in color in the electronic version.)
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In the text

$\begin{figure} \par\includegraphics[width=18cm,clip]{2484fig03.ps} \end{figure}$	Figure 3: The 6300 Å spectra of the sample stars for which the detection of [O I]emission is confused by photospheric absorption lines. Legend see Fig. 2.
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$\begin{figure} \par\includegraphics[width=18cm,clip]{2484fig04.ps} \end{figure}$	Figure 4: The 6300 Å spectra of the sample stars with undetected [O I] emission. Legend see Fig. 2.
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$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig08.ps} \end{figure}$	Figure 8: The EW of the detected [O I]emission lines versus the centroid position of the feature. The plotting symbols are as in Fig. 7. The vast majority of the features is centered around the stellar radial velocity within the error bars. The dashed line represents the average centroid position (-4 ${\rm km}~{\rm s}^{-1}$ ). The typical error bar is represented in the lower left corner.
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$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig10.ps} \end{figure}$	Figure 10: The FWHM of the detected [O I]emission lines versus the asymmetry parameter of the feature. The plotting symbols are as in Fig. 7. The dashed horizontal line represents the mean value (1.04) for $\mathcal{A}$ , the vertical line indicates the mean FWHM (47 ${\rm km}~{\rm s}^{-1}$ ). The typical error bar is represented in the upper right corner.
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2484fig11.ps} \end{figure}$	Figure 11: The [O I]-versus-H $\alpha$ luminosity. The sources with a negative H $\alpha$ EW have been included. The typical error bar is presented in the upper left corner. Plotting symbols are as in Fig. 7. The dotted line represents the median luminosity ratio L([O I]) $/L({\rm H}\alpha ) = 6.3 \times 10^{-3}$ .
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$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2484fig12.ps} \end{figure}$	Figure 12: The [O I]6300 Å luminosity versus the stellar UV luminosity. The plotting symbols are as in Fig. 7. The typical error bar is indicated in the upper left corner. The dotted line represents the median luminosity ratio L([O I]) $/L_{{\rm uv}} = 1.5 \times 10^{-5}$ .
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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{2484fig13.ps} \end{figure}$	Figure 13: Histogram of the EWs containing the 13 group I and 24 group II members for which we have a measurement of, or an upper limit to the EW of the [O I]6300 Å emission line. The filled part of the bars represents group I sources, the open part group II members. The bin size is 0.05 Å. The group I sources have slightly higher EW values than their group II counterparts.
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$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2484fig15.ps} \end{figure}$	Figure 15: The PAH luminosity versus the [O I]6300 Å luminosity. The plot includes the 12 group I, 14 group II and 5 group III sources for which (an upper limit of) both measurements was available. The dotted line represents the median PAH-over-[O I]luminosity ratio L(PAH)/L([O I]) = 130. Plotting symbols are as in Fig. 7. The typical error bar is indicated in the upper left corner.
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$\begin{figure} \par\includegraphics[width=8.4cm,clip]{2484fig18color.ps} \end{figure}$	Figure 18: The temperature structure of a flared-disk model. On the x-axis the radial distance R to the star is plotted, on the y-axis the ratio of the height above the midplane z over R. The color scale is linear and ranges from 0 to 3500 K. The dashed line represents the disk surface height $H_{\rm cg}$ . (This figure is available in color in the electronic version.)
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$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig23color.ps} \end{figure}$	Figure 23: The line profiles I(v) of the template model seen under different inclinations. From top to bottom, the inclination is $18^\circ , 30^\circ , 45^\circ$ and $70^\circ$ respectively. Note the decrease in integrated intensity and the shift of the peaks with increasing i. (This figure is available in color in the electronic version.)
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$\begin{figure} \par\includegraphics[width=8.6cm,clip]{2484fig25.ps} \end{figure}$	Figure 25: The [O I]6300 Å luminosity versus the effective temperature of the group I sources (filled diamonds). The open circles and dotted lines plotted in this figure represent the same models as in Fig. 24.
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