All Figures

$\begin{figure} \par\mbox{\includegraphics[height=8cm,angle=-90]{9804fg01.eps} \i... ...04fg03.eps} \includegraphics[height=8cm,angle=-90]{9804fg04.eps} } \end{figure}$ Figure 1: Velocity distribution from observational data, adopting a distance of 420 pc to the ONC (cf. Menten et al. 2007; Jeffries 2007). See text for details of its construction. The bin width is 0.7 km s^-1. The stars have been divided into two groups according to the disc signature $\Delta (I_{{\rm C}}-K)$ (see text): grey boxes represent star-disc systems, lines represent discless stars. For comparison a Gaussian with dispersion $\sigma$ = $\sigma _{\rm {1D}}^{\rm {JW}}$ = 2.5 km s^-1 (Jones & Walker 1988) is superposed (dashed line). a) Complete sample of stars in the ONC with available proper motions from Jones & Walker (1988) and infrared excess from Hillenbrand et al. (1998). b) Like a), but zoomed into the lower part. c) Like b), but with restricted stellar ages (see text). d) Like b), but with restricted stellar ages and velocity errors as described in the text.
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In the text

$\begin{figure} \par\includegraphics[height=9cm,angle=-90]{9804fg05.eps} \end{figure}$ Figure 2: Distribution of age and velocity of the high-velocity stars in the ONC, classified as star-disc systems (open circles) and discless stars (filled circles). The mean age of the ONC, t = 1 Myr, and the minimum one-dimensional velocity of the high-velocity sample, 3 $\sigma _{\rm {1D}}^{\rm {JW}}$ , are indicated by the horizontal and vertical dashed line, respectively. The uncertainty of the determined ages of $\sim$ 0.5 dex (see Appendix B for the derivation) is indicated by the vertical error bar. At high velocities the (horizontal) velocity error bars are smaller than the symbol size.
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In the text

$\begin{figure} \par\includegraphics[height=7.5cm,angle=-90]{9804fg06.eps} \includegraphics[height=7.5cm,angle=-90]{9804fg07.eps} \end{figure}$ Figure 3: Positions and velocities of high-velocity star-disc systems (open circles) and discless stars (filled circles) in the ONC. The frames are centered on the most massive star, $\theta^1{\rm {C}}\:{\rm {Ori}}$ , which is marked by a cross. Thin lines indicate the distance (in pc) a star would have moved in a period of 2 $\times$ 10⁴ yr. Thick lines and the opening angle reflect the error of the magnitude and the direction of the proper motion, respectively. a): sample of all high-velocity stars with ages < 1 Myr. b): restricted sample of high-velocity stars with ages < 1 Myr: only stars fulfilling the constraints on the velocity errors as dicussed in the text are shown.
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In the text

$\begin{figure} \par\includegraphics[height=9cm,angle=-90]{9804fg08.eps} \end{figure}$ Figure 4: Three-dimensional velocity dispersion as a function of time for the previous (dashed) and new (solid) numerical models of the ONC. The dotted horizontal line marks the three-dimensional velocity dispersion from Jones & Walker (1988), $\sigma _{\rm {3D}}^{\rm {JW}}$ = 4.3 km s^-1, the vertical dotted line marks the mean age of the ONC, $t_{\rm {ONC}}$ = 1 Myr.
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In the text

$\begin{figure} \par\includegraphics[height=9cm,angle=-90]{9804fg09.eps} \end{figure}$ Figure 5: Velocity distribution of cluster stars from simulations. The construction of the distribution is described in the text. The bin width is 0.7 km s^-1. The stars have been divided into two groups according to their extant disc mass (see text): boxes represent star-disc systems, impulses represent discless stars. For comparison a Gaussian with dispersion $\sigma$ = $\sigma _{\rm {1D}}^{\rm {JW}}$ = 2.5 km s^-1 is superposed (dashed line).
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In the text

$\begin{figure} \par\includegraphics[height=9cm,angle=-90]{9804fg10.eps} \end{figure}$ Figure 6: Positions and velocities of high-velocity star-disc systems (open circles) and discless stars (filled circles) from cluster simulations. The frame is centered on the cluster centre. The lines indicate the distance (in pc) a star would have moved in a period of 2 $\times$ 10⁴ yr.
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In the text

$\begin{figure} \par\includegraphics[height=7.5cm,angle=-90]{9804fg11.eps} \includegraphics[height=7.5cm,angle=-90]{9804fg12.eps} \end{figure}$ Figure 7: Tracks of two high-velocity stars from simulations. The cross marks the cluster centre. The solid line marks the trajectory up to 1 Myr, the dotted line represents later times. a) Star on a wide orbit around the cluster centre, escaping from the cluster after a close passage of the cluster centre. b) Star escaping after multiple passages of the cluster centre and a final close encounter.
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In the text

$\begin{figure} \par\includegraphics[height=9cm,angle=-90]{9804fg13.eps} \end{figure}$ Figure 8: Minimum distance of the high-velocity stars to the cluster centre, $d_{{\rm min}}$ , as a function of the initial specific angular momentum, l₀ (relative to the cluster centre). Star-disc systems are marked by open, discless stars by filled circles. Linear best-fits of both populations, star-disc systems (dotted line) and discless stars (solid line), have been included (quantitative results are discussed in the text).
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In the text

$\begin{figure} \par\includegraphics[height=9cm,angle=-90]{9804fg14.eps} \end{figure}$ Figure 9: Relative actual angular momentum of the high-velocity stars, $l_{{\rm now}}/l_0$ , as a function of the initial specific angular momentum l₀ (relative to the cluster centre). Star-disc systems are marked by open, discless stars by filled circles.
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In the text

$\begin{figure} \par\includegraphics[height=9cm,angle=-90]{9804fg08.eps} \end{figure}$	Figure 4: Three-dimensional velocity dispersion as a function of time for the previous (dashed) and new (solid) numerical models of the ONC. The dotted horizontal line marks the three-dimensional velocity dispersion from Jones & Walker (1988), $\sigma _{\rm {3D}}^{\rm {JW}}$ = 4.3 km s^-1, the vertical dotted line marks the mean age of the ONC, $t_{\rm {ONC}}$ = 1 Myr.
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$\begin{figure} \par\includegraphics[height=9cm,angle=-90]{9804fg10.eps} \end{figure}$	Figure 6: Positions and velocities of high-velocity star-disc systems (open circles) and discless stars (filled circles) from cluster simulations. The frame is centered on the cluster centre. The lines indicate the distance (in pc) a star would have moved in a period of 2 $\times$ 10⁴ yr.
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$\begin{figure} \par\includegraphics[height=9cm,angle=-90]{9804fg14.eps} \end{figure}$	Figure 9: Relative actual angular momentum of the high-velocity stars, $l_{{\rm now}}/l_0$ , as a function of the initial specific angular momentum l₀ (relative to the cluster centre). Star-disc systems are marked by open, discless stars by filled circles.
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