Astronomy & Astrophysics

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$\begin{figure} \par\includegraphics[width=8.8cm,clip]{Hb014_fig1.ps} \end{figure}$ Figure 1: Toomre diagram for the HBA stars in our sample. The concentric circles show the absolute peculiar velocity ( $v_{\rm pec}$ ), i.e. the total deviation from circular velocity (shown as an open star; the Sun's position in this diagram is shown as an open circle). The hexagons depict the stars belonging to the members of the Cometary Orbit Group (COG) discussed in this paper, the triangles denote putative $\omega$ Cen debris candidates (identified as retrograde moving stars broadly conforming to the abundance range of $\omega$ Cen giants), the other HBAs are represented by squares. Note that the COG stars are relatively close together in this plane, their larger spread in $v_{\perp }$ most likely caused by their chaotic orbits. The most deviant point of this group is HD 86986. The rather large ( $\ge$ 100 km s^-1) $v_{\rm pec}$ reveals that most probably all objects belong to the halo. Stars of the thin disk have a $v_{\rm pec}$ of mostly less than 50 km s^-1, while some thick disk stars may have a $v_{\rm pec}$ of up to 150 km s^-1.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{Hb014_fig2.ps} \end{figure}$ Figure 2: [X/H] vs. I_z diagram for eight different elements. The vertical dashed line marks the boundary between pro- and retrograde rotation, while the dotted lines $\omega$ Cen's I_z ( left) and that of the Sun ( right) to represent the I_z of a typical disk star. The grey area between the horizontal lines in the retrograde part of the plots denotes the abundance range of each element in $\omega$ Cen, as conservatively derived from the extreme values of the relatively small sample of stars analysed by Smith et al. (2000). The object symbols are used as described in Fig. 1. Two extreme objects are outside the I_z range of this plot.
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In the text