All Figures

$\begin{figure} \par\includegraphics[width=18cm,clip]{ms3503f1.eps}\end{figure}$ Figure 1: Observing strategy. Each object exposure (either target or standard star) was preceded by a calibration sequence, consisting of five bias exposures (B1 through B5), five flat field exposures (F1 through F5), and two wavelength calibration arc spectra (W1 and W2), and followed by an identical calibration sequence (B6 through B10, F6 through F10, W3 and W4). In order to minimize overhead, we used the trailing calibration sequence of each star also as the leading sequence for the next star. Time progresses from left to right.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=18cm,clip]{ms3503f2.eps}\end{figure}$ Figure 2: The stability of the detector, AURELIE. Each of the 131 star exposures has four associated wavelength calibration lamp spectra (W1 through W4): W1 and W2 were obtained before and W3 and W4 after each stellar exposure (Fig. 1). Lamp spectra W3 and W4 were generally taken $\sim$ 30-45 min later than W1 and W2. Top panel: the filled circles show the shift (in km s^-1) between the velocity scales inferred from W1 and from W2. This shift is, for our purposes, acceptably small ( $\sigma = 0.6$ km s^-1), with the exception of 21 cases (crossed symbols). These exposures are treated with extra care in this study. The dashed vertical lines separate different observing nights, the start dates of which are printed in the panel (year: 1997). Bottom panel: open circles and crosses denote the shifts between W1 and W3 and W1 and W4, respectively. Random shifts up to $\sim$ 10 km s^-1 occur ( $\sigma = 2.9$ km s^-1), most likely due to instability of the detector (Gillet et al. 1994).
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=17.8cm,clip]{ms3503f3.eps}\end{figure}$ Figure 3: Example of reduced (continuum-subtracted) spectra: HD 1438 (B8V; V = 6.10 mag; T = 30 min; left panel) and HD 24583 (B7V; V = 9.00 mag; T = 30 min; right panel). Note the near-absence of metal lines, the broad nature of the higher-order Balmer hydrogen lines and the helium lines, and the spectral differences in the helium lines.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{ms3503f4.eps}\end{figure}$ Figure 4: Repeatability errors for 86 pairs of spectra (either target or standard stars; see Sect. 4.3 for details). In the remainder of this paper, we assume that repeatability errors ( $\sigma _{\rm r}$ ) are positive. The mean and median repeatability errors are 2.1 and 2.2 km s^-1, respectively.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=18cm,clip]{ms3503f5.eps}\end{figure}$ Figure 5: Luminosity classes (LCl) and spectral types (SpT) of target stars (open circles) and standard stars (crosses). This diagram is used for selection of suitable standard stars for cross correlation. For a given target star with luminosity class ${\rm LCl_{*}}$ and spectral type ${\rm SpT}_{*}$ , we consider all $N_{\rm s}$ standard stars for which $d \leq d_{\rm max}$ (Eq. (1)). For spectral types later than B7 (>B7; dashed vertical line), we use $d_{\rm max} = 1.0$ while for stars with ${\rm SpT}_{*} = {\rm B7}$ or earlier, we use $d_{\rm max} = 1.5$ because of sparsity of (observed) standard stars. The circle demonstrates the selection of standard stars for a target star with ${\rm SpT}_{*} = {\rm B8}$ and ${\rm LCl_{*}} = {\rm V}$ ; for this object, we consider $N_{\rm s} = 3$ velocity standards as appropriate templates (the three crosses falling within the circle of radius 1). The final radial velocity $v_{\rm rad}$ for this target star (Eq. (3); Table 3) is obtained by means of a distance-weighted average of the individual radial velocities $v_{{\rm rad},i}$ obtained using all $N_{\rm e}$ exposures of the $i = 1,\ldots,N_{\rm s}=3$ standard stars (Sect. 4.4).
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{ms3503f6.eps}\end{figure}$ Figure 6: Comparison of OHP and literature radial velocities. The filled circles denote 15 single stars (i.e., non-SBs). One of these, HD 23268 with OHP and literature radial velocities of $4.1 \pm 0.6$ and $-20 \pm 8.5$ km s^-1 (Duflot et al. 1995), respectively, falls outside the plot. The four open squares refer to the 2+2 instantaneous measurements of the two single-lined SBs HD 24190 ( $v_{\rm rad} \sim 22$ km s^-1) and 25799 ( $v_{\rm rad} \sim 38$ km s^-1).
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=16.5cm,clip]{ms3503f7.eps}\end{figure}$ Figure 7: The radial velocity measurements of our 29 targets as a function of position on the sky. Squares denote our own radial velocity measurements (24 stars), while triangles denote reported systemic velocities for the five spectroscopic binaries (Table 6). Open symbols refer to certain and possible Hipparcos members (Z99), while filled symbols indicate 15 of the 17 classical Per OB2 members from B52; significant overlap between these groups exists (Sect. 5.2.1). The radial velocities of HD 20987 and 23802 fall outside the radial-velocity panels (top left and bottom right). The field of view (top right panel) is that used by Z99 in their Hipparcos analysis of the Per OB2 association. The dotted box and dashed line on the sky denote Belikov et al.'s (2002b) approximate extent of Per OB2 and the separation between their alleged subgroups a and b (see their Fig. 5). The lines in the radial-velocity panels indicate the predicted radial velocities for disk stars at 300 pc (full line) and 1 kpc (dashed line).
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{ms3503f8.eps}\end{figure}$ Figure 8: Radial velocity histogram of all 18 stars with OHP radial velocities between 10 and 35 km s^-1 (we excluded o Per/HD 23180; Sect. 5.2). We find a mean radial velocity of 23.5 km s^-1 (vertical line) and an associated dispersion of 3.9 km s^-1 (dashed vertical lines). The curve denotes a reference Gaussian with a mean of 23.5 km s^-1 and $\sigma = 3.9$ km s^-1. See Sect. 5.1 for details.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=16.5cm,clip]{ms3503f9.eps}\end{figure}$ Figure 9: Observed (left) and de-reddened (right) colour-magnitude diagram of Per OB2 (R_V = 3.2). The curves represent the zero-age main sequence (Schmidt-Kaler 1982) at the mean distance of Per OB2 (318 pc; Z99). Symbols have the same meaning as in Fig. 7, except that two new possible SBs have been given triangular shapes: HD 23802 (labeled 6) and HD 281159 (labeled 3). Numerical labels (HD numbers): 1 = 278942; 2 = 281157; 3 = 281159; 4 = 26499; 5 = 24970; 6 = 23802; 7 = 24534 (X Per); 8 = 24912 (the run-away $\xi$ Per); 9 = 23180 (o Per); 10 = 24398 ( $\zeta$ Per). See Sect. 5.4 for details.
Open with DEXTER

In the text

$\begin{figure} \par\includegraphics[width=17.8cm,clip]{ms3503f3.eps}\end{figure}$	Figure 3: Example of reduced (continuum-subtracted) spectra: HD 1438 (B8V; V = 6.10 mag; T = 30 min; left panel) and HD 24583 (B7V; V = 9.00 mag; T = 30 min; right panel). Note the near-absence of metal lines, the broad nature of the higher-order Balmer hydrogen lines and the helium lines, and the spectral differences in the helium lines.
Open with DEXTER

$\begin{figure} \par\includegraphics[width=8.8cm,clip]{ms3503f4.eps}\end{figure}$	Figure 4: Repeatability errors for 86 pairs of spectra (either target or standard stars; see Sect. 4.3 for details). In the remainder of this paper, we assume that repeatability errors ( $\sigma _{\rm r}$ ) are positive. The mean and median repeatability errors are 2.1 and 2.2 km s^-1, respectively.
Open with DEXTER