2 Observations and sample

All radial-velocity observations have been obtained at the Observatoire de Haute-Provence. Most of the data were measured with the CORAVEL scanner attached to the 1-meter Swiss telescope. Although this instrument is optimized for late-type stars, it can still yield very good results on slowly rotating F and even A stars, especially if their metallic lines are enhanced, as is the case of Ap stars. Originally, the sample was selected according to the following criteria: $T_{\rm eff} \leqslant 10~000$ K according to Geneva photometry (stars for which no Geneva photometry existed in 1985 were not retained), $\delta \geqslant -25\hbox{$^\circ$ }$, $m_V \leqslant 8.6$ (except for a few stars lying in the northern galactic polar cap and for candidate high-velocity stars proposed by Jaschek et al. 1983). A total of 1913 radial-velocity observations were made of the 119 programme stars during the period March 1980 through April 1998. Errors for the individual observations are derived following the precepts of Baranne et al. (1979) and are generally below 2.0 km s^-1  for all stars. The radial-velocity variations are large enough (10 km s^-1 $< 2\times K < 173$ km s^-1) to be clearly significant. In addition to the CORAVEL data, we use here 75 measurements for 72 stars already observed with CORAVEL, obtained with the 1.93-meter telescope at OHP, equipped with the ELODIE spectrograph. This fibre-fed echelle spectrograph has been in operation only since the end of 1993 and has a better precision than the CORAVEL scanner. All but one ELODIE data were gathered during four observing runs from October 1994 to September 1996, which were primarily aimed at determining magnetic fields (Babel et al. 1995; Babel & North 1997); the radial velocities are just a by-product of the programme. One additional data was obtained in April 2002 for HD 116114 with ELODIE.

Among all the programme stars, only 20 stars have as yet a precise orbit. $\beta$ CrB and HD 8441 (as well as the Am star HD 43478) have been published by North et al. (1998), while HD 59435 and HD 81009 have been published by Wade et al. (1996, 1999) and by Wade et al. (2000) respectively; the orbit of HD 73709 was published by Debernardi et al. (2000). The others are presented in the appendix A, as well as an improved orbit of HD 73709. The orbital elements of the 16 stars studied in this article are listed in Table A.1. The individual RV measurements of all stars of the sample, as well as the depths and widths of the correlation dips, are listed in Table 1, which is only available in electronic form at the CDS. The average radial velocities, upper limits to projected rotational velocities and some statistical quantities like $P(\chi^2)$ (see Duquennoy & Mayor 1991 for a definition of $P(\chi^2)$), are given in Table 2 (only available in electronic form at the CDS) . The list of the 48 stars observed with CORAVEL (in addition to the 119 stars mentioned above), but showing no measurable correlation dip is given in Table 3 (only available in electronic form at the CDS).