1 Introduction

Cepheid variables have been targets of numerous extensive (multicolour) photometric studies in view of their key-rôle in determining stellar structure and evolution as well as the cosmic distance scale through the regular pulsation of these variable stars. Unlike photometric data, there are only few projects aimed at measuring radial velocities of large numbers of Cepheids because such projects are more time-consuming than the photometric ones.

Radial velocity data are, however, indispensable in several respects. Their traditional use is for deriving radius variations via the Baade-Wesselink method from which the stellar radius can be derived as well as the luminosity and distance of the individual Cepheids (Gieren et al. 1993). With the advent of sensitive and precise radial velocity spectrometers (e.g. CORAVEL, ELODIE - Baranne et al. 1979, 1996), radial velocity of faint Cepheids can also be studied, allowing the analysis of Galactic kinematics and rotation parameters (Pont et al. 1997). The third major field of research where radial velocity data offer a significant contribution is the study of binary nature of Cepheids. Szabados (1995) pointed out the existence of a selection effect which hinders the discovery of duplicity among fainter Cepheids. As a matter of fact, the incidence of binaries among classical Cepheids exceeds 50 per cent.

Therefore, it is not surprising that new spectroscopic binaries involving a Cepheid component have been amply found from the data of extensive radial velocity projects. Such projects include: the observational campaigns of the Geneva group (Bersier et al. 1994; Pont et al. 1994, 1997) using the CORAVEL and more recently the ELODIE spectrographs, and those of the Moscow group (Gorynya et al. 1996 and the references therein), the latter group using a CORAVEL-type equipment. It is worth mentioning that spectroscopic binaries have been found even among Cepheids in the Magellanic Clouds (Imbert 1994), also with the help of the CORAVEL spectrograph.

The observational efforts of these teams have resulted in a unique data-base containing an unprecedented number of precise and homogeneous radial velocity measurements on classical Cepheids. The extended temporal coverage was a major contribution to help discover new SB-systems among Cepheids. Thus variations in the $\gamma$-velocity (i.e. the mean radial velocity averaged over a whole pulsational cycle) were reported e.g. in the case of BY Cas, AC Mon, UZ Sct, VY Sgr (Pont et al. 1994), MW Cyg (Gorynya et al. 1992b; Samus et al. 1993), and independently for BY Cas (Gorynya et al. 1994). Even the intercomparison of the data for Cepheids common in both samples allowed the discovery of SB-nature of such bright Cepheids as U Vul and SV Vul (Szabados 1996). (Later on, when supplementing with his own data, Imbert (1996) was able to determine the orbital elements for both the U Vul and MW Cyg systems.)

In addition to those recent datasets, there is a former project on Cepheid radial velocities performed as early as in the 1920-1930-es (Joy 1937). When comparing Joy's data with the recent ones, it turned out that many unrecognized SB-systems can be revealed even with the help of those historic data of limited accuracy (Szabados 1996).

The aim of this paper is similar: comparing the early radial velocity data with those reported by Pont et al. (1997). Because in their recent paper Pont et al. concentrated on the determination of the rotation of the Galactic disk, searching for effects of binary companions in the radial velocity data was not a main issue in that study. Nevertheless, using only their own high-precision data, CI Per is suspected to belong to a binary system. However, no attempt was made to compare the new data with the available previous radial velocity measurements. Their sample involved 48 remote, quite faint Cepheids. This is the reason why Pont et al.'s (1997) measurements form the first epoch radial velocity dataset for most of their programme stars. There have been, however, prior radial velocity data for 16 Cepheids in that sample - mostly obtained by Joy (1937) - allowing a comparison to be made between the mean values for the two epochs.

It turned out that eight Cepheids in that sample belong to spectroscopic binary systems unrecognized before. Following a brief description of the method of the analysis (Sect. 2), the available information on the new SB-Cepheids is published (Sect. 3), while Sect. 4 contains some concluding remarks.