The papers of this series are devoted to the diagnosis of the magnetic field of Ap stars from the consideration of the polarization of their spectral lines. Particular attention is paid to the information contents of the profiles of the polarized lines, an aspect whose study has become possible thanks to the use of modern linear detectors such as CCDs. The first paper of the series (Mathys & Stenflo 1986; hereafter Paper I) introduced the kind of analysis techniques that was contemplated for this project. Paper II (Mathys 1991) presented measurements of the mean longitudinal magnetic field of a sample of Ap stars. The uncertainties affecting the diagnosis of stellar magnetic fields through the methods applied in this series of papers were discussed in general terms in Paper III (Mathys 1994). The application of the results of this discussion to the determination of the longitudinal field led to the revision of the values of the latter that had been derived in Paper II. The first ever quantitative measurements of the crossover were reported in Paper IV (Mathys 1995a). Paper V (Mathys 1995b) was devoted to the mean quadratic magnetic field.
The circularly polarized spectra analyzed in Papers I to V had all been recorded between 1985 and 1988 with the same configuration of CASPEC (the ESO Cassegrain Echelle Spectrograph, attached to the ESO 3.6 m telescope) and of its Zeeman analyzer. This configuration has been described in detail in Paper I. Between 1989 and 1994, CASPEC and its Zeeman analyzer underwent a number of modifications, to bring them to their current configuration, which has been stable since early 1995. We present here the magnetic field determinations performed using observational data obtained during the 1989-1994 transition period (in part as check of the proper operation of the instrument after its various modifications). The magnetic fields have been diagnosed through application of the methods described in Papers III to V. The present data complement the results reported in those papers. In particular, new observations have been obtained for several of the stars studied therein, improving the phase coverage of their variations and the definition of their magnetic curves. On the other hand, we also present magnetic data for a number of stars that we had never studied before. These data are still very incomplete, but they are often the first measurements based on spectropolarimetry of the magnetic fields of the considered stars, which should confer them enough interest to warrant publication.
In the next section, we describe the observations and their reduction. Section 3 summarizes the methods of analysis. The resulting magnetic field measurements are presented and discussed, star by star, in Sect. 4. The main results of this study and the conclusions that can be drawn from them are summarized in Sect. 5.