Our spectroscopic data were obtained with the ESO 1.5-m telescope, equipped with a Boller & Chivens spectrograph. The spectra were recorded on a CCD and reduced with MIDAS ( NOV95). The data were bias- and flatfield-corrected. Cosmic-ray hits were removed automatically in the background, and by visual inspection in the spectrum. Subsequently, the spectra were optimally extracted (Horne 1986).
During the 1989, 1990 and 1991 runs, the exposure time was 3 min and the spectra were obtained in sets of 10, followed by a HeAr wavelength-calibration frame. Table1 lists the specific details of each run. To perform a radial-velocity study, we rectified the spectra. We used the telluric line at 5578 Å and the interstellar lines at 5990, 5995 Å to correct for possible systematic offsets in wavelength calibration. Offsets occured up to 100 kms-1, a fraction (1/6th) of the resolution (2 pixels). Note that other (weaker) telluric lines were removed during the background subtraction.
The 1995 and 1998 spectra were taken with a holographic grating, resulting
in a dispersion of 0.5 or 1.0 Å per pixel. The exposure time was
30 min.
After each spectrum an HeAr calibration frame was obtained. In these
spectra the so-called "blue fringing'' occured, which is a familiar
problem of the optics of the ESO 1.5-m telescope at high resolution, which
cannot be corrected for. Due to this effect the He II 
5411
line in the 1995 data became distorted and in 1998 the continuum between
N V 4944 and O VI 5290 was affected.
| Observer | date | d | (Å) |
S/N |
| H. E. Schwarz | 13-15/3 1989 | 5.4 | 4100-7150 | 125-200 |
| H. E. Schwarz | 28/2-2/3 1990 | 5.4 | 4100-7180 | 140-215 |
| M. Verheijen | 15-17/2 1991 | 3.7 | 3700-7300 | 130-250 |
| P. M. Veen | 2, 4/4 1995 | 0.5 | 3785-4785 | 50-60 |
| 3, 5/4 1995 | 1.0 | 4715-6735 | 70-110 | |
| P. M. Veen | 10-11/2 1998 | 0.5 | 4750-5700 | 100 |
| 12/2 1998 | 0.5 | 4900-5840 | 100 |
Copyright ESO 2002