3 The spectroscopic survey

We have used the 3.6 m ESO telescope, equipped with the Meudon-ESO Fiber Optic System MEFOS (Bellenger et al. 1991), to obtain low-resolution spectra of the QSO candidates in four observational campaigns between 1993 and 1995. MEFOS is a multifibre positioner which enables the conventional use of the ESO Boller & Chivens Spectrograph to be extended to multiobject spectroscopy. The spectra of up to 29 objects inside the $1^{\circ}$ field of the prime focus of the 3.6 m telescope can be simultaneously recorded. It consists of 29 remotely controlled arms, each carrying two spectroscopic fibers of 2.5 arcsec of diameter, one for the object, and one for the sky sampling. We used the ESO grating No. 13 (150 grooves/mm) with a resolution of 35 Å in the wavelength range 3600-8400 Å. The CCD was a 512$\times$512 Tektronics with 27 $\mu$m pixels (ESO No. 32). Wavelength calibration was carried out by comparison with exposures of He and Ar lamps. The campaign dates with the number of pointings and the exposure time are listed in Table 2. The data reduction was performed under MIDAS and followed the optimized spectra extraction from fiber spectrographs of Lissandrini et al. (1994). No absolute flux calibration has been applied. The spectra have been flux calibrated in relative fluxes just for the sake of facilitating the identification. Only the most evident cosmic rays hits have been removed.

 

Table 2: The observing log

Date	Number	Integration
	of fields	time (min)
10-Oct.-93/15-Oct.-93	15	$40-70\times 2$
30-Oct.-94/02-Nov.-94	14	45-60
22-Sep.-95/25-Sep.-95	8	40-50
22-Nov.-95/25-Nov.-95	8	60-80