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Astron. Astrophys. 359, 429-432 (2000)

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2. Observations

Table 1 lists the coordinates, magnitudes and preliminary redshifts [FORMULA] of all objects listed in the Hewitt & Burbidge (1993) catalog and located within a circle of [FORMULA] radius centered on Q0122-380. These 11 objects along with Q0122-380 itself were observed with the ESO 3.6 m telescope and ESO Faint Object Camera and Spectrograph (EFOSC1) on 1995 September 28. EFOSC1 was equipped with a thinned back-side illuminated TEK CCD with 512[FORMULA]512, 27 µm pixels. We used a 230 Å mm-1 (B300) grism in combination with a 2" wide slit to obtain spectra covering the wavelength range 3750-6950 Å at [FORMULA]20 Å (FWHM) resolution. The spatial resolution is 0.61" pixel-1.


[TABLE]

Table 1. Objects observed in the field of Q0122-380.
Notes:
[FORMULA]) Preliminary redshift listed in Hewitt & Burbidge (1993)
[FORMULA]) Angular distance from Q0122-380 in arcmin.
a) Object is a star, not a quasar.
b) No object was found at the catalog coordinates.


The seeing conditions on both nights were poor. Nevertheless, the high throughput of EFOSC1 ensured good signal-to-noise (S/N) spectra of objects as faint as [FORMULA] (S/N[FORMULA]8 in the continuum near 5500 Å). For most objects we took a single 1200 s exposure. For 0117-379, being the faintest target at [FORMULA], we exposed for 1800 s. Prior to each spectroscopic observation, EFOSC1 was used in direct (filterless) imaging mode for target verification and automated slit acquisition. One quasar candidate, 0117-378, was not found at or near its catalog coordinates.

The data were reduced within the IRAF environment, following standard techniques. The spectra were put on a relative flux scale based on the standard stars LDS 235/EG 63 and LTT 2415 (Baldwin & Stone 1984; Stone & Baldwin 1983). The absolute calibration is ill determined, due to variations in seeing and atmospheric extinction over the night.

The resulting spectra of the 8 confirmed quasars are shown in Fig. 1 along with the relevant emission line identifications. The measured redshifts given in Table 1 were determined by averaging the redshifts measured for individual emission lines (e.g. Ly[FORMULA], N V  [FORMULA]1240, C II  [FORMULA]1335, Si IV /O IV[FORMULA]1400, C IV  [FORMULA]1549, He II  [FORMULA]1640, Al III  [FORMULA]1857, C III[FORMULA]1909, and Mg II  [FORMULA]2799). For the wavelength of an emission line we adopted the average of the wavelengths of the peak (maximum signal) and of the center of a gaussian fit to the line, both determined after subtraction of the quasar continuum.

[FIGURE] Fig. 1. Spectra of the eight confirmed quasars. For reference the spectrum of Q0122-380 is given in the top-left panel. The strongest emission features and the corresponding emission-line redshifts are indicated. The spectra span the range 3750-6950 Å and the resolution is [FORMULA]20 Å. The fluxes have been normalized to the flux in a 100 Å region centered on 5470 Å. Below each spectrum, the 1-sigma noise level is shown as a thin curve. The two C IV and Si IV absorption complexes seen near [FORMULA] and [FORMULA] toward Q0122-380 are marked in its spectrum. In the spectrum of Q0125-376 the [FORMULA] absorption systems at [FORMULA] and [FORMULA] are indicated by vertical bars, the BAL-like absorption troughs by small triangles.

Two of the quasar candidates, 0121-379 and 0123-372, turn out to be Galactic stars. Their spectra are shown in Fig. 2. Unfortunately, of the observed quasar candidates 0121-379 would have been the quasar closest to Q0122-380, at an angular separation of [FORMULA].

[FIGURE] Fig. 2. Spectra of the two stars misclassified as quasars in Hewitt & Burbidge (1993). The stellar absorption features are indicated.

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Online publication: July 7, 2000
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