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Astron. Astrophys. 330, 19-24 (1998)

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2. Observations and data reduction

On the nights of 1994 August 3 and 4 we obtained two spectra of Q0151+048A, of combined integration time 6200 seconds, using the blue arm of the EMMI instrument on the ESO 3.5m NTT. We used grism # 3 (1200 grooves [FORMULA], blazed at [FORMULA]) and a [FORMULA] slit, yielding a resolution of [FORMULA]. The detector was a Tektronix [FORMULA] CCD, binned by a factor two in the dispersion direction, giving a pixel size of [FORMULA]. The readout noise of the chip was [FORMULA]. The journal of observations is provided in Table 1.


Table 1. Journal of observations

The spectra were reduced using standard techniques for bias and dark subtraction, and flatfielding. One dimensional spectra were extracted and combined using the optimising extraction routine described by Moller & Kjærgaard (1992). The final spectrum is shown in Fig. 1.

[FIGURE] Fig. 1. Combined spectrum of Q0151+048A in the region of the DLA absorption line. Flux per unit wavelength is plotted against wavelength. The lower solid line shows the [FORMULA] noise spectrum. The spectrum has not been corrected for relative slit losses which were substantial (see text x3.2).

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© European Southern Observatory (ESO) 1998

Online publication: January 8, 1998