sequence of spectral images were flat-fielded using an internal flat taken immediately after the science frames. Since the trace was too faint for its position to be accurately determined, its curvature was derived from the reference star spectrum. The frames were then pair-subtracted, effectively removing most of the sky, dark current and hot pixels contributions. Each frame was collapsed along the spectral dimension to determine the positive and negative traces positions. We then extracted the spectra using positive and negative extraction boxes that have identical but opposite integrals; this minimised the contribution from residual sky line that would have remained from the pair subtraction. The same operation was performed on the A0 telluric calibration star. Spectra derived from individual image pairs were then median-combined into final target and calibration star spectra. A telluric absorption spectrum was derived using the calibration-star spectra. A black body spectrum with a temperature of 10 000K was assumed for the A0 star and hydrogen-lines were interpolated over. The target spectrum was then divided by the derived telluric transmission spectrum. A first-order wavelength calibration was obtained from an argon-lamp spectrum, and fine-tuned by registering bright OH lines obtained from a sum of the pair of images 