@vanDokkum01. The seeing remained relatively stable during the observations, between 11 and 14, yielding the spectral resolutions reported in Table \[tab1\]. A first analysis of the spectrum revealed an absorption system associated with the host galaxy at redshift $z=2.641$ [@Jakobsson08a; @Fynbo09].\
While the mid-resolution spectra were mainly used for the spectral analysis, we aimed to flux-calibrate the low-resolution 300V spectra for the SED study. However, the two 300V spectra were obtained at high airmass (2.3 and 1.8 respectively) where the difference between the slit position angle and the parallactic angle was 126.6$^\circ$ and 133.4$^\circ$, respectively. Thus, slit losses influence the continuum level of the spectra, particularly in the blue. In order to correct for this, we computed the slit throughput in the following way. A theoretical model of the point spread function (PSF) as delivered by an 8.2 m diameter Unit Telescope, including the central obscuration caused by the secondary mirror, was built using a piece of IDL code graciously made available by Enrico Fedrigo (private communication). In particular, this model includes the dependence of the diffraction-limited theoretical PSF as a function of wavelength. This model PSF was then convolved with a Gaussian whose wavelength-dependent FWHM follows Roddier’s formula, i.e. 