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Astron. Astrophys. 342, 395-407 (1999)

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2. Observations

2.1. Optical observations

We present high resolution spectra of HS 1103+6416 obtained with the HIRES spectrograph (Vogt et al. 1994) on the W. M. Keck1 10 m telescope with a total of 3 hours exposure on the nights of 1996 May 20 and 1997 April 9. In both exposures, we used a [FORMULA] slit, which gave a resolution of 8 km s-1 and adequate sky coverage. On the night of April 9, we observed using the UV cross-disperser to increase efficiency at wavelengths below 4200 Å. The images were processed and the spectra were optimally extracted using an automated package (EE by T. Barlow) specifically designed for HIRES spectra. Thorium-Argon lamp images were obtained immediately after the observations to provide wavelength calibrations in each echelle order. The root-mean-square residuals in the wavelength calibration for each echelle order was less than 0.3 km s-1. All wavelengths are vacuum values in the heliocentric frame. Each echelle order was continuum fitted with a Legendre polynomial to normalize the intrinsic QSO flux to unity.

2.2. Ultraviolet observations

Ultraviolet spectra of HS 1103+6416 have been obtained with the FOS and GHRS onboard the HST with apertures A-1 and LSA, respectively. Details of the observations are summarized in Table 1.


[TABLE]

Table 1. Observational parameters for HST spectra of HS 1103+6416.


The STScI provided flux calibrated data together with the 1 [FORMULA] error in the flux of each pixel as a function of wavelength. The deduced signal-to-noise ratio is strongly wavelength dependent. Maximum signal-to-noise ratios for the observed wavelength ranges are given in Table 1. The wavelength zero point offset was determined by requiring that strong absorption lines by the interstellar medium are at rest. Since for some spectral regions too few ISM absorption lines are observed or some of them are obviously blended, we additionally compared a) absorption lines in overlapping regions of different observations and b) redshifts from Lyman series lines of strong LLS spanning different observations. We list in Table 1 the wavelength zeropoint offsets that were added to the reduced spectra.

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© European Southern Observatory (ESO) 1999

Online publication: February 22, 1999
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