Alternative data reduction procedures for UVES: Wavelength calibration and spectrum addition |
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| Authors: | Rodger I Thompson Jill Bechtold John H Black CJAP Martins |
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| Institution: | 1. Steward Observatory, University of Arizona, Tucson, Arizona 85721, USA;2. Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, SE-43992, Sweden;3. Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal and DAMTP, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, United Kingdom |
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| Abstract: | This paper addresses alternative procedures to the ESO supplied pipeline procedures for the reduction of UVES spectra of two quasar spectra to determine the value of the fundamental constant at early times in the universe. The procedures utilize intermediate product images and spectra produced by the pipeline with alternative wavelength calibration and spectrum addition methods. Spectroscopic studies that require extreme wavelength precision need customized wavelength calibration procedures beyond that usually supplied by the standard data reduction pipelines. An example of such studies is the measurement of the values of the fundamental constants at early times in the universe. This article describes a wavelength calibration procedure for the UV–visual Echelle spectrometer on the very large telescope, however, it can be extended to other spectrometers as well. The procedure described here provides relative wavelength precision of better than for the long-slit Thorium–Argon calibration lamp exposures. The gain in precision over the pipeline wavelength calibration is almost entirely due to a more exclusive selection of Th/Ar calibration lines. |
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