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Selection of ThAr lines for wavelength calibration of echelle spectra and implications for variations in the fine-structure constant

Murphy, M. T. ; Tzanavaris, P. ; Webb, J. K. ; Lovis, C.

In: Monthly Notices of the Royal Astronomical Society, 2007, vol. 378, no. 1, p. 221-230

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    Titre
    • Selection of ThAr lines for wavelength calibration of echelle spectra and implications for variations in the fine-structure constant
    Auteur
    • Murphy, M. T.. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
    • Tzanavaris, P.. School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
    • Webb, J. K.. School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
    • Lovis, C.. Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Monthly Notices of the Royal Astronomical Society, 2007, vol. 378, no. 1, p. 221-230. Blackwell Publishing Ltd
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:302608
    Summary
    Echelle spectrographs currently provide some of the most precise and detailed spectra in astronomy, the interpretation of which sometimes depends on the wavelength calibration accuracy. In some applications, such as constraining cosmological variations in the fundamental constants from quasar absorption lines, the wavelength calibration is crucial. Here we detail an algorithm for selecting thorium-argon (ThAr) emission lines for wavelength calibration which incorporates the properties of both a new laboratory wavelength list and the spectrograph of interest. We apply the algorithm to the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (UVES) and demonstrate a factor of ≳3 improvement in the wavelength calibration residuals (i.e. random errors) alone. It is also found that UVES spectra calibrated using a previous, widely distributed line-list contain systematic ±30 -75 m s−1 distortions of the wavelength scale over both short and long wavelength ranges. These distortions have important implications for current UVES constraints on cosmological variations in the fine-structure constant. The induced systematic errors are most severe for Mg/Feii quasar absorbers in the redshift range 1.2 ≲zabs≲ 2.3, with individual absorbers studied by recent authors containing systematic errors up to four times larger than quoted statistical errors