Possible evidence for a variable fine-structure constant from QSO absorption lines: systematic errors

doi:10.1046/j.1365-8711.2001.04841.x

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Monthly Notices of the Royal Astronomical Society

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Volume 327 Issue 4, Pages 1223 - 1236

Published Online: 7 Jul 2008

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Possible evidence for a variable fine-structure constant from QSO absorption lines: systematic errors

M.T. Murphy ¹ ^★ J.K. Webb ¹ V.V. Flambaum ¹ C.W. Churchill ² J.X. Prochaska ³

¹School of Physics, The University of New South Wales, UNSW Sydney, NSW 2052, Australia ²Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USA ³The Observatories of the Carnegie Institute of Washington, 813 Santa Barbara St., Pasadena, CA 91101, USA

Correspondence to mim@phys.unsw.edu.au

¹ We can see this as follows. We can ignore the term in q₂ since these coefficients are typically an order of magnitude smaller than the q₁ coefficients. Consider two transitions, one with a low atomic mass, the other a high atomic mass. Typically, the difference between the q₁ coefficients for a light species (e.g. Mg ii) and a heavy species (e.g. Fe ii) is ∼1000 cm⁻¹. Equation (1), applied to these two transitions, then shows that a precision of ω₀ of ∼0.02 cm⁻¹ is required in order to detect a variation of .

² iraf is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.

³ The 1953 formula is of the same form as the 1966 formula (equation 2) but has slightly different parameters: 6432.8, 2949 810, 146, 25 540 and 41 in order from left to right, numerator to denominator.

⁴ Each set of ThAr lines never included any of the ThAr lines from any other set.

KEYWORDS

atomic data • line: profiles • instrumentation: spectrographs • methods: data analysis • techniques: spectroscopic • quasars: absorption lines

ABSTRACT

Comparison of quasar (QSO) absorption spectra with laboratory spectra allows us to probe possible variations in the fundamental constants over cosmological time-scales. In a companion paper we present an analysis of Keck/HIRES spectra and report possible evidence suggesting that the fine-structure constant, α, may have been smaller in the past: over the redshift range . In this paper we describe a comprehensive investigation into possible systematic effects. Most of these do not significantly influence our results. When we correct for those which do produce a significant systematic effect in the data, the deviation of from zero becomes more significant. We are led increasingly to the interpretation that α was slightly smaller in the past.