Fundamental constants and high‐resolution spectroscopy1. Issue 1 (January 2014)

• Record Type: Journal Article
• Authors: Bonifacio, P.; Rahmani, H.; Whitmore, J.B.; Wendt, M.; Centurion, M.; Molaro, P.; Srianand, R.; Murphy, M.T.; Petitjean, P.; Agafonova, I.I.; D'Odorico, S.; Evans, T.M.; Levshakov, S.A.; Lopez, S.; Martins, C.J.A.P.; Reimers, D.; Vladilo, G.
• Is Part Of: Astronomische Nachrichten. Volume 335:Issue 1(2014)
• Page Start: 83
• Page End: 91
• Publication Date: 2014-01
• Subjects: Astronomy -- Periodicals; 520.5
• DOI: 10.1002/asna.201312005
• Languages: English
• ISSNs: 0004-6337

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Absorption‐line systems detected in high resolution quasar spectra can be used to compare the value of dimensionless fundamental constants such as the fine‐structure constant, <italic>α</italic>, and the proton‐to‐electron mass ratio, <italic>μ</italic> = m<sub>p</sub>/m<sub>e</sub>, as measured in remote regions of the Universe to their value today on Earth. In recent years, some evidence has emerged of small temporal and also spatial variations in <italic>α</italic> on cosmological scales which may reach a fractional level of ≈ 10 ppm (parts per million). We are conducting a Large Programme of observations with the Very Large Telescope's Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high‐resolution (<italic>R</italic> ≈ 60000) and high signal‐to‐noise ratio (S/N ≈ 100) spectra calibrated specifically to study the variations of the fundamental constants. We here provide a general overview of the Large Programme and report on the first results for these two constants, discussed in detail in Molaro et al. (2013) and Rahmani et al. (2013). A stringent bound for Δ<italic>α</italic> /<italic>α</italic> is obtained for the absorber at <italic>z</italic><sub>abs</sub> = 1.6919 towards HE 2217‐2818. The absorption profile is complex with several very narrow features, and is modeled with 32 velocity components. The relative variation in <italic>α</italic> in this system is +1.3 ± 2.4<sub>stat</sub> ± 1.0<sub>sys</sub> ppm if Al II <italic>λ</italic> 1670 Å and three FeII transitions are used, and +1.1 ± 2.6<sub>stat</sub> ppm in a slightly different analysis with only FeII transitions used. This is one of the tightest bounds on <italic>α</italic> ‐variation from an individual absorber and reveals no evidence for variation in <italic>α</italic> at the 3‐ppm precision level (1<italic>σ</italic> confidence). The expectation at this sky position of the recently‐reported dipolar variation of <italic>α</italic> is (3.2–5.4) ± 1.7 ppm depending on dipole model used and this constraint of Δ<italic>α</italic> /<italic>α</italic> at face value is not supporting this expectation but not inconsistent with it at the 3<italic>σ</italic> level. For the proton‐to‐electron mass ratio the analysis of the H<sub>2</sub> absorption lines of the <italic>z</italic><sub>abs</sub> ≈ 2.4018 damped Ly<italic>α</italic> system towards HE 0027–1836 provides Δ<italic>μ</italic> /<italic>μ</italic> = (–7.6 ± 8.1<sub>stat</sub> ± 6.3<sub>sys</sub>) ppm which is also consistent with a null variation. The cross‐correlation analysis between individual exposures taken over three years and comparison with almost simultaneous asteroid observations revealed the presence of a possible wavelength dependent velocity drift as well as of inter‐order distortions which probably dominate the systematic error and are a significant obstacle to achieve more accurate measurements. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)</p> </abstract>