H 2 /HD molecular data for analysis of quasar spectra in search of varying constants

W. Ubachs, E. J. Salumbides, M. T. Murphy, H. Abgrall, E. Roueff

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Abstract

Context. Absorption lines of H 2 and HD molecules observed at high redshift in the line of sight towards quasars are a test ground to search for variation of the proton-to-electron mass ratio μ. For this purpose, results from astronomical observations are compared with a compilation of molecular data of the highest accuracy, obtained in laboratory studies as well as in first-principles calculations. Aims. A comprehensive line list is compiled for H 2 and HD absorption lines in the Lyman (B 1 Σ u + - X 1 Σ g + ) and Werner (C 1 Π u - X 1 Σ g + ) band systems up to the Lyman cutoff at 912 Å. Molecular parameters listed for each line i are the transition wavelength λ i , the line oscillator strength f i , the radiative damping parameter of the excited state Γ i , and the sensitivity coefficient K i for a variation of the proton-to-electron mass ratio. Methods. The transition wavelengths λ i for the H 2 and HD molecules are determined by a variety of advanced high-precision spectroscopic experiments involving narrowband vacuum ultraviolet lasers, Fourier-transform spectrometers, and synchrotron radiation sources. Results for the line oscillator strengths f i , damping parameters Γ i , and sensitivity coefficients K i are obtained in theoretical quantum chemical calculations. Results. A new list of molecular data is compiled for future analyses of cold clouds of hydrogen absorbers, specifically for studies of μ-variation from quasar data. The list is applied in a refit of quasar absorption spectra of B0642-5038 and J1237+0647 yielding constraints on a variation of the proton-to-electron mass ratio Δμ/μ consistent with previous analyses.

Original languageEnglish
Article numberA127
Pages (from-to)1-4
Number of pages4
JournalAstronomy and Astrophysics
Volume622
Early online date7 Feb 2019
DOIs
Publication statusPublished - Feb 2019

Funding

Acknowledgements. The authors wish to thank S. A. Balashev for bringing errors and inconsistencies in the previous molecular data list to our attention. J. Bagdonaite and M. Daprà are thanked for discussions and clarifications. W.U. received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant No. 670168).

FundersFunder number
European Union’s Horizon 2020 research and innovation program
Horizon 2020 Framework Programme670168
European Research Council

    Keywords

    • Molecular data

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