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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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
Early online date7 Feb 2019
Publication statusPublished - Feb 2019


  • Molecular data


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