Robust limit on a varying proton-to-electron mass ratio from a single H2 system

The variation of the dimensionless fundamental physical constant mu=m_p/m_e can be checked through observation of Lyman and Werner lines of molecular hydrogen in the spectra of distant QSOs. Our intention is to asses the accuracy of the investigation concerning a possible variation of mu and to provide more robust results for QSO 0347-383. The goal in mind is to resolve the current controversy on variation of mu and devise explanations for the different findings. We achieve this not by another single result but by providing alternative approaches to the problem. An analysis based on independent data sets of QSO 0347-383 is put forward and new approaches for some of the steps involved in the data analysis are introduced. We analyse two independent sets of observations of the same absorption system and for the first time we apply corrections for the observed offsets between discrete spectra Drawing on two independent observations of a single absorption system in QSO 0347-383 our detailed analysis yields dmu/mu = 15 +/- (9_stat + 6_sys) x 10^{-6} at z_abs=3.025. Based on the overall goodness-of-fit we estimate the limit of accuracy to about 300 m/s, consisting of roughly 180 m/s due to the uncertainty of the fit and about 120 m/s allocated to systematics This work presents alternative approaches to handle systematics and introduces methods required for precision analysis of QSO spectra available in the near future.Comment: 9 pages, 10 figures, submitted to A&

The primordial lithium abundance

Lithium abundances in a selected sample of halo stars have been revised by using the new accurate IRFM effective temperatures by Alonso, Arribas & Martinez-Roger (1996a). From 41 plateau stars (Teff > 5700 and [Fe/H] <= -1.5) we found no evidence for intrinsic dispersion, a tiny trend with Teff and no trend with [Fe/H]. The trend with the Teff is fully consistent with the standard Li isochrones of Deliyannis, Demarque & Kawaler (1990) implying a primordial value for Li of A(Li) = 2.238 +/- 0.012 {1 sigma} +/- 0.05{sys}. The present results argue against any kind of depletion predicted by diffusion, rotational mixing or stellar winds. Therefore the Li observed in Pop II stars provides a direct and reliable estimate of the baryonic density that can rival other baryonic indicators such as the deuterium in high redshift systems. The present upwards revision of primordial Li in the framework of SBBN gives at 1 sigma two solutions for the baryonic density: Omega_{B}h^2 = 0.0062 {+0.0018,-0.0011} or Omega_{B}h^2 = 0.0146 {+0.0029,-0.0033} .Comment: Tex, uses MN.tex, 18 .ps figures; accepted MNRA