arXiv subjects
Publications and source records attributed to M. Lemoine.
Recent HST/GHRS observations of the z = 0.7010 absorber toward the QSO 1718+4807 (selected because of apparently ideal characteristics for measuring D/H) yield a D/H significantly higher D/H than some recent high-redshift measurements. Our analysis indicates D/H}= 1.8 - 2.5 x 10^{-4}. This may indicate a cosmological inhomogeneity in the deuterium abundance of at least a factor of ten.
Of the light elements, the primordial abundance of deuterium, (D/H)_p, provides the most sensitive diagnostic for the cosmological mass density parameter Omega_B. Recent high redshift (D/H) measurements are highly discrepant, although this may reflect observational uncertainties. The larger (D/H) values, which imply a low Omega_B and require the Universe to be dominated by non-baryonic matter (dynamical studies indicate a higher total density parameter), cause problems for galactic chemical evolution models since they have difficulty in reproducing the large decline down to the lower present-day (D/H). Conversely, low (D/H) values imply an Omega_B greater than derived from ^7Li and ^4He abundance measurements, and may require a deuterium abundance evolution that is too low to easily explain. Here we report the first measurement at intermediate redshift, where the observational difficulties are smaller, of a gas cloud with ideal characteristics for this experiment. Our analysis of the z = 0.7010 absorber toward 1718+4807 indicates (D/H) = 2.0 +/- 0.5 x 10^{-4} which is in the high range. This and other independent observations suggests there may be a cosmological inhomogeneity in (D/H)_p of at least a factor of ten.
We review the status of the measurements of the deuterium abundance from the local interstellar medium to the solar system and high redshifts absorbers toward quasars. We present preliminary results toward a white dwarf and a QSO. We conclude that the deuterium evolution from the Big-Bang to now is still not properly understood.
We explore possible depletion factors for Li6 in the three stars where it has been detected. To this end, we assume that 6Li/H scales as 16O/H throughout the galactic evolution, an assumption motivated by the observations of a similar scaling for 9Be. We examine the uncertainties attached to this modeling of 6Li galactic evolution; we also incorporate a recent evaluation of the primordial production of 6Li. The depletion factor D6, for 6Li, in HD84937, is constrained to be less than 4 at 95% c.l.. This depletion factor is an extreme upper limit on the depletion factor for 7Li. We conclude that the primordial abundance of 7Li cannot be higher that twice the observed value, since no current stellar model is able to reproduce the observed trends of 7Li with temperature and metallicity, and yet deplete 7Li by more than a factor 2, while satisfying D6<4. All three 6Li observations are in excellent agreement with all standard expectations: Big-Bang nucleosynthesis with 2<$η_{10}$<6.5, and standard isochrones of 6Li survival. We discuss possible deviations from our assumption of 6Li/H scaling with 16O/H, due to alpha-alpha creation of 6Li in various sites. We notably reject stellar flares as a significant source of 6Li in HD84937.