New Keck Observations of Lithium in Very Metal-poor Stars

Lithium abundances have been determined in more than 100 metal-poor halo stars both in the field and in clusters. From these data we find trends of Li with both temperature and metallicity and a real dispersion in Li abundances in the Spite Li plateau. We attribute this dispersion primarily to Li depletion (presumably due to extra mixing induced by stellar rotation) and to Galactic chemical evolution. We derive a primordial Li of 2.44 $\pm$0.18 for A(Li)$_p$ = log N(Li/H) + 12.00. This agrees with the Li abundances predicted by the $WMAP$ results. For stars cooler than the Li plateau we have evidence that Li depletion sets in at hotter temperatures for the higher metallicity stars than for the low-metal stars. This is the opposite sense of predictions from stellar models. The smooth transition of the Li content from the Li plateau stars to the cool stars adds weight to the inference of Li depletion in the plateau stars.Comment: Invited talk for IAU Symposium 228 "From Lithium to Uranium..." held in Paris in May, 2005. 6 pages, 6 figure

The Evolution of the Galaxy Cluster Luminosity-Temperature Relation

We analyzed the luminosity-temperature (L-T) relation for 2 samples of galaxy clusters which have all been observed by the ASCA satellite. We used 32 high redshift clusters (0.3<z<0.6), 53 low redshift clusters (z<0.3), and also the combination of the low and high redshift datasets. We assumed a power law relation between the bolometric luminosity of the galaxy cluster and its integrated temperature and redshift (L_{bol,44}=C*T^alpha*(1+z)^A). The results are consistent, independent of cosmology, with previous estimates of L$\sim$T$^3$ found by other authors. We observed weak or zero evolution.Comment: 20 pages, Latex, 11 figures, GIF forma

Small-Scale structure in the Galactic ISM: Implications for Galaxy Cluster Studies

Observations of extragalactic objects need to be corrected for Galactic absorption and this is often accomplished by using the measured 21 cm HI column. However, within the beam of the radio telescope there are variations in the HI column that can have important effects in interpreting absorption line studies and X-ray spectra at the softest energies. We examine the HI and DIRBE/IRAS data for lines of sight out of the Galaxy, which show evidence for HI variations in of up to a factor of three in 1 degree fields. Column density enhancements would preferentially absorb soft X-rays in spatially extended objects and we find evidence for this effect in the ROSAT PSPC observations of two bright clusters of galaxies, Abell 119 and Abell 2142. For clusters of galaxies, the failure to include column density fluctuations will lead to systematically incorrect fits to the X-ray data in the sense that there will appear to be a very soft X-ray excess. This may be one cause of the soft X-ray excess in clusters, since the magnitude of the effect is comparable to the observed values.Comment: 16 pages, 9 figures, to appear in the Astrophysical Journal, vol. 597 (1 Nov 2003

The NN2 Flux Difference Method for Constructing Variable Object Light Curves

We present a new method for optimally extracting point-source time variability information from a series of images. Differential photometry is generally best accomplished by subtracting two images separated in time, since this removes all constant objects in the field. By removing background sources such as the host galaxies of supernovae, such subtractions make possible the measurement of the proper flux of point-source objects superimposed on extended sources. In traditional difference photometry, a single image is designated as the ``template'' image and subtracted from all other observations. This procedure does not take all the available information into account and for sub-optimal template images may produce poor results. Given N total observations of an object, we show how to obtain an estimate of the vector of fluxes from the individual images using the antisymmetric matrix of flux differences formed from the N(N-1)/2 distinct possible subtractions and provide a prescription for estimating the associated uncertainties. We then demonstrate how this method improves results over the standard procedure of designating one image as a ``template'' and differencing against only that image.Comment: Accepted to AJ. To be published in November 2005 issue. 16 page, 2 figures, 2 tables. Source code available at http://www.ctio.noao.edu/essence/nn2

Beryllium in the Ultra-Lithium-Deficient,Metal-Poor Halo Dwarf, G186-26

The vast majority of low-metal halo dwarfs show a similar amount of Li; this has been attributed to the Li that was produced in the Big Bang. However, there are nine known halo stars with T $>$ 5900 K and [Fe/H] $<$ $-$1.0 that are ultra-Li-deficient. We have looked for Be in the very low metallicity star, G 186-26 at [Fe/H] = $-$2.71, which is one of the ultra-Li-deficient stars. This star is also ultra-Be deficient. Relative to Be in the Li-normal stars at [Fe/H] = $-$2.7, G 182-26 is down in Be by more than 0.8 dex. Of two potential causes for the Li-deficiency -- mass-transfer in a pre-blue straggler or extra rotationally-induced mixing in a star that was initially a very rapid rotator -- the absence of Be favors the blue-straggler hypothesis, but the rotation model cannot be ruled-out completely.Comment: Accepted for Ap.J. Letters 10 pages, 4 figure

The rare light elements in very low metallicity halo stars

Mode of access: World Wide Web.Thesis (Ph. D.)--University of Hawaii at Manoa, 2005.Includes bibliographical references (leaves 136-146).Electronic reproduction.Also available by subscription via World Wide Webxvi, 146 leaves, bound col. ill. 29 c