Beryllium in Ultra-Lithium-Deficient Halo Stars - The Blue Straggler Connection

There are nine metal-deficient stars that have Li abundances well below the Li plateau that is defined by over 100 unevolved stars with temperatures above 5800 K and values of [Fe/H] $<$ $-$1.0. Abundances of Be have been determined for most of these ultra-Li-deficient stars in order to investigate the cause of the Li deficiencies. High-resolution and high signal-to-noise spectra have been obtained in the Be II spectral region near 3130 \AA for six ultra-Li-deficient stars with the Keck I telescope and its new uv-sensitive CCD on the upgraded HIRES. The spectrum synthesis technique has been used to determine Be abundances. All six stars are found to have Be deficiencies also. Two have measurable - but reduced - Be and four have only upper limits on Be. These results are consistent with the idea that these Li- and Be-deficient stars are analogous to blue stragglers. The stars have undergone mass transfer events (or mergers) which destroy or dilute both Li and Be. The findings cannot be matched by the models that predict that the deficiencies are due to extra-mixing in a subset of halo stars that were initially rapid rotators, with the possible exception of one star, G 139-8. Because the ultra-Li-deficient stars are also Be-deficient, they appear to be genuine outliers in population of halo stars used to determine the value of primordial Li; they no longer have the Li in their atmospheres that was produced in the Big Bang.Comment: 17 pages of text, 12 figures, 3 tables Submitted to Ap

Na Li, piano, March 24, 2018

This is the concert program of the Na Li, piano performance on Saturday, March 24, 2018 at 6:00 p.m., at the Concert Hall, 855 Commonwealth Avenue. Works performed were Sonate pour violoncelle et piano by Claude Debussy, Fiançailles pour rire by Francis Poulenc, Viola Sonata No. 1 in F minor, Op. 120 No. 1 by Johannes Brahms, and Doce canciones populares by Carlos Guastavino. Digitization for Boston University Concert Programs was supported by the Boston University Humanities Library Endowed Fund

Pre-MS depletion, accretion and primordial 7Li

We reconsider the role of pre-main sequence (pre-MS) Li depletion on the basis of new observational and theoretical evidence: i) new observations of Halpha emissions in young clusters show that mass accretion could be continuing till the first stages of the MS, ii) theoretical implications from helioseismology suggest large overshooting values below the bottom of the convective envelopes. We argue here that a significant pre-MS 7Li destruction, caused by efficient overshoot mixing, could be followed by a matter accretion after 7Li depletion has ceased on MS thus restoring Li almost to the pristine value. As a test case we show that a halo dwarf of 0.85 Msun with an extended overshooting envelope starting with an initial abundance of A(Li) = 2.74 would burn Li completely, but an accretion rate of the type 1e-8xe^{-t/3e6} Msun yr$^{-1}$ would restore Li to end with an A(Li) = 2.31. A self-regulating process is required to produce similar final values in a range of different stellar masses to explain the PopII Spite plateau. However, this framework could explain why open cluster stars have lower Li abundances than the pre-solar nebula, the absence of Li in the most metal poor dwarfs and a number of other features which lack of a satisfactory explanation.Comment: To be published in Memorie della Societ\`a Astronomica Italiana Supplementi Vol. 22, Proceedings of Lithium in the cosmos, Iocco F., Bonifacio P., Vangioni E., ed

Mons. F. S. Caruana Isqof ta' Malta (1759-1847)

L-awtur jagħti tagħrif bijografiku dwar Mons. F. S. Caruana, Isqof ta’ Malta, li miet fl-1847 u li xi awturi jfaħħruh u jpinġuh bħala patrijott, filantropu u industrijalist.N/

Two-component Fermi gas with a resonant interaction

We consider a two-component Fermi gas interacting via a Feshbach molecular state. It is shown that an important energy scale is $E_g=g^4m^3/(64\pi^2)$ where $g$ is the Feshbach coupling constant and $m$ the mass of the particles. Only when $E_g\gg \epsilon_{\rm F}$ where $\epsilon_{\rm F}$ is the Fermi energy can the gas be expected to enter a universal state in the unitarity limit on the atomic side of the resonance where there are no molecules present. The universal state is distinct from the molecular gas state on the other side of the resonance. We furthermore calculate the energy of the gas for this universal state and our results are related to current experiments on $^{6}$Li and $^{40}$K.Comment: 4 pages, 2 figure