• 18 Sco: A Solar Twin Rich In Refractory And Neutron-Capture Elements. Implications For Chemical Tagging 

      Melendez, Jorge; Ramirez, Ivan; Karakas, Amanda I.; Yong, David; Monroe, TalaWanda R.; Bedell, Megan; Bergemann, Maria; Asplund, Martin; Maia, Marcelo Tucci; Bean, Jacob; do Nascimento, Jose-Dias; Bazot, Michael; Alves-Brito, Alan; Freitas, Fabricio C.; Castro, Matthieu (2014-08)
      We study with unprecedented detail the chemical composition and stellar parameters of the solar twin 18 Sco in a strictly differential sense relative to the Sun. Our study is mainly based on high-resolution (R similar to ...
    • Abundances Of Neutron-Capture Elements In Metal-Poor Stars 

      Gratton, Raffaele Gratton; Sneden, Christopher (1994-06)
      We use a large set of high S/N, high resolution spectra of 19 stars with -2.8 <[Fe/H]< 0 to study the abundances of neutron-rich elements in metal-poor stars. Basic data (atmospheric parameters, iron abundances, abundance ...
    • Detection of the Second r-Process Peak Element Tellurium in Metal-Poor Stars 

      Roederer, Ian U.; Lawler, James E.; Cowan, John J.; Beers, Timothy C.; Frebel, Anna; Ivans,, Inese I.; Schatz, Hendrik; Sobeck, Jennifer S.; Sneden, Christopher (2012-03)
      Using near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, we detect neutral tellurium in three metal-poor stars enriched by products of r-process nucleosynthesis, ...
    • The End Of Nucleosynthesis: Production Of Lead And Thorium In The Early Galaxy 

      Roederer, Ian U.; Kratz, Karl-Ludwig; Frebel, Anna; Christlieb, Norbert; Pfeiffer, Bernd; Cowan, John J.; Sneden, Christopher (2009-06)
      We examine the Pb and Th abundances in 27 metal-poor stars (-3.1 < [Fe/H] < -1.4) whose very heavy metal (Z > 56) enrichment was produced only by the rapid (r-) nucleosynthesis process. New abundances are derived from ...
    • Heavy Element Abundances In Giant Stars Of The Globular Clusters M4 And M5 

      Yong, David; Karakas, Amanda I.; Lambert, David L.; Chieffi, Alessandro; Limongi, Marco (2008-12)
      We present a comprehensive abundance analysis of 27 heavy elements in bright giant stars of the globular clusters M4 and M5 based on high-resolution, high signal-to-noise ratio spectra obtained with the Magellan Clay ...
    • Hubble Space Telescope Near-Ultraviolet Spectroscopy Of The Bright CEMP-No Star BD+44 Degrees 493 

      Placco, Vinicius M.; Beers, Timothy C.; Roederer, Ian U.; Cowan, John J.; Frebel, Anna; Filler, Dan; Ivans, Inese I.; Lawler, James E.; Schatz, Hendrik; Sneden, Christopher; Sobeck, Jennifer S.; Aoki, Wako; Smith, Verne V. (2014-07)
      We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the extremely metal-poor star BD+44 degrees 493 a ninth magnitude subgiant with [Fe/H] = -3.8 and enhanced carbon, based on data ...
    • An Observational Perspective On Some Aspects Of Early Stellar Nucleosynthesis 

      Sneden, C.; Lawler, J. E. (2008-03)
      Some basic abundance results for low metallicity stars that were formed in the early days of the Milky Way Galaxy are summarized. Discussion is centered on two nucleosynthetic groups: the light a elements (Mg, Si, and Ca), ...
    • Rubidium In The Interstellar Medium 

      Walker, Kyle M.; Federman, S. R.; Knauth, David C.; Lambert, David L. (2009-11)
      We present observations of interstellar rubidium toward o Per, zeta Per, AE Aur, HD 147889, chi Oph, zeta Oph, and 20 Aql. Theory suggests that stable (85)Rb and long-lived (87)Rb are produced predominantly by high-mass ...
    • Transition Probabilities Of Astrophysical Interest In The Niobium Ions Nb+ And Nb2+ 

      Nilsson, H.; Hartman, H.; Engstrom, L.; Lundberg, H.; Sneden, Christopher; Fivet, V.; Palmeri, P.; Quinet, P.; Biemont, E. (2010)
      Aims. We attempt to derive accurate transition probabilities for astrophysically interesting spectral lines of Nb II and Nb III and determine the niobium abundance in the Sun and metal-poor stars rich in neutron-capture ...
    • The Two Metallicity Groups Of The Globular Cluster M22: A Chemical Perspective 

      Marino, A. F.; Sneden, Christopher; Kraft, R. P.; Wallerstein, G.; Norris, J. E.; Da Costa, G.; Milone, A. P.; Ivans,, II; Gonzalez, G.; Fulbright, J. P.; Hilker, M.; Piotto, G.; Zoccali, M.; Stetson, P. B. (2011-08)
      We present a detailed chemical composition analysis of 35 red giant stars in the globular cluster M22. High resolution spectra for this study were obtained at five observatories, and analyzed in a uniform manner. We have ...
    • The Two Metallicity Groups Of The Globular Cluster M22: A Chemical Perspective 

      Marino, A. F.; Sneden, Christopher; Kraft, R. P.; Wallerstein, G.; Norris, J. E.; Da Costa, G.; Milone, A. P.; Ivans,, II; Gonzalez, G.; Fulbright, J. P.; Hilker, M.; Piotto, G.; Zoccali, M.; Stetson, P. B. (2011-08)
      We present a detailed chemical composition analysis of 35 red giant stars in the globular cluster M22. High resolution spectra for this study were obtained at five observatories, and analyzed in a uniform manner. We have ...