Kirby, Evan N., Guhathakurta, Puragra, Bolte, Michael, Sneden, Christopher, Geha, Marla C.
We present measurements of Fe, Mg, Si, Ca, and Ti abundances for 388 radial velocity member stars in the Sculptor dwarf spheroidal galaxy (dSph), a satellite of the Milky Way. This is the largest...
The End of Nucleosynthesis: Production of Lead and Thorium in the Early Galaxy (2009)
Roederer, Ian U., Kratz, Karl-Ludwig, Frebel, Anna, Christlieb, Norbert, Pfeiffer, Bernd, Cowan, John J., ...
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...
Sneden, Christopher, Lawler, James E., Cowan, John J., Ivans, Inese I., Hartog, Elizabeth A. Den
We have derived new abundances of the rare-earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric...
Kirby, Evan N., Guhathakurta, Puragra, Sneden, Christopher
We present a technique that applies spectral synthesis to medium resolution spectroscopy (MRS, R ~ 6000) in the red (6300 A < lambda < 9100 A) to measure [Fe/H] and [alpha/Fe] of individual red giant...
Roederer, Ian U., Frebel, Anna, Shetrone, Matthew D., Prieto, Carlos Allende, Rhee, Jaehyon, Gallino, Roberto, ...
We present the first detailed abundance analysis of the metal-poor giant HKII 17435-00532. This star was observed as part of the University of Texas long-term project "Chemical Abundances of Stars in...
Allende Prieto, Carlos, Sivarani, Thirupathi, Beers, Timothy C., Lee, Young Sun, Koesterke, Lars, Shetrone, Matthew, ...
We report high-resolution spectroscopy of 125 field stars previously observed as part of the Sloan Digital Sky Survey and its program for Galactic studies, the Sloan Extension for Galactic...
CS22964-161: A Double-Lined Carbon- and s-Process-Enhanced Metal-Poor Binary Star (2007)
Thompson, Ian B., Ivans, Inese I., Bisterzo, Sara, Sneden, Christopher, Gallino, Roberto, Vauclair, Sylvie, ...
A detailed high-resolution spectroscopic analysis is presented for the carbon-rich low metallicity Galactic halo object CS 22964-161. We have discovered that CS 22964-161 is a double-lined...
Europium, Samarium, and Neodymium Isotopic Fractions in Metal-Poor Stars (2007)
Roederer, Ian U., Lawler, James E., Sneden, Christopher, Cowan, John J., Sobeck, Jennifer S., Pilachowski, Catherine A.
We have derived isotopic fractions of europium, samarium, and neodymium in two metal-poor giants with differing neutron-capture nucleosynthetic histories. These isotopic fractions were measured from...
Sobeck, Jennifer S., Lawler, James E., Sneden, Christopher
Branching fraction measurements from Fourier transform spectra in conjunction with published radiative lifetimes are used to determine transition probabilities for 263 lines of neutral chromium....
Kratz, Karl-Ludwig, Farouqi, Khalil, Pfeiffer, Bernd, Truran, James W., Sneden, Christopher, Cowan, John J.
Abundances of heavier elements (barium and beyond) in many neutron-capture-element-rich halo stars accurately replicate the solar system r-process pattern. However, abundances of lighter...
Accurate M Dwarf Metallicities from Spectral Synthesis: A Critical Test of Model Atmospheres (2006)
Bean, Jacob L., Sneden, Christopher, Hauschildt, Peter H., Johns-Krull, Christopher M., Benedict, G. Fritz
We describe a method for accurately determining M dwarf metallicities with spectral synthesis based on abundance analyses of visual binary stars. We obtained high resolution, high signal-to-noise...
Nucleosynthesis: Stellar and Solar Abundances and Atomic Data (2006)
Cowan, John J., Lawler, James E., Sneden, Christopher, Hartog, E. A. Den, Collier, Jason
Abundance observations indicate the presence of often surprisingly large amounts of neutron capture (i.e., s- and r-process) elements in old Galactic halo and globular cluster stars. These...
Near-UV Observations of HD221170: New Insights into the Nature of r-Process-Rich Stars (2006)
Ivans, Inese I., Simmerer, Jennifer, Sneden, Christopher, Lawler, James E., Cowan, John J., Gallino, Roberto, ...
Employing high resolution spectra obtained with the near-UV sensitive detector on the Keck I HIRES, supplemented by data obtained with the McDonald Observatory 2-d coude, we have performed a...
Ivans, Inese I., Sneden, Christopher, Gallino, Roberto, Cowan, John J., Preston, George W.
Employing spectra obtained with the new Keck I HIRES near-UV sensitive detector, we have performed a comprehensive chemical composition analysis of the binary blue metal-poor star CS29497-030....
HST Observations of Heavy Elements in Metal-Poor Galactic Halo Stars (2005)
Cowan, John J., Sneden, Christopher, Beers, Timothy C., Lawler, James E., Simmerer, Jennifer, Truran, James W., ...
We present new abundance determinations of neutron-capture elements Ge, Zr, Os, Ir, and Pt in a sample of 11 metal-poor (-3.1
Neutron-Capture Element Abundances in Halo Stars (2004)
Cowan, John J., Sneden, Christopher
We present new abundance observations of neutron-capture elements in Galactic stars. These include new Hubble Space Telescope (HST) detections of the elements Ge, Zr and Pt in a group of 11 halo...
Halo Star Abundances and Heavy Element Nucleosynthesis (2004)
Cowan, John J., Sneden, Christopher
We present new Hubble Space Telescope (HST) abundance observations of the neutron-capture elements Ge, Zr, Os and Pt in a group of 11 Galactic halo stars, including the well studied r-process rich CS...
Galactic evolution of Sr, Y, and Zr : a multiplicity of nucleosynthetic processes (2004)
Travglio, Claudia, Gallino, Roberto, Arnone, Enrico, Cowan, John, Jordan, Faith, Sneden, Christopher
Sneden, Christopher, Kraft, Robert P., Guhathakurta, Puragra, Peterson, Ruth C., Fulbright, Jon P.
We report new chemical abundances of 23 bright red giants of the globular cluster M3, based on high-resolution spectra obtained with the Keck I telescope. Combining these data with a...
Advances in r-Process Nucleosynthesis (2003)
Cowan, John J., Sneden, Christopher
During the last several decades, there have been a number of advances in understanding the rapid neutron-capture process (i.e., the r-process). These advances include large quantities of...
Searching for Planets in the Hyades IV: Differential Abundance Analysis of Hyades Dwarfs (2003)
Paulson, Diane B., Sneden, Christopher, Cochran, William D.
We present a differential abundance analysis of Hyades F-K dwarfs in search for evidence of stellar enrichment from accreted hydrogen deficient disk material. Metallicites and relative abundance...
A Comparison of Copper Abundances in Globular Cluster and Halo Field Giant Stars (2003)
Simmerer, Jennifer, Sneden, Christopher, Ivans, Inese I., Kraft, Robert P., Shetrone, Matthew D., Smith, Verne V.
We derive [Cu/Fe] for 117 giant stars in ten globular clusters (M3, M4, M5, M10, M13, M15, M71, NGC 7006, NCG 288, and NGC 362) and find that globular cluster Cu abundances appear to follow [Cu/Fe]...
The r-Process and Chronometers (2002)
Cowan, John J., Sneden, Christopher, Truran, James W.
We present detailed abundance observations of the metal-poor ([Fe/H] = --2.0) Galactic halo star BD+17 3248. We have detected gold in this star, for the first time in any halo star. We also detected...
The Chemical Composition and Age of the Metal-Poor Halo Star BD +17^\circ 3248 (2002)
Cowan, John J., Sneden, Christopher, Burles, Scott, Ivans, Inese I., Beers, Timothy C., Truran, James W., ...
We have combined new high-resolution spectra obtained with the Hubble Space Telescope (HST) and ground-based facilities to make a comprehensive new abundance analysis of the metal-poor, halo star BD...
Europium Isotopic Abundances in Very Metal-poor Stars (2002)
Sneden, Christopher, Cowan, John J., Lawler, James E., Burles, Scott, Beers, Timothy C., Fuller, George M.
Europium isotopic abundance fractions are reported for the very metal-poor, neutron-capture-rich giant stars CS 22892-052, HD 115444, and BD +17 3248. The abundance fractions, derived from analysis...
Snider, Shawn, Prieto, Carlos Allende, Von Hippel, Ted, Beers, Timothy C., Sneden, Christopher, Qu, Yuan, ...
We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (Teff, logg, and [Fe/H]) for Galactic F- and G-type stars. The ANNs are fed with...
Ivans, Inese I., Kraft, Robert P., Sneden, Christopher, Smith, Graeme H., Rich, R. Michael, Shetrone, Matthew
We present a chemical composition analysis of 36 giant stars in the mildly metal-poor globular cluster M5 (NGC 5904). The analysis makes use of high resolution data acquired at the Keck I telescope...
Burris, Debra L., Pilachowski, Catherine A., Armandroff, Taft E., Sneden, Christopher, Cowan, John J.
New abundances for neutron-capture (n-capture) elements in a large sample of metal-poor giants from the Bond survey are presented. The spectra were acquired with the KPNO 4-m echelle and coude feed...
Evidence of Multiple r-Process Sites in the Early Galaxy: New Observations of CS 22892-052 (2000)
Sneden, Christopher, Cowan, John J., Ivans, Inese I., Fuller, George M., Burles, Scott, Beers, Timothy C., ...
First results are reported of a new abundance study of neutron-capture elements in the ultra-metal-poor (UMP; [Fe/H] = -3.1) halo field giant star CS 22892-052. Using new high resolution, high...
Do AGB Stars Differ Chemically from RGB Stars in Globular Clusters? (2000)
Sneden, Christopher, Ivans, Inese I., Kraft, Robert P.
Recent improvements in globular cluster colour-magnitude diagrams, coupled with an increase in large-sample spectroscopic abundance studies of cluster giants, finally allow some attempts at a...
The r-Process Enriched Low Metallicity Giant HD 115444 (1999)
Westin, Jenny, Sneden, Christopher, Gustafsson, Bengt, Cowan, John J.
New high resolution, very high signal-to-noise spectra of ultra-metal-poor (UMP) giant stars HD 115444 and HD 122563 have been gathered with the High-Resolution Echelle Spectrometer of the McDonald...
Ivans, Inese I., Sneden, Christopher, Kraft, Robert P., Suntzeff, Nicholas B., Smith, Verne V., Langer, G. Edward, ...
We present a chemical composition analysis of 36 giants in the nearby mildy metal-poor ( = -1.18) "CN-bimodal" globular cluster M4. Confronted with a cluster that has large and variable interstellar...
An Extremely Lithium-Rich Bright Red Giant in the Globular Cluster M3 (1999)
Kraft, Robert P., Peterson, Ruth C., Guhathakurta, Puragra, Sneden, Christopher, Fulbright, Jon P., Langer, G. Edward
We have serendipitously discovered an extremely lithium-rich star on the red giant branch of the globular cluster M3 (NGC 5272). An echelle spectrum obtained with the Keck I HIRES reveals a Li I 6707...
R-Process Abundances and Chronometers in Metal-Poor Stars (1998)
Cowan, John J., Pfeiffer, B., Sneden, Christopher, Burles, Scott, ...
Rapid neutron-capture (i.e., r-process) nucleosynthesis calculations, employing internally consistent and physically realistic nuclear physics input (QRPA beta-decay rates and the ETFSI-Q nuclear...
Stellar Abundance Observations (1998)
Cowan, John J, Sneden, Christopher, Truran, James W, Burris, Debra L
Ground- and space-based observations of stellar heavy element abundances are providing a clearer picture of the chemical evolution of the Galaxy. A large number of (r)apid and (s)low neutron capture...