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Your search keyword '"Galaxy : evolution"' showing total 4 results
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4 results on '"Galaxy : evolution"'

1. The Extremely Metal-poor, Neutron Capture-rich Star CS 22892-052: A Comprehensive Abundance Analysis**Based on observations made at four facilities: (1) the NASA/ESA Hubble Space Telescope (HST), obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555; (2) the Keck I Telescope of the W. M. Keck Observatory, which is operated by the California Association for Research in Astronomy (CARA, Inc.) on behalf of the University of California and the California Institute of Technology; (3) the H. J. Smith Telescope of McDonald Observatory, which is operated by The University of Texas at Austin; and (4) the Very Large Telescope of the European Southern Observatory at Paranal, Chile, from UVES commissioning data and program 165.N-0276(A).

Author

Sneden, Christopher, Cowan, John J, Lawler, James E, Ivans, Inese I, Burles, Scott, Beers, Timothy C, Primas, Francesca, Hill, Vanessa, Truran, James W, Fuller, George M, Pfeiffer, Bernd, and Kratz, Karl-Ludwig

Subjects
Galaxy : abundances, Galaxy : evolution, Galaxy : halo, nuclear reactions, nucleosynthesis, abundances, stars : abundances, stars : Population II, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Physical Chemistry (incl. Structural), Astronomy & Astrophysics
Abstract

High-resolution spectra obtained with three ground-based facilities and the Bubble Space Telescope (HST) have been combined to produce a new abundance analysis of CS 22892-052, an extremely metal-poor giant with large relative enhancements of neutron capture elements. A revised model stellar atmosphere has been derived with the aid of a large number of Fe peak transitions, including both neutral and ionized species of six elements. Several elements, including Mo, Lu, Au, Pt, and Pb, have been detected for the first time in CS 22892-052, and significant upper limits have been placed on the abundances of Ga, Ge, Cd, Sn, and U in this star. In total, abundance measurements or upper limits have been determined for 57 elements, far more than previously possible. New Be and Li detections in CS 22892-052 indicate that the abundances of both these elements are significantly depleted compared to unevolved main-sequence turnoff stars of similar metallicity. Abundance comparisons show an excellent agreement between the heaviest n-capture elements (Z ≥ 56) and scaled solar system r-process abundances, confirming earlier results for CS 22892-052 and other metal-poor stars. New theoretical r-process calculations also show good agreement with CS 22892-052 abundances and the solar r-process abundance components. The abundances of lighter elements (40 ≤ Z ≤ 50), however, deviate from the same scaled abundance curves that match the heavier elements, suggesting different synthesis conditions or sites for the low-mass and high-mass ends of the abundance distribution. The detection of Th and the upper limit on the U abundance together imply a lower limit of 10.4 Gyr on the age of CS 22892-052, quite consistent with the Th/Eu age estimate of 12.8 ± ≃ 3 Gyr. An average of several Chronometric ratios yields an age 14.2 ± ≃ 3 Gyr.

Published
2003

2. The Chemical Composition and Age of the Metal-poor Halo Star BD +17°3248**Based on observations made at three facilities: (1) the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555; (2) the Keck I Telescope of the W. M. Keck Observatory, which is operated by the California Association for Research in Astronomy (CARA, Inc.) on behalf of the University of California and the California Institute of Technology; and (3) the H. J. Smith Telescope of McDonald Observatory, which is operated by the University of Texas at Austin.

Author

Cowan, John J, Sneden, Christopher, Burles, Scott, Ivans, Inese I, Beers, Timothy C, Truran, James W, Lawler, James E, Primas, Francesca, Fuller, George M, Pfeiffer, Bernd, and Kratz, Karl-Ludwig

Subjects
Galaxy : abundances, Galaxy : evolution, Galaxy : halo, nuclear reactions, nucleosynthesis, abundances, stars : abundances, stars : Population II, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Physical Chemistry (incl. Structural), Astronomy & Astrophysics
Published
2002

3. Chemical abundances and dust in planetary nebulae in the Galactic bulge

Subjects
Galaxy : abundances, EMISSION FEATURES, ELEMENTAL ABUNDANCES, STATISTICAL DISTANCE SCALE, Galaxy : evolution, POLYCYCLIC AROMATIC-HYDROCARBONS, infrared : general, H-II REGIONS, Galaxy : bulge, planetary nebulae : general, CRYSTALLINE SILICATE DUST, ISM : lines and bands, CENTRAL STARS, METALLICITY GRADIENT, stars : AGB and post-AGB, SPITZER-SPACE-TELESCOPE, INFRARED SPECTROGRAPH
Abstract

We present mid-infrared Spitzer spectra of 11 planetary nebulae in the Galactic bulge. We derive argon, neon, sulfur, and oxygen abundances for them using mainly infrared line fluxes combined with some optical line fluxes from the literature. Due to the high extinction toward the bulge, the infrared spectra allow us to determine abundances for certain elements more accurately than previously possible with optical data alone. Abundances of argon and sulfur ( and in most cases neon and oxygen) in planetary nebulae in the bulge give the abundances of the interstellar medium at the time their progenitor stars formed; thus, these abundances give information about the formation and evolution of the bulge. The abundances of bulge planetary nebulae tend to be slightly higher than those in the disk on average, but they do not follow the trend of the disk planetary nebulae, thus confirming the difference between bulge and disk evolution. In addition, the bulge planetary nebulae show peculiar dust properties compared to the disk nebulae. Oxygen-rich dust features (crystalline silicates) dominate the spectra of all of the bulge planetary nebulae; such features are more scarce in disk nebulae. In addition, carbon-rich dust features (polycyclic aromatic hydrocarbons) appear in roughly half of the bulge planetary nebulae in our sample, which is interesting in light of the fact that this dual chemistry is comparatively rare in the Milky Way as a whole.

Published
2008

4. Distances to galactic high-velocity clouds

Author

Reynier Peletier, H. van Woerden, Donald G. York, Zeljko Ivezic, Ronald Wilhelm, Bart P. Wakker, J. C. Barentine, U. J. Schwarz, Philipp Richter, J. C. Howk, Timothy C. Beers, and Kapteyn Astronomical Institute

Subjects
galaxy : halo, TELESCOPE, Metallicity, Milky Way, DATA RELEASE, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Star (graph theory), ISM : clouds, METALLICITIES, galaxy : evolution, Ionization, Astrophysics::Solar and Stellar Astrophysics, stars : distances, Astrophysics::Galaxy Astrophysics, HORIZONTAL-BRANCH, Physics, Astrophysics (astro-ph), Astronomy and Astrophysics, Horizontal branch, galaxy : structure, Accretion (astrophysics), GALAXY, Bracket (mathematics), Space and Planetary Science, HALO, galaxy : general, Intergalactic travel, DIGITAL SKY SURVEY, MILKY-WAY, ABUNDANCE, STARS
Abstract

We report the first determination of a distance bracket for the high-velocity cloud (HVC) complex C. Combined with previous measurements showing that this cloud has a metallicity of 0.15 times solar, these results provide ample evidence that complex C traces the continuing accretion of intergalactic gas falling onto the Milky Way. Accounting for both neutral and ionized hydrogen as well as He, the distance bracket implies a mass of 3-14x10^6 M_sun, and the complex represents a mass inflow of 0.1-0.25 M_sun/yr. We base our distance bracket on the detection of CaII absorption in the spectrum of the blue horizontal branch star SDSS J120404.78+623345.6, in combination with a significant non-detection toward the BHB star BS 16034-0114. These results set a strong distance bracket of 3.7-11.2 kpc on the distance to complex C. A more weakly supported lower limit of 6.7 kpc may be derived from the spectrum of the BHB star BS 16079-0017., Accepted for publication in ApJ Letters

Published
2007

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