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Item The Century Survey Galactic Halo Project. III. A Complete 4300 Deg(2) Survey Of Blue Horizontal Branch Stars In The Metal-Weak Thick Disk And Inner Halo(2008-02) Brown, Warren R.; Beers, Timothy C.; Wilhelm, Ronald; Prieto, Carlos Allende; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.; Prieto, Carlos AllendeWe present a complete spectroscopic survey of 2414 2MASS-selected blue horizontal branch ( BHB) candidates selected over 4300 deg(2) of the sky. We identify 655 BHB stars in this non-kinematically selected sample. We calculate the luminosity function of field BHB stars, and find evidence for very few hot BHB stars in the field. The BHB stars located at a distance from the Galactic plane | Z| < 4 kpc trace what is clearly a metal-weak thick disk population, with a mean metallicity of [Fe/H]=-1.7, a rotation velocity gradient of dv(rot)/d|Z|=-28 +/- 3.4 km s(-1) in the region |Z| < 6 kpc, and a density scale height of h(Z) = 1.26 +/- 0.1 kpc. The BHB stars located at 5 < | Z| < 9 kpc are a predominantly inner-halo population, with a mean metallicity of [ Fe/ H] = - 2.0 and a mean Galactic rotation of - 4 +/- 31 km s(-1). We infer the density of halo and thick disk BHB stars is 104 +/- 37 kpc(-3) near the Sun, and the relative normalization of halo to thick-disk BHB stars is 4 +/- 1% near the Sun.Item Could The Ultra-Metal-Poor Stars Be Chemically Peculiar And Not Related To The First Stars?(2008-04) Venn, Kim A.; Lambert, David L.; Lambert, David L.Chemically peculiar stars define a class of stars that show unusual elemental abundances due to stellar photospheric effects and not due to natal variations. In this paper, we compare the elemental abundance patterns of the ultra-metal-poor stars with metallicities [Fe/H]similar to-5 to those of a subclass of chemically peculiar stars. These include post-AGB stars, RV Tauri variable stars, and the Lambda Bootis stars, which range in mass, age, binarity, and evolutionary status, yet can have iron abundance determinations as low as [Fe/H]similar to-5. These chemical peculiarities are interpreted as due to the separation of gas and dust beyond the stellar surface, followed by the accretion of dust-depleted gas. Contrary to this, the elemental abundances in the ultra-metal-poor stars are thought to represent yields of the most metal-poor supernovae and, therefore, observationally constrain the earliest stages of chemical evolution in the universe. Detailed chemical abundances are now available for HE 1327-2326 and HE 0107-5240, the two extreme ultra-metal-poor stars in our Galaxy, and for HE 0557-4840, another ultra-metal-poor star found by the Hamburg/ESO survey. There are interesting similarities in their abundance ratios to those of the chemically peculiar stars; e. g., the abundances of the elements in their photospheres are related to the condensation temperature of that element. If these three stars are chemically peculiar, then their CNO abundances suggest true metallicities of [X/H] similar to-2 to -4. It is important to establish the nature of these stars, since they are used as tests of the early chemical evolution of the Galaxy.Item Discovery Of A Low-Mass Bipolar Molecular Outflow From L1014-Irs With The Submillimeter Array(2005-11) Bourke, Tyler L.; Crapsi, Antonio; Myers, Phillip C.; Evans, Neal J.; Wilner, David J.; Huard, Tracy L.; Jorgensen, Jes K.; Young, Chadwick H.; Evans, Neal J.; Young, Chadwick H.Using the Submillimeter Array, we report the discovery of a compact low-mass bipolar molecular outflow from L1014-IRS and confirm its association with the L1014 dense core at 200 pc. Consequently, L1014-IRS is the lowest luminosity (L similar to 0.09 L-.), and perhaps the lowest mass, source known to be driving a bipolar molecular outflow, which is one of the smallest known in size (similar to 500 AU), mass (<10(-4) M-.), and energetics (e.g., with a M, force <10(-7) M-. km s(-1) yr(-1)).Item Distances To Galactic High-Velocity Clouds. I. Cohen Stream, Complex Gcp, Cloud G1(2008-01) Wakker, B. P.; York, D. G.; Wilhelm, R.; Barentine, John C.; Richter, P.; Beers, Timothy C.; Ivezic, Z.; Howk, J. C.; Barentine, John C.The high- and intermediate-velocity interstellar clouds (HVCs/IVCs) are tracers of energetic processes in and around the Milky Way. Clouds with near-solar metallicity about 1 kpc above the disk trace the circulation of material between disk and halo (the Galactic fountain). The Magellanic Stream consists of gas tidally extracted from the SMC, tracing the dark matter potential of the Milky Way. Several other HVCs have low metallicity and appear to trace the continuing accretion of infalling intergalactic gas. These assertions are supported by the metallicities (0.1 to 1 solar) measured for about 10 clouds in the past decade. Direct measurements of distances to HVCs have remained elusive, however. In this paper we present four new distance brackets, using VLT observations of interstellar Ca II H and K absorption toward distant Galactic halo stars. We derive distance brackets of 5.0 to 11.7 kpc for the Cohen Stream (likely to be an infalling low-metallicity cloud), 9.8 to 15.1 kpc for Complex GCP (also known as the Smith Cloud or HVC 40-15+100 and with still unknown origin), 1.0 to 2.7 kpc for an IVC that appears associated with the return flow of the fountain in the Perseus arm, and 1.8 to 3.8 kpc for cloud g1, which appears to be in the outflow phase of the fountain. Our measurements further demonstrate that the Milky Way is accreting substantial amounts of gaseous material, which influences the Galaxy's current and future dynamical and chemical evolution.Item Europium, Samarium, And Neodymium Isotopic Fractions In Metal-Poor Stars(2008-03) Roederer, Ian U.; Lawler, James E.; Sneden, Christopher; Cowan, John J.; Sobeck, Jennifer S.; Pilachowski, Catherine A.; Roederer, Ian U.; Sneden, Christopher; Sobeck, Jennifer S.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 new high-resolution (R similar to 120; 000), high signal-to-noise ratio (S/N similar to 160-1000) spectra obtained with the 2d-coude spectrograph of McDonald Observatory's 2.7m Smith telescope. Synthetic spectra were generated using recent high-precision laboratory measurements of hyperfine and isotopic subcomponents of several transitions of these elements and matched quantitatively to the observed spectra. We interpret our isotopic fractions by the nucleosynthesis predictions of the stellar model, which reproduces s-process nucleosynthesis from the physical conditions expected in low-mass, thermally pulsing stars on the AGB, and the classical method, which approximates s-process nucleosynthesis by a steady neutron flux impinging on Fe-peak seed nuclei. Our Eu isotopic fraction in HD 175305 is consistent with an r-process origin by the classical method and is consistent with either an r- or an s-process origin by the stellar model. Our Sm isotopic fraction in HD 175305 suggests a predominantly r- process origin, and our Sm isotopic fraction in HD 196944 is consistent with an s-process origin. The Nd isotopic fractions, while consistent with either r-process or s-process origins, have very little ability to distinguish between any physical values for the isotopic fraction in either star. This study for the first time extends the n-capture origin of multiple rare earths in metal-poor stars from elemental abundances to the isotopic level, strengthening the r-process interpretation for HD 175305 and the s-process interpretation for HD 196944.Item A Hubble Space Telescope Transit Light Curve For GJ 436B(2008-08) Bean, J. L.; Benedict, G. F.; Charbonneau, D.; Homeier, D.; Taylor, D. C.; McArthur, B.; Seifahrt, A.; Dreizler, S.; Reiners, A.; Benedict, G. F.We present time series photometry for six partial transits of GJ 436b obtained with the Fine Guidance Sensor instrument on the Hubble Space Telescope (HST). Our analysis of these data yields independent estimates of the host star's radius R-* = 0.505(-0.029) (+0.020) R-circle dot, and the planet's orbital period P = 2.643882(-0.000058)(+0.000060) d, orbital inclination i = 85.80 degrees(-0.25 degrees),(+ 0.21 degrees), mean central transit time T-c = 2 454 455.279241(-0.00025)(+0.00026) HJD, and radius Rp = 4.90(-0.33)(+ 0.45) R-circle plus. The radius we determine for the planet is larger than the previous findings from analyses of an infrared light curve obtained with the Spitzer Space Telescope. Although this discrepancy has a 92% formal significance (1.7s), it might be indicative of systematic errors that still influence the analyses of even the highest-precision transit light curves. Comparisons of all the measured radii to theoretical models suggest that GJ 436b has a H/ He envelope of similar to 10% by mass. We point out the similarities in structure between this planet and Uranus and Neptune and discuss possible parallels between these planets' formation environments and dynamical evolution. We also find that the transit times for GJ 436b are constant to within 10s over the 11 planetary orbits that the HST data span. However, the ensemble of published values exhibits a long-term drift and our mean transit time is 128 s later than that expected from the Spitzer ephemeris. The sparseness of the currently available data hinders distinguishing between an error in the orbital period or perturbations arising from an additional object in the system as the cause of the apparent trend. Assuming the drift is due to an error in the orbital period we obtain an improved estimate for it of P = 2.643904 +/- 0.000005 d. This value and our measured transit times will serve as important benchmarks in future studies of the GJ 436 system.Item A New ZZ Ceti White Dwarf Pulsator: G30-20(2002-11) Mukadam, Anjum S.; Kepler, S. O.; Winget, D. E.; Bergeron, P.; Mukadam, Anjum S.; Winget, D. E.We report the discovery of a new hydrogen atmosphere variable white dwarf (DAV; ZZ Ceti), G30-20, a high-amplitude, long-period pulsator. The Fourier transform of its light curve shows power around 1050-1125 s. We suspect the existence of multiple periodicities in this region, probably corresponding to different radial order (k) modes, but our observations are not long enough to resolve them. This discovery increases the number of known DAVs to 32. Our best fit to its optical spectrum gives T-eff = 11; 070 +/- 180 K and log g = 7.95 +/- 0.06. This implies that G30-20 is the coolest known DAV.Item The Pulsation Modes Of The Pre-White Dwarf PG 1159-035(2008-01) Costa, J. E. S.; Kepler, S. O.; Winget, D. E.; O'Brien, M. S.; Kawaler, S. D.; Costa, A. F. M.; Giovannini, O.; Kanaan, A.; Mukadam, A. S.; Mullally, F.; Nitta, A.; Provencal, J. L.; Shipman, H.; Wood, M. A.; Ahrens, T. J.; Grauer, A.; Kilic, M.; Bradley, P. A.; Sekiguchi, K.; Crowe, R.; Jiang, X. J.; Sullivan, D.; Sullivan, T.; Rosen, R.; Clemens, J. Christopher; Janulis, R.; O'Donoghue, D.; Ogloza, W.; Baran, A.; Silvotti, R.; Marinoni, S.; Vauclair, G.; Dolez, N.; Chevreton, M.; Dreizler, S.; Schuh, S.; Deetjen, J.; Nagel, T.; Solheim, J. E.; Perez, J. M. G.; Ulla, A.; Barstow, M.; Burleigh, M.; Good, S.; Metcalfe, T. S.; Kim, S. L.; Lee, H.; Sergeev, A.; Akan, M. C.; Cakirli, O.; Paparo, M.; Viraghalmy, G.; Ashoka, B. N.; Handler, G.; Hurkal, O.; Johannessen, F.; Kleinman, S. J.; Kalytis, R.; Krzesinski, J.; Klumpe, E.; Larrison, J.; Lawrence, T.; Meistas, E.; Martinez, P.; Nather, R. E.; Fu, J. N.; Pakstiene, E.; Rosen, R.; Romero-Colmenero, E.; Riddle, R.; Seetha, S.; Silvestri, N. M.; Vuckovic, M.; Warner, B.; Zolao, S.; Althaus, L. G.; Corsico, A. H.; Montgomery, M. H.; D. E. Winget; F. MullallyContext. PG 1159-035, a pre-white dwarf with T-eff similar or equal to 140000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters. Methods. We used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods. Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M-circle dot = 0.59 +/- 0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r(c)/R-*, = 0.83 +/- 0.05. From the multiplet splitting, we calculated the rotational period P-rot = 1.3920 +/- 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for l = 1 modes and less than 50% for l = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.Item Rubidium And Lead Abundances In Giant Stars Of The Globular Clusters M4 And M5(2008-02) Yong, David; Lambert, David L.; Paulson, Diane B.; Carney, Bruce W.; Lambert, David L.We present measurements of the neutron-capture elements Rb and Pb for bright giants in the globular clusters M4 and M5. The clusters are of similar metallicity ([Fe/ H] similar or equal to -1.2), but M4 is decidedly s-process enriched relative to M5: [Ba/Fe] = +0.6 for M4 but 0.0 for M5. The Rb and Pb abundances were derived by comparing synthetic spectra with high-resolution, high signal-to-noise ratio spectra obtained with MIKE on the Magellan Telescope. Abundances of Y, Zr, La, and Eu were also obtained. In M4, the mean abundances from 12 giants are [Rb/Fe] = 0.39 +/- 0.02 (sigma = 0.07), [Rb/Zr] = 0.17 +/- 0.03 (sigma = 0.08), and [Pb/Fe] = 0.30 +/- 0.02 (sigma = 0.07). In M5, the mean abundances from two giants are [Rb/Fe] = 0.00 +/- 0.05 (sigma = 0.06), [Rb/Zr] = 0.08 +/- 0: 08 (sigma = 0.11), and [Pb/Fe] = -0.35 +/- 0.02 (sigma = 0.04). Within the measurement uncertainties, the abundance ratios [Rb/Fe], [Pb/Fe], and [Rb/X] for X = Y, Zr, and La are constant from star to star in each cluster, and none of these ratios are correlated with O or Na abundances. While M4 has a higher Rb abundance than M5, the ratios [Rb/X] are similar in both clusters, indicating that the nature of the s-products is very similar for each cluster but the gas from which M4's stars formed had a higher concentration of these products.Item A "Starless'' Core That Isn't: Detection of A Source in the L1014 Dense Core With the Spitzer Space Telescope(2004-09) Young, Chadwick H.; Jorgensen, Jes K.; Shirley, Yancy L.; Kauffmann, Jens; Huard, Tracy; Lai, Shih-Ping; Lee, Chang Won; Crapsi, Antonio; Bourke, Tyler L.; Dullemond, Cornelis P.; Brooke, Timothy Y.; Porras, Alicia; Spiesman, William; Allen, Lori E.; Blake, Geoffrey A.; Evans, Neal J., II; Harvey, Paul M.; Koerner, David W.; Mundy, Lee G.; Myers, Philip C.; Padgett, Deborah L.; Sargent, Anneila I.; Stapelfeldt, Karl R.; van Dishoeck, Ewine F.; Bertoldi, Frank; Chapman, Nicholas; Cieza, Lucas; DeVries, Christopher H.; Ridge, Naomi A.; Wahhaj, Zahed; Young, Chadwick H.; Spiesman, William; Evans, Neal J., II; Harvey, Paul M.; Cieza, LucasWe present observations of L1014, a dense core in the Cygnus region previously thought to be starless, but data from the Spitzer Space Telescope show the presence of an embedded source. We propose a model for this source that includes a cold core, heated by the interstellar radiation field, and a low-luminosity internal source. The low luminosity of the internal source suggests a substellar object. If L1014 is representative, other "starless'' cores may turn out to harbor central sources.