Browsing by Subject "galactic chemical evolution"

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The Apokasc Catalog: An Asteroseismic and Spectroscopic Joint Survey of Targets in the Kepler Fields
(2014-12) Nidever, David L.; Zasowski, Gail; Majewski, Steven R.; Bird, Jonathan; Robin, Annie C.; Martinez-Valpuesta, Inma; Beaton, Rachael L.; Schoenrich, Ralph; Schultheis, Mathias; Wilson, John C.; Skrutskie, Michael F.; O'Connell, Robert W.; Shetrone, Matthew; Schiavon, Ricardo P.; Johnson, Jennifer A.; Weiner, Benjamin; Gerhard, Ortwin; Schneider, Donald P.; Prieto, Carlos Allende; Sellgren, Kris; Bizyaev, Dmitry; Brewington, Howard; Brinkmann, Jon; Eisenstein, Daniel J.; Frinchaboy, Peter M.; Perez, Ana Elia Garcia; Holtzman, Jon; Hearty, Fred R.; Malanushenko, Elena; Malanushenko, Viktor; Muna, Demitri; Oravetz, Daniel; Pan, Kaike; Simmons, Audrey; Snedden, Stephanie; Weaver, Benjamin A.; Shetrone, Matthew
We present the first APOKASC catalog of spectroscopic and asteroseismic properties of 1916 red giants observed in the Kepler fields. The spectroscopic parameters provided from the Apache Point Observatory Galactic Evolution Experiment project are complemented with asteroseismic surface gravities, masses, radii, and mean densities determined by members of the Kepler Asteroseismology Science Consortium. We assess both random and systematic sources of error and include a discussion of sample selection for giants in the Kepler fields. Total uncertainties in the main catalog properties are of the order of 80 K in Teff, 0.06 dex in [M/ H], 0.014 dex in log g, and 12% and 5% in mass and radius, respectively; these reflect a combination of systematic and random errors. Asteroseismic surface gravities are substantially more precise and accurate than spectroscopic ones, and we find good agreement between their mean values and the calibrated spectroscopic surface gravities. There are, however, systematic underlying trends with Teff and log g. Our effective temperature scale is between 0 and 200 K cooler than that expected from the infrared flux method, depending on the adopted extinction map, which provides evidence for a lower value on average than that inferred for the Kepler Input Catalog (KIC). We find a reasonable correspondence between the photometric KIC and spectroscopic APOKASC metallicity scales, with increased dispersion in KIC metallicities as the absolute metal abundance decreases, and offsets in T-eff and log g consistent with those derived in the literature. We present mean fitting relations between APOKASC and KIC observables and discuss future prospects, strengths, and limitations of the catalog data.
Chemodynamics Of The Milky Way I. The First Year Of APOGEE Data
(2014-04) Anders, F.; Chiappini, C.; Santiago, B. X.; Rocha-Pinto, H. J.; Girardi, L.; da Costa, L. N.; Maia, M. A. G.; Steinmetz, M.; Minchev, I.; Schultheis, M.; Boeche, C.; Miglio, A.; Montalban, J.; Schneider, D. P.; Beers, T. C.; Cunha, K.; Prieto, C. A.; Balbinot, E.; Bizyaev, D.; Brauer, D. E.; Brinkmann, J.; Frinchaboy, P. M.; Perez, A. E. G.; Hayden, M. R.; Hearty, F. R.; Holtzman, J.; Johnson, J. A.; Kinemuchi, K.; Majewski, S. R.; Malanushenko, E.; Malanushenko, V.; Nidever, D. L.; O'Connell, R. W.; Pan, K.; Robin, A. C.; Schiavon, R. P.; Shetrone, M.; Skrutskie, M. F.; Smith, V. V.; Stassun, K.; Zasowski, G.; Shetrone, Matthew D.
Context. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) features the first multi-object high-resolution fiber spectrograph in the near-infrared ever built, thus making the survey unique in its capabilities: APOGEE is able to peer through the dust that obscures stars in the Galactic disc and bulge in the optical wavelength range. Here we explore the APOGEE data included as part of the Sloan Digital Sky Survey's 10th data release (SDSS DR10). Aims. The goal of this paper is to a) investigate the chemo-kinematic properties of the Milky Way disc by exploring the first year of APOGEE data; and b) to compare our results to smaller optical high-resolution samples in the literature, as well as results from lower resolution surveys such as the Geneva-Copenhagen Survey (GCS) and the RAdial Velocity Experiment (RAVE). Methods. We select a high-quality (HQ) sample in terms of chemistry (amounting to around 20 000 stars) and, after computing distances and orbital parameters for this sample, we employ a number of useful subsets to formulate constraints on Galactic chemical and chemodynamical evolution processes in the solar neighbourhood and beyond (e.g., metallicity distributions - MDFs, [alpha/Fe] vs. [Fe/H] diagrams, and abundance gradients). Results. Our red giant sample spans distances as large as 10 kpc from the Sun. Given our chemical quality requirements, most of the stars are located between 1 and 6 kpc from the Sun, increasing by at least a factor of eight the studied volume with respect to the most recent chemodynamical studies based on the two largest samples obtained from RAVE and the Sloan Extension for Galactic Understanding and Exploration (SEGUE). We find remarkable agreement between the MDF of the recently published local (d < 100 pc) high-resolution high-S/N HARPS sample and our local HQ sample (d < 1 kpc). The local MDF peaks slightly below solar metallicity, and exhibits an extended tail towards [Fe/H] = -1, whereas a sharper cutoff is seen at larger metallicities (the APOGEE sample shows a slight overabundance of stars with metallicities larger than similar or equal to+0.3 with respect to the HARPS sample). Both samples also compare extremely well in an [alpha/Fe] vs. [Fe/H] diagram. The APOGEE data also confirm the existence of a gap in the abundance diagram. When expanding our sample to cover three different Galactocentric distance bins (inner disc, solar vicinity and outer disc), we find the high-[alpha/Fe] stars to be rare towards the outer zones (implying a shorter scale-length of the thick disc with respect to the thin disc), as previously suggested in the literature. Finally, we measure the gradients in [Fe/H] and [alpha/Fe], and their respective MDFs, over a range of 6 < R < 11 kpc in Galactocentric distance, and a 0 < z < 3 kpc range of distance from the Galactic plane. We find a good agreement with the gradients traced by the GCS and RAVE dwarf samples. For stars with 1.5 < z < 3 kpc (not present in the previous samples), we find a positive metallicity gradient and a negative gradient in [alpha/Fe].
The (Cn)-N-14/(Cn)-N-15 Ratio in Diffuse Molecular Clouds
(2015-05) Ritchey, A. M.; Federman, S. R.; Lambert, David L.; Lambert, D. L.
We report the first detection of (CN)-N-15 in diffuse molecular gas from a detailed examination of CN absorption lines in archival spectra, obtained with the Ultraviolet and Visual Echelle Spectrograph of the Very Large Telescope of stars probing local diffuse clouds. Absorption from the (CN)-N-15 isotopologue is confidently detected ( at greater than or similar to 4 sigma) in three out of the four directions studied and appears as a very weak feature between the main (12) CN and (CN)-C-13 absorption components. Column densities for each CN isotopologue are determined through profile fitting, after accounting for weak additional line-of-sight components of (CN)-C-12, which are seen in the absorption profiles of CH and CH+ as well. The weighted mean value of N-14/(CN)-N-15 for the three sight lines with detections of (CN)-N-15 is 274 +/- 18. Since the diffuse molecular clouds toward our target stars have relatively high gas kinetic temperatures and relatively low visual extinctions, their N-14/(CN)-N-15 ratios should not be affected by chemical fractionation. The mean N-14/(CN)-N-15 ratio that we obtain should therefore be representative of the ambient N-14/N-15 ratio in the local interstellar medium. Indeed, our mean value agrees well with that derived from millimeter-wave observations of CN, HCN, and HNC in local molecular clouds.
Heavy Element Abundances In Giant Stars Of The Globular Clusters M4 And M5
(2008-12) Yong, David; Karakas, Amanda I.; Lambert, David L.; Chieffi, Alessandro; Limongi, Marco; Lambert, David L.
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 Telescope. We confirm and expand on previous results for these clusters by showing that (1) all elements heavier than, and including, Si have constant abundances within each cluster, (2) the elements from Ca to Ni have indistinguishable compositions in M4 and M5, (3) Si, Cu, Zn, and all s-process elements are approximately 0.3 dex overabundant in M4 relative to M5, and (4) the r-process elements Sm, Eu, Gd, and Th are slightly overabundant in M5 relative to M4. The cluster-to-cluster abundance differences for Cu and Zn are intriguing, especially in light of their uncertain nucleosynthetic origins. We confirm that stars other than Type Ia supernovae must produce significant amounts of Cu and Zn at or below the clusters' metallicities. If intermediate-mass AGB stars or massive stars are responsible for the Cu and Zn enhancements in M4, the similar [Rb/Zr] ratios and (preliminary) Mg isotope ratios in both clusters may be problematic for either scenario. For the elements from Ba to Hf, we assume that the s-and r-process contributions are scaled versions of the solar s-and r-process abundances. We quantify the relative fractions of s-and r-process material for each cluster and show that they provide an excellent fit to the observed abundances.
High-Resolution Spectroscopy Of Extremely Metal-Poor Stars In The Least Evolved Galaxies: Ursa Major II And Coma Berenices
(2010-01) Frebel, Anna; Simon, Joshua D.; Geha, Marla; Willman, Beth; Frebel, Anna
We present spectra of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way (MW), Ursa Major II, and Coma Berenices obtained with the Keck/High Resolution Echelle Spectrometer (HIRES). These observations include the first high-resolution spectroscopic observations of extremely metal-poor ([Fe/H] < -3.0) stars not belonging to the MW halo field star population. We obtain abundance measurements and upper limits for 26 elements between carbon and europium. The entire sample of stars spans a range of -3.2 < [Fe/H] < -2.3, and we confirm that each galaxy contains a large intrinsic spread of Fe abundances. A comparison with MW halo stars of similar metallicities reveals substantial agreement between the abundance patterns of the ultra-faint dwarf galaxies and the MW halo for the light, alpha, and iron-peak elements (C to Zn). This agreement contrasts with the results of earlier studies of more metal-rich stars (-2.5 less than or similar to [Fe/H] less than or similar to -1.0) in more luminous dwarf spheroidal galaxies, which found significant abundance discrepancies with respect to the MW halo data. The abundances of neutron-capture elements (Sr to Eu) in the ultra-faint dwarf galaxies are extremely low, consistent with the most metal-poor halo stars, but not with the typical halo abundance pattern at [Fe/H] greater than or similar to -3.0. Not only are our results broadly consistent with a galaxy formation model that predicts that massive dwarf galaxies are the source of the metal-rich component ([Fe/H] > -2.5) of the MW halo, but they also suggest that the faintest known dwarfs may be the primary contributors to the metal-poor end of the MW halo metallicity distribution.
Improved Log(gf) Values for Lines of Ti I and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937 (Accurate Transition Probabilities for Ti I)
(2013-04) Lawler, James E.; Guzman, A.; Wood, M. P.; Sneden, Christopher; Cowan, John J.; Sneden, Christopher
New atomic transition probability measurements for 948 lines of Ti I are reported. Branching fractions from Fourier transform spectra and from spectra recorded using a 3 m echelle spectrometer are combined with published radiative lifetimes from laser-induced fluorescence measurements to determine these transition probabilities. Generally good agreement is found in comparisons to the NIST Atomic Spectra Database. The new Ti I data are applied to re-determine the Ti abundance in the photospheres of the Sun and metal-poor star HD 84937 using many lines covering a range of wavelength and excitation potential to explore possible non-local thermal equilibrium effects. The variation of relative Ti/Fe abundance with metallicity in metal-poor stars observed in earlier studies is supported in this study.
Improved Log(gf) Values of Selected Lines in Mn I and Mn II for Abundance Determinations in FGK Dwarfs and Giants
(2011-06) Den Hartog, E. A.; Lawler, James E.; Sobeck, Jennifer S.; Sneden, Christopher; Cowan, John J.; Sneden, Christopher
The goal of the present work is to produce transition probabilities with very low uncertainties for a selected set of multiplets of Mn I and Mn II. Multiplets are chosen based upon their suitability for stellar abundance analysis. We report on new radiative lifetime measurements for 22 levels of Mn I from the e(8)D, z(6)P, z(6)D, z(4)F, e(8)S, and e(6)S terms and six levels of Mn II from the z(5)P and z(7)P terms using time-resolved laser-induced fluorescence on a slow atom/ion beam. New branching fractions for transitions from these levels, measured using a Fourier-transform spectrometer, are reported. When combined, these measurements yield transition probabilities for 47 transitions of Mn I and 15 transitions of Mn II. Comparisons are made to data from the literature and to Russell-Saunders (LS) theory. In keeping with the goal of producing a set of transition probabilities with the highest possible accuracy and precision, we recommend a weighted mean result incorporating our measurements on Mn I and II as well as independent measurements or calculations that we view as reliable and of a quality similar to ours. In a forthcoming paper, these Mn I/II transition probability data will be utilized to derive the Mn abundance in stars with spectra from both space-based and ground-based facilities over a 4000 angstrom wavelength range. With the employment of a local thermodynamic equilibrium line transfer code, the Mn I/II ionization balance will be determined for stars of different evolutionary states.
Improved Ni I Log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937
(2014-04) Wood, M. P.; Lawler, James E.; Sneden, Christopher; Cowan, John J.; Sneden, Christopher
Atomic transition probability measurements for 371 Ni I lines in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrograph are combined with published radiative lifetimes to determine these transition probabilities. Generally good agreement is found in comparisons to previously reported Ni I transition probability measurements. Use of the new echelle spectrograph, independent radiometric calibration methods, and independent data analysis routines enable a reduction of systematic errors and overall improvement in transition probability uncertainty over previous measurements. The new Ni I data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ni abundances. Lines covering a wide range of wavelength and excitation potential are used to search for non-LTE effects.
Improved V I Log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937
(2014-12) Lawler, James E.; Wood, M. P.; Den Hartog, E. A.; Feigenson, T.; Sneden, Christopher; Cowan, John J.; Sneden, Christopher
New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log epsilon(V) = 3.956 +/- 0.004 (sigma = 0.037) based on 93 V I lines and log epsilon(V) = 1.89 +/- 0.03 (sigma = 0.07) based on nine Vi lines, respectively, using the Holweger-Muller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.
Improved V II Log(gf) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937
(2014-10) Wood, M. P.; Lawler, James E.; Den Hartog, E. A.; Sneden, Christopher; Cowan, John J.; Sneden, Christopher
New experimental absolute atomic transition probabilities are reported for 203 lines of VII. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported VII transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new VII data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log epsilon(V) = 3.95 from 15 VII lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H]= -2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.
Isotopic Titanium Abundances In Local M Dwarfs
(2009-07) Chavez, Joy; Lambert, David L.; Chavez, Joy; Lambert, David L.
Relative abundances of the five stable isotopes of titanium (Ti-46 to Ti-50) are measured for 11 M dwarfs belonging to the thin disk (four stars), thick disk (three stars), the halo (one star), and either the thick or the thin disk (three stars). Over the metallicity range of the sample (-1 < [Fe/H] < 0), the isotopic ratios are approximately constant at the solar system ratios. There is no discernible difference between the isotopic ratios for thin and thick disk stars. Isotopic ratios are in fair accord with recent calculations of Galactic chemical evolution despite the fact that such calculations underpredict [Ti/Fe] by about 0.4 dex at all metallicities.