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Diaz, Beltran A. I. "Chemical abundances in spiral galaxies." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372064.
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Cunha, Katia, Verne V. Smith, Sten Hasselquist, Diogo Souto, Matthew D. Shetrone, Prieto Carlos Allende, Dmitry Bizyaev, et al. "Adding the s-Process Element Cerium to the APOGEE Survey: Identification and Characterization of Ce ii Lines in the H-band Spectral Window." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625301.
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Nine Ce II lines have been identified and characterized within the spectral window observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey (between lambda 1.51 and 1.69 mu m). At solar metallicities, cerium is an element that is produced predominantly as a result of the slow capture of neutrons (the s-process) during asymptotic giant branch stellar evolution. The Ce II lines were identified using a combination of a high-resolution (R = lambda/delta lambda = 100,000) Fourier Transform Spectrometer (FTS) spectrum of a Boo and an APOGEE spectrum (R. =. 22,400) of a metal-poor, but s-process enriched, red giant (2M16011638-1201525). Laboratory oscillator strengths are not available for these lines. Astrophysical gf-values were derived using alpha Boo as a standard star, with the absolute cerium abundance in alpha Boo set by using optical Ce II lines that have precise published laboratory gf-values. The near-infrared Ce II lines identified here are also analyzed, as consistency checks, in a small number of bright red giants using archival FTS spectra, as well as a small sample of APOGEE red giants, including two members of the open cluster NGC 6819, two field stars, and seven metal-poor N-and Al-rich stars. The conclusion is that this set of Ce II lines can be detected and analyzed in a large fraction of the APOGEE red giant sample and will be useful for probing chemical evolution of the s-process products in various populations of the Milky Way.
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Wesson, Roger. "Heavy element abundances in emission line nebulae." Thesis, University College London (University of London), 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430104.
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Neves, Vasco de Matos Ferreira Mendes. "Abundances of elements in exoplanet host stars." Master's thesis, Universidade de Aveiro, 2008. http://hdl.handle.net/10773/15237.
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Mestrado em FísicaIn this work we present an uniform study of the chemical abundances of 12 elements (Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg and Al) derived from the spectra of 451 stars of one of the HARPS GTO planet search programs, which has 66 planet bearing stars. The main goal of this study is the investigation of the possible differences between the abundances of the stars with and without planets. We have confirmed that there is an overabundance of metallicity in planet host stars, common to all species, as expected. We have also found that there is no difference in the galactic chemical evolution trends between stars with and without planets, as observed in the [X/Fe] vs. [Fe/H] plots. The stars that harbour planetary companions simply seem to be in the high metallicity tail of the distribution. We have only found one case of clear overabundance for a fixed [Fe/H] (HD147513) where the pollution scenario might be important. This particular star needs to be investigated in a future work. We also need to explore the possibility of the existence of a different population of stars with high [X/Fe] ratios in the region of [Fe/H] < 0 that was detected in the plots of [X/Fe] vs [Fe/H].
Neste trabalho apresentamos um estudo uniforme de abundâncias químicas de 12 elementos (Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg e Al) a partir dos espectros de 451 estrelas de um dos programas HARPS GTO de procura de exoplanetas. Destas estrelas, 66 têm planetas confirmados. O objectivo principal deste trabalho é a investigação das possíveis diferenças entre as abundâncias químicas de estrelas com e sem planetas. Confirmámos que existe uma maior abundância química de todos os elementos nas estrelas com planetas, como era esperado. Constatámos também, através da análise dos gráficos de [X/Fe] vs. [Fe/H], que não existem diferenças nas tendências da evolução química da galáxia entre estrelas com e sem planetas. As estrelas que têm planetas parecem estar apenas no extremo de maior metalicidade da distribuição. Encontrámos apenas um caso em que se verifica uma maior abundância de alguns elementos para um [Fe/H] fixo (HD147513), onde o cenário de enriquecimento químico por poluição poderá ser importante. Este caso em particular precisa de ser investigado num trabalho futuro. É necessário também explorar a possível existência de uma população diferente de estrelas com maior metalicidade na região de [Fe/H] < 0 detectada nos gráficos de [X/Fe] vs. [Fe/H].
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Folsom, Colin Peter. "Chemical abundances of very young intermediate mass stars." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601478.
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On the main sequence, roughly 10-20% of A- and B-type stars display a wide range of chemical peculiarities in their photospheres. It is unknown when during stellar evolution these chemical peculiarities develop, and the mechanisms for the formation of some peculiarities are Dot fully understood. In order to provide strong observational constraints, this thesis investigates chemical abundances in Herbig Ae and Be (HAeBe) stars, which are pre-main sequence progenitors of A and B stars. A detailed abundance analysis was performed for 20 HAeBe stars, and 1 dusty young star, using high resolution, high signal-to-noise ratio spectra. The abundance analysis proceeded by directly fitting synthetic spectra to observations, determining effective temperature, surface gravity, microturbulence, and projected rotational velocity self-consistently with chemical abundances. The synthetic spectra were computed with the program ZEEMAN, which was developed further, optimising it for nonmagnetic spectrum synthesis, adding an automatic fitting routine, and parallelising the program. Eleven of the stars are found to display 'Boots chemical peculiarities, one star shows weak Ap/Bp peculiarities, and the remaining 9 stars are found to be chemically normal. The star with weak Ap/Bp peculiarities has a confirmed magnetic field detection in the literature, as do one],. Boo star and one chemically normal star. The other stars have been searched for magnetic fields, but have no confirmed detections. I argue that the large incidence of Boo chemical peculiarities among HAeSe stars provides strong evidence in favour of a selective accretion hypothesis for the formation of A Boo peculiarities. Among the magnetic stars, it appears that Ap/Bp peculiarities can form on the pre-main sequence but, unlike the main sequence, there' are also chemically normal magnetic HAeBe stars.
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Hamilton, Brandi B. "Modeling Exoplanet Interiors from Host Star Elemental Abundances." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou157382737367536.
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Miller, Benjamin Randolph. "Abundances and trends of atmospheric chlorodifluoromethane and bromomethane /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p3035423.
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Wilson, Robert F., Johanna Teske, Steven R. Majewski, Katia Cunha, Verne Smith, Diogo Souto, Chad Bender, et al. "Elemental Abundances of Kepler Objects of Interest in APOGEE. I. Two Distinct Orbital Period Regimes Inferred from Host Star Iron Abundances." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/626528.
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The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed similar to 600 transiting exoplanets and exoplanet candidates from Kepler (Kepler Objects of Interest, KOIs), most with >= 18 epochs. The combined multi-epoch spectra are of high signal-to-noise ratio (typically >= 100) and yield precise stellar parameters and chemical abundances. We first confirm the ability of the APOGEE abundance pipeline, ASPCAP, to derive reliable [Fe/H] and effective temperatures for FGK dwarf stars-the primary Kepler host stellar type-by comparing the ASPCAP-derived stellar parameters with those from independent high-resolution spectroscopic characterizations for 221 dwarf stars in the literature. With a sample of 282 close-in (P < 100 days) KOIs observed in the APOGEE KOI goal program, we find a correlation between orbital period and host star [Fe/H] characterized by a critical period, P-crit = 8.3(-4.1)(+0.1) days, below which small exoplanets orbit statistically more metal-enriched host stars. This effect may trace a metallicity dependence of the protoplanetary disk inner radius at the time of planet formation or may be a result of rocky planet ingestion driven by inward planetary migration. We also consider that this may trace a metallicity dependence of the dust sublimation radius, but we find no statistically significant correlation with host T-eff and orbital period to support such a claim.
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Andrews, Brett H. "Decoding Galaxy Evolution with Gas-phase and Stellar Elemental Abundances." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1406218333.
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Dudley, Jonathan. "Cosmological parameter estimation using SZ-selected galaxy cluster abundances." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=116972.
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The observational record of the growth of structure in the universe over cosmic time offers a unique and invaluable cosmological measure. The abundance and evolutionary history of structure in the universe are dependent upon the parameters which define the cosmological framework. In this work, we formulate a method for deriving cosmological constraints from the observed abundance of galaxy clusters. These objects are the most massive gravitationally collapsed structures in the universe and act as tracers of the underlying density field. We develop a technique for comparing theoretical cluster abundances with observed galaxy cluster catalogs. In this process, we explore and constrain the parameter space for departures from the canonical cosmological model. The motivation and framework for this investigation are presented in the opening chapters. An introduction to modern cosmological theory and methods for calculating theoretical galaxy cluster abundances are presented. A description of the physical observables associated with galaxy clusters follows, including a summary of detection methods. A cluster likelihood, defined through comparisons between observed cluster abundances with those predicted from theory, is developed.The focus of this work rests in the analysis of the cluster likelihood. The fiducial LCDM model is explored and parameter constraints are presented. The cluster dataset is shown to provide useful constraints on numerous parameters and the inclusion of supplementary data is investigated. The cluster-scale normalization parameter sigma_8 is well-constrained by this analysis, where we find sigma_8=0.745+-0.082 when considering only the cluster data and sigma_8=0.796+-0.026 for a combination of cluster and complementary datasets. The normalization of the scaling relation between the cluster observable and its mass and redshift is also constrained by this joint analysis such that, when compared with predictions from numerical simulations, we find A_SZ, meas./A_SZ, fid.=0.82+-0.17. Also explored are two extensions to the standard cosmological model, a non-cosmological-constant form of dark energy and non-Gaussian primordial fluctuations. In both cases the cluster likelihood is demonstrated to provide informative constraints, demonstrating consistency with a cosmological constant form of dark energy and Gaussian primordial fluctuations. Through a combination of cluster and complementary datasets we constrain the dark energy equation of state parameter to be w=-1.07+-0.12. The degree of non-Gaussianity inferred from a catalog of massive galaxy clusters is also constrained, finding f_NL=-36 (-491+456) at 68% confidence for a particular non-Gaussian model.Les données observationnelles de la croissance des structures dans l'univers représentent une mesure cosmologique unique et inestimable. La quantité et l'historique d'évolution des structures dans l'univers dépendent des paramètres qui définissent le contexte cosmologique. Dans le présent travail, nous formulons une méthode pour déduire des contraintes cosmologiques à partir d'observations du nombre d'amas de galaxies. Ces objets demeurent les structures les plus massives à être issues de l'effondrement gravitationnel dans l'univers et agissent comme traceurs du champ de densité sous-jacent. Nous développons une technique servant à comparer le nombre d'amas de galaxies théorique aux données des catalogues d'amas de galaxies observés. Ce faisant, nous explorons et contraignions l'espace de paramètres à la recherche de déviations par rapport au modèle cosmologique standard. L'intérêt et le cadre de travail de cette recherche sont détaillés dans les premiers chapitres. Une introduction à la théorie de la cosmologie moderne et aux méthodes de calcul du nombre théorique d'amas de galaxies sera présentée. Ensuite, nous faisons la description des observables physiques associés aux amas de galaxies, incluant un résumé des méthodes de détection. Nous développons par après une fonction de vraisemblance des amas de galaxies définie par une comparaison entre les amas observés et les amas prédits par la théorie. Le fil conducteur de ce travail réside dans l'analyse de la fonction de vraisemblance des amas de galaxies. Le modèle standard de la cosmologie, dit LCDM, est exploré et les contraintes sur ses paramètres sont présentées. L'utilisation d'ensembles de données sur les amas de galaxies permet d'améliorer les contraintes sur plusieurs de ces paramètres. L'impact sur ces contraintes de l'ajout de données supplémentaires est également considéré. Cette analyse permet de contraindre significativement le paramètre de normalisation des fluctuations à l'échelle des amas de galaxies \sigma_8. Nous obtenons sigma_8=0.745+-0.082 en ne considérant que les données d'amas de galaxies et sigma_8=0.796+-0.026 en ajoutant des ensembles de données complémentaires. La normalisation du rapport d'échelle entre l'observable d'un amas de galaxies et sa masse est aussi contrainte par cette analyse conjointe. En comparant les résultats de notre analyse à ceux de simulations numériques, nous trouvons A_SZ, meas./A_SZ, fid.=0.82+-0.17$. Nous explorons de plus deux extensions au modèle cosmologique standard, une forme d'énergie sombre ne correspondant pas à une constante cosmologique ainsi que des fluctuations primordiales non-Gaussiennes. Dans les deux cas, la fonction de vraisemblance des amas de galaxies a permis de produire des contraintes informatives. Nous contraignons le paramètre de l'équation d'état de l'énergie sombre comme étant w=-1.07+-0.12$. En appliquant la fonction de vraisemblance à un catalogue d'amas de galaxies massifs, nous trouvons que le degré de non-Gaussianité correspond à f_NL=-36 (-491+456), à un niveau de confiance de 68%, pour un modèle de non-Gaussianité donné.
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Lipman, Keith. "Chemical abundances of primeval galaxies from QSO absorption lines." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363292.
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García, Pérez Ana E., Carlos Allende Prieto, Jon A. Holtzman, Matthew Shetrone, Szabolcs Mészáros, Dmitry Bizyaev, Ricardo Carrera, et al. "ASPCAP: THE APOGEE STELLAR PARAMETER AND CHEMICAL ABUNDANCES PIPELINE." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621372.
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The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has built the largest moderately high-resolution (R approximate to 22,500) spectroscopic map of the stars across the Milky Way, and including dust-obscured areas. The APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) is the software developed for the automated analysis of these spectra. ASPCAP determines atmospheric parameters and chemical abundances from observed spectra by comparing observed spectra to libraries of theoretical spectra, using. 2 minimization in a multidimensional parameter space. The package consists of a FORTRAN90 code that does the actual minimization and a wrapper IDL code for book-keeping and data handling. This paper explains in detail the ASPCAP components and functionality, and presents results from a number of tests designed to check its performance. ASPCAP provides stellar effective temperatures, surface gravities, and metallicities precise to 2%, 0.1 dex, and 0.05 dex, respectively, for most APOGEE stars, which are predominantly giants. It also provides abundances for up to 15 chemical elements with various levels of precision, typically under 0.1 dex. The final data release (DR12) of the Sloan Digital Sky Survey III contains an APOGEE database of more than 150,000 stars. ASPCAP development continues in the SDSS-IV APOGEE-2 survey.
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Ramírez, Santana Solange V. "Stellar abundances in the inner bulge and galactic center /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488196234909106.
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Woolf, Vincent Martell. "Mercury elemental and isotopic abundances in mercury-manganese stars /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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van, den Brink Nemo. "Chemical abundances in main-sequence stars in open cluster M67." Thesis, Uppsala universitet, Teoretisk astrofysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-169017.
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The discovery of a solar twin in the open star cluster M67 (Önehag et al. 2011) implies a near-solar chemical composition for the cluster. This study uses high-resolution spectroscopic data of five main-sequence stars in M67 to analyze their abundance of a few key elements and compare results to the solar-twin composition and the composition of field twins (Melendez et al. 2009). The derived composition was also compared to predictions of stellar-structure models including the effects of element diffusion. (Richard, private communication). It is found that all analyzed elements are, to varying degree, less abundant in the five main sequence stars than in the solar twin. With the possible exception of iron, all derived abundances also fall clearly below the diffusion predictions.
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Szymanski, A. "Absolute gamma-ray abundances of light rhenium and tungsten isotopes." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376142.
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Gay, A. M. "The abundances of ultra-heavy elements in the cosmic rays." Thesis, University of Bristol, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376608.
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Ballero, Silvia Kuna. "Evolution of chemical abundances in active and quiescent spiral bulges." Doctoral thesis, Università degli studi di Trieste, 2008. http://hdl.handle.net/10077/2560.
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2006/2007In this thesis I develop a chemical evolution model which takes advantage of the most recent high-quality abundance observations in the Galactic bulge to put constraints on its formation and evolution and to obtain a baseline model for bulges in general. I adopt updated massive star nucleosynthesis and follow the evolution of several alpha-elements and Fe by varying the evolutionary parameters. The [alpha/Fe] ratios in the bulge are correctly predicted to be supersolar for a wide range in [Fe/H], and the stellar metallicity distribution is reproduced assuming a short formation timescale, a high star formation efficiency and an initial mass function flatter than the disk. Metallicity-dependent oxygen yields with stellar mass loss are included in the chemical evolution models for the bulge and the solar neighbourhood. The agreement between predicted and observed [O/Mg] trends above solar metallicity is significantly improved; a normalisation problem probably indicates that the adopted semi-empirical yields need adjustment. The difference between [O/Fe] and the other [alpha/Fe] ratios in the bulge and solar neighbourhood is explained. I test the so-called universal initial mass function, suitable for ellipticals and disks, to see if the bulge stellar metallicity distribution can be reproduced by varying the yields for very massive stars, and included M31 in my analysis. I show that assuming a flatter initial mass function than the universal one is necessary, and that a variation exists in the initial mass function among different environments. Finally, I investigate the evolution of spiral bulges hosting Seyfert nuclei, with detailed calculations of the galactic potential and of the feedback from the central supermassive black hole in an Eddington-limited accretion regime. New spectro-photometrical evolution codes covering a wide range of stellar ages and metallicities allowed to model the photometric features of local bulges. I successfully predict the observed black hole-host bulge mass relation. The observed present-day nuclear bolometric luminosity is achieved only for the most massive bulges, otherwise a rejuvenation is necessary. The observed high star formation rates and metallicities, constancy of chemical abundances with the redshift and bulge present-day colours are reproduced, but a steeper initial mass function is required to match the colour-magnitude relation and the present K-band bulge luminosity.
In questa tesi, ho sviluppato un modello di evoluzione chimica che si avvale di recenti osservazioni ad alta qualità di abbondanze chimiche nel bulbo della Via Lattea, per porre dei vincoli sui suoi meccanismi di formazione ed evoluzione e ottenere un modello generale per i bulbi di spirale. Ho adottato una nucleosintesi aggiornata per le stelle massicce e seguito l'evoluzione di diversi elementi-alpha e del ferro, variando i parametri evolutivi. Si prevede correttamente che i rapporti [alpha/Fe] nel bulbo siano soprasolari per un ampio intervallo in [Fe/H]. La distribuzione in metallicità è riprodotta con un tempo di formazione breve, un'alta efficienza di formazione stellare e una funzione iniziale di massa più piatta che nel disco. Yields di ossigeno con perdita di massa stellare in funzione della metallicità sono stati inclusi nei modelli di evoluzione chimica del bulbo e dei dintorni solari. L'accordo tra gli andamenti di [O/Mg] previsti e osservati per metallicità soprasolari risulta sensibilmente migliorato; si spiega inoltre la differenza tra il rapporto [O/Fe] e gli altri [alpha/Fe] nel bulbo e nei dintorni solari. Un problema di normalizzazione indica che probabilmente gli yields semi-empirici adottati necessitano una revisione. Ho verificato se con la cosiddetta funzione iniziale di massa universale, adeguata per galassie ellittiche e dischi, la distribuzione in metallicità stellare del bulge può essere riprodotta calibrando gli yields delle stelle supermassicce, includendo M31 nell'analisi. Si dimostra che una funzione iniziale di massa più piatta di quella universale è necessaria, e che esiste una variazione nella funzione iniziale di massa tra i diversi ambienti. Infine, ho studiato l'evoluzione di bulbi di spirali che ospitano galassie di Seyfert, mediante calcoli dettagliati del potenziale galattico e del feedback dal buco nero supermassiccio centrale in un regime di accrescimento limitato dal tasso di Eddington. Nuovi codici spettro-fotometrici che coprono un ampio intervallo di età stellari e di metallicità hanno permesso di modellizzare le caratteristiche fotometriche dei bulbi locali. La relazione osservata tra massa del buco nero e del bulbo ospite è prevista con successo. La luminosità bolometrica nucleare misurata al tempo presente si consegue solo per i bulbi più massicci, negli altri casi è necessario un "ringiovanimento". Le osservazioni di alto tasso di formazione stellare, alte metallicità, invarianza di abbondanze chimiche col redshift e colori dei bulbi locali sono riprodotte; una funzione iniziale di massa più ripida è invece richiesta per la relazione colore-magnitudo e la luminosità dei bulbi in banda K al tempo presente.
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Schiavon, Ricardo P., Olga Zamora, Ricardo Carrera, Sara Lucatello, A. C. Robin, Melissa Ness, Sarah L. Martell, et al. "Chemical tagging with APOGEE: discovery of a large population of N-rich stars in the inner Galaxy." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623045.
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Formation of globular clusters (GCs), the Galactic bulge, or galaxy bulges in general is an important unsolved problem in Galactic astronomy. Homogeneous infrared observations of large samples of stars belonging to GCs and the Galactic bulge field are one of the best ways to study these problems. We report the discovery by APOGEE (Apache Point Observatory Galactic Evolution Experiment) of a population of field stars in the inner Galaxy with abundances of N, C, and Al that are typically found in GC stars. The newly discovered stars have high [N/Fe], which is correlated with [Al/Fe] and anticorrelated with [C/Fe]. They are homogeneously distributed across, and kinematically indistinguishable from, other field stars within the same volume. Their metallicity distribution is seemingly unimodal, peaking at [Fe/H] similar to -1, thus being in disagreement with that of the Galactic GC system. Our results can be understood in terms of different scenarios. N-rich stars could be former members of dissolved GCs, in which case the mass in destroyed GCs exceeds that of the surviving GC system by a factor of similar to 8. In that scenario, the total mass contained in so-called 'first-generation' stars cannot be larger than that in 'second-generation' stars by more than a factor of similar to 9 and was certainly smaller. Conversely, our results may imply the absence of a mandatory genetic link between 'second-generation' stars and GCs. Last, but not least, N-rich stars could be the oldest stars in the Galaxy, the by-products of chemical enrichment by the first stellar generations formed in the heart of the Galaxy.
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Wyrwas, Richard Ben Jr. "Vanadium Oxide Anions Clusters: Their Abundances, Structures and Reactions with SO₂." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4908.
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Early transition metal oxide clusters have been a focus of study for several years. The production of vanadium oxide cluster anions in a pulsed helium flow reactor provides a relatively precise way of introducing defect sites and controlling the oxidation state of the vanadium atoms. The composition of the clusters can be changed from the V2O5 stoichiometry, where the vanadium atom is in a +5 oxidation state, to more reduced stoichiometries yielding a mixture of oxidation states containing atoms in the +2 oxidation state. The subsequent addition of reactant gases such as H2O and SO2 yields very intense adsorption reactions as well as a demonstration of the robustness of particular defect free clusters. For example, the cluster has been identified as a defect free cluster where all vanadium atoms are in the +5 oxidation state and all oxygen atoms are predicted to be in the 2- state. The cluster has been shown to not adsorb SO2- while clusters in a reduced oxidation state, such as and readily adsorb one or more SO2 molecules. The adsorption process has been shown to be size dependent, with the smallest monovanadium oxide anions being the most reactive.
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Booth, Donna Wade. "Depth-related variations of trace metal abundances in south Florida sediments." FIU Digital Commons, 1992. http://digitalcommons.fiu.edu/etd/1730.
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Variations in trace element abundances with depth in soils and sediments may be due to natural processes or reflect anthropogenic influences. The depth related variations of five major elements (Fe, Si, Al, Ca and Mg), seventeen trace elements (Mn, Cr, Ti, P, Ni, Ba, Sc, Sr, Sb, Zn, Pb, Cd, Co, V, Be, Cu and Y) and volatile loss patterns were examined for sediment cores from five sites in South Florida (Lake Okeechobee, SFWMD Water Conservation area 3B, F.I.U., the Everglades and Chekika State Recreation Area). Principal component analysis of the chemical data combined with microscopic examination of the soils reveal that depth-related variations can be explained by varying proportions of three natural soil constituents and one anthropogenic component. The results can be used as a geochemical baseline for human influence on South Florida soils.
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Linnerud, Marit. "Patterns in spatial and temporal variation in population abundances of vertebrates." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for biologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-21308.
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In this thesis I investigate the heterogeneity of population abundance by using the Taylor’s power law relationship of mean and variance, in time and space. Within the framework of stochastic population dynamics, the existence of a temporal Taylor’s power law were confirmed for a large number of British bird populations. Theoretical expectations predicted that environmental stochasticity would increase the slope of the mean-variance relationship while demographic stochasticity would reduce it. In addition, the slope should also be influenced by the strength of density dependence. Here, species specific slopes were mainly explained by the effect of life history variation on interspecific variation in demographic variance. It is generally acknowledged that the spatial power law depend on scale, however, few studies have accounted for this. By using a model which incorporates both the local point process and spatial covariance of population densities, the variance was estimated as a function of area and parameters characterizing the underlying density process, thus generating a non-linear Taylor’s spatial scaling law. Using a novel method to estimate the underlying density field, the spatial aggregation pattern was investigated by the slope of the variance-area relationship in populations of birds and fish. For the bird species no effect of behavioural characteristics was found to influence interspecific differences in the spatial aggregation patterns. Instead, interspecific differences in overall abundance in the UK influenced the slopes, thus indicating a link between local processes and variation of abundance patterns at a regional level. For the fish species, interspecifc differences in the spatial aggregation of the distributions were related to behavioural differences. Consequently, the effect of sampling area on the spatial distribution may be predicted from basic behavioural characteristics. The work of this thesis contributes to the ongoing discussion of Taylor’s power laws. It introduces framework to aid interpretation of future research, which is especially important in the context of other macroecologial pattern.
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Simpson, Jeffrey. "Spectral Matching for Elemental Abundances of Evolved Stars of Globular Clusters." Thesis, University of Canterbury. Physics and Astronomy, 2013. http://hdl.handle.net/10092/8460.
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In order to understand the origin of globular clusters, large samples of their stars need to be observed and analyzed for their chemical composition. This is especially true for the complex, multimetallic cluster ω Centauri, with its large range of iron, carbon, nitrogen, oxygen, sodium and barium abundances. In order to accomplish this, an automated spectral matching pipeline was developed to determine these abundances. This thesis made use of photometry and low resolution spectroscopy to analyze the chemical composition of evolved stars in three clusters: ω Cen, 47 Tuc and NGC 6752. The latter two clusters are monometallic and selected due to their similar metallicities to the metal-rich and metal-poor stars in ω Cen. This allowed them to be used as test-cases for the spectral matching pipeline.
For ω Cen, two analyses were performed. In the first, 221 giant branch stars were selected that had known [O/Fe]. These stars showed the expected anticorrelation in [C/Fe]to [N/Fe]. In the second, spectral indices were used to estimate the oxygen abundance of the stars, leading to a determination of whether a particular star was oxygen-rich or oxygen-poor. From this a catalogue of abundances of iron, carbon and barium of 848 giant branch stars were determined, of which 557 also had well-defined nitrogen abundances. k-means clustering analysis was used to group the stars in ω Cen into four homogeneous groups based upon these abundances. These groups suggest that there were at least four main periods of star formation in the cluster. The exact order of these star formation events is not yet understood, with some models predicting the groups formed from iron-poorest to iron-richest, while others suggest the potential for iron-poorer groups to form after iron-rich groups.
These results compare well with those found from higher resolution studies and show the value of more extensive lower resolution spectral surveys. They also highlight the need for large samples of stars when working with a complex object like ω Cen.
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Tsangarides, Stelios Andreou. "Abundances and radial-velocity monitoring of carbon-enhanced, metal-poor stars." Thesis, Open University, 2005. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417494.
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Ignace, Richard, J. Cassinelli, G. Tracy, E. Churchwell, and H. J. Lamers. "Neon Abundances from a Spitzer/IRS Survey of Wolf-Rayet Stars." Digital Commons @ East Tennessee State University, 2007. https://dc.etsu.edu/etsu-works/6272.
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We report on neon abundances derived from Spitzer high resolution spectral data of eight Wolf-Rayet (WR) stars using the forbidden line of [Ne III] 15.56 μm. Our targets include four WN stars of subtypes 4–7, and four WC stars of subtypes 4–7. We derive ion fraction abundances γ of Ne2+ for the winds of each star. The ion fraction abundance is a product of the ionization fraction Qi in stage i and the abundance by number AE of element E relative to all nuclei. Values generally consistent with solar are obtained for the WN stars, and values in excess of solar are obtained for the WC stars.
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Rich, Robert Michael Mould Jeremy. "Abundances and kinematics of k giants in the galactic nuclear bulge /." Diss., Pasadena, Calif. : California Institute of Technology, 1986. http://resolver.caltech.edu/CaltechETD:etd-09102008-152942.
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Wyrwas, Richard Ben. "Vanadium oxide anion clusters their abundances, structures and reactions with SO₂ /." Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-11212004-204032/unrestricted/wyrwas%5Frichard%5Fb%5F200412%5Fphd.pdf.
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Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2005.Whetten, Robert L., Committee Chair ; First, Phillip N, Committee Member ; Sherrill, C. David, Committee Member ; Wine, Paul H., Committee Member ; El-Sayed, Mostafa A, Committee Member. Includes bibliographical references.
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MARCELLI, LAURA. "PAMELA mission: in flight perfomances and preliminary measurements of nuclear abundances." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/639.
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L'esperimento PAMELA (acronimo per “Payload for Antimatter-Matter Exploration and Light nuclei Astrophysics”) ha come obiettivo principale la ricerca e lo studio dei raggi cosmici con particolare attenzione alla ricerca della componente di antimateria presente in essi sotto forma di particelle e nuclei (antiprotoni, 80 MeV - 190 GeV, e positroni, 50 MeV - 270 GeV) al fine di mettere in evidenza il contributo, se esistente, proveniente da una possibile sorgente di materia oscura. PAMELA inoltre ricercherà antinuclei primordiali (in particolare anti-elio) e servirà da verifica per i modelli di propagazione dei raggi cosmici attraverso una precisa ricostruzione dello spettro energetico delle antiparticelle e lo studio dei nuclei leggeri e dei loro isotopi. Inoltre investigherà i fenomeni connessi alla fisica solare e terrestre.
PAMELA è allogiata, come carico pagante, in un container pressurizzato a bordo di un satellite russo per il telerivelamento Resurs-DK1. Tale satellite è stato lanciato nello spazio con un’orbita ellittica (350 - 600 km di altezza) e con un'inclinazione di 70.0 gradi dal vettore Soyuz-U il 15 Giugno 2006 dal cosmodromo russo di Baikonur in Kazakhstan.
Lo strumento PAMELA è costituito da uno spettrometro magnetico, un sistema di tempo di volo (TOF, “Time Of Flight”), un calorimetro elettromagnetico ad immagine, un sistema di anticoincidenza, un rivelatore a scintillazione addizionale ed un rivelatore di neutroni. La combinazione di questi rivelatori permette una buona discriminazione delle antiparticelle su un fondo molto abbondante.
La durata della missione è prevista essere di almeno tre anni, durante i quali verrà collezionata una statistica senza precedenti. Il limite inferiore nel rapporto anti-He/He è fissato essere inferiore a 10^(-7).
Prima del lancio e durante i primi mesi da presa dati è stato sviluppato il software di Quick Look (per il monitoraggio in tempo reale) e per l'analisi dei dati. Inoltre sono state stimate le lunghezze di attenuazione e l'efficienza di trigger per il sistema di scintillatori del TOF nella configurazione di volo.
I risultati preliminari del rapporto nucleare Boro/Carbonio nell'intervallo energetico da 200 MeV/n fino a 25 GeV/n sono stati ottenuti combinando i dati provenienti dal Calorimetro, dallo spettrometro magnetico e dal sistema di tempo di volo.
Questa misura è molto importante per mettere vincoli ai parametri dei modelli cosmologici e, di conseguenza, per rendere più facilmente visibile una possibile piccola contaminazione da sorgenti primarie negli spettri degli antiprotoni e positroni. Una migliore conoscenza dei modelli di propagazione è fondamentale per la ricerca della materia esotica, come la materia oscura o antimateria prodotta in processi esotici, poichè una segnatura di tali processi può essere riconosciuta solamente conoscendo con ottima precisione i flussi di tali particelle prodotti dai canali convenzionali e i meccanismi di accelerazione e trasporto.PAMELA (a “Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics”) experiment is a satellite-borne apparatus designed for precision studies of the charged particles in the cosmic radiation. The primary scientific goal is the study of the antimatter component of the cosmic radiation (antiprotons, 80 MeV - 190 GeV; and positrons, 50 MeV - 270 GeV) in order to search for evidence of dark matter particle annihilations. PAMELA will also search for primordial antinuclei (in particular, anti-helium), and test cosmic-ray propagation models through precise measurements of the antiparticle energy spectrum and studies of light nuclei and their isotopes. In addition, it will measure the light nuclear component of cosmic rays and investigate phenomena connected with Solar and Earth physics. PAMELA is installed inside a pressurized container attached to a Russian Resurs DK1 earth-observation satellite that was launched into space in an elliptical (350 - 600 km of altitude) orbit with an inclination of 70.0 degrees by a Soyuz-U rocket on June 15th 2006 from the Baikonur cosmodrome in Kazakhstan. The PAMELA apparatus comprises a magnetic spectrometer, a Time of Flight system, a silicon-tungsten electromagnetic calorimeter, an anticoincidence system, a shower tail catcher scintillator and a neutron detector. The combination of these devices allows antiparticles to be reliably identified from a large background of other charged particles. The semipolar orbit (70.0°) allows PAMELA to investigate a wide range of energies for antiprotons (80 MeV - 190 GeV) and positrons (50 MeV - 270 GeV). Three years of data taking will provide unprecedented statistics in this energy range and will set the upper limit for the ratio anti-He/He below 10^(-7). Before launch and during the first months of data taking, Quick Look Software (for mission monitoring in real time) and Data Analysis Software were developed. Furthermore measurements of the the light attenuation lengths and trigger efficiencies of the TOF scintillator system in the "flight" configuration were performed. Preliminary results of Boron to Carbon nuclear ratio in cosmic rays in the energy range from 200 MeV/n up to 25 GeV/n have been derived using combined data from Calorimeter, Tracker and TOF systems. This measurement is very important to put constraints to propagation parameters of cosmological models and, as a consequence, to make more easily visibile a possible small contamination from primary sources in antiprotons and positrons spectra. A better determination of the cosmic ray propagation is fundamental for the search of exotic matter, like dark matter candidates or antimatter produced in exotic processes, since the signature of such processes can be recognized only by knowing with great precision the fluxes due to the conventional production, acceleration and transport mechanisms.
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Armour, Mary-Helen. "A multicomponent echelle spectral data analysis of four planetary nebulae." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ56161.pdf.
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Park, In Hee. "Dark cloud modeling for the ortho-to-para abundance ratio of the cyclic C 3 H 2." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1117125089.
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Modelski, Kimberly A. "Comparison of climatic conditions and mosquito abundances in New Castle County, Delaware." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 3.25 Mb., 229 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435830.
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Dimmer, Claudia Helene. "Sources, abundances and seasonality of tropospheric halocarbons in the remote northern hemisphere." Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299316.
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Kohzu, Ayato. "13C and 15N natural abundances in the fungal body and their ecophysiological implications." 京都大学 (Kyoto University), 2000. http://hdl.handle.net/2433/181151.
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Stoll, Rebecca A. "Measuring and Extrapolating the Chemical Abundances of Normal and Superluminous Core-Collapse Supernovae." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373284666.
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Behr, Bradford B. McCarthy Jim Cohen Judith G. "A new spin on horizontal-branch stars : anomalous abundances and rapid rotation rates /." Diss., Pasadena, Calif. : California Institute of Technology, 2000. http://resolver.caltech.edu/CaltechETD:etd-09172008-111737.
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Rosales, Ortega Fernando Fabián. "Multi-dimensional analysis of the chemical and physical properties of spiral galaxies." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/224843.
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The PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey: PINGS, a 2-dimensional spectroscopic mosaicking of 17 nearby disk galaxies in the optical wavelength range. This project represents the first attempt to obtain continuous coverage spectra of the whole surface of a galaxy in the nearby universe. The final data set comprises more than 50000 individual spectra, covering in total an observed area of nearly 80 arcmin square. The powerful capabilities of wide-field 2D spectroscopic studies areproven. The chemical composition of the whole surface of a spiral galaxy ischaracterised for the first time as a function not only of radius, but of theintrinsic morphology of the galaxy, allowing a more realistic determination oftheir physical properties. The methodology, analysis and results of thisdissertation will hopefully contribute in a significant way to understand thenature of the physical and chemical properties of the gas phase in spiralgalaxies.
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Pereira, Tiago Mendes Domingos, and tiago@mso anu edu au. "Confronting the new generation of stellar model atmospheres with observations." The Australian National University. Research School of Astronomy and Astrophysics, 2009. http://thesis.anu.edu.au./public/adt-ANU20100701.165106.
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Stellar model atmospheres are a fundamental tool for our understanding of stars. Because the chemical composition of stars cannot be measured directly, the inferred stellar parameters are model dependent. In recent years great progress has been made in the modeling of stellar atmospheres, allowing the relaxation of simplifying assumptions made in previous models. The use of new 3D model atmospheres to infer the solar chemical composition has resulted in a decrease of the solar metallicity. This result has caused some controversy and is being challenged.
The main aim of this thesis is to ascertain if the new models of stellar atmospheres are realistic and can be trusted to derive the chemical composition of stars in general, and the Sun in particular. Other objectives also include the study of line formation in the Sun at high spatial resolution, and possible implications in the modeling.
The Sun is the ideal test-bench for detailed analyses of stellar atmospheres. With the solar surface being resolved in great detail and at different viewing angles, a wealth of information can be gathered that allows for very robust tests of atmosphere models. The testing detailed here addresses several fronts. On one hand, the model�s temperature structure is directly tested with the classical tests of continuum centre-to-limb variations and absolute fluxes. On the other hand, the line formation is tested at different viewing angles and high spatial and spectral resolution. Here the main focus is on oxygen lines, as oxygen has an important contribution for the total solar metallicity. However, other lines are also tested. High quality data were specifically obtained for these line formation tests, using the Swedish 1-m Solar Telescope.
For the temperature structure tests we find a surprisingly good agreement between the 3D model and the observations, surpassing even semi-empirical models. The solar 1D non-LTE models have a very similar behaviour to 1D LTE models, confirming that LTE is a good approximation in the solar photosphere. The 3D theoretical model performs consistently better than its 1D counterparts. The oxygen line formation tests are carried out in great detail, with a careful wavelength calibration, revised atomic data, and allowing for departures from LTE. Again we find a reassuring agreement between the 3D model predictions and the observations, both for the centre-to-limb variation of the lines and the line formation at high spatial resolution. The observations at different viewing angles also allowed the empirical determination of the role of hydrogen collisions with oxygen, important when deriving the oxygen abundance.
The tests undertaken here show that the 3D model atmospheres are indeed very realistic. Their predicted temperature structure and velocity fields compare very favourably with observations of the Sun. Together with previous tests, this indicates they can be relied upon to derive the chemical composition of the Sun and similar late-type stars.
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Martinez, Osorio Yeisson Fabian. "Atomic Processes in Stellar Atmospheres : Inelastic Collisions and Effects on Late-type Spectra." Doctoral thesis, Uppsala universitet, Teoretisk astrofysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-249168.
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Chemical abundances as measured from stellar spectral lines are often subject to uncertainties due to lack of accurate data for inelastic collisions, which is needed for non-local thermodynamic equilibrium (non-LTE) modelling. For cool stars, understanding of collision processes with electrons and hydrogen atoms is required to achieve high precision measurements. In this thesis, I have investigated the role of these collisions on the non-LTE formation of Li and Mg spectral lines in late-type stars. In the case of Li, electron impact excitation processes were calculated using the R-matrix with pseudo states method and the results found to agree well with recent calculations using the convergent close-coupling technique. These modern data were employed in non-LTE calculations by updating an existing model atom, which already included modern data for hydrogen collision processes. Our results were compared with calculations using older semi-empirical approximation calculations and only small differences were found: about 0.01 dex (~ 2%) or less in the abundance corrections. We therefore conclude that the influence of uncertainties in the electron collision data on non-LTE calculations is negligible. Indeed, together with the collision data for the charge transfer process Li + H ↔ Li+ + H- now available, and barring the existence of an unknown important collisional process, the collisional data in general is not a source of significant uncertainty in non-LTE Li line formation calculations. In the case of Mg, electron impact excitation processes were again calculated with the Rmatrix with pseudo states method, and used together with recent hydrogen collision calculations to build and test a model atom, without free parameters, for non-LTE modelling. Both electron and hydrogen collision processes, including charge transfer and excitation, are found to be important thermalising agents in various cases. The modelled spectra agree well with observed spectra from benchmark stars in the optical and infrared. The modelling predicts non-LTE abundance corrections ∆A(Mg)NLTE–LTE in dwarfs, both solar metallicity and metal-poor, to be very small (of order 0.01 dex), even smaller than found in previous studies. In giants, corrections vary greatly between lines, but can be as large as 0.4 dex. Results of calculations in a large grid of 1D model atmospheres are presented, and the implications for studies of Mg discussed. The propagation of uncertainties in the inelastic collision data to those in stellar abundances is investigated, and found to lead to small uncertainties, once again typically less than 0.01 dex (2%), although for few stellar models in specific lines (e.g., metal-poor suns, in the 7691 Å line) uncertainties can be as large as 0.03 dex (7%).
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Coelho, Pedro Miguel Janeiro Duarte. "Environmental factors influencing the settlement of Diplodus spp. juveniles in temperate marine rocky shores." Master's thesis, Universidade de Évora, 2018. http://hdl.handle.net/10174/24400.
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Long-term monitoring programs can reveal trends emerging from yearly fluctuations that are difficult to evaluate in short-term studies. A 10-year study focused on four Diplodus species whose juveniles regularly use coastal reefs as nursery areas was performed in a recently classified Marine Protected Area (MPA). Differences in microhabitat use and a photographic guide for juvenile identification is provided. Environmental variables such as sea surface temperatures, air temperature, wave period and wind speed explain 53,4% of the interannual variation in juvenile abundances. A decreasing trend observed in juveniles from 2012-2017 was mirrored by adult fish landings in adjacent fishing ports, highlighting the importance of monitoring programs within MPA's for the management of species with commercial interest. Furthermore, the biogeographic transition between warm and cold temperate habitats along the Portuguese coast, enables the identification of sudden settlement pulses of warm water species in years with milder temperatures; Resumo:
Os programas de monitorização a longo prazo são importantes por permitirem destrinçar pequenas variações interanuais, impossíveis de verificar em estudos de curta duração. Este estudo de 10 anos realizou-se numa zona marinha rochosa normalmente usada como berçário por algumas espécies de Diplodus recente classificada como Área Marinha Protegida (AMP). Variáveis ambientais como a temperatura da água do mar (SST) e do ar, período da onda e velocidade do vento explicam 53,4% da variação interanual das suas abundâncias. De 2012 a 2017 as suas abundâncias têm sofrido um decréscimo acentuado, também observado nos desembarques da pesca comercial destas espécies em lota. Esta relação mostra a importância dos trabalhos de monitorização em AMP para a gestão de recursos pesqueiros. A localização biogeográfica da costa portuguesa, na transição entre águas temperadas quentes e frias, permite observar pulsos de recrutamento de espécies de águas mais quentes interrompidos por ciclos de águas mais frias.
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Somers, Garrett E. "Exploring Non-Standard Stellar Physics with Lithium Depletion." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468861662.
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Mayombo, Ntambwe Albert Serge. "Epiphytic diatom assemblages associated with South African kelps: Ecklonia maxima and Laminaria pallida." University of Western Cape, 2020. http://hdl.handle.net/11394/7717.
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Magister Scientiae (Biodiversity and Conservation Biology)Kelp forests are dynamic and productive ecosystems which host large biodiversity of sessile fauna and flora, including diatoms. These microalgae occur at the base of coastal marine food webs and contribute substantially to the productivity of marine ecosystems. Diatoms constitute one of the most common and species-rich groups of both phytoplankton and phytobenthos. Possessing a unique silica cell wall, diatoms play a key role in the global carbon and silicon cycles. As the changes in species composition of diatom communities are a direct reaction to the combination of environmental factors prevailing in their ecosystems, diatom analysis is widely and successfully used in biomonitoring of various environmental conditions and paleoecological reconstructions.
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Harju, J., F. Daniel, O. Sipilae, P. Caselli, J. E. Pineda, R. K. Friesen, A. Punanova, et al. "Deuteration of ammonia in the starless core Ophiuchus/H-MM1." EDP SCIENCES S A, 2017. http://hdl.handle.net/10150/624367.
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Context. Ammonia and its deuterated isotopologues probe physical conditions in dense molecular cloud cores. The time-dependence of deuterium fractionation and the relative abundances of different nuclear spin modifications are supposed to provide a means of determining the evolutionary stages of these objects. Aims. We aim to test the current understanding of spin-state chemistry of deuterated species by determining the abundances and spin ratios of NH2D, NHD2 and ND3 in a quiescent, dense cloud. Methods. Spectral lines of NH3, NH2D, NHD2, ND3 and N2D+ were observed towards a dense, starless core in Ophiuchus with the APEX, GBT and IRAM 30-m telescopes. The observations were interpreted using a gas-grain chemistry model combined with radiative transfer calculations. The chemistry model distinguishes between the different nuclear spin states of light hydrogen molecules, ammonia and their deuterated forms. Different desorption schemes can be considered. Results. High deuterium fractionation ratios with NH2D = NH3 similar to 0 : 4, NHD2 = NH2D similar to 0 : 2 and ND3 = NHD2 similar to 0 : 06 are found in the core. The observed ortho/para ratios of NH2D and NHD2 are close to the corresponding nuclear spin statistical weights. The chemistry model can approximately reproduce the observed abundances, but consistently predicts too low ortho/para-NH2D, and too large ortho/para-NHD2 ratios. The longevity of N2H+ and NH3 in dense gas, which is prerequisite to their strong deuteration, can be attributed to the chemical inertia of N-2 on grain surfaces. Conclusions. The discrepancies between the chemistry model and the observations are likely to be caused by the fact that the model assumes complete scrambling in principal gas-phase deuteration reactions of ammonia, which means that all the nuclei are mixed in reactive collisions. If, instead, these reactions occur through proton hop/hydrogen abstraction processes, statistical spin ratios are to be expected. The present results suggest that while the deuteration of ammonia changes with physical conditions and time, the nuclear spin ratios of ammonia isotopologues do not probe the evolutionary stage of a cloud.
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Watson, L. Scott. "Solar models including revised abundances and dark matter : constraints from helioseismology and neutrino observations." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491613.
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This thesis presents several topics in both standard and non-standard solar models using the Iben Stellar Evolution Code. First, a set of standard solar models are developed using the abundance determination of Grevesse & Noels (1993) and the more recent determination of Asplund et al. (2005a,b). This recent solar photospheric abundance analysis reduces the abundances of heavy elements, most notably C, N, 0, Ne and Ar, by 0.15 to 0.20 dex, lowering the solar Z/X to 0.0165, compared to the previous Grevesse & Noels value of Z/X = 0.0245. A comparison study between these models show evolutions based on newer determinations with reduced heavy-element abundances break the previously excellent agreement between the standard solar model and the helioseismic inferences of sound speed profile, convection zone base radius and surface Y abundance. Multiple approaches taken to reconcile the new abundances with helioseismology are discussed, and models with selective enhancements to diffusion given special attention. The results of all attempts provide an incomplete and unsatisfactory solution. Evolution, helioseismic and g-mode calculations were done in a separate study of nonstandard solar models for spin-dependent interactions with 5 - 20 GeV mass WIMPs in a parameter space loosely constrained by detection experiments. Results for models with 10-40 ::; (O''annV) ::; 10-27 cm3 s-l show that solar modelling can only constrain parameters for \VIMP background densities Px > 103 GeV cm-3 if their annihilation is dominated by scalar interactions; the case for neutralinos. For dark matter annihilating through vector interactions, such as scalar dark matter, the solar model can be used to place constraints on WHviP parameters at a background density of Px ,...., 0.3 GeVcm-3, which is predicted for the Sun.
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Neilson, Roy. "Trophic inter-relationships between soil invertebrates and plants investigated using stable isotope natural abundances." Thesis, University of Dundee, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327546.
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Hencheck, Michael. "Nucleosynthesis during the rapid hydrogen burning process and the abundances of 92Mo and 94Mo /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487856906261345.
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Gao, Xudong [Verfasser], and Karin [Akademischer Betreuer] Lind. "Low-mass Stellar Evolution Traced with Non-LTE Abundances / Xudong Gao ; Betreuer: Karin Lind." Heidelberg : Universitätsbibliothek Heidelberg, 2020. http://d-nb.info/120588386X/34.
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Chornock, R., E. Berger, D. Kasen, P. S. Cowperthwaite, M. Nicholl, V. A. Villar, K. D. Alexander, et al. "The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626063.
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We present a near-infrared spectral sequence of the electromagnetic counterpart to the binary neutron star merger GW170817 detected by Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)/Virgo. Our data set comprises seven epochs of J + H spectra taken with FLAMINGOS-2 on Gemini-South between 1.5 and 10.5 days after the merger. In the initial epoch, the spectrum is dominated by a smooth blue continuum due to a high-velocity, lanthanide-poor blue kilonova component. Starting the following night, all of the subsequent spectra instead show features that are similar to those predicted in model spectra of material with a high concentration of lanthanides, including spectral peaks near 1.07 and 1.55 mu m. Our fiducial model with 0.04 M-circle dot of ejecta, an ejection velocity of v = 0.1c, and a lanthanide concentration of X-lan = 10(-2) provides a good match to the spectra taken in the first five days, although it over-predicts the late-time fluxes. We also explore models with multiple fitting components, in each case finding that a significant abundance of lanthanide elements is necessary to match the broad spectral peaks that we observe starting at 2.5 days after the merger. These data provide direct evidence that binary neutron star mergers are significant production sites of even the heaviest r-process elements.
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Latour, M., P. Chayer, E. M. Green, A. Irrgang, and G. Fontaine. "Spectral analysis of four surprisingly similar hot hydrogen-rich subdwarf O stars." EDP SCIENCES S A, 2018. http://hdl.handle.net/10150/626530.
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Context. Post-extreme horizontal branch stars (post-EHB) are helium-shell burning objects evolving away from the EHB and contracting directly towards the white dwarf regime. While the stars forming the EHB have been extensively studied in the past, their hotter and more evolved progeny are not so well characterized. Aims. We perform a comprehensive spectroscopic analysis of four such bright sdO stars, namely Feige 34, Feige 67, AGK+81 degrees 266, and LS II + 18 degrees 9, among which the first three are used as standard stars for flux calibration. Our goal is to determine their atmospheric parameters, chemical properties, and evolutionary status to better understand this class of stars that are en route to become white dwarfs. Methods. We used non-local thermodynamic equilibrium model atmospheres in combination with high quality optical and UV spectra. Photometric data were also used to compute the spectroscopic distances of our stars and to characterize the companion responsible for the infrared excess of Feige 34. Results. The four bright sdO stars have very similar atmospheric parameters with T-eff between 60 000 and 63 000 K and log g (cm s(-2)) in the range 5.9 to 6.1. This places these objects right on the theoretical post-EHB evolutionary tracks. The UV spectra are dominated by strong iron and nickel lines and suggest abundances that are enriched with respect to those of the Sun by factors of 25 and 60. On the other hand, the lighter elements, C, N, O, Mg, Si, P, and S are depleted. The stars have very similar abundances, although AGK + 81 degrees 266 shows differences in its light element abundances. For instance, the helium abundance of this object is 10 times lower than that observed in the other three stars. All our stars show UV spectral lines that require additional line broadening that is consistent with a rotational velocity of about 25 km s(-1). The infrared excess of Feige 34 is well reproduced by a M0 main-sequence companion and the surface area ratio of the two stars suggests that the system is a physical binary. However, the lack of radial velocity variations points towards a low inclination and/or long orbital period. Spectroscopic and HIPPARCOS distances are in good agreement for our three brightest stars. Conclusions. We performed a spectroscopic analysis of four hot sdO stars that are very similar in terms of atmospheric parameters and chemical compositions. The rotation velocities of our stars are significantly higher than what is observed in their immediate progenitors on the EHB, suggesting that angular momentum may be conserved as the stars evolve away from the EHB.
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García, Pérez Ana E., Melissa Ness, Annie C. Robin, Inma Martinez-Valpuesta, Jennifer Sobeck, Gail Zasowski, Steven R. Majewski, et al. "The Bulge Metallicity Distribution from the APOGEE Survey." IOP PUBLISHING LTD, 2018. http://hdl.handle.net/10150/626538.
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The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides spectroscopic information of regions of the inner Milky Way, which are inaccessible to optical surveys. We present the first large study of the metallicity distribution of the innermost Galactic regions based on high-quality measurements for 7545 red giant stars within 4.5 kpc of the Galactic center, with the goal to shed light on the structure and origin of the Galactic bulge. Stellar metallicities are found, through multiple Gaussian decompositions, to be distributed in several components, which is indicative of the presence of various stellar populations such as the bar or the thin and the thick disks. Super-solar ([Fe/H] = +0.32) and solar ([Fe/H] = +0.00) metallicity components, tentatively associated with the thin disk and the Galactic bar, respectively, seem to be major contributors near the midplane. A solar-metallicity component extends outwards in the midplane but is not observed in the innermost regions. The central regions (within 3 kpc of the Galactic center) reveal, on the other hand, the presence of a significant metal-poor population ([Fe/H] = -0.46), tentatively associated with the thick disk, which becomes the dominant component far from the midplane (vertical bar Z vertical bar >= +0.75 kpc). Varying contributions from these different components produce a transition region at +0.5 kpc <= vertical bar Z vertical bar <= +1.0 kpc, characterized by a significant vertical metallicity gradient.
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Mulders, Gijs D., Ilaria Pascucci, Dániel Apai, Antonio Frasca, and Joanna Molenda-Żakowicz. "A SUPER-SOLAR METALLICITY FOR STARS WITH HOT ROCKY EXOPLANETS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622435.
Full textAbstract:
Host star metallicity provides a measure of the conditions in protoplanetary disks at the time of planet formation. Using a sample of over 20,000 Kepler stars with spectroscopic metallicities from the LAMOST survey, we explore how the exoplanet population depends on host star metallicity as a function of orbital period and planet size. We find that exoplanets with orbital periods less than 10 days are preferentially found around metal-rich stars ([Fe/H] similar or equal to 0.15 +/- 0.05 dex). The occurrence rates of these hot exoplanets increases to similar to 30% for super-solar metallicity stars from similar to 10% for stars with a sub-solar metallicity. Cooler exoplanets, which reside at longer orbital periods and constitute the bulk of the exoplanet population with an occurrence rate of greater than or similar to 90%, have host star metallicities consistent with solar. At short orbital periods, P < 10 days, the difference in host star metallicity is largest for hot rocky planets (< 1.7 R-circle plus), where the metallicity difference is [Fe/H] similar or equal to 0.25 +/- 0.07 dex. The excess of hot rocky planets around metal-rich stars implies they either share a formation mechanism with hot Jupiters, or trace a planet trap at the protoplanetary disk inner edge, which is metallicity dependent. We do not find statistically significant evidence for a previously identified trend that small planets toward the habitable zone are preferentially found around low-metallicity stars. Refuting or confirming this trend requires a larger sample of spectroscopic metallicities.