bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extremely metal-poor stars in dwarf galaxies
Authors: Frebel Anna , Simon Joshua D. , Kirby Evan , Geha Marla , Willman Beth 
Published: March 2010

AbstractWe present Keck/HIRES spectra of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way, Ursa Major II and Coma Berenices, and a Magellan/MIKE spectrum of a star in the classical dwarf spheroidal galaxy (dSph) Sculptor. Our data include the first high-resolution spectroscopic observations of extremely metal-poor stars ([Fe/H] < −3.0) not belonging to the Milky Way (MW) stellar halo field population. We obtain abundance measurements and upper limits for up to 26 elements between carbon and europium. The stars span a range of −3.8 < [Fe/H] < −2.3, with the ultra-faints having large spreads in Fe. A comparison with MW halo stars of similar metallicity reveals substantial agreement between the abundance patterns of the ultra-faint dwarf galaxies and Sculptor and the MW halo for the light, α and iron-peak elements (C to Zn). This agreement contrasts with the results of earlier studies of more metal-rich stars (−2.5 ≲[Fe/H]≲ −1.0) in more luminous dwarfs, which found significant abundance discrepancies with respect to the MW halo data. The abundances of neutron-capture elements (Sr to Eu) in all three galaxies are extremely low, consistent with the most metal-poor halo stars, but not with the typical halo abundance pattern at [Fe/H]≳ −3.0. Our results are broadly consistent with a galaxy formation model which predicts that massive dwarf galaxies are the source of the metal-rich component ([Fe/H]≳ −2.5) of the MW inner halo, but we propose that dwarf galaxies similar to the dSphs are the primary contributors to the metal-poor end of the metallicity distribution of the MW outer halo.
Feh-Duf: very high-velocity low-metallicity star with peculiar chemical abundance
Authors: Drake Natalia A. , Pereira Claudio B. 
Published: March 2010

AbstractWe present the results of a study of the very high velocity (υrad = +448.0 ± 1.0 kms−1) low-metallicity ([Fe/H] = −1.93) star Feh-Duf ((Fehrenbach & Duflot 1981) showing peculiar chemical abundance. Using high-resolution spectrum, we showed that this star has enhanced carbon and heavy s-process element abundance ([C/Fe] = +0.58, [hs/Fe] = +0.88 dex) while the [Y/Fe] = −0.07 dex). The carbon isotopic ratio is low (12C/13C=8). We found that oxygen abundance is reduced ([O/Fe] = +0.10 dex) as compared with Galactic field stars of a similar metallicity. The evolution state of this star and its possible extragalactic origin are discussed.
Chemical evolution models for local group dwarf spheroidal galaxies: the evolution of Fe-peak elements
Authors: Lanfranchi Gustavo A. , Matteucci Francesca , Cescutti Gabriele 
Published: March 2010

AbstractThe evolution of Fe-peak elements of several Local Group Dwarf Spheroidal Galaxies are discussed based on the comparison between a chemical evolution model and obsevations. In our scenario, the evolution of these galaxies are mainly controlled by a low star formation efficiency coupled with very intense galactic winds. The low star formation rate gives rise to the observed low metallicities and to [alpha/Fe] and [s/Fe] ratios below solar, whereas the intense galactic winds are responsible for the sharp decrease observed in several abundance ratios. The shape of the stellar metallicity distributions are defined by both parameters and the observed data cannot be reproduced without evoking galactic winds. The same scenario applied to a standard model fits very well several Fe-peak elements, with different nucleosynthesis prescriptions for each set of elements.
The Effect of the Corotation on the Radial Gradient of Metallicity of Spiral Galaxies
Authors: Scarano Sergio , Lépine Jacques R. D. 
Published: March 2010

AbstractThe corotation radius in a spiral galaxy is the place where the spiral pattern speed has the same velocity of the rotation curve. By compiling results coming from the literature for 20 spiral galaxies we verified a strong correlation between the radius of the minima or inflections of the metallicity distribution and the corotation radius.
Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars from SDSS DR7
Authors: Carollo D. , Beers T. C. , Chiba M. , Norris J. E. , Freeman K. C. , Lee Y. S. 
Published: March 2010

AbstractThe structure and kinematics of the recognized stellar components of the Milky Way are explored, based on well-determined atmospheric parameters and kinematic quantities for 32360 “calibration stars” from the Sloan Digital Sky Survey (SDSS) and its first extension, (SDSS-II), which included the sub-survey SEGUE: Sloan Extension for Galactic Understanding and Exploration. Full space motions for a sub-sample of 16920 stars, exploring a local volume within 4 kpc of the Sun, are used to derive velocity ellipsoids for the inner- and outer-halo components of the Galaxy, as well as for the canonical thick-disk and proposed metal-weak thick-disk populations. This new sample of calibration stars represents an increase of 60% relative to the numbers used in a previous analysis. A Maximum Likelihood analysis of a local sub-sample of 16920 calibration stars has been developed in order to extract kinematic information for the major Galactic components (thick disk, inner halo, and outer halo), as well as for the elusive metal-weak thick disk (MWTD). We measure velocity ellipsoids for the thick disk, the MWTD, the inner halo, and the outer halo, demonstrate that the MWTD may be a component that is kinematically and chemically independent of the canonical thick disk (and put limits on the metallicity range of the MWTD), and derive the inferred spatial density profiles of the inner/outer halo components. We also present evidence for tilts in the velocity ellipsoids for stars in our sample as a function of height above the plane, for several ranges in metallicity, and confirm the shift of the observed metallicity distribution function (MDF) from the inner-halo to the outer-halo dominated sample.
CNO abundances in the Galactic bulge
Authors: Ryde Nils A. E. 
Published: March 2010

AbstractThe carbon, nitrogen, and oxygen abundances and trends in the bulge are discussed in the context of our recent analysis of these elements in an on-going project based on near-IR spectra (Rydeet al. 2009). We obtained these using the CRIRES spectrometer on the VLT. The formation and evolution of the Milky Way bulge can be constrained by studying elemental abundances of bulge stars. Due to the large and variable visual extinction in the line-of-sight towards the bulge, an analysis in the near-IR is preferred.
Planetary nebulae and star formation history in the Galactic disk and bulge
Authors: Milanova Yulia , Kholtygin Alexander 
Published: March 2010

AbstractThe modern observations of the planetary nebulae (PNe) were used to create a new catalogue of He, C, N, O, Ne, S and some other element abundances for more than 300 Galactic and extragalactic PNe. This catalogue was a start point for studying the star formation history in the Galactic disk. We have found that He, C, N and O abundances in the thin disk PNe are very close to those in bulge PNe. We also established that the abundances of the same elements in the PNe belonging the halo of the Milky Way and the Magellanic Clouds are similar. We have estimated the mean ages of the progenitors of PNe in the thin and thick disks and in the bulge. The evidences in the favor of the suggestion that the formation of the intermediate-mass star began in bulge and only then continued in the thin disk were found.
Chemo-dynamical simulations of galaxies
Authors: Kobayashi Chiaki 
Published: March 2010

AbstractWe simulate the formation and evolution of galaxies with a self-consistent 3D hydrodynamical model including star formation, supernova feedback, and chemical enrichment. Hypernova feedback plays an essential role not only in solving the [Zn/Fe] problem, but also reproducing the cosmic star formation rate history and the mass-metallicity relations. In the Milky-Way type galaxy, the star formation history, and thus the kinematics and chemical abundances are different in bulge, disk, and thick disk.
Metal-poor globular clusters of the galactic bulge
Authors: Barbuy B. , Ortolani S. , Zoccali M. , Hill V. , Minniti D. , Bica E. , Renzini A. , Gómez A. 
Published: March 2010

AbstractVery few abundance analyses of individual stars in metal-poor globular clusters in the galactic bulge are available. The main purpose of this study is to derive abundances in individual stars of such clusters, in order to establish their abundance pattern, trying to characterize the oldest bulge stellar populations.
Abundance distribution functions for nearby late-type dwarfs
Authors: Bragança Gustavo A. , Rocha-Pinto Helio J. , de Mello Gustavo F. Porto , Rangel Rafael H. O. , Maciel Walter J. 
Published: March 2010

AbstractA major role to the understanding of the chemical evolution of the Galaxy is played by studies of stellar chemical abundance distribution. In the last years, there has been an increase in the number of spectroscopic surveys of late-type stars. Classical problems on the chemical evolution of the Galaxy, such as the G dwarf problem and the age-metallicity relation, can be reinvestigated with better accuracy. We present a chemical abundance survey of 325 solar neighborhood G dwarfs stars situated within 25 pc from the Sun. We reinvestigate classical observational constraints, namely the metallicity distribution, using a number of chemical elements (Na, Si, Ca, Ni, Fe and Ba) as metallicity indicators. The abundance probability density function for each of the surveyed element was derived using a Gaussian kernel estimator. We have found mean values of −0.11, −0.14, −0.07, −0.05, −0.16 and −0.12 dex for the [Fe/H], [Na/H], [Si/H], [Ca/H], [Ni/H] and [Ba/H] pdfs, respectively. We also show that abundance distributions having higher mean values have smaller dispersion, in contradiction to the predictions of the Simple Model with Delayed Production. We discuss this result in the context and present an alternate explanation for this pattern.
Planetary nebulae in the inner Milky Way
Authors: Cavichia Oscar , Costa Roberto D. D. , Maciel Walter J. 
Published: March 2010

AbstractNew abundances of planetary nebulae located towards the bulge of the Galaxy are derived based on observations made at LNA (Brazil). We present accurate abundances of the elements He, N, S, O, Ar, and Ne for 56 PNe located towards the galactic bulge. The data shows a good agreement with other results in the literature, in the sense that the distribution of the abundances is similar to those works. From the statistical analysis performed, we can suggest a bulge-disk interface at 2.2 kpc for the intermediate mass population, marking therefore the outer border of the bulge and inner border of the disk.
Quantitative Spectral Analysis of hot Post-AGB Stars
Authors: Costa-Mello Daniel R. , Daflon Simone , Pereira Claudio B. 
Published: March 2010

AbstractPost-AGB (PAGB) stars are luminous objects of low and intermediate mass in a final and short stage of evolution in the transition between AGB stars and planetary nebulae (PNe). In this work we present a quantitative spectral analysis of some hot PAGBs based on high resolution spectra. The stellar parameters and chemical composition were obtained from the synthesis of non-LTE spectra.
Sulfur Abundances in Orion B Stars
Authors: Daflon Simone , Cunha Katia , de la Reza Ramiro , Holtzman Jon , Chiappini Cristina 
Published: March 2010

AbstractSulfur abundances are derived for a sample of ten B MS star members of the Orion association. The analysis is based on LTE model atmospheres and non-LTE line formation theory by means of spectrum synthesis analysis of Sii and Siii lines. The abundance distribution obtained for the Orion targets is homogeneous within the errors in the analysis: A(S)=7.15±0.05. This abundance result is in agreement with the solar value and with results for the Orion nebula. The sulfur abundances for Orion combined with previous results for other OB-type stars produce a relatively shallow sulfur abundance gradient with a slope of −0.037±0.012 dex Kpc−1.
Chemical Analysis of B stars within 9–11 kpc from the Galactic Center
Authors: Herencia Maria Isela Zevallos , Daflon Simone 
Published: March 2010

AbstractRadial gradients of metallicity are supported by observations of different young objects in the Galactic thin disk. The shape of the abundance distributions, however, is not completely constrained. Some works describe the abundance distributions as a function of the Galactocentric distance RG by linear fits with a single slope. On the other hand some analyses of open clusters, cepheids and OB stars suggest a discontinuity in the abundance distributions around RG=10 kpc. In this work we analyse a sample of 13 B stars members of four open clusters located within RG=9-11 kpc in order to better constrain the chemical distribution in this region of the disk.
Uncovering the Evolutionary Sequences for the C-J Stars Based on their Chemical Abundances
Authors: de Mello Ana Beatriz , Lorenz-Martins Silvia 
Published: March 2010

AbstractWe present chemical abundances obtained by fitting synthetic spectra to the FEROS data of 12 C-J stars, normal and silicate carbon one. The Li and 13C abundance, as well as the s-process elements abundance indicates no evidence of a diferent mechanism of formation between the two kinds of C-J stars. We also studied the α elements, and that suggests a scenario that put the carbon C-R stars as a possible progenitor of the beither C-J stars. We made also available a study of the radial velocity of some stars of the sample calculated at different epochs. That allowed us to make some discussion about the probable binary system of some silicon C-J carbon stars. Based on these abundances and radial velocities, we discuss possible evolutive sequences for the C-J.
Investigation of ancient substructures in the Milky Way: chemical composition study
Authors: Stonkutė Edita , Nordström Birgitta , Tautvaišienė Gražina 
Published: March 2010

AbstractFrom high resolution spectra taken with the spectrograph FIES on the Nordic Optical Telescope, La Palma, we measure abundances of oxygen and α-elements in order to characterize stars which from their dynamical properties are suspected to have originated in disrupted satellites. We find that the chemical composition of investigated stars is homogeneous and distinct from Galactic disk dwarfs, which is providing further evidence of their extragalactic origin.
Investigation of the chemical structure of our Galaxy using radial pulsating stars as tracers
Authors: Suran Marian Doru 
Published: March 2010

AbstractIn this paper we try to determine the properties of different galactic components (2 < r < 12kpc) using radial pulsating stars (RPS stars) as tracers. For RPS stars in Galaxy we use a quasi-seismological inversion method (Post Theoretical Mass Method, PTM) which allows us to determine the mass M and the abundance Z for each star. Based on PTM method and using RPS stars as tracers we could determine the chemical structure and evolution of the Galaxy: abundance gradients and segregation between different evolutionary populations. This method is planned to be extended further using the RPS star observed by the KEPLER space mission.
Superbubble Hii regions: how self-enriched should they be?
Authors: Wofford Aida 
Published: March 2010

AbstractI modeled the pollution of low metallicity (Z=0.001) superbubble Hii regions with the ejecta from single stellar populations of 104−106M⊙ in mass. I found that the He, C, N, and O abundance enhancements in the Hii regions, due to pollution with the enriched winds from Wolf-Rayet stars, are insignificant at 5Myr. The few localized metal enhancements observed so far in resolved extragalactic Hii regions are not associated with superbubbles and remain to be modeled in detail.
Metallicity and Planet Formation: Models
Authors: Boss Alan P. 
Published: March 2010

AbstractPlanets typically are considerably more metal-rich than even the most metal-rich stars, one indication that planet formation must differ greatly from star formation. There is general agreement that terrestrial planets form by the collisional accumulation of solids composed of heavy elements in the inner regions of protoplanetary disks. Two competing mechanisms exist for the formation of giant planets, core accretion and disk instability, though hybrid combinations are possible as well. In core accretion, a higher metallicity in the protoplanetary disk leads directly to larger core masses and hence to more gas giant planets. Given the strong correlation of gas giant planets detected by Doppler spectroscopy with stellar metallicity, this has often been taken as proof that core accretion is the mechanism that forms giant planets. Recent work, however, implies that the formation of gas giants by disk instability can be enhanced by higher metallicities, though not as dramatically as for core accretion. In both scenarios, the ongoing accretion of planetesimals by gas giant protoplanets leads to strong enrichments of heavy elements in their gaseous envelopes. Both scenarios also imply that gas giant planets should have significant solid cores, raising questions for gas giant interior models without cores. Exoplanets with large inferred core masses seem likely to have formed by core accretion, while gas giants at distances beyond 20 AU seem more likely to have formed by disk instability. Given the wide variety of exoplanets found to date, it appears that both mechanisms are needed to explain the formation of the known population of giant planets.
The Diversity of Extrasolar Terrestrial Planets
Authors: Bond Jade C. , Lauretta Dante S. , O'Brien David P. 
Published: March 2010

AbstractExtrasolar planetary host stars are enriched in key planet-building elements. These enrichments have the potential to drastically alter the building blocks available for terrestrial planet formation. Here we report on the combination of dynamical models of late-stage terrestrial planet formation within known extrasolar planetary systems with chemical equilibrium models of the composition of solid material within the disk. This allows us to constrain the bulk elemental composition of extrasolar terrestrial planets. A wide variety of resulting planetary compositions exist, ranging from those that are essentially “Earth-like”, containing metallic Fe and Mg-silicates, to those that are dominated by graphite and SiC. This implies that a diverse range of terrestrial planets are likely to exist within extrasolar planetary systems.
Metallicity and Planet Formation – Observations
Authors: Valenti Jeff A. 
Published: March 2010

AbstractEarly abundance measurements established that stars known to host giant planets are metal rich compared to the Sun. More extensive abundance measurements then showed that giant planet hosts are metal rich compared to the parent sample in planet searches. Stars spanning a range of convection zone depths all show the same metallicity effect, ruling out significant abundance enhancements due to selective accretion. Most known planets migrated inwards from the snow line, but subsamples closer to and further from the star have similar iron abundances, so the stopping point of migration does not depend on metallicity. Stars recently discovered to host Neptune mass planets may be metal poor compared to the Sun, particularly if one focusses on stars that do not also host higher mass planets. This would be consistent with core-accretion models of planet formation. Before drawing physical conclusions, it will be necessary to check for metallicity bias in the subsample of stars around which Neptune mass planets could have been found. M dwarf abundances are currently too uncertain to relate planet frequency and host star metallicity, due mainly to missing or incorrect molecular line data.
A New Spin on Red Giant Rapid Rotators: Evidence for Chemical Exchange Between Planets and Evolved Stars
Authors: Carlberg Joleen K. , Majewski Steven R. , Smith Verne V. , Cunha Katia , Patterson Richard J. , Bizyaev Dmitry , Arras Phil , Rood Robert T. 
Published: March 2010

AbstractRapid rotation in red giant stars may be one signature of the past engulfment of a planetary companion. Models of the future tidal interaction of known exoplanet host stars with their planets show that many of these stars will accrete one or more of their planets, and the orbital angular momentum of these accreted planets is sometimes sufficient to spin up the host stars to a level commonly accepted as “rapid rotation” for giant stars. Planets accreted during the red giant phase should leave behind a chemical signature in the form of unusual abundance patterns in the host red giant's atmosphere. Proposed signatures of planet accretion include the enhancement of Li and 12C; both species are generally depleted in giant star atmospheres by convection but could be replenished by planet accretion. Moreover, accreted planets may preferentially enhance the stellar abundance of refractory elements assuming that the refractory nature of these elements leads to their relative enhancements in the planets themselves. Here we present preliminary results of a search for these predicted chemical signatures through high resolution spectroscopic abundance analysis of both rapidly rotating giant stars (i.e., stars with a higher probability of having experienced planet accretion) and normally rotating giant stars. We find that the rapid rotators are enhanced in Li relative to the slow rotators — a result consistent with Li replenishment through planet absorption.
Planetary populations according to the orbital angular momentum
Authors: Amarante João A. S. , Rocha-Pinto Helio J. 
Published: March 2010

AbstractWe investigate the angular momentum distribution of known exoplanetary systems, as a function of the planetary mass, orbital semimajor axis and metallicity of the host star. We find exoplanets seems to be classified according to at least two ‘populations’, with respect to their angular momentum properties. This classification is independent on the composition of the planet and seems to be valid for both jovian and neptunian planets, and probably can be extrapolated to the terrestrial planets of the Solar System. We analyse these ‘populations’ considering the phenomenon of planetary migration.
Lithium abundance as a boundary condition for age and mass determination of solar twin stars
Authors: Castro M. , do Nascimento J.-D. , da Costa J. S. , Meléndez J. , Bazot M. , Théado S. , de Mello G. F. Porto , De Medeiros J. R. 
Published: March 2010

AbstractWe explore the non-standard mixing history of five solar twins to determine as precisely as possible their mass and age. For this, we computed a grid of evolutionary models with non-standard mixing at given metallicities with the Toulouse-Geneva code for a range of stellar masses. We choose the evolutionary model that best fit the low lithium abundances observed in the solar twins. Our best model for each solar twin provides a mass and age solution constrained by their Li content and Teff determination. Li depletion due to the additional mixing in solar-twins is strongly mass dependent. An accurate lithium abundance measurement connected with non-standard models provides a more precise information about the age and mass better than that determined only by classical methods.
Distribution of refractory and volatile elements in CoRoT planet host stars
Authors: Chavero C. , de la Reza R. , Domingos R. C. , Drake N. A. , Pereira C. B. , Winter O. C. 
Published: March 2010

AbstractWe report on preliminary results of spectroscopic determination of the atmospheric parameters and chemical abundances of the parent stars of the recently discovered transiting planets CoRoT-2b and CoRoT-4b. We found a flat distribution of the relative abundances as a function of their condensation temperatures. Also, we introduce a new methodology to investigate a relation between the abundances of these stars and the internal migration of their planets.