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Anna Frebel - One of the best experts on this subject based on the ideXlab platform.
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The Hobby-Eberly Telescope Chemical Abundances of Stars in the Halo CASH Project I. Observations of the First Year
2020Co-Authors: Frank N. Bash, Anna Frebel, Justyn R. Maund, Juntai Shen, M. H. Siegel, C. Allende Prieto, Ian U. Roederer, Matthew D. Shetrone, J. Rhee, Christopher SnedenAbstract:We present preliminary results obtained from the first year of observations of a new, long-term project of the University of Texas, the HobbyEberly Telescope Chemical Abundances of Stars in the Halo (CASH ) Project.
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jinabase a database for Chemical Abundances of metal poor stars
Astrophysical Journal Supplement Series, 2018Co-Authors: Abdu Abohalima, Anna FrebelAbstract:Reconstructing the Chemical evolution of the Milky Way is crucial for understanding the formation of stars, planets, and galaxies throughout cosmic time. Different studies associated with element production in the early universe and how elements are incorporated into gas and stars are necessary to piece together how the elements evolved. These include establishing Chemical abundance trends, as set by metal-poor stars, comparing nucleosynthesis yield predictions with stellar abundance data, and theoretical modeling of Chemical evolution. To aid these studies, we have collected Chemical abundance measurements and other information such as stellar parameters, coordinates, magnitudes, and radial velocities, for extremely metal-poor stars from the literature. The database, JINAbase, contains 1658 unique stars, 60% of which have [Fe/H]<2.5. This information is stored in an SQL database, together with a user-friendly queryable web application (this http URL). Objects with unique Chemical element signatures (e.g., r-process stars, s-process and CEMP stars) are labeled or can be classified as such. The web application enables fast selection of customized comparison samples from the literature for the aforementioned studies and many more. Using the multiple entries for three of the most well studied metal-poor stars, we evaluate systematic uncertainties of Chemical Abundances measurements. We provide a brief guide on the selection of Chemical elements for model comparisons for non- spectroscopists who wish to learn about metal-poor stars and the details of Chemical Abundances measurements.
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the r process alliance Chemical Abundances for a trio of r process enhanced stars one strong one moderate and one mild
The Astrophysical Journal, 2018Co-Authors: Madelyn Cain, Anna Frebel, Timothy C Beers, Maude Gull, Alexander P Ji, Vinicius M Placco, Jorge MelendezAbstract:We present detailed Chemical Abundances of three new bright (V ~ 11), extremely metal-poor ([Fe/H] ~ -3.0), r-process-enhanced halo red giants based on high-resolution, high-S/N Magellan/MIKE spectra. We measured Abundances for 20-25 neutron-capture elements in each of our stars. J1432-4125 is among the most r-process rich r-II stars, with [Eu/Fe]= +1.44+-0.11. J2005-3057 is an r-I star with [Eu/Fe] = +0.94+-0.07. J0858-0809 has [Eu/Fe] = +0.23+-0.05 and exhibits a carbon abundance corrected for evolutionary status of [C/Fe]_corr = +0.76, thus adding to the small number of known carbon-enhanced r-process stars. All three stars show remarkable agreement with the scaled solar r-process pattern for elements above Ba, consistent with enrichment of the birth gas cloud by a neutron star merger. The Abundances for Sr, Y, and Zr, however, deviate from the scaled solar pattern. This indicates that more than one distinct r-process site might be responsible for the observed neutron-capture element abundance pattern. Thorium was detected in J1432-4125 and J2005-3057. Age estimates for J1432-4125 and J2005-3057 were adopted from one of two sets of initial production ratios each by assuming the stars are old. This yielded individual ages of 12+-6 Gyr and 10+-6 Gyr, respectively.
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the Chemical Abundances of stars in the halo cash project ii a sample of 14 extremely metal poor stars
The Astrophysical Journal, 2011Co-Authors: Julie K Hollek, Anna Frebel, Ian U. Roederer, Matthew D. Shetrone, Christopher Sneden, Timothy C Beers, Sungju Kang, Christopher ThomAbstract:We present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The Abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R {approx}15, 000) and corresponding high-resolution (R {approx}35, 000) Magellan Inamori Kyocera Echelle spectra. The stars span a metallicity range from [Fe/H] from -2.9 to -3.9, including four new stars with [Fe/H] < -3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]< - 3. We also find four neutron-capture-enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H] {approx}< -3.0) of the brightest stars included in CASH and are used to calibrate a newly developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire {approx}500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manualmore » analysis from a high-resolution spectrum.« less
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the Chemical Abundances of stars in the halo cash project ii a sample of 16 extremely metal poor stars
arXiv: Astrophysics of Galaxies, 2011Co-Authors: Julie K Hollek, Anna Frebel, Ian U. Roederer, Matthew D. Shetrone, Christopher Sneden, Timothy C Beers, Sungju Kang, Christopher ThomAbstract:We present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The Abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R~15,000) and corresponding high-resolution (R~35,000) Magellan MIKE spectra. The stars span a metallicity range from [Fe/H] from -2.9 to -3.9, including four new stars with [Fe/H]<-3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]<-3. We also find four neutron-capture enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H]<-3.0) of the brightest stars included in CASH and are used to calibrate a newly-developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire ~500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manual analysis from a high-resolution spectrum.
Matthew D. Shetrone - One of the best experts on this subject based on the ideXlab platform.
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The Hobby-Eberly Telescope Chemical Abundances of Stars in the Halo CASH Project I. Observations of the First Year
2020Co-Authors: Frank N. Bash, Anna Frebel, Justyn R. Maund, Juntai Shen, M. H. Siegel, C. Allende Prieto, Ian U. Roederer, Matthew D. Shetrone, J. Rhee, Christopher SnedenAbstract:We present preliminary results obtained from the first year of observations of a new, long-term project of the University of Texas, the HobbyEberly Telescope Chemical Abundances of Stars in the Halo (CASH ) Project.
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apogee Chemical Abundances of the sagittarius dwarf galaxy
The Astrophysical Journal, 2017Co-Authors: Sten Hasselquist, Verne V. Smith, Jon A Holtzman, Matthew D. Shetrone, Andrew Mcwilliam, J G Fernandeztrincado, Timothy C Beers, Steven R Majewski, David L Nidever, B TangAbstract:The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides the opportunity to measure elemental Abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze the Chemical abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed Chemical Abundances and the first time C, N, P, K, V, Cr, Co, and Ni have been studied at high-resolution in this galaxy. We find that the Sgr stars with [Fe/H] $\gtrsim$ -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light IMF, one lacking the most massive stars that would normally pollute the ISM with the hydrostatic elements. We use a simple Chemical evolution model, flexCE to further backup our claim and conclude that recent stellar generations of Fornax and the LMC could also have formed according to a top-light IMF.
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two groups of red giants with distinct Chemical Abundances in the bulge globular cluster ngc 6553 through the eyes of apogee
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: B Tang, R. Carrera, Ricardo P Schiavon, D A Garciahernandez, Roger E Cohen, S Villanova, Steven R Majewski, D Geisler, O Zamora, Matthew D. ShetroneAbstract:Multiple populations revealed in globular clusters (GCs) are important windows to the formation and evolution of these stellar systems. The metal-rich GCs in the Galactic bulge are an indispensable part of this picture, but the high optical extinction in this region has prevented extensive research. In this work, we use the high-resolution near-infrared (NIR) spectroscopic data from Apache Point Observatory Galactic Evolution Experiment (APOGEE) to study the Chemical Abundances of NGC 6553, which is one of the most metal-rich bulge GCs. We identify 10 red giants as cluster members using their positions, radial velocities, iron Abundances, and NIR photometry. Our sample stars show a mean radial velocity of −0.14 ± 5.47 km s−1, and a mean [Fe/H] of −0.15 ± 0.05. We clearly separate two populations of stars in C and N in this GC for the first time. NGC 6553 is the most metal-rich GC where the multiple stellar population phenomenon is found until now. Substantial Chemical variations are also found in Na, O, and Al. However, the two populations show similar Si, Ca, and iron-peak element Abundances. Therefore, we infer that the CNO, NeNa, and MgAl cycles have been activated, but the MgAl cycle is too weak to show its effect on Mg. Type Ia and Type II supernovae do not seem to have significantly polluted the second generation stars. Comparing with other GC studies, NGC 6553 shows similar Chemical variations as other relatively metal-rich GCs. We also confront current GC formation theories with our results, and suggest possible avenues for improvement in the models.
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Chemical Abundances in the globular clusters ngc 5024 and ngc 5466 from optical and infrared spectroscopy
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: Matthew D. Shetrone, M P Lamb, K Venn, Charli M Sakari, B J PritzlAbstract:Detailed Chemical Abundances for ve stars in two Galactic globular clusters, NGC 5466 and NGC 5024, are presented from high resolution optical (from the HobbyEberley Telescope) and infrared spectra (from the SDSS-III APOGEE survey). We nd [Fe/H] = -1.97 0.13 dex for NGC 5466, and [Fe/H] = -2.06 0.13 dex for NGC 5024, and the typical abundance pattern for globular clusters for the remaining elements, e.g., both show evidence for mixing in their light element abundance ratios (C, N), and AGB contributions in their heavy element Abundances (Y, Ba, and Eu). These clusters were selected to examine Chemical trends that may correlate them with the Sgr dwarf galaxy remnant, but at these low metallicities no obvious dierences from the Galactic abundance pattern are found. Regardless, we compare our results from the optical and infrared analyses to nd that oxygen and silicon Abundances determined from the infrared spectral lines are in better agreement with the other alpha-element ratios and with smaller random errors.
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Chemical Abundances in field red giants from high resolution h band spectra using the apogee spectral linelist
The Astrophysical Journal, 2013Co-Authors: Verne V. Smith, Katia Cunha, Carlos Allende Prieto, Matthew D. Shetrone, Ricardo P Schiavon, Szabolcs Meszaros, Steven R Majewski, Dmitry Bizyaev, Ana Garcia E Perez, Jon A HoltzmanAbstract:High-resolution H-band spectra of five bright field K, M, and MS giants, obtained from the archives of the Kitt Peak National Observatory Fourier transform spectrometer, are analyzed to determine Chemical Abundances of 16 elements. The Abundances were derived via spectrum synthesis using the detailed linelist prepared for the Sloan Digital Sky Survey III Apache Point Galactic Evolution Experiment (APOGEE), which is a high-resolution near-infrared spectroscopic survey to derive detailed Chemical abundance distributions and precise radial velocities for 100,000 red giants sampling all Galactic stellar populations. The red giant sample studied here was chosen to probe which Chemical elements can be derived reliably from the H-band APOGEE spectral region. These red giants consist of two K-giants (α Boo and μ Leo), two M-giants (β And and δ Oph), and one thermally pulsing asymptotic giant branch (TP-AGB) star of spectral type MS (HD 199799). Measured Chemical Abundances include the cosmoChemically important isotopes 12C, 13C, 14N, and 16O, along with Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The K and M giants exhibit the abundance signature of the first dredge-up of CN-cycle material, while the TP-AGB star shows clear evidence of the addition of 12C synthesized during 4He-burning thermal pulses and subsequent third dredge-up. A comparison of the Abundances derived here with published values for these stars reveals consistent results to ~0.1 dex. The APOGEE spectral region and linelist is thus well suited for probing both Galactic Chemical evolution, as well as internal nucleosynthesis and mixing in populations of red giants via high-resolution spectroscopy.
R. Carrera - One of the best experts on this subject based on the ideXlab platform.
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The OCCASO Survey: Open Clusters Chemical Abundances from Spanish Observatories
Eas Publications Series, 2020Co-Authors: L. Casamiquela, R. Carrera, Carme Jordi, L. Balaguer-núñezAbstract:Stellar clusters are crucial in the study of a variety of topics including the star formation process, stellar nucleosynthesis and evolution, dynamical interaction among stars, or the assembly and evolution of galaxies. In particular, Open Clusters (OCs) have been widely used to constrain the formation and evolution of the Milky Way disc. They provide information about the Chemical patterns and the existence of radial and vertical gradients or an age-metallicity relation. However, all these investigations are hampered by the fact that only a small fraction of clusters have been studied homogeneously. Galactic surveys performed from the ground such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE), the Gaia-ESO Survey (GES), or the GALactic Archaeology with HERMES (GALAH) include OCs among their targets. OCs are also sampled from the space by the Gaia and Kepler missions.The OCCASO goal is to derive Abundances for more than 20 Chemical species in at least 6 Red Clump stars in ∼30 Northern hemisphere OCs. In order to ensure the reliability of the derived Chemical Abundances, these are derived using different analysis techniques similar to what is being performed by GES.One of the OCCASO requirements is the homogeneity between instruments, methods and model atmospheres used, and in the same scale than the GES-UVES Abundances. For this reason we are performing different tests checking internal and external consistency. Derived stellar atmosphere parameters and Fe Abundances will be published in the first data release scheduled for the first semester of 2015.The online pdf of the poster with first results is available at https://gaia.ub.edu/Twiki/pub/GREATITNFC/ProgramFinalconference/poster_OCCASO.pdf.
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two groups of red giants with distinct Chemical Abundances in the bulge globular cluster ngc 6553 through the eyes of apogee
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: B Tang, R. Carrera, Ricardo P Schiavon, D A Garciahernandez, Roger E Cohen, S Villanova, Steven R Majewski, D Geisler, O Zamora, Matthew D. ShetroneAbstract:Multiple populations revealed in globular clusters (GCs) are important windows to the formation and evolution of these stellar systems. The metal-rich GCs in the Galactic bulge are an indispensable part of this picture, but the high optical extinction in this region has prevented extensive research. In this work, we use the high-resolution near-infrared (NIR) spectroscopic data from Apache Point Observatory Galactic Evolution Experiment (APOGEE) to study the Chemical Abundances of NGC 6553, which is one of the most metal-rich bulge GCs. We identify 10 red giants as cluster members using their positions, radial velocities, iron Abundances, and NIR photometry. Our sample stars show a mean radial velocity of −0.14 ± 5.47 km s−1, and a mean [Fe/H] of −0.15 ± 0.05. We clearly separate two populations of stars in C and N in this GC for the first time. NGC 6553 is the most metal-rich GC where the multiple stellar population phenomenon is found until now. Substantial Chemical variations are also found in Na, O, and Al. However, the two populations show similar Si, Ca, and iron-peak element Abundances. Therefore, we infer that the CNO, NeNa, and MgAl cycles have been activated, but the MgAl cycle is too weak to show its effect on Mg. Type Ia and Type II supernovae do not seem to have significantly polluted the second generation stars. Comparing with other GC studies, NGC 6553 shows similar Chemical variations as other relatively metal-rich GCs. We also confront current GC formation theories with our results, and suggest possible avenues for improvement in the models.
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The Open Cluster Chemical Abundances from Spanish Observatories survey (OCCASO)
2015Co-Authors: R. Carrera, L. Casamiquela, L. Balaguer-núñez, Carme Jordi, Elena Pancino, C. Allende-prieto, S. Blanco-cuaresma, C. E. Martínez-vázquez, S. Murabito, A. Del PinoAbstract:We present the motivation, design and current status of the Open Cluster Chemical Abundances from Spanish Observatories survey (OCCASO). Using the high resolution spectroscopic facilities available at Spanish observatories, OCCASO will derive Chemical Abundances in a sample of 20 to 25 OCs older than 0.5 Gyr. This sample will be used to study in detail the formation and evolution of the Galactic disc using OCs as tracers.
P. Jofre - One of the best experts on this subject based on the ideXlab platform.
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How much can we trust high-resolution spectroscopic stellar Chemical Abundances?
arXiv: Solar and Stellar Astrophysics, 2016Co-Authors: S. Blanco-cuaresma, L. Casamiquela, Thomas Nordlander, U. Heiter, P. Jofre, Thomas Masseron, Hugo M. Tabernero, Shruthi S. Bhat, Andrew R. Casey, J. MelendezAbstract:To study stellar populations, it is common to combine Chemical Abundances from different spectroscopic surveys/studies where different setups were used. These inhomogeneities can lead us to inaccurate scientific conclusions. In this work, we studied one aspect of the problem: When deriving Chemical Abundances from high-resolution stellar spectra, what differences originate from the use of different radiative transfer codes?
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iSpec: Stellar atmospheric parameters and Chemical Abundances
2014Co-Authors: S. Blanco-cuaresma, U. Heiter, C. Soubiran, P. JofreAbstract:iSpec is an integrated software framework written in Python for the treatment and analysis of stellar spectra and Abundances. Spectra treatment functions include cosmic rays removal, continuum normalization, resolution degradation, and telluric lines identification. It can also perform radial velocity determination and correction and resampling. iSpec can also determine atmospheric parameters (i.e effective temperature, surface gravity, metallicity, micro/macroturbulence, rotation) and individual Chemical Abundances by using either the synthetic spectra fitting technique or equivalent widths method. The synthesis is performed with SPECTRUM (ascl:9910.002).
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determining stellar atmospheric parameters and Chemical Abundances of fgk stars with ispec
Astronomy and Astrophysics, 2014Co-Authors: S Blancocuaresma, P. Jofre, C. Soubiran, Ulrike HeiterAbstract:Context. An increasing number of high-resolution stellar spectra is available today thanks to many past and ongoing extensive spectroscopic surveys. Consequently, the scientific community needs automatic procedures to derive atmospheric parameters and individual element Abundances. Aims. Based on the widely known SPECTRUM code by R.O. Gray, we developed an integrated spectroscopic software framework suitable for the determination of atmospheric parameters (i.e., e ective temperature, surface gravity, metallicity) and individual Chemical Abundances. The code, named iSpec and freely distributed, is written mainly in Python and can be used on di erent platforms. Methods. iSpec can derive atmospheric parameters by using the synthetic spectral fitting technique and the equivalent width method. We validated the performance of both approaches by developing two di erent pipelines and analyzing the Gaia FGK benchmark stars spectral library. The analysis was complemented with several tests designed to assess other aspects, such as the interpolation of model atmospheres and the performance with lower quality spectra. Results. We provide a code ready to perform automatic stellar spectral analysis. We successfully assessed the results obtained for FGK stars with high-resolution and high signal-to-noise spectra.
Timothy C Beers - One of the best experts on this subject based on the ideXlab platform.
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the r process alliance Chemical Abundances for a trio of r process enhanced stars one strong one moderate and one mild
The Astrophysical Journal, 2018Co-Authors: Madelyn Cain, Anna Frebel, Timothy C Beers, Maude Gull, Alexander P Ji, Vinicius M Placco, Jorge MelendezAbstract:We present detailed Chemical Abundances of three new bright (V ~ 11), extremely metal-poor ([Fe/H] ~ -3.0), r-process-enhanced halo red giants based on high-resolution, high-S/N Magellan/MIKE spectra. We measured Abundances for 20-25 neutron-capture elements in each of our stars. J1432-4125 is among the most r-process rich r-II stars, with [Eu/Fe]= +1.44+-0.11. J2005-3057 is an r-I star with [Eu/Fe] = +0.94+-0.07. J0858-0809 has [Eu/Fe] = +0.23+-0.05 and exhibits a carbon abundance corrected for evolutionary status of [C/Fe]_corr = +0.76, thus adding to the small number of known carbon-enhanced r-process stars. All three stars show remarkable agreement with the scaled solar r-process pattern for elements above Ba, consistent with enrichment of the birth gas cloud by a neutron star merger. The Abundances for Sr, Y, and Zr, however, deviate from the scaled solar pattern. This indicates that more than one distinct r-process site might be responsible for the observed neutron-capture element abundance pattern. Thorium was detected in J1432-4125 and J2005-3057. Age estimates for J1432-4125 and J2005-3057 were adopted from one of two sets of initial production ratios each by assuming the stars are old. This yielded individual ages of 12+-6 Gyr and 10+-6 Gyr, respectively.
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apogee Chemical Abundances of the sagittarius dwarf galaxy
The Astrophysical Journal, 2017Co-Authors: Sten Hasselquist, Verne V. Smith, Jon A Holtzman, Matthew D. Shetrone, Andrew Mcwilliam, J G Fernandeztrincado, Timothy C Beers, Steven R Majewski, David L Nidever, B TangAbstract:The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides the opportunity to measure elemental Abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze the Chemical abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed Chemical Abundances and the first time C, N, P, K, V, Cr, Co, and Ni have been studied at high-resolution in this galaxy. We find that the Sgr stars with [Fe/H] $\gtrsim$ -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light IMF, one lacking the most massive stars that would normally pollute the ISM with the hydrostatic elements. We use a simple Chemical evolution model, flexCE to further backup our claim and conclude that recent stellar generations of Fornax and the LMC could also have formed according to a top-light IMF.
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the Chemical Abundances of stars in the halo cash project ii a sample of 14 extremely metal poor stars
The Astrophysical Journal, 2011Co-Authors: Julie K Hollek, Anna Frebel, Ian U. Roederer, Matthew D. Shetrone, Christopher Sneden, Timothy C Beers, Sungju Kang, Christopher ThomAbstract:We present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The Abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R {approx}15, 000) and corresponding high-resolution (R {approx}35, 000) Magellan Inamori Kyocera Echelle spectra. The stars span a metallicity range from [Fe/H] from -2.9 to -3.9, including four new stars with [Fe/H] < -3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]< - 3. We also find four neutron-capture-enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H] {approx}< -3.0) of the brightest stars included in CASH and are used to calibrate a newly developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire {approx}500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manualmore » analysis from a high-resolution spectrum.« less
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the Chemical Abundances of stars in the halo cash project ii a sample of 16 extremely metal poor stars
arXiv: Astrophysics of Galaxies, 2011Co-Authors: Julie K Hollek, Anna Frebel, Ian U. Roederer, Matthew D. Shetrone, Christopher Sneden, Timothy C Beers, Sungju Kang, Christopher ThomAbstract:We present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The Abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R~15,000) and corresponding high-resolution (R~35,000) Magellan MIKE spectra. The stars span a metallicity range from [Fe/H] from -2.9 to -3.9, including four new stars with [Fe/H]<-3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]<-3. We also find four neutron-capture enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H]<-3.0) of the brightest stars included in CASH and are used to calibrate a newly-developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire ~500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manual analysis from a high-resolution spectrum.
