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Sample records for carbon-enhanced metal-poor stars

  1. Carbon-enhanced metal-poor stars in different environments

    CERN Document Server

    Salvadori, Stefania; de Bennassuti, Matteo

    2015-01-01

    The origin of carbon-enhanced metal-poor (CEMP) stars and their possible connections with the chemical elements produced by the first stellar generations is still highly debated. We briefly review observations of CEMP stars in different environments (Galactic stellar halo, ultra-faint and classical dwarf galaxies) and interpret their properties using cosmological chemical-evolution models for the formation of the Local Group. We discuss the implications of current observations for the properties of the first stars, clarify why the fraction of carbon-enhanced to carbon-normal stars varies in dwarf galaxies with different luminosity, and discuss the origin of the first CEMP(-no) star found in the Sculptor dwarf galaxy.

  2. Fluorine in a Carbon-Enhanced Metal-Poor Star

    OpenAIRE

    Schuler, S. C.; Cunha, K.; Smith, V.V.; Sivarani, T.; Beers, T. C.; Lee, Y. S.

    2007-01-01

    The fluorine abundance of the Carbon-Enhanced Metal-Poor (CEMP) star HE 1305+0132 has been derived by analysis of the molecular HF (1-0) R9 line at 2.3357 microns in a high-resolution (R = 50,000) spectrum obtained with the Phoenix spectrometer and Gemini-South telescope. Our abundance analysis makes use of a CNO-enhanced ATLAS12 model atmosphere characterized by a metallicity and CNO enhancements determined utilizing medium-resolution (R = 3,000) optical and near-IR spectra. The effective ir...

  3. Binarity in Carbon-Enhanced Metal-Poor stars

    CERN Document Server

    Starkenburg, Else; McConnachie, Alan W; Venn, Kim A

    2014-01-01

    A substantial fraction of the lowest metallicity stars show very high enhancements in carbon. It is debated whether these enhancements reflect the stars' birth composition, or if their atmospheres were subsequently polluted, most likely by accretion from an AGB binary companion. Here we investigate and compare the binary properties of three carbon-enhanced sub-classes: The metal-poor CEMP-s stars that are additionally enhanced in barium; the higher metallicity (sg)CH- and Ba II stars also enhanced in barium; and the metal-poor CEMP-no stars, not enhanced in barium. Through comparison with simulations, we demonstrate that all barium-enhanced populations are best represented by a ~100% binary fraction with a shorter period distribution of at maximum ~20,000 days. This result greatly strengthens the hypothesis that a similar binary mass transfer origin is responsible for their chemical patterns. For the CEMP-no group we present new radial velocity data from the Hobby-Eberly Telescope for 15 stars to supplement t...

  4. The physics of carbon-enhanced metal-poor stars

    Science.gov (United States)

    Stancliffe, Richard

    2014-09-01

    A surprising fraction of metal-poor stars turn out to be rich in carbon. Of these, many show enhanced levels of heavy elements, particularly those formed by the slow neutron capture process. The proposed formation scenario for these objects involves mass transfer from an asymptotic giant branch star in a binary system. I will discuss (some) of the important (and uncertain!) physical processes that we must understand if we wish to learn the origin of these enigmatic, ancient objects.

  5. Modelling the evolution and nucleosynthesis of carbon-enhanced metal-poor stars

    CERN Document Server

    Pols, O R; Lugaro, M; de Mink, S E

    2008-01-01

    We present the results of binary population simulations of carbon-enhanced metal-poor (CEMP) stars. We show that nitrogen and fluorine are useful tracers of the origin of CEMP stars, and conclude that the observed paucity of very nitrogen-rich stars puts strong constraints on possible modifications of the initial mass function at low metallicity. The large number fraction of CEMP stars may instead require much more efficient dredge-up from low-metallicity asymptotic giant branch stars.

  6. A SEARCH FOR UNRECOGNIZED CARBON-ENHANCED METAL-POOR STARS IN THE GALAXY

    International Nuclear Information System (INIS)

    We have developed a new procedure to search for carbon-enhanced metal-poor (CEMP) stars from the Hamburg/ESO (HES) prism-survey plates. This method employs an extended line index for the CH G band, which we demonstrate to have superior performance when compared to the narrower G-band index formerly employed to estimate G-band strengths for these spectra. Although CEMP stars have been found previously among candidate metal-poor stars selected from the HES, the selection on metallicity undersamples the population of intermediate-metallicity CEMP stars (-2.5 ≤ [Fe/H] ≤ -1.0); such stars are of importance for constraining the onset of the s-process in metal-deficient asymptotic giant branch stars (thought to be associated with the origin of carbon for roughly 80% of CEMP stars). The new candidates also include substantial numbers of warmer carbon-enhanced stars, which were missed in previous HES searches for carbon stars due to selection criteria that emphasized cooler stars. A first subsample, biased toward brighter stars (B< 15.5), has been extracted from the scanned HES plates. After visual inspection (to eliminate spectra compromised by plate defects, overlapping spectra, etc., and to carry out rough spectral classifications), a list of 669 previously unidentified candidate CEMP stars was compiled. Follow-up spectroscopy for a pilot sample of 132 candidates was obtained with the Goodman spectrograph on the SOAR 4.1 m telescope. Our results show that most of the observed stars lie in the targeted metallicity range, and possess prominent carbon absorption features at 4300 A. The success rate for the identification of new CEMP stars is 43% (13 out of 30) for [Fe/H] < -2.0. For stars with [Fe/H] < -2.5, the ratio increases to 80% (four out of five objects), including one star with [Fe/H] < -3.0.

  7. 3D molecular line formation in dwarf carbon-enhanced metal-poor stars

    CERN Document Server

    Behara, N T; Bonifacio, P; Sbordone, L; Hernandez, J I Gonzalez; Caffau, E

    2009-01-01

    We present a detailed analysis of the carbon and nitrogen abundances of two dwarf carbon-enhanced metal-poor (CEMP) stars: SDSS J1349-0229 and SDSS J0912+0216. We also report the oxygen abundance of SDSS J1349-0229. These stars are metal-poor, with [Fe/H] < -2.5, and were selected from our ongoing survey of extremely metal-poor dwarf candidates from the Sloan Digital SkySurvey (SDSS). The carbon, nitrogen and oxygen abundances rely on molecular lines which form in the outer layers of the stellar atmosphere. It is known that convection in metal-poor stars induces very low temperatures which are not predicted by `classical' 1D stellar atmospheres. To obtain the correct temperature structure, one needs full 3D hydrodynamical models. Using CO5BOLD 3D hydrodynamical model atmospheres and the Linfor3D line formation code, molecular lines of CH, NH, OH and C2 were computed, and 3D carbon, nitrogen and oxygen abundances were determined. The resulting carbon abundances were compared to abundances derived using atom...

  8. THE MOST METAL-POOR STARS. III. THE METALLICITY DISTRIBUTION FUNCTION AND CARBON-ENHANCED METAL-POOR FRACTION , ,

    International Nuclear Information System (INIS)

    We examine the metallicity distribution function (MDF) and fraction of carbon-enhanced metal-poor (CEMP) stars in a sample that includes 86 stars with [Fe/H] ≤ –3.0, based on high-resolution, high signal-to-noise spectroscopy, of which some 32 objects lie below [Fe/H] = –3.5. After accounting for the completeness function, the 'corrected' MDF does not exhibit the sudden drop at [Fe/H] = –3.6 that was found in recent samples of dwarfs and giants from the Hamburg/ESO survey. Rather, the MDF decreases smoothly down to [Fe/H] = –4.1. Similar results are obtained from the 'raw' MDF. We find that the fraction of CEMP objects below [Fe/H] = –3.0 is 23% ± 6% and 32% ± 8% when adopting the Beers and Christlieb and Aoki et al. CEMP definitions, respectively. The former value is in fair agreement with some previous measurements, which adopt the Beers and Christlieb criterion.

  9. Formation and evolution of carbon-enhanced metal-poor stars

    International Nuclear Information System (INIS)

    Carbon-enhanced metal-poor (CEMP) stars play a key role in characterising the star formation history of the Galactic halo. In particular, the fraction of CEMP stars among extremely metalpoor stars (EMP stars, defined by [Fe/H] < -2.5) is useful information in constraining the stellar IMF in the early universe. In our previous work, it is proposed that the typical mass of EMP stars should be around 10 Msun at [Fe/H] < -2 under the assumption that all the CEMP stars belong to binary systems and originate from a mass transfer from the former AGB stars. In this paper, we explore the origin of CEMP stars without the enhancement of s-process element abundances (so called CEMP-no stars) that dominate the CEMP population at [Fe/H] < -3.5. The reason for the large CEMP-no fraction is currently an important issue to elucidate the star formation history in the early universe in terms of the chemical evolution of the Galaxy, the contribution of AGB stars to the CEMP populations, and the IMF of first stars and EMP stars. We will discuss the reason for the increasing CEMP-no fraction (or decreasing CEMP-s (CEMP stars with s-process element enhancement) fraction) with decreasing metallicity, using binary population synthesis based on the stellar evolution and nucleosynthesis of first stars and EMP stars, taking into account the possible effect of mass loss and the hot bottom burning at low metallicity. (author)

  10. Radiative levitation in carbon-enhanced metal-poor stars with s-process enrichment

    CERN Document Server

    Matrozis, E

    2016-01-01

    A significant fraction of all metal-poor stars are carbon-rich. Most of these carbon-enhanced metal-poor (CEMP) stars also show enhancement in elements produced mainly by the s-process (CEMP-s stars) and evidence suggests that the origin of these non-standard abundances can be traced to mass transfer from a binary asymptotic giant branch (AGB) companion. Thus, observations of CEMP-s stars are commonly used to infer the nucleosynthesis output of low-metallicity AGB stars. A crucial step in this exercise is understanding what happens to the accreted material after mass transfer ceases. Here we present models of the post-mass-transfer evolution of CEMP-s stars considering the physics of thermohaline mixing and atomic diffusion, including radiative levitation. We find that stars with typical CEMP-s star masses (M ~ 0.85 Msun) have very shallow convective envelopes (Menv +4). We are therefore unable to reproduce the spread in the observed abundances with these models and conclude that some other physical process m...

  11. Abundances of carbon-enhanced metal-poor stars as constraints on their formation

    CERN Document Server

    Hansen, C J; Hansen, T T; Kennedy, C R; Placco, V M; Beers, T C; Andersen, J; Cescutti, G; Chiappini, C

    2015-01-01

    An increasing fraction of carbon-enhanced metal-poor (CEMP) stars is found as their iron abundance, [Fe/H], decreases below [Fe/H] = -2.0. The CEMP-s stars have the highest absolute carbon abundances, [C/H], and are thought to owe their enrichment in carbon and the slow neutron-capture (s-process) elements to mass transfer from a former asymptotic giant-branch (AGB) binary companion. The most Fe-poor CEMP stars are normally single, exhibit somewhat lower [C/H] than CEMP-s stars, but show no s-process element enhancement (CEMP-no stars). CNO abundance determinations offer clues to their formation sites. C, N, Sr, and Ba abundances (or limits) and 12C/13C ratios where possible are derived for a sample of 27 faint metal-poor stars for which the X-shooter spectra have sufficient S/N ratios. These moderate resolution, low S/N (~10-40) spectra prove sufficient to perform limited chemical tagging and enable assignment of these stars into the CEMP sub-classes (CEMP-s and CEMP-no). According to the derived abundances,...

  12. Carbon-Enhanced Metal-Poor Stars: Relics from the Dark Ages

    CERN Document Server

    Cooke, Ryan

    2014-01-01

    We use detailed nucleosynthesis calculations and a realistic prescription for the environment of the first stars to explore the first episodes of chemical enrichment that occurred during the dark ages. Based on these calculations, we propose a novel explanation for the increased prevalence of carbon-enhanced metal-poor (CEMP) stars with decreasing Fe abundance: The observed chemistry for the most metal-poor Galactic halo stars is the result of an intimate link between the explosions of the first stars and their host minihalo's ability to retain its gas. Specifically, high energy supernovae produce a near solar ratio of C/Fe, but are effective in evacuating the gas from their host minihalo, thereby suppressing the formation of a second generation of stars. On the other hand, minihalos that host low energy supernovae are able to retain their gas and form a second stellar generation but, as a result, the second stars are borne with a supersolar ratio of C/Fe. Our models are able to accurately reproduce the obser...

  13. On the Binarity of Carbon-Enhanced, Metal-Poor Stars

    CERN Document Server

    Tsangarides, S A; Beers, T C

    2004-01-01

    We report on a programme to monitor the radial velocities of a sample of candidate and confirmed carbon-enhanced, metal-poor (CEMP) stars. We observed 45 targets using the Echelle Spectrographs of three 4m class telescopes. Radial velocities for these objects were calculated by cross-correlation of their spectra with the spectrum of HD 140283, and have errors < 1 km/s. Sixteen of our programme's targets have reported carbon excess, and nine of these objects also exhibit s-process enhancements (CEMP-s). We combine these stars' radial velocities with other literature studies in search of binarity. The search reveals that four of our CEMP-s stars (44%) are in binary systems. Using the analysis of Lucatello et al. (2004), we find that all the CEMP-s stars in our sample are binaries. This conclusion implies that CEMP-s stars may be the very metal-poor relatives of CH and Ba II stars, which are believed to have acquired their peculiar abundance patterns by mass transfer from a thermally-pulsing AGB companion.

  14. A holistic approach to carbon-enhanced metal-poor stars

    CERN Document Server

    Masseron, T; Plez, B; Van Eck, S; Primas, F; Goriely, S; Jorissen, A

    2009-01-01

    Carbon-Enhanced Metal-Poor (CEMP) stars are known to be the direct witnesses of the nucleosynthesis of the first low- and intermediate-mass stars, because they have been polluted by a now-extinct AGB star. To put CEMP stars in a broad context, we collect abundances for about 180 stars of various metallicities (from solar down to [Fe/H]=-4), luminosity classes (dwarfs and giants), and abundance patterns (C-rich and poor, Ba-rich and poor, etc), from our own sample and from literature. First, we introduce a class of CEMP stars sharing the properties of CEMP-s stars and CEMP-no stars. We also show that there is a strong correlation between Ba and C in the s-only CEMP stars. This strongly points at the operation of the 13C neutron source in low-mass AGB stars. For the CEMP-rs stars (enriched with elements from both the s- and r-processes), the correlation of the N abundances with abundances of heavy elements from the 2nd and 3rd s-process peaks bears instead the signature of the 22Ne neutron source. Adding to the...

  15. Binary properties of CH and Carbon-Enhanced Metal-Poor stars

    CERN Document Server

    Jorissen, A; Van Winckel, H; Merle, T; Boffin, H M J; Andersen, J; Nordstroem, B; Udry, S; Masseron, T; Lenaerts, L; Waelkens, C

    2015-01-01

    The HERMES spectrograph installed on the 1.2-m Mercator telescope has been used to monitor the radial velocity of 13 low-metallicity carbon stars, among which 7 Carbon-Enhanced Metal-Poor (CEMP) stars and 6 CH stars. All stars but one show clear evidence for binarity. New orbits are obtained for 8 systems. The sample covers an extended range in orbital periods, extending from 3.4 d (for the dwarf carbon star HE 0024-2523) to about 54 yr (for the CH star HD 26, the longest known among barium, CH and extrinsic S stars). Three systems exhibit low-amplitude velocity variations with periods close to 1 yr superimposed on a long-term trend. In the absence of an accurate photometric monitoring of these systems, it is not clear yet whether these variations are the signature of a very low-mass companion, or of regular envelope pulsations. The period - eccentricity (P - e) diagram for the 40 low-metallicity carbon stars with orbits now available shows no difference between CH and CEMP-s stars (the latter corresponding t...

  16. The first carbon-enhanced metal-poor star found in the Sculptor dwarf spheroidal

    CERN Document Server

    Skuladottir, Asa; Salvadori, Stefania; Hill, Vanessa; Pettini, Max; Shetrone, Matthew D; Starkenburg, Else

    2014-01-01

    The origin of carbon-enhanced metal-poor (CEMP) stars and their possible connection with the chemical elements produced by the first stellar generation is still highly debated. In contrast to the Galactic halo, not many CEMP stars have been found in the dwarf spheroidal galaxies around the Milky Way. Here we present detailed abundances from ESO VLT/UVES high-resolution spectroscopy for ET0097, the first CEMP star found in the Sculptor dwarf spheroidal. This star has $\\text{[Fe/H]}=-2.03\\pm0.10$, $\\text{[C/Fe]}=0.51\\pm0.10$ and $\\text{[N/Fe]}=1.18\\pm0.20$. The traditional definition of CEMP stars is $\\text{[C/Fe]}\\geq0.70$, but taking into account that this luminous red giant branch star has undergone mixing, it was intrinsically less nitrogen enhanced and more carbon-rich when it was formed, and so it falls under the definition of CEMP stars, as proposed by Aoki et al. (2007) to account for this effect. By making corrections for this mixing, we conclude that the star had $\\text{[C/Fe]}\\approx0.8$ during its e...

  17. Carbon-enhanced metal-poor stars: relics from the dark ages

    Energy Technology Data Exchange (ETDEWEB)

    Cooke, Ryan J.; Madau, Piero, E-mail: rcooke@ucolick.org [Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)

    2014-08-20

    We use detailed nucleosynthesis calculations and a realistic prescription for the environment of the first stars to explore the first episodes of chemical enrichment that occurred during the dark ages. Based on these calculations, we propose a novel explanation for the increased prevalence of carbon-enhanced metal-poor (CEMP) stars with decreasing Fe abundance: the observed chemistry for the most metal-poor Galactic halo stars is the result of an intimate link between the explosions of the first stars and their host minihalo's ability to retain its gas. Specifically, high-energy supernovae produce a near solar ratio of C/Fe, but are effective in evacuating the gas from their host minihalo, thereby suppressing the formation of a second generation of stars. On the other hand, minihalos that host low-energy supernovae are able to retain their gas and form a second stellar generation, but, as a result, the second stars are born with a supersolar ratio of C/Fe. Our models are able to accurately reproduce the observed distributions of [C/Fe] and [Fe/H], as well as the fraction of CEMP stars relative to non-CEMP stars as a function of [Fe/H] without any free parameters. We propose that the present lack of chemical evidence for very massive stars (≳ 140 M {sub ☉}) that ended their lives as a highly energetic pair-instability supernova does not imply that such stars were rare or did not exist; the chemical products of these very massive first stars may have been evacuated from their host minihalos and were never incorporated into subsequent generations of stars. Finally, our models suggest that the most Fe-poor stars currently known may have seen the enrichment from a small multiple of metal-free stars, and need not have been exclusively enriched by a solitary first star. These calculations also add further support to the possibility that some of the surviving dwarf satellite galaxies of the Milky Way are the relics of the first galaxies.

  18. Carbon Abundance Plateaus among Carbon-Enhanced Metal-Poor Stars

    Science.gov (United States)

    Yoon, Jinmi; He, Siyu; Placco, Vinicius; Carollo, Daniela; Beers, Timothy C.

    2016-01-01

    A substantial fraction of low-metallicity stars in the Milky Way, the Carbon-Enhanced Metal-Poor (CEMP) stars, exhibit enhancements of their carbon-to-iron relative to the solar value ([C/Fe] > +0.7). They can be divided into several sub-classes, depending on the nature and degree of the observed enhancements of their neutron-capture elements, providing information on their likely progenitors. CEMP-s stars (which exhibit enhanced s-process elements) are thought to be enhanced by mass transfer from an evolved AGB companion, while CEMP-no stars (which exhibit no over-abundances of neutron-capture elements) appear to be associated with explosions of the very first generations of stars. High-resolution spectroscopic analyses are generally required in order to make these sub-classifications.Several recent studies have suggested the existence of bimodality in the distribution of absolute carbon abundances among CEMP stars -- most CEMP-no stars belong to a low-C band ((A(C) ˜ 6.5), while most CEMP-s stars reside on a high-C band (A(C) ˜ 8.25). The number of CEMP stars considered by individual studies is, however, quite small, so we have compiled all available high-resolution spectroscopic data for CEMP stars, in order to further investigate the existence of the claimed carbon bi-modality, and to consider what can be learned about the progenitors of CEMP-s and CEMP-no stars based on the observed distribution of A(C) on the individual plateaus.We acknowledge partial support from the grant PHY 14-30152; Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the US National Science Foundation.

  19. Radiative levitation in carbon-enhanced metal-poor stars with s-process enrichment

    Science.gov (United States)

    Matrozis, E.; Stancliffe, R. J.

    2016-07-01

    A significant fraction of all metal-poor stars are carbon-rich. Most of these carbon-enhanced metal-poor (CEMP) stars also show enhancement in elements produced mainly by the s-process (CEMP-s stars), and evidence suggests that the origin of these non-standard abundances can be traced to mass transfer from a binary asymptotic giant branch (AGB) companion. Thus, observations of CEMP-s stars are commonly used to infer the nucleosynthesis output of low-metallicity AGB stars. A crucial step in this exercise is understanding what happens to the accreted material after mass transfer ceases. Here we present models of the post-mass-transfer evolution of CEMP-s stars considering the physics of thermohaline mixing and atomic diffusion, including radiative levitation. We find that stars with typical CEMP-s star masses, M ≈ 0.85 M⊙, have very shallow convective envelopes (Menv ≲ 10-7 M⊙). Hence, the surface abundance variations arising from the competition between gravitational settling and radiative levitation should be orders of magnitude larger than observed (e.g. [C/Fe] +4). Lower-mass stars (M ≈ 0.80 M⊙) retain thicker convective envelopes and thus show variations more in line with observations, but are generally too unevolved (log g > 4) when they reach the age of the Universe. We are therefore unable to reproduce the spread in the observed abundances with these models and conclude that some other physical process must largely suppress atomic diffusion in the outer layers of CEMP-s stars. We demonstrate that this could be achieved by some additional (turbulent) mixing process operating at the base of the convective envelope, as found by other authors. Alternatively, mass-loss rates around 10-13 M⊙yr-1 could also negate most of the abundance variations by eroding the surface layers and forcing the base of the convective envelope to move inwards in mass. Since atomic diffusion cannot have a substantial effect on the surface abundances of CEMP-s stars, the

  20. The Origin of Carbon-Enhancement and Initial Mass Function of Extremely Metal-Poor Stars in the Galactic Halo

    OpenAIRE

    Komiya, Yutaka; Suda, Takuma; Minaguchi, Hiroki; Shigeyama, Toshikazu; Aoki, Wako; Fujimoto, Masayuki Y.

    2006-01-01

    It is known that the carbon-enhanced, extremely metal-poor (CEMP) stars constitute a substantial proportion in the extremely metal-poor (EMP) stars of the Galactic Halo, by far larger than CH stars in Population II stars. We investigate their origin with taking into account an additional evolutionary path to the surface carbon-enrichment, triggered by hydrogen engulfment by the helium flash convection, in EMP stars of $[Fe/H] \\lesssim -2.5$. This process is distinct from the third dredge-up o...

  1. The intermediate neutron-capture process and carbon-enhanced metal-poor stars

    CERN Document Server

    Hampel, Melanie; Lugaro, Maria; Meyer, Bradley S

    2016-01-01

    Carbon-enhanced metal-poor (CEMP) stars in the Galactic Halo display enrichments in heavy elements associated with either the s (slow) or the r (rapid) neutron-capture process (e.g., barium and europium respectively), and in some cases they display evidence of both. The abundance patterns of these CEMP-s/r stars, which show both Ba and Eu enrichment, are particularly puzzling since the s and the r processes require neutron densities that are more than ten orders of magnitude apart, and hence are thought to occur in very different stellar sites with very different physical conditions. We investigate whether the abundance patterns of CEMP-s/r stars can arise from the nucleosynthesis of the intermediate neutron-capture process (the i process), which is characterised by neutron densities between those of the s and the r processes. Using nuclear network calculations, we study neutron capture nucleosynthesis at different constant neutron densities n ranging from $10^7$ to $10^{15}$ cm$^{-3}$. With respect to the cl...

  2. Abundances of carbon-enhanced metal-poor stars as constraints on their formation

    Science.gov (United States)

    Hansen, C. J.; Nordström, B.; Hansen, T. T.; Kennedy, C. R.; Placco, V. M.; Beers, T. C.; Andersen, J.; Cescutti, G.; Chiappini, C.

    2016-04-01

    Context. An increasing fraction of carbon-enhanced metal-poor (CEMP) stars is found as their iron abundance, [Fe/H], decreases below [Fe/H] =-2.0. The CEMP-s stars have the highest absolute carbon abundances, [C/H], and are thought to owe their enrichment in carbon and the slow neutron-capture (s-process) elements to mass transfer from a former asymptotic giant branch (AGB) binary companion. The most Fe-poor CEMP stars are normally single, exhibit somewhat lower [C/H] than CEMP-s stars, but show no s-process element enhancement (CEMP-no stars). Abundance determinations of CNO offer clues to their formation sites. Aims: Our aim is to use the medium-resolution spectrograph X-Shooter/VLT to determine stellar parameters and abundances for C, N, Sr, and Ba in several classes of CEMP stars in order to further classify and constrain the astrophysical formation sites of these stars. Methods: Atmospheric parameters for our programme stars were estimated from a combination of V-K photometry, model isochrone fits, and estimates from a modified version of the SDSS/SEGUE spectroscopic pipeline. We then used X-Shooter spectra in conjunction with the 1D local thermodynamic equilibrium spectrum synthesis code MOOG, 1D ATLAS9 atmosphere models to derive stellar abundances, and, where possible, isotopic 12C/13C ratios. Results: Abundances (or limits) of C, N, Sr, and Ba are derived for a sample of 27 faint metal-poor stars for which the X-Shooter spectra have sufficient signal-to-noise ratios (S/N). These moderate resolution, low S/N (~10-40) spectra prove sufficient to perform limited chemical tagging and enable assignment of these stars into the CEMP subclasses (CEMP-s and CEMP-no). According to the derived abundances, 17 of our sample stars are CEMP-s and 3 are CEMP-no, while the remaining 7 are carbon-normal. For four CEMP stars, the subclassification remains uncertain, and two of them may be pulsating AGB stars. Conclusions: The derived stellar abundances trace the formation

  3. Footprints of the weak s-process in the carbon-enhanced metal-poor star ET0097

    CERN Document Server

    Yang, Guochao; Liu, Nian; Cui, Wenyuan; Liang, Yanchun; Zhang, Bo

    2016-01-01

    Historically, the weak s-process contribution to metal-poor stars is thought to be extremely small, due to the effect of the secondary-like nature of the neutron source 22Ne(a;n)25Mg in massive stars, which means that metal-poor weak s-process stars could not be found. ET0097 is the first observed carbon-enhanced metal-poor (CEMP) star in the Sculptor dwarf spheroidal galaxy. Because C is enriched and the elements heavier than Ba are not overabundant, ET0097 can be classified as a CEMP-no star. However, this star shows overabundances of lighter n-capture elements (i.e., Sr, Y and Zr). In this work, having adopted the abundance decomposition approach, we investigate the astrophysical origins of the elements in ET0097. We find that the light elements and iron-peak elements (from O to Zn) of the star mainly originate from the primary process of massive stars and the heavier n-capture elements (heavier than Ba) mainly come from the main r-process. However, the lighter n-capture elements such as Sr, Y and Zr shoul...

  4. Footprints of the weak s-process in the carbon-enhanced metal-poor star ET0097

    Science.gov (United States)

    Yang, Guochao; Li, Hongjie; Liu, Nian; Cui, Wenyuan; Liang, Yanchun; Zhang, Bo

    2016-09-01

    Historically, the weak s-process contribution to metal-poor stars is thought to be extremely small, due to the effect of the secondary-like nature of the neutron source 22Ne(α , n)25Mg in massive stars, which means that metal-poor "weak s-process stars" could not be found. ET0097 is the first observed carbon-enhanced metal-poor (CEMP) star in the Sculptor dwarf spheroidal galaxy. Because C is enriched and the elements heavier than Ba are not overabundant, ET0097 can be classified as a CEMP-no star. However, this star shows overabundances of lighter n-capture elements (i.e., Sr, Y and Zr). In this work, having adopted the abundance decomposition approach, we investigate the astrophysical origins of the elements in ET0097. We find that the light elements and iron-peak elements (from O to Zn) of the star mainly originate from the primary process of massive stars and the heavier n-capture elements (heavier than Ba) mainly come from the main r-process. However, the lighter n-capture elements such as Sr, Y and Zr should mainly come from the primary weak s-process. The contributed fractions of the primary weak s-process to the Sr, Y and Zr abundances of ET0097 are about 82 %, 84 % and 58 % respectively, suggesting that the CEMP star ET0097 should have the footprints of the weak s-process. The derived result should be a significant evidence that the weak s-process elements can be produced in metal-poor massive stars.

  5. FORMATION OF CARBON-ENHANCED METAL-POOR STARS IN THE PRESENCE OF FAR-ULTRAVIOLET RADIATION

    International Nuclear Information System (INIS)

    Recent discoveries of carbon-enhanced metal-poor stars like SMSS J031300.36–670839.3 provide increasing observational insights into the formation conditions of the first second-generation stars in the universe, reflecting the chemical conditions after the first supernova explosion. Here, we present the first cosmological simulations with a detailed chemical network including primordial species as well as C, C+, O, O+, Si, Si+, and Si2+ following the formation of carbon-enhanced metal-poor stars. The presence of background UV flux delays the collapse from z = 21 to z = 15 and cool the gas down to the cosmic microwave background temperature for a metallicity of Z/Z ☉ = 10–3. This can potentially lead to the formation of lower-mass stars. Overall, we find that the metals have a stronger effect on the collapse than the radiation, yielding a comparable thermal structure for large variations in the radiative background. We further find that radiative backgrounds are not able to delay the collapse for Z/Z ☉ = 10–2 or a carbon abundance as in SMSS J031300.36–670839.3

  6. Detection of Phosphorus, Sulphur, and Zinc in the Carbon-Enhanced Metal-Poor Star BD+44 493

    CERN Document Server

    Roederer, Ian U; Beers, Timothy C

    2016-01-01

    The carbon-enhanced metal-poor star BD+44 493 ([Fe/H]=-3.9) has been proposed as a candidate second-generation star enriched by metals from a single Pop III star. We report the first detections of P and S and the second detection of Zn in any extremely metal-poor carbon-enhanced star, using new spectra of BD+44 493 collected by the Cosmic Origins Spectrograph on the Hubble Space Telescope. We derive [P/Fe]=-0.34 +/- 0.21, [S/Fe]=+0.07 +/- 0.41, and [Zn/Fe]=-0.10 +/- 0.24. We increase by ten-fold the number of Si I lines detected in BD+44 493, yielding [Si/Fe]=+0.15 +/- 0.22. The solar [S/Fe] and [Zn/Fe] ratios exclude the hypothesis that the abundance pattern in BD+44 493 results from depletion of refractory elements onto dust grains. Comparison with zero-metallicity supernova models suggests that the stellar progenitor that enriched BD+44 493 was massive and ejected much less than 0.07 Msun of Ni-56, characteristic of a faint supernova.

  7. FORMATION OF CARBON-ENHANCED METAL-POOR STARS IN THE PRESENCE OF FAR-ULTRAVIOLET RADIATION

    Energy Technology Data Exchange (ETDEWEB)

    Bovino, S.; Schleicher, D. R. G.; Latif, M. A. [Institut für Astrophysik Georg-August-Universität, Friedrich-Hund Platz 1, 37077 Göttingen (Germany); Grassi, T., E-mail: sbovino@astro.physik.uni-goettingen.de [Centre for Star and Planet Formation, Natural History Museum of Denmark, Øster Voldgade 5-7, 1350 Copenhagen (Denmark)

    2014-08-01

    Recent discoveries of carbon-enhanced metal-poor stars like SMSS J031300.36–670839.3 provide increasing observational insights into the formation conditions of the first second-generation stars in the universe, reflecting the chemical conditions after the first supernova explosion. Here, we present the first cosmological simulations with a detailed chemical network including primordial species as well as C, C{sup +}, O, O{sup +}, Si, Si{sup +}, and Si{sup 2+} following the formation of carbon-enhanced metal-poor stars. The presence of background UV flux delays the collapse from z = 21 to z = 15 and cool the gas down to the cosmic microwave background temperature for a metallicity of Z/Z {sub ☉} = 10{sup –3}. This can potentially lead to the formation of lower-mass stars. Overall, we find that the metals have a stronger effect on the collapse than the radiation, yielding a comparable thermal structure for large variations in the radiative background. We further find that radiative backgrounds are not able to delay the collapse for Z/Z {sub ☉} = 10{sup –2} or a carbon abundance as in SMSS J031300.36–670839.3.

  8. Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars

    Science.gov (United States)

    Lee, Young Sun; Beers, Timothy C.; Masseron, Thomas; Plez, Bertrand; Rockosi, Constance M.; Sobeck, Jennifer; Yanny, Brian; Lucatello, Sara; Sivarani, Thirupathi; Placco, Vinicius M.; Carollo, Daniela

    2013-11-01

    We describe a method for the determination of stellar [C/Fe] abundance ratios using low-resolution (R = 2000) stellar spectra from the Sloan Digital Sky Survey (SDSS) and its Galactic sub-survey, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). By means of a star-by-star comparison with a set of SDSS/SEGUE spectra with available estimates of [C/Fe] based on published high-resolution analyses, we demonstrate that we can measure [C/Fe] from SDSS/SEGUE spectra with S/N >= 15 Å-1 to a precision better than 0.35 dex for stars with atmospheric parameters in the range T eff = [4400, 6700] K, log g = [1.0, 5.0], [Fe/H] = [-4.0, +0.5], and [C/Fe] = [-0.25, +3.5]. Using the measured carbon-to-iron abundance ratios obtained by this technique, we derive the frequency of carbon-enhanced stars ([C/Fe] >= +0.7) as a function of [Fe/H], for both the SDSS/SEGUE stars and other samples from the literature. We find that the differential frequency slowly rises from almost zero to about 14% at [Fe/H] ~ -2.4, followed by a sudden increase, by about a factor of three, to 39% from [Fe/H] ~ -2.4 to [Fe/H] ~ -3.7. Although the number of stars known with [Fe/H] 4.0 remains small, the frequency of carbon-enhanced metal-poor (CEMP) stars below this value is around 75%. We also examine how the cumulative frequency of CEMP stars varies across different luminosity classes. The giant sample exhibits a cumulative CEMP frequency of 32% for [Fe/H] <= -2.5, 31% for [Fe/H] <= -3.0, and 33% for [Fe/H] <= -3.5 a roughly constant value. For the main-sequence turnoff stars, we obtain a lower cumulative CEMP frequency, around 10% for [Fe/H] <= -2.5, presumably due to the difficulty of identifying CEMP stars among warmer turnoff stars with weak CH G-bands. The dwarf population displays a large change in the cumulative frequency for CEMP stars below [Fe/H] = -2.5, jumping from 15% for [Fe/H] <= -2.5 to about 75% for [Fe/H] <= -3.0. When we impose a restriction with respect to distance

  9. CARBON-ENHANCED METAL-POOR STARS IN SDSS/SEGUE. I. CARBON ABUNDANCE ESTIMATION AND FREQUENCY OF CEMP STARS

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Young Sun [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); Beers, Timothy C.; Placco, Vinicius M. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Masseron, Thomas [Institut d' Astronomie et d' Astrophysique, Université Libre de Bruxelles, CP 226, Boulevard du Triomphe, B-1050 Bruxelles (Belgium); Plez, Bertrand [Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS, F-34095 Montpellier (France); Rockosi, Constance M. [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Sobeck, Jennifer [Laboratoire Lagrange (UMR7293), Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d' Azur, BP 4229, F-06304 Nice Cedex 04 (France); Yanny, Brian [Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States); Lucatello, Sara [INAF-Osservatorio Astronomico di Padova, vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Sivarani, Thirupathi [Indian Institute of Astrophysics, 2nd block Koramangala, Bangalore-560034 (India); Carollo, Daniela, E-mail: yslee@nmsu.edu [Department of Physics and Astronomy, Astronomy, Astrophysics and Astrophotonic Research Center, Macquarie University, North Ryde, NSW 2019 (Australia)

    2013-11-01

    We describe a method for the determination of stellar [C/Fe] abundance ratios using low-resolution (R = 2000) stellar spectra from the Sloan Digital Sky Survey (SDSS) and its Galactic sub-survey, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). By means of a star-by-star comparison with a set of SDSS/SEGUE spectra with available estimates of [C/Fe] based on published high-resolution analyses, we demonstrate that we can measure [C/Fe] from SDSS/SEGUE spectra with S/N ≥ 15 Å{sup –1} to a precision better than 0.35 dex for stars with atmospheric parameters in the range T {sub eff} = [4400, 6700] K, log g = [1.0, 5.0], [Fe/H] = [–4.0, +0.5], and [C/Fe] = [–0.25, +3.5]. Using the measured carbon-to-iron abundance ratios obtained by this technique, we derive the frequency of carbon-enhanced stars ([C/Fe] ≥ +0.7) as a function of [Fe/H], for both the SDSS/SEGUE stars and other samples from the literature. We find that the differential frequency slowly rises from almost zero to about 14% at [Fe/H] ∼ –2.4, followed by a sudden increase, by about a factor of three, to 39% from [Fe/H] ∼ –2.4 to [Fe/H] ∼ –3.7. Although the number of stars known with [Fe/H] < –4.0 remains small, the frequency of carbon-enhanced metal-poor (CEMP) stars below this value is around 75%. We also examine how the cumulative frequency of CEMP stars varies across different luminosity classes. The giant sample exhibits a cumulative CEMP frequency of 32% for [Fe/H] ≤ –2.5, 31% for [Fe/H] ≤ –3.0, and 33% for [Fe/H] ≤ –3.5; a roughly constant value. For the main-sequence turnoff stars, we obtain a lower cumulative CEMP frequency, around 10% for [Fe/H] ≤ –2.5, presumably due to the difficulty of identifying CEMP stars among warmer turnoff stars with weak CH G-bands. The dwarf population displays a large change in the cumulative frequency for CEMP stars below [Fe/H] = –2.5, jumping from 15% for [Fe/H] ≤ –2.5 to about 75% for [Fe/H] ≤ –3

  10. Detection of Phosphorus, Sulphur, and Zinc in the Carbon-enhanced Metal-poor Star BD+44 493

    Science.gov (United States)

    Roederer, Ian U.; Placco, Vinicius M.; Beers, Timothy C.

    2016-06-01

    The carbon-enhanced metal-poor star BD+44°493 ([Fe/H] = ‑3.9) has been proposed as a candidate second-generation star enriched by metals from a single Pop III star. We report the first detections of P and S and the second detection of Zn in any extremely metal-poor carbon-enhanced star, using new spectra of BD+44°493 collected by the Cosmic Origins Spectrograph on the Hubble Space Telescope. We derive [P/Fe] = ‑0.34 ± 0.21, [S/Fe] = +0.07 ± 0.41, and [Zn/Fe] = ‑0.10 ± 0.24. We increase by 10-fold the number of Si i lines detected in BD+44°493, yielding [Si/Fe] = +0.15 ± 0.22. The [S/Fe] and [Zn/Fe] ratios exclude the hypothesis that the abundance pattern in BD+44°493 results from depletion of refractory elements onto dust grains. Comparison with zero-metallicity supernova (SN) models suggests that the stellar progenitor that enriched BD+44°493 was massive and ejected much less than 0.07 M ⊙ of 56Ni, characteristic of a faint SN. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under NASA contract NAS 5-26555. These observations are associated with program GO-14231.

  11. G64-12 and G64-37 are Carbon-Enhanced Metal-Poor Stars

    CERN Document Server

    Placco, Vinicius M; Reggiani, Henrique; Melendez, Jorge

    2016-01-01

    We present new high-resolution chemical-abundance analyses for the well-known high proper-motion subdwarfs G64-12 and G64-37, based on very high signal-to-noise spectra (S/N ~ 700/1) with resolving power R ~ 95,000. These high-quality data enable the first reliable determination of the carbon abundances for these two stars; we classify them as carbon-enhanced metal-poor (CEMP) stars based on their carbonicities, which both exceed [C/Fe] = +1.0. They are sub-classified as CEMP- no Group-II stars, based on their location in the Yoon-Beers diagram of absolute carbon abundance, A(C) vs. [Fe/H], as well as on the conventional diagnostic [Ba/Fe]. The relatively low absolute carbon abundances of CEMP-no stars, in combination with the high effective temperatures of these two stars (Teff ~ 6500 K) weakens their CH molecular features to the point that accurate carbon abundances can only be estimated from spectra with very high S/N. A comparison of the observed abundance patterns with the predicted yields from massive, ...

  12. Modelling the observed properties of carbon-enhanced metal-poor stars using binary population synthesis

    CERN Document Server

    Abate, C; Stancliffe, R J; Izzard, R G; Karakas, A I; Beers, T C; Lee, Y S

    2015-01-01

    The stellar population in the Galactic halo is characterised by a large fraction of CEMP stars. Most CEMP stars are enriched in $s$-elements (CEMP-$s$ stars), and some of these are also enriched in $r$-elements (CEMP-$s/r$ stars). One formation scenario proposed for CEMP stars invokes wind mass transfer in the past from a TP-AGB primary star to a less massive companion star which is presently observed. We generate low-metallicity populations of binary stars to reproduce the observed CEMP-star fraction. In addition, we aim to constrain our wind mass-transfer model and investigate under which conditions our synthetic populations reproduce observed abundance distributions. We compare the CEMP fractions and the abundance distributions determined from our synthetic populations with observations. Several physical parameters of the binary stellar population of the halo are uncertain, e.g. the initial mass function, the mass-ratio and orbital-period distributions, and the binary fraction. We vary the assumptions in o...

  13. Metal-Poor Stars

    OpenAIRE

    Frebel, Anna

    2008-01-01

    The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of the chemical evolution of the Galaxy. In particular, these stars allow us to study the formation and evolution of the elements and the involved nucleosynthesis processes. This knowledge is invaluable for our understanding of the cosmic chemical evolution and the onset of star- and galaxy formation. Metal-poor stars are the local equivalent of the high-redshift Universe, and offer cru...

  14. Metal-Poor Stars

    CERN Document Server

    Frebel, Anna

    2008-01-01

    The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of the chemical evolution of the Galaxy. In particular, these stars allow us to study the formation and evolution of the elements and the involved nucleosynthesis processes. This knowledge is invaluable for our understanding of the cosmic chemical evolution and the onset of star- and galaxy formation. Metal-poor stars are the local equivalent of the high-redshift Universe, and offer crucial observational constraints on the nature of the first stars. This review presents the history of the first discoveries of metal-poor stars that laid the foundation to this field. Observed abundance trends at the lowest metallicities are described, as well as particular classes of metal-poor stars such as r-process and C-rich stars. Scenarios on the origins of the abundances of metal-poor stars and the application of large samples of metal-poor stars to cosmological questions are discussed.

  15. The role of binaries in the enrichment of the early Galactic halo. III. Carbon-enhanced metal-poor stars -- CEMP-s stars

    CERN Document Server

    Hansen, T T; Nordström, B; Beers, T C; Placco, V M; Yoon, J; Buchhave, L A

    2016-01-01

    Detailed spectroscopic studies of metal-poor halo stars have highlighted the important role of carbon-enhanced metal-poor (CEMP) stars in understanding the early production and ejection of carbon in the Galaxy and in identifying the progenitors of the CEMP stars among the first stars formed after the Big Bang. Recent work has also classified the CEMP stars by absolute carbon abundance, A(C), into high- and low-C bands, mostly populated by binary and single stars, respectively. Our aim is to determine the frequency and orbital parameters of binary systems among the CEMP-s stars, which exhibit strong enhancements of neutron-capture elements associated with the s-process. This allows us to test whether local mass transfer from a binary companion is necessary and sufficient to explain their dramatic carbon excesses. Eighteen of the 22 stars exhibit clear orbital motion, yielding a binary frequency of 82+-10%, while four stars appear to be single (18+-10%). We thus confirm that the binary frequency of CEMP-s stars...

  16. Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars

    CERN Document Server

    Lee, Young Sun; Masseron, Thomas; Plez, Bertrand; Rockosi, Constance M; Sobeck, Jennifer; Yanny, Brian; Lucatello, Sara; Sivarani, Thirupathi; Placco, Vinicius M; Carollo, Daniela

    2013-01-01

    We describe a method for the determination of stellar [C/Fe] abundance ratios using low-resolution (R = 2000) stellar spectra from the SDSS and SEGUE. By means of a star-by-star comparison with a set of SDSS/SEGUE spectra with available estimates of [C/Fe] based on published high-resolution analyses, we demonstrate that we can measure [C/Fe] from SDSS/SEGUE spectra with S/N > 15 to a precision better than 0.35 dex. Using the measured carbon-to-iron abundance ratios obtained by this technique, we derive the frequency of carbon-enhanced stars ([C/Fe] > +0.7) as a function of [Fe/H], for both the SDSS/SEGUE stars and other samples from the literature. We find that the differential frequency slowly rises from almost zero to about 14% at [Fe/H] ~ -2.4, followed by a sudden increase, by about a factor of three, to 39% from [Fe/H] ~ -2.4 to [Fe/H] ~ -3.7. We also examine how the cumulative frequency of CEMP stars varies across different luminosity classes. The giant sample exhibits a cumulative CEMP frequency of 32%...

  17. The role of binaries in the enrichment of the early Galactic halo. II. Carbon-Enhanced Metal-Poor Stars - CEMP-no stars

    CERN Document Server

    Hansen, T T; Nordström, B; Beers, T C; Placco, V M; Yoon, J; Buchhave, L A

    2015-01-01

    The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon - the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds, or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Our aim is to determine the frequency and orbital parameters of binaries among CEMP stars with and without over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars, respectively - as a test of this local mass-transfer scenario. This paper discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider a similar sample of CEMP-s stars. Most programme stars exhibit no statistically significant radial-velocit variation...

  18. The role of binaries in the enrichment of the early Galactic halo. III. Carbon-enhanced metal-poor stars - CEMP-s stars

    Science.gov (United States)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Placco, V. M.; Yoon, J.; Buchhave, L. A.

    2016-04-01

    Context. Detailed spectroscopic studies of metal-poor halo stars have highlighted the important role of carbon-enhanced metal-poor (CEMP) stars in understanding the early production and ejection of carbon in the Galaxy and in identifying the progenitors of the CEMP stars among the first stars formed after the Big Bang. Recent work has also classified the CEMP stars by absolute carbon abundance, A(C), into high- and low-C bands, mostly populated by binary and single stars, respectively. Aims: Our aim is to determine the frequency and orbital parameters of binary systems among the CEMP-s stars, which exhibit strong enhancements of neutron-capture elements associated with the s-process. This allows us to test whether local mass transfer from a binary companion is necessary and sufficient to explain their dramatic carbon excesses. Methods: We have systematically monitored the radial velocities of a sample of 22 CEMP-s stars for several years with ~monthly, high-resolution, low S/N échelle spectra obtained at the Nordic Optical Telescope (NOT) at La Palma, Spain. From these spectra, radial velocities with an accuracy of ≈100 m s-1 were determined by cross-correlation with optimised templates. Results: Eighteen of the 22 stars exhibit clear orbital motion, yielding a binary frequency of 82 ± 10%, while four stars appear to be single (18 ± 10%). We thus confirm that the binary frequency of CEMP-s stars is much higher than for normal metal-poor giants, but not 100% as previously claimed. Secure orbits are determined for eleven of the binaries and provisional orbits for six long-period systems (P > 3000 days), and orbital circularisation timescales are discussed. Conclusions: The conventional scenario of local mass transfer from a former asymptotic giant branch (AGB) binary companion does appear to account for the chemical composition of most CEMP-s stars. However, the excess of C and s-process elements in some single CEMP-s stars was apparently transferred to their

  19. The role of binaries in the enrichment of the early Galactic halo. II. Carbon-enhanced metal-poor stars: CEMP-no stars

    Science.gov (United States)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Placco, V. M.; Yoon, J.; Buchhave, L. A.

    2016-02-01

    Context. The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon; these are the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Aims: Our aim is to determine the frequency and orbital parameters of binaries among CEMP stars with and without over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars, respectively - as a test of this local mass-transfer scenario. This paper discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider a similar sample of CEMP-s stars. Methods: High-resolution, low S/N spectra of the stars were obtained at roughly monthly intervals over a time span of up to eight years with the FIES spectrograph at the Nordic Optical Telescope. Radial velocities of ~100 m s-1 precision were determined by cross-correlation after each observing night, allowing immediate, systematic follow-up of any variable object. Results: Most programme stars exhibit no statistically significant radial-velocity variation over this period and appear to be single, while four are found to be binaries with orbital periods of 300-2000 days and normal eccentricity; the binary frequency for the sample is 17 ± 9%. The single stars mostly belong to the recently identified low-C band, while the binaries have higher absolute carbon abundances. Conclusions: We conclude that the nucleosynthetic process responsible for the strong carbon excess in these ancient stars is unrelated to their binary status; the carbon was imprinted on their natal molecular clouds in the early Galactic interstellar

  20. Carbon-enhanced metal-poor star frequencies in the galaxy: corrections for the effect of evolutionary status on carbon abundances

    International Nuclear Information System (INIS)

    We revisit the observed frequencies of carbon-enhanced metal-poor (CEMP) stars as a function of the metallicity in the Galaxy, using data from the literature with available high-resolution spectroscopy. Our analysis excludes stars exhibiting clear overabundances of neutron-capture elements and takes into account the expected depletion of surface carbon abundance that occurs due to CN processing on the upper red giant branch. This allows for the recovery of the initial carbon abundance of these stars, and thus for an accurate assessment of the frequencies of carbon-enhanced stars. The correction procedure we develop is based on stellar-evolution models and depends on the surface gravity, log g, of a given star. Our analysis indicates that for stars with [Fe/H] ≤–2.0, 20% exhibit [C/Fe] ≥+0.7. This fraction increases to 43% for [Fe/H] ≤–3.0 and 81% for [Fe/H] ≤–4.0, which is higher than have been previously inferred without taking the carbon abundance correction into account. These CEMP star frequencies provide important inputs for Galactic and stellar chemical evolution models, as they constrain the evolution of carbon at early times and the possible formation channels for the CEMP-no stars. We also have developed a public online tool with which carbon corrections using our procedure can be easily obtained.

  1. Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances

    CERN Document Server

    Placco, Vinicius M; Beers, Timothy C; Stancliffe, Richard J

    2014-01-01

    We revisit the observed frequencies of Carbon-Enhanced Metal-Poor (CEMP) stars as a function of the metallicity in the Galaxy, using data from the literature with available high-resolution spectroscopy. Our analysis excludes stars exhibiting clear over-abundances of neutron-capture elements, and takes into account the expected depletion of surface carbon abundance that occurs due to CN processing on the upper red-giant branch. This allows for the recovery of the initial carbon abundance of these stars, and thus for an accurate assessment of the frequencies of carbon-enhanced stars. The correction procedure we develope is based on stellar-evolution models, and depends on the surface gravity, log g, of a given star. Our analysis indicates that, for stars with [Fe/H]=+0.7. This fraction increases to 43% for [Fe/H]<=-3.0 and 81% for [Fe/H]<=-4.0, which is higher than have been previously inferred without taking the carbon-abundance correction into account. These CEMP-star frequencies provide important input...

  2. Carbon-Enhanced Metal-Poor Stars: CEMP-s and CEMP-no Sub-Classes in the Halo System of the Milky Way

    CERN Document Server

    Carollo, Daniela; Beers, Timothy; Placco, Vinicius; Tumlinson, Jason; Martell, Sarah

    2014-01-01

    We explore the kinematics and orbital properties of a sample of 323 very metal-poor stars in the halo system of the Milky Way, and with high-resolution spectroscopy available, selected from the recent studies of Aoki et al. and Yong et al. The combined sample contains a significant fraction of carbon-enhanced metal-poor (CEMP) stars (22% or 29% depending on whether a strict or relaxed criterion is applied for this definition). Barium abundances (or upper limits) are available for the great majority of the CEMP stars, allowing for their separation into the CEMP-s and CEMP-no sub-classes. A new method to assign membership to the inner- and outer-halo populations of the Milky Way is developed, making use of the integrals of motion, and applied to determine the relative fractions of CEMP stars in these two sub-classes for each halo component. Although limited by small-number statistics, the data suggest that the inner halo of the Milky Way exhibits a somewhat higher relative number of CEMP-s stars than CEMP-no st...

  3. Carbon-enhanced metal-poor stars in SDSS/Segue. II. Comparison of CEMP-star frequencies with binary population-synthesis models

    International Nuclear Information System (INIS)

    We present a comparison of the frequencies of carbon-enhanced metal-poor (CEMP) giant and main-sequence turnoff (MSTO) stars with predictions from binary population-synthesis models involving asymptotic giant-branch (AGB) mass transfer. The giant and MSTO stars are selected from the Sloan Digital Sky Survey and the Sloan Extension for Galactic Understanding and Exploration. We consider two initial mass functions (IMFs)—a Salpeter IMF, and a mass function with a characteristic mass of 10 M ☉. For giant stars, the comparison indicates a good agreement between the observed CEMP frequencies and the AGB binary model using a Salpeter IMF for [Fe/H] > – 1.5, and a characteristic mass of 10 M ☉ for [Fe/H] < – 2.5. This result suggests that the IMF shifted from high- to low-mass dominated in the early history of the Milky Way, which appears to have occurred at a 'chemical time' between [Fe/H] =–2.5 and [Fe/H] =–1.5. The CEMP frequency for the turnoff stars with [Fe/H] < – 3.0 is much higher than the AGB model prediction from the high-mass IMF, supporting the previous assertion that one or more additional mechanisms, not associated with AGB stars, are required for the production of carbon-rich material below [Fe/H] =–3.0. We also discuss possible effects of first dredge-up and extra mixing in red giants and internal mixing in turnoff stars on the derived CEMP frequencies.

  4. Carbon-enhanced metal-poor stars in SDSS/Segue. II. Comparison of CEMP-star frequencies with binary population-synthesis models

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Young Sun [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); Suda, Takuma [National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Stancliffe, Richard J., E-mail: yslee@nmsu.edu [Argelander-Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn (Germany)

    2014-06-20

    We present a comparison of the frequencies of carbon-enhanced metal-poor (CEMP) giant and main-sequence turnoff (MSTO) stars with predictions from binary population-synthesis models involving asymptotic giant-branch (AGB) mass transfer. The giant and MSTO stars are selected from the Sloan Digital Sky Survey and the Sloan Extension for Galactic Understanding and Exploration. We consider two initial mass functions (IMFs)—a Salpeter IMF, and a mass function with a characteristic mass of 10 M {sub ☉}. For giant stars, the comparison indicates a good agreement between the observed CEMP frequencies and the AGB binary model using a Salpeter IMF for [Fe/H] > – 1.5, and a characteristic mass of 10 M {sub ☉} for [Fe/H] < – 2.5. This result suggests that the IMF shifted from high- to low-mass dominated in the early history of the Milky Way, which appears to have occurred at a 'chemical time' between [Fe/H] =–2.5 and [Fe/H] =–1.5. The CEMP frequency for the turnoff stars with [Fe/H] < – 3.0 is much higher than the AGB model prediction from the high-mass IMF, supporting the previous assertion that one or more additional mechanisms, not associated with AGB stars, are required for the production of carbon-rich material below [Fe/H] =–3.0. We also discuss possible effects of first dredge-up and extra mixing in red giants and internal mixing in turnoff stars on the derived CEMP frequencies.

  5. Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. I. Detailed analysis of 15 binary stars with known orbital periods

    CERN Document Server

    Abate, C; Karakas, A I; Izzard, R G

    2015-01-01

    AGB stars are responsible for producing a variety of elements, including carbon, nitrogen, and the heavy elements produced in the slow neutron-capture process ($s$-elements). There are many uncertainties involved in modelling the evolution and nucleosynthesis of AGB stars, and this is especially the case at low metallicity, where most of the stars with high enough masses to enter the AGB have evolved to become white dwarfs and can no longer be observed. The stellar population in the Galactic halo is of low mass ($\\lesssim 0.85M_{\\odot}$) and only a few observed stars have evolved beyond the first giant branch. However, we have evidence that low-metallicity AGB stars in binary systems have interacted with their low-mass secondary companions in the past. The aim of this work is to investigate AGB nucleosynthesis at low metallicity by studying the surface abundances of chemically peculiar very metal-poor stars of the halo observed in binary systems. To this end we select a sample of 15 carbon- and $s$-element-en...

  6. The Chemical Abundances of Stars in the Halo (CASH) Project. III. A New Classification Scheme for Carbon-Enhanced Metal-poor Stars with S-process Element Enhancement

    CERN Document Server

    Hollek, Julie K; Placco, Vinicius M; Karakas, Amanda I; Shetrone, Matthew; Sneden, Christopher; Christlieb, Norbert

    2015-01-01

    We present a detailed abundance analysis of 23 elements for a newly discovered carbon-enhanced metal-poor (CEMP) star, HE 0414-0343, from the Chemical Abundances of Stars in the Halo (CASH) Project. Its spectroscopic stellar parameters are Teff = 4863 K, log g = 1.25, vmic = 2.20 km/s, and [Fe/H] = -2.24. Radial velocity measurements covering seven years indicate HE 0414-0343 to be a binary. HE 0414-0343 has [C/Fe] = 1.44 and is strongly enhanced in neutron-capture elements but its abundances cannot be reproduced by a solar-type s-process pattern alone. Traditionally, it could be classified as "CEMP-r/s" star. Based on abundance comparisons with AGB star nucleosynthesis models, we suggest a new physically-motivated origin and classification scheme for CEMP-s stars and the still poorly-understood CEMP-r/s. The new scheme describes a continuous transition between these two so-far distinctly treated subgroups: CEMP-sA, CEMP-sB, and CEMP-sC. Possible causes for a continuous transition include the number of therma...

  7. Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. II. Statistical analysis of a sample of 67 CEMP-$s$ stars

    CERN Document Server

    Abate, C; Izzard, R G; Karakas, A I

    2015-01-01

    Many observed CEMP stars are found in binary systems and show enhanced abundances of $s$-elements. The origin of the chemical abundances of these CEMP-$s$ stars is believed to be accretion in the past of enriched material from a primary star in the AGB phase. We investigate the mechanism of mass transfer and the process of nucleosynthesis in low-metallicity AGB stars by modelling the binary systems in which the observed CEMP-$s$ stars were formed. For this purpose we compare a sample of $67$ CEMP-$s$ stars with a grid of binary stars generated by our binary evolution and nucleosynthesis model. We classify our sample CEMP-$s$ stars in three groups based on the observed abundance of europium. In CEMP$-s/r$ stars the europium-to-iron ratio is more than ten times higher than in the Sun, whereas it is lower than this threshold in CEMP$-s/nr$ stars. No measurement of europium is currently available for CEMP-$s/ur$ stars. On average our models reproduce well the abundances observed in CEMP-$s/nr$ stars, whereas in C...

  8. THE RAVE SURVEY: RICH IN VERY METAL-POOR STARS

    International Nuclear Information System (INIS)

    Very metal-poor stars are of obvious importance for many problems in chemical evolution, star formation, and galaxy evolution. Finding complete samples of such stars which are also bright enough to allow high-precision individual analyses is of considerable interest. We demonstrate here that stars with iron abundances [Fe/H] <-2 dex, and down to below -4 dex, can be efficiently identified within the Radial Velocity Experiment (RAVE) survey of bright stars, without requiring additional confirmatory observations. We determine a calibration of the equivalent width of the calcium triplet lines measured from the RAVE spectra onto true [Fe/H], using high spectral resolution data for a subset of the stars. These RAVE iron abundances are accurate enough to obviate the need for confirmatory higher-resolution spectroscopy. Our initial study has identified 631 stars with [Fe/H] ≤-2, from a RAVE database containing approximately 200,000 stars. This RAVE-based sample is complete for stars with [Fe/H] ∼<-2.5, allowing statistical sample analysis. We identify three stars with [Fe/H] ∼<-4. Of these, one was already known to be 'ultra metal-poor', one is a known carbon-enhanced metal-poor star, but we obtain [Fe/H] = -4.0, rather than the published [Fe/H] = -3.3, and derive [C/Fe] = +0.9, and [N/Fe] = +3.2, and the third is at the limit of our signal-to-noise ratio. RAVE observations are ongoing and should prove to be a rich source of bright, easily studied, very metal-poor stars.

  9. Lithium Abundance of Metal-poor Stars

    Institute of Scientific and Technical Information of China (English)

    Hua-Wei Zhang; Gang Zhao

    2003-01-01

    High-resolution, high signal-to-noise ratio spectra have been obtained for 32 metal-poor stars. The equivalent widths of Li λ6708A were measured and the lithium abundances were derived. The average lithium abundance of 21 stars on the lithium plateau is 2.33±0.02 dex. The Lithium plateau exhibits a marginal trend along metallicity, dA(Li)/d[Fe/H] = 0.12±0.06, and no clear trend with the effective temperature. The trend indicates that the abundance of lithium plateau may not be primordial and that a part of the lithium was produced in Galactic Chemical Evolution (GCE).

  10. Toward ab initio extremely metal poor stars

    CERN Document Server

    Ritter, Jeremy S; Milosavljevic, Milos; Bromm, Volker

    2016-01-01

    Extremely metal poor stars have been the focus of much recent attention owing to the expectation that their chemical abundances can shed light on the metal and dust yields of the earliest supernovae. We present our most realistic simulation to date of the astrophysical pathway to the first metal enriched stars. We simulate the radiative and supernova hydrodynamic feedback of a 60 Msun Population III star starting from cosmological initial conditions realizing Gaussian density fluctuations. We follow the gravitational hydrodynamics of the supernova remnant at high spatial resolution through its freely-expanding, adiabatic, and radiative phases, until gas, now metal-enriched, has resumed runaway gravitational collapse. Our findings are surprising: while the Population III progenitor exploded with a low energy of 10^51 erg and injected an ample metal mass of 6 Msun, the first cloud to collapse after the supernova explosion is a dense surviving primordial cloud on which the supernova blastwave deposited metals on...

  11. Abundances In Very Metal Poor Dwarf Stars

    CERN Document Server

    Cohen, J G; McWilliam, A; Shectman, S; Thompson, I; Wasserburg, G J; Ivans, I I; Dehn, M; Karlsson, T; Melendez, J; Cohen, Judith G.; Christlieb, Norbert; William, Andrew Mc; Shectman, Steve; Thompson, Ian; Ivans, Inese; Dehn, Matthias; Karlsson, Torgny

    2004-01-01

    We discuss the detailed composition of 28 extremely metal-poor dwarfs, 22 of which are from the Hamburg/ESO Survey, based on Keck Echelle spectra. Our sample has a median [Fe/H] of -2.7 dex, extends to -3.5 dex, and is somewhat less metal-poor than was expected from [Fe/H](HK,HES) determined from low resolution spectra. Our analysis supports the existence of a sharp decline in the distribution of halo stars with metallicity below [Fe/H] = -3.0 dex. So far no additional turnoff stars with [Fe/H]}<-3.5 have been identified in our follow up efforts. For the best observed elements between Mg and Ni, we find that the abundance ratios appear to have reached a plateau, i.e. [X/Fe] is approximately constant as a function of [Fe/H], except for Cr, Mn and Co, which show trends of abundance ratios varying with [Fe/H]. These abundance ratios at low metallicity correspond approximately to the yield expected from Type II SN with a narrow range in mass and explosion parameters; high mass Type II SN progenitors are requir...

  12. Th Ages for Metal-Poor Stars

    CERN Document Server

    Johnson, J A; Johnson, Jennifer A.; Bolte, Michael

    2001-01-01

    With a sample of 22 metal-poor stars, we demonstrate that the heavy element abundance pattern (Z > 55) is the same as the r-process contributions to the solar nebula. This bolsters the results of previous studies that there is a universal r-process production pattern. We use the abundance of thorium in five metal-poor stars, along with an estimate of the initial Th abundance based on the abundances of stable r-process elements, to measure their ages. We have four field red giants with errors of 4.2 Gyr in their ages and one M92 giant with an error of 5.6 Gyr, based on considering the sources of observational error only. We obtain an average age of 11.4 Gyr, which depends critically on the assumption of an initial production ratio of Th/Eu of 0.496. If the Universe is 15 Gyr old, then the initial Th/Eu value should be 0.590, in agreement with some theoretical models of the r-process.

  13. Toward ab initio extremely metal poor stars

    Science.gov (United States)

    Ritter, Jeremy S.; Safranek-Shrader, Chalence; Milosavljević, Miloš; Bromm, Volker

    2016-09-01

    Extremely metal poor stars have been the focus of much recent attention owing to the expectation that their chemical abundances can shed light on the metal and dust yields of the earliest supernovae. We present our most realistic simulation to date of the astrophysical pathway to the first metal enriched stars. We simulate the radiative and supernova hydrodynamic feedback of a 60 M⊙ Population III star starting from cosmological initial conditions realizing Gaussian density fluctuations. We follow the gravitational hydrodynamics of the supernova remnant at high spatial resolution through its freely-expanding, adiabatic, and radiative phases, until gas, now metal-enriched, has resumed runaway gravitational collapse. Our findings are surprising: while the Population III progenitor exploded with a low energy of 1051 erg and injected an ample metal mass of 6 M⊙, the first cloud to collapse after the supernova explosion is a dense surviving primordial cloud on which the supernova blast wave deposited metals only superficially, in a thin, unresolved layer. The first metal-enriched stars can form at a very low metallicity, of only 2 - 5 × 10-4 Z⊙, and can inherit the parent cloud's highly elliptical, radially extended orbit in the dark matter gravitational potential.

  14. The EMBLA Survey - Metal-poor stars in the Galactic bulge

    Science.gov (United States)

    Howes, Louise M.; Asplund, Martin; Keller, Stefan C.; Casey, Andrew R.; Yong, David; Lind, Karin; Frebel, Anna; Hays, Austin; Alves-Brito, Alan; Bessell, Michael S.; Casagrande, Luca; Marino, Anna F.; Nataf, David M.; Owen, Christopher I.; Da Costa, Gary S.; Schmidt, Brian P.; Tisserand, Patrick

    2016-04-01

    Cosmological models predict the oldest stars in the Galaxy should be found closest to the centre of the potential well, in the bulge. The EMBLA Survey successfully searched for these old, metal-poor stars by making use of the distinctive SkyMapper photometric filters to discover candidate metal-poor stars in the bulge. Their metal-poor nature was then confirmed using the AAOmega spectrograph on the AAT. Here we present an abundance analysis of 10 bulge stars with -2.8 <[Fe/H]<- 1.7 from MIKE/Magellan observations, in total determining the abundances of 22 elements. Combining these results with our previous high-resolution data taken as part of the Gaia-ESO Survey, we have started to put together a picture of the chemical and kinematic nature of the most metal-poor stars in the bulge. The currently available kinematic data is consistent with the stars belonging to the bulge, although more accurate measurements are needed to constrain the stars' orbits. The chemistry of these bulge stars deviates from that found in halo stars of the same metallicity. Two notable differences are the absence of carbon-enhanced metal-poor bulge stars, and the alpha-element abundances exhibit a large intrinsic scatter and include stars which are underabundant in these typically enhanced elements.

  15. Spectroscopic analysis of metal-poor stars from LAMOST: early results

    CERN Document Server

    Li, Hai-Ning; Christlieb, Norbert; Wang, Liang; Wang, Wei; Zhang, Yong; Hou, Yonghui; Yuan, Hailong

    2015-01-01

    We report on early results from a pilot program searching for metal-poor stars with LAMOST and follow-up high-resolution observation acquired with the MIKE spectrograph attached to the Magellan~II telescope. We performed detailed abundance analysis for eight objects with iron abundances [Fe/H] < -2.0, including five extremely metal-poor (EMP; [Fe/H] < -3.0) stars with two having [Fe/H] < -3.5. Among these objects, three are newly discovered EMP stars, one of which is confirmed for the first time with high-resolution spectral observations. Three program stars are regarded as carbon-enhanced metal-poor (CEMP) stars, including two stars with no enhancement in their neutron-capture elements, which thus possibly belong to the class of CEMP-no stars; one of these objects also exhibits significant enhancement in nitrogen, and is thus a potential carbon and nitrogen-enhanced metal-poor star. The [X/Fe] ratios of the sample stars generally agree with those reported in the literature for other metal-poor stars...

  16. The origin of low [alpha/Fe] ratios in extremely metal-poor stars

    CERN Document Server

    Kobayashi, Chiaki; Tominaga, Nozomu; Nomoto, Ken'ichi

    2014-01-01

    We show that the low ratios of $\\alpha$ elements (Mg, Si, and Ca) to Fe recently found for a small fraction of extremely metal-poor stars can be naturally explained with the nucleosynthesis yields of core-collapse supernovae, i.e., $13-25M_\\odot$ supernovae, or hypernovae. For the case without carbon enhancement, the ejected iron mass is normal, consistent with observed light curves and spectra of nearby supernovae. On the other hand, the carbon enhancement requires much smaller iron production, and the low [$\\alpha$/Fe] of carbon enhanced metal-poor stars can also be reproduced with $13-25M_\\odot$ faint supernovae or faint hypernovae. Iron-peak element abundances, in particular Zn abundances, are important to put further constraints on the enrichment sources from galactic archaeology surveys.

  17. THE ORIGIN OF LOW [α/Fe] RATIOS IN EXTREMELY METAL-POOR STARS

    Energy Technology Data Exchange (ETDEWEB)

    Kobayashi, Chiaki [School of Physics, Astronomy and Mathematics, Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom); Ishigaki, Miho N.; Tominaga, Nozomu; Nomoto, Ken' ichi, E-mail: c.kobayashi@herts.ac.uk [Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, Kashiwa, Chiba 277-8583 (Japan)

    2014-04-10

    We show that the low ratios of α elements (Mg, Si, and Ca) to Fe recently found for a small fraction of extremely metal-poor stars can be naturally explained with the nucleosynthesis yields of core-collapse supernovae, i.e., 13-25 M {sub ☉} supernovae, or hypernovae. For the case without carbon enhancement, the ejected iron mass is normal, consistent with observed light curves and spectra of nearby supernovae. On the other hand, the carbon enhancement requires much smaller iron production, and the low [α/Fe] of carbon-enhanced metal-poor stars can also be reproduced with 13-25 M {sub ☉} faint supernovae or faint hypernovae. Iron-peak element abundances, in particular Zn abundances, are important to put further constraints on the enrichment sources from galactic archaeology surveys.

  18. High-resolution spectroscopic studies of ultra metal-poor stars found in the LAMOST survey

    Science.gov (United States)

    Li, Haining; Aoki, Wako; Zhao, Gang; Honda, Satoshi; Christlieb, Norbert; Suda, Takuma

    2015-10-01

    We report on the observations of two ultra metal-poor (UMP) stars with [Fe/H] ˜ -4.0, including one new discovery. The two stars are studied in the on-going and quite efficient project to search for extremely metal-poor (EMP) stars with LAMOST and Subaru. Detailed abundances or upper limits of abundances have been derived for 15 elements from Li to Eu based on high-resolution spectra obtained with the High Dispersion Spectrograph (HDS) mounted in the Subaru Telescope. The abundance patterns of both UMP stars are consistent with the "normal population" among the low-metallicity stars. Both of the two program stars show carbon-enhancement without any excess of heavy neutron-capture elements, indicating that they belong to the subclass of (carbon-enhanced metal-poor) CEMP-no stars, as is the case of most UMP stars previously studied. The [Sr/Ba] ratios of both CEMP-no UMP stars are above [Sr/Ba] ˜ -0.4, suggesting the origin of the carbon-excess is not compatible with the mass transfer from an asymptotic giant branch companion where the s-process has operated. Lithium abundance is measured in the newly discovered UMP star LAMOST J125346.09+075343.1, making it the second UMP turnoff star with Li detection. The Li abundance of LAMOST J125346.09+075343.1 is slightly lower than the values obtained for less metal-poor stars with similar temperatures, and provides a unique data point at [Fe/H] ˜ -4.2 to support the "meltdown" of the Li Spite plateau at extremely low metallicity. Comparison with the other two UMP and HMP (hyper metal-poor, with [Fe/H] < -5.0) turnoff stars suggests that the difference in lighter elements such as CNO and Na might cause notable difference in lithium abundances among CEMP-no stars.

  19. Abundance analysis of extremely metal-poor stars

    Science.gov (United States)

    Hansen, T.; Hansen, C. J.; Christlieb, N.; Andersen, J.

    2016-01-01

    The outer atmosphere of the first generations of low-mass (M elements into the early ISM. Thus a detailed abundance analysis of low-mass, metal-poor stars can help us track these gasses and provide insight into the formation processes that took place in the very early stages of our Galaxy. Preliminary result of a 25-star homogeneously analysed sample of metal- poor candidates from the Hamburg/ESO survey is presented. The main focus is on the most metal-poor stars of the sample; stars with [Fe/H] abundance pattern of these ultra metal-poor (UMP) stars is used to extract key information of the earliest ongoing formation processes (ranging from hydrostatic burning to neutron-capture processes).

  20. Near-Field Cosmology with Metal-Poor Stars

    CERN Document Server

    Frebel, Anna

    2015-01-01

    The oldest, most metal-poor stars in the Galactic halo and satellite dwarf galaxies present an opportunity to explore the chemical and physical conditions of the earliest star forming environments in the Universe. We review the fields of stellar archaeology and dwarf galaxy archaeology by examining the chemical abundance measurements of various elements in extremely metal-poor stars. Focus on the carbon-rich and carbon-normal halo star populations illustrates how these provide insight into the Population III star progenitors responsible for the first metal enrichment events. We extend the discussion to near-field cosmology, which is concerned with the formation of the first stars and galaxies and how metal-poor stars can be used to constrain these processes. Complementary abundance measurements in high-redshift gas clouds further help to establish the early chemical evolution of the Universe. The data appear consistent with the existence of two distinct channels of star formation at the earliest times.

  1. The RAVE Survey : Rich in Very Metal-poor Stars

    NARCIS (Netherlands)

    Fulbright, Jon P.; Wyse, Rosemary F. G.; Ruchti, Gregory R.; Gilmore, G. F.; Grebel, Eva; Bienaymé, O.; Binney, J.; Bland-Hawthorn, J.; Campbell, R.; Freeman, K. C.; Gibson, B. K.; Helmi, A.; Munari, U.; Navarro, J. F.; Parker, Q. A.; Reid, W.; Seabroke, G. M.; Siebert, A.; Siviero, A.; Steinmetz, M.; Watson, F. G.; Williams, M.; Zwitter, T.

    2010-01-01

    Very metal-poor stars are of obvious importance for many problems in chemical evolution, star formation, and galaxy evolution. Finding complete samples of such stars which are also bright enough to allow high-precision individual analyses is of considerable interest. We demonstrate here that stars w

  2. Extremely metal-poor star candidates in the SDSS

    Science.gov (United States)

    Xu, Si-Yao; Zhang, Hua-Wei; Liu, Xiao-Wei

    2013-03-01

    For a sample of metal-poor stars (-3.3 Digital Sky Survey (SDSS), calculated effective temperatures from (g - z)0 color, deduced stellar surface gravities by fitting stellar isochrones, and determined metallicities based on the aforementioned quantities. Metallicities thus derived from the Ca II K line are in much better agreement with the results determined from high-resolution spectra than the values given in the SDSS Data Release 7. The metallicities derived from the Mg I b lines have a large dispersion owing to the large measurement errors, whereas those deduced from the Ca II triplet lines are too high due to both non-local thermodynamical equilibrium (NLTE) effects and measurement errors. Abundances after correction for the NLTE effect for the Mg I b lines and Ca II triplet lines are also presented. Following this method, we have identified six candidates of ultra-metal-poor stars with [Fe/H] ~ -4.0 from a sample of 166 metal-poor star candidates. One of them, SDSS J102915+172927, was recently confirmed to be an ultra-metal-poor ([Fe/H] 4.0) star with the lowest metallicity ever measured. Follow-up high-resolution spectroscopy for the other five ultra-metal-poor stars in our sample will therefore be of great interest.

  3. Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way.

    Science.gov (United States)

    Howes, L M; Casey, A R; Asplund, M; Keller, S C; Yong, D; Nataf, D M; Poleski, R; Lind, K; Kobayashi, C; Owen, C I; Ness, M; Bessell, M S; Da Costa, G S; Schmidt, B P; Tisserand, P; Udalski, A; Szymański, M K; Soszyński, I; Pietrzyński, G; Ulaczyk, K; Wyrzykowski, Ł; Pietrukowicz, P; Skowron, J; Kozłowski, S; Mróz, P

    2015-11-26

    The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium ('metals') have been found in the outer regions ('halo') of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions ('bulges') of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during the first 1-2 billion years, leading to a dearth of early, metal-poor stars. Here we report observations of extremely metal-poor stars in the Milky Way bulge, including one star with an iron abundance about 10,000 times lower than the solar value without noticeable carbon enhancement. We confirm that most of the metal-poor bulge stars are on tight orbits around the Galactic Centre, rather than being halo stars passing through the bulge, as expected for stars formed at redshifts greater than 15. Their chemical compositions are in general similar to typical halo stars of the same metallicity although intriguing differences exist, including lower abundances of carbon. PMID:26560034

  4. Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way

    CERN Document Server

    Howes, L M; Asplund, M; Keller, S C; Yong, D; Nataf, D M; Poleski, R; Lind, K; Kobayashi, C; Owen, C I; Ness, M; Bessell, M S; Da Costa, G S; Schmidt, B P; Tisserand, P; Udalski, A; Szymański, M K; Soszyński, I; Pietrzyński, G; Ulaczyk, K; Wyrzykowski, Ł; Pietrukowicz, P; Skowron, J; Kozłowski, S; Mróz, P

    2015-01-01

    The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium ('metals') have been found in the outer regions ('halo') of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions ('bulges') of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during the first 1-2 billion years, leading to a dearth of early, metal-poor stars. Here we report observations of extremely metal-poor stars in the Milky Way bulge, including one star with an iron abundance about 10,000 times lower than the solar value without noticeable carbon enhancement. We confirm that the most metal-poor bulge stars are on tight orbits around the Galactic Centre, rather than being halo stars passing through...

  5. Behavior of sulfur in extremely metal-poor stars

    Science.gov (United States)

    Takada-Hidai, Masahide; Sargent, Wallace L. W.

    The LTE abundances of sulfur (S) were explored in the sample of 15 metal-poor stars with the metallicity range of -4Takada-Hidai et al. (2005), we found that the behavior of [S/Fe] against [Fe/H] shows a nearly flat trend in the range of metallicity down to [Fe/H]˜-4.

  6. Asteroseismic modelling of the metal-poor star Tau Ceti

    CERN Document Server

    Tang, Yanke; 10.1051/0004-6361/201014886

    2010-01-01

    Context. Asteroseismology is an effcient tool not only for testing stellar structure and evolutionary theory but also constraining the parameters of stars for which solar-like oscillations are detected, presently. As an important southern asteroseismic target, Tau Ceti, is a metal-poor star. The main features of the oscillations and some frequencies of ? Ceti have been identified. Many scientists propose to comprehensively observe this star as part of the Stellar Observations Network Group. Aims. Our goal is to obtain the optimal model and reliable fundamental parameters for the metal-poor star Tau Ceti by combining all non-asteroseismic observations with these seismological data. Methods. Using the Yale stellar evolution code (YREC), a grid of stellar model candidates that fall within all the error boxes in the HR diagram have been constructed, and both the model frequencies and large- and small- frequency separations are calculated using the Guenther's stellar pulsation code. The \\chi2c minimization is perf...

  7. The Best and Brightest Metal-Poor Stars

    CERN Document Server

    Schlaufman, Kevin C

    2014-01-01

    The chemical abundances of large samples of extremely metal-poor (EMP) stars can be used to investigate metal-free stellar populations, supernovae, and nucleosynthesis as well as the formation and galactic chemical evolution of the Milky Way and its progenitor halos. However, current progress on the study of EMP stars is being limited by their faint apparent magnitudes. The acquisition of high signal-to-noise spectra for faint EMP stars requires a major telescope time commitment, making the construction of large samples of EMP star abundances prohibitively expensive. We have developed a new, efficient selection that uses only public, all-sky APASS optical, 2MASS near-infrared, and WISE mid-infrared photometry to identify bright metal-poor star candidates through their lack of molecular absorption near 4.6 microns. We have used our selection to identify 11,916 metal-poor star candidates with V < 14, increasing the number of publicly-available candidates by more than a factor of five in this magnitude range....

  8. Europium Isotopic Abundances in Very Metal-poor Stars

    CERN Document Server

    Sneden, C; Lawler, J E; Burles, S M; Beers, T C; Fuller, G M; Sneden, Christopher; Cowan, John J.; Lawler, James E.; Burles, Scott; Beers, Timothy C.; Fuller, George M.

    2002-01-01

    Europium isotopic abundance fractions are reported for the very metal-poor, neutron-capture-rich giant stars CS 22892-052, HD 115444, and BD +17 3248. The abundance fractions, derived from analysis of several strong Eu II lines appearing in high-resolution spectra of these stars, are in excellent agreement with each other and with their values in the Solar System: fraction(\\iso{Eu}{151}) ~= fraction(\\iso{Eu}{153}) ~= 0.5. Detailed abundance studies of very metal-poor stars have previously shown that the total elemental abundances of stable atoms with atomic numbers z >= 56 typically match very closely those of a scaled solar-system r-process abundance distribution. The present results for the first time extend this agreement to the isotopic level.

  9. SPECTROSCOPIC ANALYSIS OF METAL-POOR STARS FROM LAMOST: EARLY RESULTS

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hai-Ning; Zhao, Gang; Wang, Liang; Wang, Wei; Yuan, Hailong [Key Lab of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang, Beijing 100012 (China); Christlieb, Norbert [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Zhang, Yong; Hou, Yonghui, E-mail: lhn@nao.cas.cn, E-mail: gzhao@nao.cas.cn [Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042 (China)

    2015-01-10

    We report on early results from a pilot program searching for metal-poor stars with LAMOST and follow-up high-resolution observation acquired with the MIKE spectrograph attached to the Magellan II telescope. We performed detailed abundance analysis for eight objects with iron abundances [Fe/H] < -2.0, including five extremely metal-poor (EMP; [Fe/H] < -3.0) stars with two having [Fe/H] < -3.5. Among these objects, three are newly discovered EMP stars, one of which is confirmed for the first time with high-resolution spectral observations. Three program stars are regarded as carbon-enhanced metal-poor (CEMP) stars, including two stars with no enhancement in their neutron-capture elements, which thus possibly belong to the class of CEMP-no stars; one of these objects also exhibits significant enhancement in nitrogen, and is thus a potential carbon and nitrogen-enhanced metal-poor star. The [X/Fe] ratios of the sample stars generally agree with those reported in the literature for other metal-poor stars in the same [Fe/H] range. We also compared the abundance patterns of individual program stars with the average abundance pattern of metal-poor stars and find only one chemically peculiar object with abundances of at least two elements (other than C and N) showing deviations larger than 0.5 dex. The distribution of [Sr/Ba] versus [Ba/H] agrees that an additional nucleosynthesis mechanism is needed aside from a single r-process. Two program stars with extremely low abundances of Sr and Ba support the prospect that both main and weak r-processes may have operated during the early phase of Galactic chemical evolution. The distribution of [C/N] shows that there are two groups of carbon-normal giants with different degrees of mixing. However, it is difficult to explain the observed behavior of the [C/N] of the nitrogen-enhanced unevolved stars based on current data.

  10. La and Eu Abundances in Metal-poor Halo Stars

    Science.gov (United States)

    Cardillo, Harrison; Burris, Debra L.

    2016-01-01

    Elements with atomic number greater than Z=26 (the Iron Peak) cannot be formed through fusion in a star's core; the majority of these elements are produced through one of two neutron-capture processes. Early in the history of the Galaxy, the rapid neutron-capture process (r-process) is believed to be responsible for the production of elements Z=56 and beyond. These elements require at least one generation of stars to have completed their life cycle in order to be synthesized. Therefore, if we observe the heavy metal abundances in what are called Population II stars (metal-poor stars), then we can begin to make inferences about the chemistry of the earliest stars in the Galaxy. To contribute to this picture of the early universe, the Lanthanum and Europium abundances of low-metallicity stars will be measured and trends in these abundances based on comparisons to existing related literature will be sought.

  11. High-resolution spectroscopic studies of ultra metal-poor stars found in LAMOST survey

    CERN Document Server

    Li, Haining; Zhao, Gang; Honda, Satoshi; Christlieb, Norbert; Suda, Takuma

    2015-01-01

    We report on the observations of two ultra metal-poor (UMP) stars with [Fe/H]~-4.0 including one new discovery. The two stars are studied in the on-going and quite efficient project to search for extremely metal-poor (EMP) stars with LAMOST and Subaru. Detailed abundances or upper limits of abundances have been derived for 15 elements from Li to Eu based on high-resolution spectra obtained with Subaru/HDS. The abundance patterns of both UMP stars are consistent with the "normal-population" among the low-metallicity stars. Both of the two program stars show carbon-enhancement without any excess of heavy neutron-capture elements, indicating that they belong to the subclass of CEMP-no stars, as is the case of most UMP stars previously studied. The [Sr/Ba] ratios of both CEMP-no UMP stars are above [Sr/Ba]~-0.4, suggesting the origin of the carbon-excess is not compatible with the mass transfer from an AGB companion where the s-process has operated. Lithium abundance is measured in the newly discovered UMP star L...

  12. Inefficient star formation in extremely metal poor galaxies

    OpenAIRE

    Shi, Yong; Armus, Lee; Helou, George; Stierwalt, Sabrina; Gao, Yu; Wang, Junzhi; Zhang, Zhi-Yu; Gu, Qiusheng

    2014-01-01

    The first galaxies contain stars born out of gas with few or no ‘metals’ (that is, elements heavier than helium). The lack of metals is expected to inhibit efficient gas cooling and star formation, but this effect has yet to be observed in galaxies with an oxygen abundance (relative to hydrogen) below a tenth of that of the Sun. Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epoc...

  13. Abundance anomalies in metal-poor stars from Population III supernova ejecta hydrodynamics

    CERN Document Server

    Sluder, Alan; Safranek-Shrader, Chalence; Milosavljevic, Milos; Bromm, Volker

    2015-01-01

    We present a simulation of the long-term evolution of a Population III supernova remnant in a cosmological minihalo. Employing passive Lagrangian tracer particles, we investigate how chemical stratification and anisotropy in the explosion can affect the abundances of the first low-mass, metal-enriched stars. We find that reverse shock heating can leave the inner mass shells at entropies too high to cool, leading to carbon-enhancement in the re-collapsing gas. This hydrodynamic selection effect could explain the observed incidence of carbon-enhanced metal-poor (CEMP) stars at low metallicity. We further explore how anisotropic ejecta distributions, recently seen in direct numerical simulations of core-collapse explosions, may translate to abundances in metal-poor stars. We find that some of the observed scatter in the Population II abundance ratios can be explained by an incomplete mixing of supernova ejecta, even in the case of only one contributing enrichment event. We demonstrate that the customary hypothes...

  14. The RAVE Survey: Rich in Very Metal-Poor Stars

    CERN Document Server

    Fulbright, Jon P; Ruchti, Gregory R; Gilmore, G F; Grebel, Eva; ~Bienayme, O; Binney, J; Bland-Hawthorn, J; Campbell, R; Freeman, K C; Gibson, B K; Helmi, A; Munari, U; Navarro, J F; Parker, Q A; Reid, W; Seabroke, G M; Siebert, A; Siviero, A; Steinmetz, M; Watson, F G; Williams, M; Zwitter, T

    2010-01-01

    Very metal-poor stars are of obvious importance for many problems in chemical evolution, star formation, and galaxy evolution. Finding complete samples of such stars which are also bright enough to allow high-precision individual analyses is of considerable interest. We demonstrate here that stars with iron abundances [Fe/H] < -2 dex, and down to below -4 dex, can be efficiently identified within the Radial Velocity Experiment (RAVE) survey of bright stars, without requiring additional confirmatory observations. We determine a calibration of the equivalent width of the Calcium triplet lines measured from the RAVE spectra onto true [Fe/H], using high spectral resolution data for a subset of the stars. These RAVE iron abundances are accurate enough to obviate the need for confirmatory higher-resolution spectroscopy. Our initial study has identified 631 stars with [Fe/H] <= -2, from a RAVE database containing approximately 200,000 stars. This RAVE-based sample is complete for stars with [Fe/H] < -2.5, a...

  15. Radioactive Ages of Metal-Poor Halo Stars

    Institute of Scientific and Technical Information of China (English)

    Ji Li; Gang Zhao

    2004-01-01

    The abundances of long-lived radioactive elements Th and U observed in metal-poor halo stars can be used as chronometers to determine the age of individual stars, and hence set a lower limit on the age of the Galaxy and hence of the universe.This radioactive dating requires the zero-decay productions of Th and U, which involves complicated r-process nucleosynthesis calculations. Several parametric rprocess models have been used to calculate the initial abundance ratios of Th/Eu and U/Th, but, due to the sharp sensitivity of these models to nuclear physics inputs, the calculations have relatively large uncertainties which lead to large uncertainties in the age determinations. In order to reduce these uncertainties, we present a simple method to estimate the initial productions of Th and U, which only depends on the solar system abundances and the stellar abundances of stable r-process elements.From our calculations of the initial abundance ratios of Th/Eu and U/Th, we reestimate the ages of those very metal-poor halo stars with published abundances of Th and U. Our age estimates are consistent, within the errors, with the other age determinations derived from r-process models, and offer useful constrains for r-process theoretical calculations. The advantages and limitations of our simple method of radioactive dating are discussed.

  16. A New Type of Extremely Metal Poor Star

    CERN Document Server

    Cohen, J G; Christlieb, N; Shectman, S; Thompson, I; Melendez, J; Reimers, L W D; Cohen, Judith G.; William, Andrew Mc; Christlieb, Norbert; Shectman, Stephen; Thompson, Ian; Melendez, Jorge; Reimers, Lutz Wisotzki & Dieter

    2007-01-01

    We present an abundance analysis for the extremely metal poor star HE1424-0241 based on high dispersion spectra from HIRES at Keck. This star is a giant on the lower red giant branch with [Fe/H] ~ -4.0 dex. Relative to Fe, HE1424-0241 has normal Mg, but it shows a very large deficiency of Si, with epsilon(Si)/epsilon(Fe) ~ 1/10 and epsilon(Si)/epsilon(Mg) ~ 1/25 that of all previously known extremely metal poor giants or dwarfs. It also has a moderately large deficiency of Ca and a smaller deficit of Ti, combined with enhanced Mn and Co and normal or low C. We suggest that in HE1424-0241 we see the effect of a very small number of contributing supernovae, and that the SNII contributing to the chemical inventory of HE1424-0241 were biased in progenitor mass or in explosion characteristics so as to reproduce its abnormal extremely low Si/Mg ratio. HE1424-0241 shows a deficiency of the explosive alpha-burning elements Si, Ca and Ti coupled with a ratio [Mg/Fe] normal for EMP stars; Mg is produced via hydrostatic...

  17. Extremely metal-poor stars in SDSS fields

    CERN Document Server

    Bonifacio, Piercarlo; François, Patrick; Sbordone, Luca; Ludwig, Hans-G; Spite, Monique; Molaro, Paolo; Spite, François; Cayrel, Roger; Hammer, François; Hill, Vanessa; Nonino, Mario; Randich, Sofia; Stelzer, Beate; Zaggia, Simone

    2011-01-01

    Some insight on the first generation of stars can be obtained from the chemical composition of their direct descendants, extremely metal-poor stars (EMP), with metallicity less than or equal to 1/1000 of the solar metalllicity. Such stars are exceedingly rare, the most successful surveys, for this purpose, have so far provided only about 100 stars with 1/1000 the solar metallicity and 4 stars with about 1/10000 of the solar metallicity. The Sloan Digital Sky Survey has the potential to provide a large number of candidates of extremely low metallicity. X-Shooter has the unique capability of performing the necessary follow-up spectroscopy providing accurate metallicities and abundance ratios for several elements (Mg, Al, Ca, Ti, Cr, Sr,...) for EMP candidates. We here report on the results for the first two stars observed in the course of our franco-italian X-Shooter GTO. The two stars were targeted to be of metallicity around -3.0, the analysis of the X-Shooter spectra showed them to be of metallicity around -...

  18. The frequency of giant planets around metal-poor stars

    CERN Document Server

    Mortier, A; Sozzetti, A; Mayor, M; Latham, D; Bonfils, X; Udry, S

    2012-01-01

    Context. The discovery of about 700 extrasolar planets, so far, has lead to the first statistics concerning extrasolar planets. The presence of giant planets seems to depend on stellar metallicity and mass. For example, they are more frequent around metal-rich stars,with an exponential increase in planet occurrence rates with metallicity. Aims. We analyzed two samples of metal-poor stars (-2.0 \\leq [Fe/H] \\leq 0.0) to see if giant planets are indeed rare around these objects. Radial velocity datasets were obtained with two different spectrographs (HARPS and HIRES). Detection limits for these data,expressed in minimum planetary mass and period, are calculated. These produce trustworthy numbers for the planet frequency. Methods. A general Lomb Scargle (GLS) periodogram analysis was used together with a bootstrapping method to produce the detection limits. Planet frequencies were calculated based on a binomial distribution function within metallicity bins. Results. Almost all hot Jupiters and most giant planets ...

  19. Searching for dust around hyper metal poor stars

    Energy Technology Data Exchange (ETDEWEB)

    Venn, Kim A.; Divell, Mike; Starkenburg, Else [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC, V8P 5C2 (Canada); Puzia, Thomas H. [Institute of Astrophysics, Pontificia Universidad Catolica de Chile, Av. Vicuna Mackenna 4860, 7820436 Macul, Santiago (Chile); Côté, Stephanie [NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada); Lambert, David L., E-mail: kvenn@uvic.ca [McDonald Observatory and the Department of Astronomy, University of Texas at Austin, RLM 15.308, Austin, TX 78712 (United States)

    2014-08-20

    We examine the mid-infrared fluxes and spectral energy distributions for stars with iron abundances [Fe/H] <–5, and other metal-poor stars, to eliminate the possibility that their low metallicities are related to the depletion of elements onto dust grains in the formation of a debris disk. Six out of seven stars examined here show no mid-IR excesses. These non-detections rule out many types of circumstellar disks, e.g., a warm debris disk (T ≤ 290 K), or debris disks with inner radii ≤1 AU, such as those associated with the chemically peculiar post-asymptotic giant branch spectroscopic binaries and RV Tau variables. However, we cannot rule out cooler debris disks, nor those with lower flux ratios to their host stars due to, e.g., a smaller disk mass, a larger inner disk radius, an absence of small grains, or even a multicomponent structure, as often found with the chemically peculiar Lambda Bootis stars. The only exception is HE0107-5240, for which a small mid-IR excess near 10 μm is detected at the 2σ level; if the excess is real and associated with this star, it may indicate the presence of (recent) dust-gas winnowing or a binary system.

  20. Searching for dust around hyper metal poor stars

    International Nuclear Information System (INIS)

    We examine the mid-infrared fluxes and spectral energy distributions for stars with iron abundances [Fe/H] <–5, and other metal-poor stars, to eliminate the possibility that their low metallicities are related to the depletion of elements onto dust grains in the formation of a debris disk. Six out of seven stars examined here show no mid-IR excesses. These non-detections rule out many types of circumstellar disks, e.g., a warm debris disk (T ≤ 290 K), or debris disks with inner radii ≤1 AU, such as those associated with the chemically peculiar post-asymptotic giant branch spectroscopic binaries and RV Tau variables. However, we cannot rule out cooler debris disks, nor those with lower flux ratios to their host stars due to, e.g., a smaller disk mass, a larger inner disk radius, an absence of small grains, or even a multicomponent structure, as often found with the chemically peculiar Lambda Bootis stars. The only exception is HE0107-5240, for which a small mid-IR excess near 10 μm is detected at the 2σ level; if the excess is real and associated with this star, it may indicate the presence of (recent) dust-gas winnowing or a binary system.

  1. Chemical abundances of distant extremely metal-poor unevolved stars

    CERN Document Server

    Bonifacio, P; Caffau, E; Ludwig, H -G; Spite, M; Hernández, J I González; Behara, N T

    2012-01-01

    Aims: The purpose of our study is to determine the chemical composition of a sample of 16 candidate Extremely Metal-Poor (EMP) dwarf stars, extracted from the Sloan Digital Sky Survey (SDSS). There are two main purposes: in the first place to verify the reliability of the metallicity estimates derived from the SDSS spectra; in the second place to see if the abundance trends found for the brighter nearer stars studied previously also hold for this sample of fainter, more distant stars. Methods: We used the UVES at the VLT to obtain high-resolution spectra of the programme stars. The abundances were determined by an automatic analysis with the MyGIsFOS code, with the exception of lithium, for which the abundances were determined from the measured equivalent widths of the Li I resonance doublet. Results: All candidates are confirmed to be EMP stars, with [Fe/H]<= -3.0. The chemical composition of the sample of stars is similar to that of brighter and nearer samples. We measured the lithium abundance for 12 st...

  2. METAL-POOR STARS OBSERVED WITH THE MAGELLAN TELESCOPE. I. CONSTRAINTS ON PROGENITOR MASS AND METALLICITY OF AGB STARS UNDERGOING s-PROCESS NUCLEOSYNTHESIS

    OpenAIRE

    Placco, Vinicius M.; Beers, Timothy C.; Karakas, Amanda I.; Kennedy, Catherine R.; Rossi, Silvia; Christlieb, N.; Stancliffe, Richard J.; Frebel, Anna L.

    2013-01-01

    We present a comprehensive abundance analysis of two newly discovered carbon-enhanced metal-poor (CEMP) stars. HE 2138?3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if non-local thermodynamic equilibrium corrections are included ([Pb/Fe] = +3.84). HE 2258?6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO...

  3. Metal-Poor Stars Observed with the Magellan Telescope I. Constraints on Progenitor Mass and Metallicity of AGB Stars Undergoing s-Process Nucleosynthesis

    OpenAIRE

    Placco, Vinicius M.; Frebel, Anna; Beers, Timothy C.; Karakas, Amanda I.; Kennedy, Catherine R.; Rossi, Silvia; Christlieb, Norbert; Stancliffe, Richard J.

    2013-01-01

    We present a comprehensive abundance analysis of two newly-discovered carbon-enhanced metal-poor (CEMP) stars. HE2138-3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if NLTE corrections are included ([Pb/Fe] = +3.84). HE2258-6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and foll...

  4. Inefficient star formation in extremely metal poor galaxies.

    Science.gov (United States)

    Shi, Yong; Armus, Lee; Helou, George; Stierwalt, Sabrina; Gao, Yu; Wang, Junzhi; Zhang, Zhi-Yu; Gu, Qiusheng

    2014-10-16

    The first galaxies contain stars born out of gas with few or no 'metals' (that is, elements heavier than helium). The lack of metals is expected to inhibit efficient gas cooling and star formation, but this effect has yet to be observed in galaxies with an oxygen abundance (relative to hydrogen) below a tenth of that of the Sun. Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epochs. Carbon monoxide emission is unreliable as a tracer of gas at low metallicities, and while dust has been used to trace gas in low-metallicity galaxies, low spatial resolution in the far-infrared has typically led to large uncertainties. Here we report spatially resolved infrared observations of two galaxies with oxygen abundances below ten per cent of the solar value, and show that stars formed very inefficiently in seven star-forming clumps in these galaxies. The efficiencies are less than a tenth of those found in normal, metal rich galaxies today, suggesting that star formation may have been very inefficient in the early Universe. PMID:25318522

  5. Searching for Dust around Hyper Metal-Poor Stars

    CERN Document Server

    Venn, Kim A; Divell, Mike; Cote, Stephanie; Lambert, David L; Starkenburg, Else

    2014-01-01

    We examine the mid-infrared fluxes and spectral energy distributions for metal-poor stars with iron abundances [Fe/H] $\\lesssim-5$, as well as two CEMP-no stars, to eliminate the possibility that their low metallicities are related to the depletion of elements onto dust grains in the formation of a debris disk. Six out of seven stars examined here show no mid-IR excess. These non-detections rule out many types of circumstellar disks, e.g. a warm debris disk ($T\\!\\le\\!290$ K), or debris disks with inner radii $\\le1$ AU, such as those associated with the chemically peculiar post-AGB spectroscopic binaries and RV Tau variables. However, we cannot rule out cooler debris disks, nor those with lower flux ratios to their host stars due to, e.g. a smaller disk mass, a larger inner disk radius, an absence of small grains, or even a multicomponent structure, as often found with the chemically peculiar Lambda Bootis stars. The only exception is HE0107-5240, for which a small mid-IR excess near 10 microns is detected at ...

  6. Inefficient Star Formation In Extremely Metal Poor Galaxies

    CERN Document Server

    Shi, Yong; Helou, George; Stierwalt, Sabrina; Gao, Yu; Wang, Junzhi; Zhang, Zhi-Yu; Gu, Qiusheng

    2014-01-01

    The first galaxies contain stars born out of gas with little or no metals. The lack of metals is expected to inhibit efficient gas cooling and star formation but this effect has yet to be observed in galaxies with oxygen abundance relative to hydrogen below a tenth of that of the Sun. Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epochs. Carbon Monoxide (CO) emission is unreliable as tracers of gas at low metallicities, and while dust has been used to trace gas in low-metallicity galaxies, low-spatial resolution in the far-infrared has typically led to large uncertainties. Here we report spatially-resolved infrared observations of two galaxies with oxygen abundances below 10 per cent solar, and show that stars form very inefficiently in seven star-forming clumps of these galaxies. The star formation efficiencies are more than ten times lower than found in normal, metal rich galaxies today, sugge...

  7. First stars VII. Lithium in extremely metal poor dwarfs

    CERN Document Server

    Bonifacio, P; Sivarani, T; Cayrel, R; Spite, M; Spite, F; Plez, B; Andersen, J; Barbuy, B; Beers, T C; Depagne, E; Hill, V; François, P; Nordström, B; Primas, F

    2006-01-01

    Aims. This study aims to determine the level and constancy of the Spite plateau as definitively as possible from homogeneous high-quality VLT-UVES spectra of 19 of the most metal-poor dwarf stars known. Methods. Our high-resolution (R ~ 43000), high S/N spectra are analysed with OSMARCS 1D LTE model atmospheres and turbospectrum synthetic spectra to determine effective temperatures, surface gravities, and metallicities as well as Li abundances for our stars. Results. Eliminating a cool subgiant and a spectroscopic binary, we find 8 stars to have -3.5 < [Fe/H] < -3.0 and 9 stars with -3.0 < [Fe/H] < -2.5. Our best value for the mean level of the plateau is A(Li) =2.10 +- 0.09. The scatter around the mean is entirely explained by our estimate of the observational error and does not allow for any intrinsic scatter in the Li abundances. In addition, we conclude that a systematic error of the order of 200 K in any of the current temperature scales remains possible. The iron excitation equilibria in our...

  8. FORMATION HISTORY OF METAL-POOR HALO STARS WITH THE HIERARCHICAL MODEL AND THE EFFECT OF INTERSTELLAR MATTER ACCRETION ON THE MOST METAL-POOR STARS

    International Nuclear Information System (INIS)

    We investigate star formation and chemical evolution in the early universe by considering the merging history of the Galaxy in the Λ cold dark matter scenario according to the extended Press-Schechter theory. We give some possible constraints from comparisons with observation of extremely metal-poor (EMP) stars, made available by the recent large-scale surveys and by the follow-up high-resolution spectroscopy. We demonstrate that (1) the hierarchical structure formation can explain the characteristics of the observed metallicity distribution function including a break around [Fe/H] = -4; (2) a high-mass initial mass function (IMF) of peak mass ∼10 Msun with the contribution of binaries, derived from the statistics of carbon-enhanced EMP stars, predicts the frequency of low-mass survivors consistent with the number of EMP stars observed for -4 ∼ [Fe/H] ∼> -2.5, or even larger, as far as the field stars of the Galactic halo are concerned. We further study the effects of surface pollution through the accretion of interstellar matter (ISM) along the chemical and dynamical evolution of the Galaxy for low-mass Population III and EMP survivors. Because of the shallower potential of smaller halos, the accretion of ISM in the mini-halos in which these stars were born dominates the surface metal pollution. This can account for the surface iron abundances as observed for the HMP stars if the cooling and concentration of gas in their birth mini-halos are taken into account. We also study the feedback effect from the very massive Population III stars. The metal pre-pollution by pair-instability SNe is shown to be compatible with the observed lack of their nucleosynthetic signatures when some positive feedback on gas cooling works and changes the IMF from being very massive to being high mass.

  9. The lithium isotopic ratio in very metal-poor stars

    CERN Document Server

    Lind, Karin; Asplund, Martin; Collet, Remo; Magic, Zazralt

    2013-01-01

    Un-evolved, very metal-poor stars are the most important tracers of the cosmic abundance of lithium in the early universe. Combining the standard Big Bang nucleosynthesis model with Galactic production through cosmic ray spallation, these stars at [Fe/H]<-2 are expected to show an undetectably small 6Li/7Li isotopic signature. Evidence to the contrary may necessitate an additional pre-galactic production source or a revision of the standard model of Big Bang nucleosynthesis. We revisit the isotopic analysis of four halo stars, two with claimed 6Li-detections in the literature, to investigate the influence of improved model atmospheres and line formation treatment. For the first time, a combined 3D, NLTE (non-local thermodynamic equilibrium) modelling technique for Li, Na, and Ca lines is utilised to constrain the intrinsic line-broadening and to determine the Li isotopic ratio. We discuss the influence of 3D NLTE effects on line profile shapes and assess the realism of our modelling using the Ca excitation...

  10. High-Resolution Spectroscopy of Extremely Metal-Poor Stars from SDSS/SEGUE: II. Binary Fraction

    CERN Document Server

    Aoki, Wako; Beers, Timothy C; Honda, Satoshi

    2014-01-01

    The fraction of binary systems in various stellar populations of the Galaxy and the distribution of their orbital parameters are important but not well-determined factors in studies of star formation, stellar evolution, and Galactic chemical evolution. While observational studies have been carried out for a large sample of nearby stars, including some metal-poor, Population II stars, almost no constraints on the binary nature for extremely metal-poor (EMP; [Fe/H] < -3.0) stars have yet been obtained. Here we investigate the fraction of double-lined spectroscopic binaries and carbon-enhanced metal-poor (CEMP) stars, many of which could have formed as pairs of low-mass and intermediate-mass stars, to estimate the lower limit of the fraction of binary systems having short periods. The estimate is based on a sample of very metal-poor stars selected from the Sloan Digital Sky Survey, and observed at high spectral resolution in a previous study by Aoki et al. That survey reported three double-lined spectroscopic...

  11. Germanium, Arsenic, and Selenium Abundances in Metal-Poor Stars

    CERN Document Server

    Roederer, Ian U

    2012-01-01

    The elements germanium (Ge, Z=32), arsenic (As, Z=33), and selenium (Se, Z=34) span the transition from charged-particle or explosive synthesis of the iron-group elements to neutron-capture synthesis of heavier elements. Among these three elements, only the chemical evolution of germanium has been studied previously. Here we use archive observations made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope and observations from several ground-based facilities to study the chemical enrichment histories of seven stars with metallicities -2.6 < [Fe/H] < -0.4. We perform a standard abundance analysis of germanium, arsenic, selenium, and several other elements produced by neutron-capture reactions. When combined with previous derivations of germanium abundances in metal-poor stars, our sample reveals an increase in the [Ge/Fe] ratios at higher metallicities. This could mark the onset of the weak s-process contribution to germanium. In contrast, the [As/Fe] and [Se/Fe] ratios rema...

  12. Exploring the Origin of Lithium, Carbon, Strontium and Barium with four new Ultra Metal-Poor Stars

    CERN Document Server

    Hansen, T; Christlieb, N; Yong, D; Bessell, M S; Pérez, A E García; Beers, T C; Placco, V M; Frebel, A; Norris, J E; Asplund, M

    2014-01-01

    We present an elemental abundance analysis for four newly discovered ultra metal-poor stars from the Hamburg/ESO survey, with $\\mathrm{[Fe/H]}\\leq-4$. Based on high-resolution, high signal-to-noise spectra, we derive abundances for 17 elements in the range from Li to Ba. Three of the four stars exhibit moderate to large over-abundances of carbon, but have no enhancements in their neutron-capture elements. The most metal-poor star in the sample, HE~0233$-$0343 ($\\mathrm{[Fe/H]} = -4.68$), is a subgiant with a carbon enhancement of $\\mathrm{[C/Fe]}= +3.5$, slightly above the carbon-enhancement plateau suggested by Spite et al. No carbon is detected in the spectrum of the fourth star, but the quality of its spectrum only allows for the determination of an upper limit on the carbon abundance ratio of $\\mathrm{[C/Fe]} < +1.7$. We detect lithium in the spectra of two of the carbon-enhanced stars, including HE~0233$-$0343. Both stars with Li detections are Li-depleted, with respect to the Li plateau for metal-poo...

  13. Molecular line formation in the extremely metal-poor star BD+44 493

    CERN Document Server

    Aoki, Wako

    2015-01-01

    Molecular absorption lines of OH (99 lines) and CH (105 lines) are measured for the carbon-enhanced metal-poor star BD+44 493 with [Fe/H]=-3.8. The abundances of oxygen and carbon determined from individual lines based on an 1D-LTE analysis exhibit significant dependence on excitation potentials of the lines; d log e/d chi ~ -0.15 - -0.2 dex/eV, where e and chi are elemental abundances from individual spectral lines and their excitation potentials, respectively. The dependence is not explained by the uncertainties of stellar parameters, but suggests that the atmosphere of this object possesses a cool layer that is not reproduced by the 1D model atmosphere. This result agrees with the predictions by 3D model calculations. Although absorption lines of neutral iron exhibit similar trend, it is much weaker than found in molecular lines and that predicted by 3D LTE models.

  14. Abundances of 30 elements in 23 metal-poor stars

    CERN Document Server

    Johnson, J A

    2002-01-01

    We report the abundances of 30 elements in 23 metal-poor ([Fe/H] 0.10 dex, the relative abundances, especially between closely allied atoms such as the rare earth group, often show only small (<0.03 dex) changes. We found that some strong lines of FeI, MnI and CrI consistently gave lower abundances by ~0.2 dex, a number larger than the quoted errors in the gf values. After considering a model with depth-dependent microturbulent velocity and a model with hotter temperatures in the upper layers, we conclude that the latter did a better job of resolving the problem and agreeing with observational evidence for the structure of stars. The error analysis includes the effects of correlation of Teff, log g, and microturbulent velocity errors, which is crucial for certain element ratios, such as [Mg/Fe]. The abundances presented here are being analyzed and discussed in a separate series of papers.

  15. High-resolution spectroscopy of extremely metal-poor stars from SDSS/Segue. II. Binary fraction

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, Wako; Suda, Takuma [National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Beers, Timothy C. [Department of Physics and JINA Center for the Evolution of the Elements, University of Notre Dame,225 Nieuwland Science Hall, Notre Dame, IN 46656 (United States); Honda, Satoshi, E-mail: aoki.wako@nao.ac.jp, E-mail: takuma.suda@nao.ac.jp, E-mail: tbeers@nd.edu, E-mail: honda@nhao.jp [Center for Astronomy, University of Hyogo, 407-2, Nishigaichi, Sayo-cho, Sayo, Hyogo 679-5313 (Japan)

    2015-02-01

    The fraction of binary systems in various stellar populations of the Galaxy and the distribution of their orbital parameters are important but not well-determined factors in studies of star formation, stellar evolution, and Galactic chemical evolution. While observational studies have been carried out for a large sample of nearby stars, including some metal-poor Population II stars, almost no constraints on the binary nature for extremely metal-poor (EMP; [Fe/H] <−3.0) stars have yet been obtained. Here we investigate the fraction of double-lined spectroscopic binaries and carbon-enhanced metal-poor (CEMP) stars, many of which could have formed as pairs of low-mass and intermediate-mass stars, to estimate the lower limit of the fraction of binary systems having short periods. The estimate is based on a sample of very metal-poor stars selected from the Sloan Digital Sky Survey and observed at high spectral resolution in a previous study by Aoki et al. That survey reported 3 double-lined spectroscopic binaries and 11 CEMP stars, which we consider along with a sample of EMP stars from the literature compiled in the SAGA database. We have conducted measurements of the velocity components for stacked absorption features of different spectral lines for each double-lined spectroscopic binary. Our estimate indicates that the fraction of binary stars having orbital periods shorter than 1000 days is at least 10%, and possibly as high as 20% if the majority of CEMP stars are formed in such short-period binaries. This result suggests that the period distribution of EMP binary systems is biased toward short periods, unless the binary fraction of low-mass EMP stars is significantly higher than that of other nearby stars.

  16. Metal-poor stars: The fingerprints of the first stars and the early galaxy

    Science.gov (United States)

    Lai, David K.

    2008-10-01

    The chemical composition of metal-poor stars are fossil records of the first generations of stars and of the early Galactic environment. In this thesis I cover two of the main challenges in studying metal-poor stars. The first is finding metal-poor candidates, and the second is the high-resolution spectral follow-up study of a sample of metal-poor stars. In the first part of my thesis I explore one process to identify and study very metal-poor stars (VMP, [Fe/H] = 1.0. I explore how the metallicity distribution function of any particular sample is an important aspect in determining this fraction. The second part of this thesis is a detailed study of a sample of VMP stars using high-resolution spectral analysis. Most of the stars in the sample came from the ESI study. These observations were carried out with the High Resolution Echelle Spectrometer (HIRES) instrument at Keck, with spectral resolution of R~45,000. From these HIRES spectra, I have measured the abundances of up to 25 elements from C through Eu in 28 VMP stars. In this sample I have discovered a new star that is highly enhanced by r-process material, CS 31078-018, and a new [Fe/H]= -4.0 star, CS 30336-049. The abundance ratios in the stars in this sample may be the products of nucleosynthesis in the very first stars. With this in mind I have compared the abundance ratios of the sample in aggregate, as well as the abundance ratios of CS 30336-049, with the zero-metallicity supernova type II nucleosynthesis models of Heger & Woosley (2008). From this comparison I show that metal-free progenitor with masses ~ 10 to 20 [Special characters omitted.] can match our abundances very well. In the last part of this dissertation I discuss a future direction in the study of metal-poor stars. The Sloan Digital Sky Survey, and in particular by its extension, the Sloan Extension for Galactic Understanding and Exploration (SEGUE), has greatly increased the number of metal-poor candidates to date. Through a well

  17. Chemistry of the Most Metal-poor Stars in the Bulge and the z > 10 Universe

    OpenAIRE

    Casey, Andrew R.; Schlaufman, Kevin C.

    2015-01-01

    Metal-poor stars in the Milky Way are local relics of the epoch of the first stars and the first galaxies. However, a low metallicity does not prove that a star formed in this ancient era, as metal-poor stars form over a range of redshift in different environments. Theoretical models of Milky Way formation have shown that at constant metallicity, the oldest stars are those closest to the center of the Galaxy on the most tightly-bound orbits. For that reason, the most metal-poor stars in the b...

  18. Observational Constraints on First-Star Nucleosynthesis. II. Spectroscopy of an Ultra Metal-Poor CEMP-no Star

    CERN Document Server

    Placco, Vinicius M; Beers, Timothy C; Yoon, Jinmi; Chiti, Anirudh; Heger, Alexander; Chan, Conrad; Casey, Andrew R; Christlieb, Norbert

    2016-01-01

    We report on the first high-resolution spectroscopic analysis of HE0020-1741, a bright (V=12.9), ultra metal-poor ([Fe/H] = -4.1), carbon-enhanced ([C/Fe] = +1.7) star selected from the Hamburg/ESO Survey. This star exhibits low abundances of neutron-capture elements ([Ba/Fe] = -1.1), and an absolute carbon abundance A(C) = 6.1; based on either criterion, HE0020-1741 is sub-classified as a CEMP-no star. We show that the light-element abundance pattern of HE0020-1741 is consistent with predicted yields from a massive (M = 21.5 Mo), primordial composition, supernova (SN) progenitor. We also compare the abundance patterns of other ultra metal-poor stars from the literature with available measures of C, N, Na, Mg, and Fe abundances with an extensive grid of SN models (covering the mass range 10 Mo - 100 Mo), in order to probe the nature of their likely stellar progenitors. Our results suggest that at least two classes of progenitors are required at [Fe/H] < -4.0, as the abundance patterns for more than half of...

  19. The IMF of Extremely Metal-Poor Stars and the Probe into the Star-Formation Process of the Milky Way

    OpenAIRE

    Komiya, Yutaka; Suda, Takuma; Habe, Asao; Fujimoto, Masayuki Y.

    2007-01-01

    We discuss the star formation history of the Galaxy, based on the observations of extremely metal-poor stars (EMP) in the Galactic halo, to gain an insight into the evolution and structure formation in the early universe. The initialmass function (IMF) of EMP stars is derived from the observed fraction of carbon-enhanced EXP (CEMP) stars among the EMP survivors, which are thought to originate from the evolution in the close binary systems with mass transfer. Relying upon the theory of the evo...

  20. Observational nuclear astrophysics: neutron-capture element abundances in old, metal-poor stars

    International Nuclear Information System (INIS)

    The chemical abundances of metal-poor stars provide a great deal of information regarding the individual nucleosynthetic processes that created the observed elements and the overall process of chemical enrichment of the galaxy since the formation of the first stars. Here we review the abundance patterns of the neutron-capture elements (Z ⩾ 38) in those metal-poor stars and our current understanding of the conditions and sites of their production at early times. We also review the relative contributions of these different processes to the build-up of these elements within the galaxy over time, and outline outstanding questions and uncertainties that complicate the interpretation of the abundance patterns observed in metal-poor stars. It is anticipated that future observations of large samples of metal-poor stars will help discriminate between different proposed neutron-capture element production sites and better trace the chemical evolution of the galaxy. (paper)

  1. Chemistry of the Most Metal-poor Stars in the Bulge and the z > 10 Universe

    CERN Document Server

    Casey, Andrew R

    2015-01-01

    Metal-poor stars in the Milky Way are local relics of the epoch of the first stars and the first galaxies. However, a low metallicity does not prove that a star formed in this ancient era, as metal-poor stars form over a range of redshift in different environments. Theoretical models of Milky Way formation have shown that at constant metallicity, the oldest stars are those closest to the center of the Galaxy on the most tightly-bound orbits. For that reason, the most metal-poor stars in the bulge of the Milky Way provide excellent tracers of the chemistry of the high-redshift universe. We report the dynamics and detailed chemical abundances of three stars in the bulge with [Fe/H] $\\lesssim-2.7$, two of which are the most metal-poor stars in the bulge in the literature. We find that with the exception of scandium, all three stars follow the abundance trends identified previously for metal-poor halo stars. These three stars have the lowest [Sc II/Fe] abundances yet seen in $\\alpha$-enhanced giant stars in the G...

  2. The Frequency of Carbon Stars Among Extremely Metal-Poor Stars

    CERN Document Server

    Cohen, J G; Thompson, I; McWilliam, A; Christlieb, N; Melendez, J; Zickgraf, F J; Swenson, S R A; Cohen, Judith G.; Shectman, Stephen; Thompson, Ian; William, Andrew Mc; Christlieb, Norbert; Melendez, Jorge; Zickgraf, Franz-Josef; Swenson, Solange Ramirez & Amber

    2005-01-01

    We demonstrate that there are systematic scale errors in the [Fe/H] values determined by the Hamburg/ESO Survey (and by inference by the HK Survey in the past) for certain extremely metal poor highly C-enhanced giants. The consequences of these scale errors are that a) the fraction of carbon stars at extremely low metallicities has been overestimated in several papers in the recent literature b) the number of extremely metal poor stars known is somewhat lower than has been quoted in the recent literature c) the yield for extremely metal poor stars by the HES Survey is somewhat lower than is stated in the recent literature. A preliminary estimate for the frequency of Carbon stars among the giants in the HES sample with -4 1.0 dex without detectable C2 bands raises the fraction to 14 +-4$%. We rely on the results of an extensive set of homogeneous detailed abundance analyses of stars expected to have [Fe/H] < -3.0 dex selected from the HES to establish these claims. We have found that the Fe-metallicity of ...

  3. First stars XIII. Two extremely metal-poor RR Lyrae stars?

    CERN Document Server

    Hansen, C J; Bonifacio, P; Spite, M; Andersen, J; Beers, T C; Cayrel, R; Spite, F; Molaro, P; Barbuy, B; Depagne, E; Hill, P Francois V; Plez, B; Sivarani, T

    2011-01-01

    The chemical composition of extremely metal-poor stars (EMP stars; [Fe/H]<~ -3) is a unique tracer of early nucleosynthesis in the Galaxy. As such stars are rare, we wish to find classes of luminous stars which can be studied at high resolution. We aim to determine the detailed chemical composition of the two EMP stars CS30317-056 and CS22881-039, originally thought to be red horizontal-branch (RHB) stars, and compare it to earlier results for EMP stars as well as to nucleosynthesis yields from various supernova (SN) models. In the analysis, we discovered that our targets are in fact the two most metal-poor RR Lyrae stars known. Our detailed abundance analysis, taking into account the variability of the stars, is based on VLT/UVES spectra (R~ 43000) and 1D LTE OSMARCS model atmospheres and synthetic spectra. For comparison with SN models we also estimate NLTE corrections for a number of elements. We derive LTE abundances for the 16 elements O, Na, Mg, Al, Si, S, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Sr and Ba, i...

  4. FORMATION HISTORY OF METAL-POOR HALO STARS WITH THE HIERARCHICAL MODEL AND THE EFFECT OF INTERSTELLAR MATTER ACCRETION ON THE MOST METAL-POOR STARS

    OpenAIRE

    Komiya, Yutaka; Habe, Asao; Suda, Takuma; Fujimoto, Masayuki Y.

    2010-01-01

    We investigate the star formation and chemical evolution in the early universe by considering the merging history of the Galaxy in the {\\Lambda}CDM scenario according to the extended Press-Schechter theory. We give some possible constraints from comparisons with observation of extremely metal-poor (EMP) stars. We demonstrate that (1) The hierarchical structure formation can explain the characteristics of the observed metallicity distribution function (MDF) including a break around [Fe/H]~-4. ...

  5. DETAILED ABUNDANCES OF TWO VERY METAL-POOR STARS IN DWARF GALAXIES

    International Nuclear Information System (INIS)

    The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae (SNe). These SNe could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way (MW) halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two MW dSphs. One star, in the Sculptor dSph, has [Fe I/H] = -2.40. The other star, in the Ursa Minor dSph, has [Fe I/H] = -3.16. Both stars fall in the previously discovered low-metallicity, high-[α/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of SN yields is the cause. The earliest SNe in low-mass dSphs have less gas to pollute than the earliest SNe in massive halo progenitors. As a result, dSph stars at –3 < [Fe/H] < –2 sample SNe with [Fe/H] << –3, whereas halo stars in the same metallicity range sample SNe with [Fe/H] ∼ –3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo.

  6. Metal-Poor Stars Observed with the Magellan Telescope. III. New Extremely and Ultra Metal-Poor Stars from SDSS/SEGUE and Insights on the Formation of Ultra Metal-Poor Stars

    CERN Document Server

    Placco, Vinicius M; Lee, Young Sun; Jacobson, Heather R; Beers, Timothy C; Pena, Jose M; Chan, Conrad; Heger, Alexander

    2015-01-01

    We report the discovery of one extremely metal-poor (EMP; [Fe/H]<-3) and one ultra metal-poor (UMP; [Fe/H]<-4) star selected from the SDSS/SEGUE survey. These stars were identified as EMP candidates based on their medium-resolution (R~2,000) spectra, and were followed-up with high-resolution (R~35,000) spectroscopy with the Magellan-Clay Telescope. Their derived chemical abundances exhibit good agreement with those of stars with similar metallicities. We also provide new insights on the formation of the UMP stars, based on comparison with a new set of theoretical models of supernovae nucleosynthesis. The models were matched with 20 UMP stars found in the literature, together with one of the program stars (SDSS J1204+1201), with [Fe/H]=-4.34. From fitting their abundances, we find that the supernovae progenitors, for stars where carbon and nitrogen are measured, had masses ranging from 20.5 M_sun to 28 M_sun and explosion energies from 0.3 to 0.9x10^51 erg. These results are highly sensitive to the carbo...

  7. Spectroscopic Studies of Extremely Metal-Poor Stars with the Subaru High Dispersion Spectrograph. V. The Zn-Enhanced Metal-Poor Star BS 16920-017

    CERN Document Server

    Honda, Satoshi; Beers, Timothy C; Takada-Hidai, Masahide

    2011-01-01

    We report Zn abundances for 18 very metal-poor stars studied in our previous work, covering the metallicity range -3.2 < [Fe/H] < -2.5. The [Zn/Fe] values of most stars show an increasing trend with decreasing [Fe/H] in this metallicity range, confirming the results found by previous studies. However, the extremely metal-poor star BS 16920-017 ([Fe/H] = -3.2) exhibits a significantly high [Zn/Fe] ratio ([Zn/Fe] = +1.0). Comparison of the chemical abundances of this object with HD 4306, which has similar atmospheric parameters to BS 16920-017, clearly demonstrates a deficiency of alpha elements and neutron-capture elements in this star, along with enhancements of Mn and Ni, as well as Zn. The association with a hypernova explosion that has been proposed to explain the high Zn abundance ratios found in extremely metal-poor stars is a possible explanation, although further studies are required to fully interpret the abundance pattern of this object.

  8. Abundances of heavy elements in ultra-metal-poor star CS 22892-052

    Institute of Scientific and Technical Information of China (English)

    张波; 张彩霞; 李冀; 梁艳春; 彭秋和

    1999-01-01

    Based on the heavy element nucleosynthesis theory, with the solar heavy-nuclide abundances and the observed abundances of three elements which are the representatives of the individul neutron-capture processes, a method to determine the relative contributions from the individul neutron-capture processes to the abundances of heavy elements in metal-poor stars is applied. With this method, the abundances of heavy elements in ultra-metal-poor star CS 22892-052 are calculated. It is found that the observed abundances of heavy elements in this star are well matched by our calculations in error limits, except for thorium.

  9. Metal-poor Stars Observed with the Magellan Telescope. III. New Extremely and Ultra Metal-poor Stars from SDSS/SEGUE and Insights on the Formation of Ultra Metal-poor Stars

    Science.gov (United States)

    Placco, Vinicius M.; Frebel, Anna; Lee, Young Sun; Jacobson, Heather R.; Beers, Timothy C.; Pena, Jose M.; Chan, Conrad; Heger, Alexander

    2015-08-01

    We report the discovery of one extremely metal-poor (EMP; [{Fe}/{{H}}] \\lt -3) and one ultra metal-poor (UMP; [{Fe}/{{H}}] \\lt -4) star selected from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration survey. These stars were identified as EMP candidates based on their medium-resolution (R ˜ 2000) spectra, and were followed up with high-resolution (R ˜ 35,000) spectroscopy with the Magellan/Clay Telescope. Their derived chemical abundances exhibit good agreement with those of stars with similar metallicities. We also provide new insights on the formation of the UMP stars, based on comparisons with a new set of theoretical models of supernovae (SNe) nucleosynthesis. The models were matched with 20 UMP stars found in the literature, together with one of the program stars (SDSS J1204+1201), with [{Fe}/{{H}}]=-4.34. From fitting their abundances, we find that the SNe progenitors, for stars where carbon and nitrogen are measured, had masses ranging from 20.5 {M}⊙ to 28 {M}⊙ and explosion energies from 0.3 to 0.9× {10}51 {erg}. These results are highly sensitive to the carbon and nitrogen abundance determinations, which is one of the main drivers for a future high-resolution follow-up of UMP candidates. In addition, we are able to reproduce the different CNO abundance patterns found in UMP stars with a single progenitor type by varying its mass and explosion energy. Magellan Telescopes located at Las Campanas Observatory, Chile.

  10. Test observations that search for metal-poor stars with the Guoshoujing Telescope (LAMOST)

    International Nuclear Information System (INIS)

    Metal-deficient stars are regarded as fossils of the early generation of stars and therefore make crucial observational targets related to stellar astrophysics. They provide fundamental information and insights on properties of the very early stage of the chemical history of the Galaxy and have been investigated for decades. The unique design of the Guoshoujing Telescope (LAMOST), such as its large field and multi-object observational capability, enables it to be an excellent tool for searching for these metal-poor stars in the Milky Way. This work reports the result of test observations which search for metal-poor stars with LAMOST, during which nine candidate metal-poor stars with [Fe/H] ≤ -1.0 were newly detected based on the low-resolution spectroscopic observations of the LAMOST commissioning data. The sample of stars demonstrates the efficiency of selecting from the input catalog, as well as the ability of LAMOST to enlarge the sample of metal-poor stars in the Milky Way. Furthermore, the sample of stars could be used for future calibrations of the LAMOST stellar parameter pipeline. (research papers)

  11. Identification of metal-poor stars using the artificial neural network

    CERN Document Server

    Giridhar, Sunetra; Kunder, Andrea; Muneer, S; Selvakumar, G

    2013-01-01

    Identification of metal-poor stars among field stars is extremely useful for studying the structure and evolution of the Galaxy and of external galaxies. We search for metal-poor stars using the artificial neural network (ANN) and extend its usage to determine absolute magnitudes. We have constructed a library of 167 medium-resolution stellar spectra (R ~ 1200) covering the stellar temperature range of 4200 to 8000 K, log g range of 0.5 to 5.0, and [Fe/H] range of -3.0 to +0.3 dex. This empirical spectral library was used to train ANNs, yielding an accuracy of 0.3 dex in [Fe/H], 200 K in temperature, and 0.3 dex in log g. We found that the independent calibrations of near-solar metallicity stars and metal-poor stars decreases the errors in T_eff and log g by nearly a factor of two. We calculated T_eff, log g, and [Fe/H] on a consistent scale for a large number of field stars and candidate metal-poor stars. We extended the application of this method to the calibration of absolute magnitudes using nearby stars ...

  12. The EMBLA Survey -- Metal-poor stars in the Galactic bulge

    CERN Document Server

    Howes, Louise M; Keller, Stefan C; Casey, Andrew R; Yong, David; Lind, Karin; Frebel, Anna; Hays, Austin; Alves-Brito, Alan; Bessell, Michael S; Casagrande, Luca; Marino, Anna F; Nataf, David M; Owen, Christopher I; Da Costa, Gary S; Schmidt, Brian P; Tisserand, Patrick

    2016-01-01

    Cosmological models predict the oldest stars in the Galaxy should be found closest to the centre of the potential well, in the bulge. The EMBLA Survey successfully searched for these old, metal-poor stars by making use of the distinctive SkyMapper photometric filters to discover candidate metal-poor stars in the bulge. Their metal-poor nature was then confirmed using the AAOmega spectrograph on the AAT. Here we present an abundance analysis of 10 bulge stars with -2.8<[Fe/H]<-1.7 from MIKE/Magellan observations, in total determining the abundances of 22 elements. Combining these results with our previous high-resolution data taken as part of the Gaia-ESO Survey, we have started to put together a picture of the chemical and kinematic nature of the most metal-poor stars in the bulge. The currently available kinematic data is consistent with the stars belonging to the bulge, although more accurate measurements are needed to constrain the stars' orbits. The chemistry of these bulge stars deviates from that ...

  13. First Stars XIV. Sulphur abundances in extremely metal-poor (EMP) stars

    CERN Document Server

    Spite, Monique; Andrievsky, S M; Korotin, S A; Depagne, E; Spite, F; Bonifacio, P; Ludwig, H -G; Cayrel, R; Francois, P; Hill, V; Plez, B; Andersen, J; Barbuy, B; Beers, T C; Molaro, P; Nordstrom, B; Primas, F

    2010-01-01

    Sulphur is important: the site of its formation is uncertain, and at very low metallicity the trend of [S/Fe] against [Fe/H] is controversial. Below [Fe/H]=-2.0, [S/Fe] remains constant or it decreases with [Fe/H], depending on the author and the multiplet used in the analysis. Moreover, although sulphur is not significantly bound in dust grains in the ISM, it seems to behave differently in DLAs and in old metal-poor stars. We aim to determine precise S abundance in a sample of extremely metal-poor stars taking into account NLTE and 3D effects. NLTE profiles of the lines of the multiplet 1 of SI have been computed using a new model atom for S. We find sulphur in EMP stars to behave like the other alpha-elements, with [S/Fe] remaining approximately constant below [Fe/H]=-3. However, [S/Mg] seems to decrease slightly as a function of [Mg/H]. The overall abundance patterns of O, Na, Mg, Al, S, and K are best matched by the SN model yields by Heger & Woosley. The [S/Zn] ratio in EMP stars is solar, as found a...

  14. Nucleosynthesis in Low Mass Very Metal Poor AGB Stars

    Science.gov (United States)

    Serenelli, A.

    The evolution of a 1.5 M⊙, Z= 10-5 stellar model has been followed starting at the ZAMS up to the thermally pulsating asymptotic giant branch (TP-AGB) phase. Calculations were done using the LPCODE [1], to which some changes were done. The most important and relevant to this work is the incorporation of a full nuclear network from H to Po, comprising about 525 isotopes and 910 nuclear reactions, appropriate for the computation of the s-process occurring in AGB stars. Convection is treated according to the mixing length theory (λMLT = 1.7) and convective mixing as a diffusive process. Diffusive overshooting is also included according to [2] and the free parameter f adopted is 0.015. Mass loss is given by the Reimers formula, with the parameter η = 1.

  15. The Frequency of Carbon Rich Stars Among Extremely Metal Poor Stars

    CERN Document Server

    Cohen, J G; Thompson, I; McWilliam, A; Christlieb, N; Melendez, J; Zickgraf, F J; Swenson, S R A; Cohen, Judith G.; Shectman, Stephen; Thompson, Ian; William, Andrew Mc; Christlieb, Norbert; Melendez, Jorge; Zickgraf, Franz-Josef; Swenson, Solange Ram\\'{\\i}rez & Amber

    2005-01-01

    We demonstrate that there are systematic scale errors in the [Fe/H] values determined by the Hamburg/ESO Survey (and by the HK Survey by inference) for certain extremely metal poor (EMP) highly C-enhanced giants. The consequences of these scale errors are that a) the fraction of carbon stars at extremely low metallicities has been substantially overestimated in several papers in the recent literature b) the number of EMP stars known is somewhat lower than has been quoted in the recent literature c) the yield for EMP stars by the HK and the HES Survey is somewhat lower than is stated in the recent literature. A preliminary estimate for the frequency of Carbon stars among the giants in the HES sample with -4 +1.0 dex is 14.4 \\pm 4%. Here we present the key results of detailed abundance analyses of 14 C-stars selected from the HES as candidate EMP stars, of ~50 such stars analyzed. About 80% of such C-stars show highly enhanced Ba as well, with C enhanced by a factor of about 100, and [Ba/C] roughly Solar. Thes...

  16. Extremely-Metal Poor Stars in the Milky Way: A Second Generation Formed after Reionization

    OpenAIRE

    Trenti, Michele; Shull, Michael

    2009-01-01

    Cosmological simulations of Population III star formation suggest an initial mass function (IMF) biased toward very massive stars (M>100Msun) formed in minihalos at redshift z>20, when the cooling is driven by molecular hydrogen. However, this result conflicts with observations of extremely-metal poor (EMP) stars in the Milky Way halo, whose r-process elemental abundances appear to be incompatible with those expected from very massive Population III progenitors. We propose a new solution to t...

  17. Super and massive AGB stars - III. Nucleosynthesis in metal-poor and very metal-poor stars - Z=0.001 and 0.0001

    CERN Document Server

    Doherty, Carolyn L; Lau, Herbert H B; Lattanzio, John C; Siess, Lionel; Campbell, Simon W

    2014-01-01

    We present a new grid of stellar models and nucleosynthetic yields for super-AGB stars with metallicities Z=0.001 and 0.0001, applicable for use within galactic chemical evolution models. Contrary to more metal rich stars where hot bottom burning is the main driver of the surface composition, in these lower metallicity models the effect of third dredge-up and corrosive second dredge-up also have a strong impact on the yields. These metal-poor and very metal-poor super-AGB stars create large amounts of He4, C13 and N14, as well as the heavy magnesium isotopes Mg25 and Mg26. There is a transition in yield trends at metallicity Z approximately 0.001, below which we find positive yields of C12, O16, N15, Al27 and Si28, which is not the case for higher metallicities. We explore the large uncertainties derived from wind prescriptions in super-AGB stars, finding approximately 2 orders of magnitude difference in yields of Ne22, Na23, Mg24,25,26, Al27 and our s-process proxy isotope g. We find inclusion of variable co...

  18. Are the Formation and Abundances of Metal-Poor Stars the Result of Dust Dynamics?

    CERN Document Server

    Hopkins, Philip F

    2015-01-01

    Large dust grains can fluctuate dramatically in their local density, relative to gas, in neutral, turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains under these conditions. This can have important consequences for star formation and stellar abundances in extremely metal-poor stars. Low-mass stars could form in dust-enhanced regions almost immediately after some dust forms, even if the galaxy-average metallicity is too low for fragmentation to occur. The abundances of these 'promoted' stars may contain interesting signatures, as the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced or fluctuate independently. Remarkably, otherwise puzzling abundance patterns of some metal-poor stars can be well-fit by standard core-collapse SNe yields, if we al...

  19. Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars

    Science.gov (United States)

    Carney, Bruce W.; Gray, David F.; Yong, David; Latham, David W.; Manset, Nadine; Zelman, Rachel; Laird, John B.

    2008-03-01

    We report the results for rotational velocities, Vrot sin i, and macroturbulence dispersions, ζRT, for 12 metal-poor field red giant branch (RGB) stars and 7 metal-poor field red horizontal branch (RHB) stars. The results are based on Fourier transform analyses of absorption line profiles from high-resolution (R ≈ 120,000), high-S/N (≈215 per pixel; ≈345 per resolution element) spectra obtained with the Gecko spectrograph at the Canada-France-Hawaii Telescope (CFHT). The stars were selected from the authors' previous studies of 20 RHB and 116 RGB stars, based primarily on larger-than-average line-broadening values. We find that ζRT values for the metal-poor RGB stars are very similar to those for metal-rich disk giants studied earlier by Gray and his collaborators. Six of the RGB stars have small rotational values, less than 2.0 km s-1, while five show significant rotation/enhanced line broadening, over 3 km s-1. We confirm the rapid rotation rate for RHB star HD 195636, found earlier by Preston. This star's rotation is comparable to that of the fastest known rotating blue horizontal branch (BHB) stars, when allowance is made for differences in radii and moments of inertia. The other six RHB stars have somewhat lower rotation but show a trend to higher values at higher temperatures (lower radii). Comparing our results with those for BHB stars from Kinman et al., we find that the fraction of rapidly rotating RHB stars is somewhat lower than is found among BHB stars. The number of rapidly rotating RHB stars is also smaller than we would have expected from the observed rotation of the RGB stars. We devise two empirical methods to translate our earlier line-broadening results into Vrot sin i for all the RGB and RHB stars they studied. Binning the RGB stars by luminosity, we find that most metal-poor field RGB stars show no detectable sign, on average, of rotation, which is not surprising given the stars' large radii. However, the most luminous stars, with MV

  20. CHEMICAL ABUNDANCES OF METAL-POOR RR LYRAE STARS IN THE MAGELLANIC CLOUDS

    International Nuclear Information System (INIS)

    We present for the first time a detailed spectroscopic study of chemical element abundances of metal-poor RR Lyrae stars in the Large and Small Magellanic Cloud (LMC and SMC). Using the MagE echelle spectrograph at the 6.5 m Magellan telescopes, we obtain medium resolution (R ∼ 2000-6000) spectra of six RR Lyrae stars in the LMC and three RR Lyrae stars in the SMC. These stars were chosen because their previously determined photometric metallicities were among the lowest metallicities found for stars belonging to the old populations in the Magellanic Clouds. We find the spectroscopic metallicities of these stars to be as low as [Fe/H]spec = –2.7 dex, the lowest metallicity yet measured for any star in the Magellanic Clouds. We confirm that for metal-poor stars, the photometric metallicities from the Fourier decomposition of the light curves are systematically too high compared to their spectroscopic counterparts. However, for even more metal-poor stars below [Fe/H]phot < –2.8 dex this trend is reversed and the spectroscopic metallicities are systematically higher than the photometric estimates. We are able to determine abundance ratios for 10 chemical elements (Fe, Na, Mg, Al, Ca, Sc, Ti, Cr, Sr, and Ba), which extend the abundance measurements of chemical elements for RR Lyrae stars in the Clouds beyond [Fe/H] for the first time. For the overall [α/Fe] ratio, we obtain an overabundance of 0.36 dex, which is in very good agreement with results from metal-poor stars in the Milky Way halo as well as from the metal-poor tail in dwarf spheroidal galaxies. Comparing the abundances with those of the stars in the Milky Way halo we find that the abundance ratios of stars of both populations are consistent with another. Therefore, we conclude that from a chemical point of view early contributions from Magellanic-type galaxies to the formation of the Galactic halo as claimed in cosmological models are plausible.

  1. THE r-PROCESS IN METAL-POOR STARS AND BLACK HOLE FORMATION

    International Nuclear Information System (INIS)

    Nucleosynthesis of heavy nuclei in metal-poor stars is generally thought to occur via the r-process because the r-process is a primary process that would have operated early in the Galaxy's history. This idea is strongly supported by the fact that the abundance pattern in many metal-poor stars matches well the inferred solar r-process abundance pattern in the mass range between the second and third r-process abundance peaks. Nevertheless, a significant number of metal-poor stars do not share this standard r-process template. In this Letter, we suggest that the nuclides observed in many of these stars are produced by the r-process, but that it is prevented from running to completion in more massive stars by collapse to black holes before the r-process is completed, creating a 'truncated r-process', or 'tr-process'. We find that the observed fraction of tr-process stars is qualitatively what one would expect from the initial mass function and that an apparent sharp truncation observed at around mass 160 could result from a combination of collapses to black holes and the difficulty of observing the higher mass rare-earth elements. We test the tr-process hypothesis with r-process calculations that are terminated before all r-process trajectories have been ejected. We find qualitative agreement between observation and theory when black hole collapse and observational realities are taken into account.

  2. VERY METAL-POOR STARS IN THE OUTER GALACTIC BULGE FOUND BY THE APOGEE SURVEY

    International Nuclear Information System (INIS)

    Despite its importance for understanding the nature of early stellar generations and for constraining Galactic bulge formation models, at present little is known about the metal-poor stellar content of the central Milky Way. This is a consequence of the great distances involved and intervening dust obscuration, which challenge optical studies. However, the Apache Point Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber, high-resolution spectroscopic survey within Sloan Digital Sky Survey III, is exploring the chemistry of all Galactic stellar populations at infrared wavelengths, with particular emphasis on the disk and the bulge. An automated spectral analysis of data on 2403 giant stars in 12 fields in the bulge obtained during APOGEE commissioning yielded five stars with low metallicity ([Fe/H] ≤ –1.7), including two that are very metal-poor [Fe/H] ∼ –2.1 by bulge standards. Luminosity-based distance estimates place the 5 stars within the outer bulge, where 1246 of the other analyzed stars may reside. A manual reanalysis of the spectra verifies the low metallicities, and finds these stars to be enhanced in the α-elements O, Mg, and Si without significant α-pattern differences with other local halo or metal-weak thick-disk stars of similar metallicity, or even with other more metal-rich bulge stars. While neither the kinematics nor chemistry of these stars can yet definitively determine which, if any, are truly bulge members, rather than denizens of other populations co-located with the bulge, the newly identified stars reveal that the chemistry of metal-poor stars in the central Galaxy resembles that of metal-weak thick-disk stars at similar metallicity.

  3. The Extreme Overabundance of Molybdenum in Two Metal-Poor Stars

    CERN Document Server

    Peterson, Ruth C

    2011-01-01

    We report determinations of the molybdenum abundances in five mildly to extremely metal-poor turnoff stars using five Mo II lines near 2000A. In two of the stars, the abundance of molybdenum is found to be extremely enhanced, as high or higher than the neighboring even-Z elements ruthenium and zirconium. Of the several nucleosynthesis scenarios envisioned for the production of nuclei in this mass range in the oldest stars, a high-entropy wind (HEW) acting in a core-collapse supernova seems uniquely capable of the twin aspects of a high molybdenum overproduction confined to a narrow mass range. Whatever the details of the nucleosynthesis mechanism, however, this unusual excess suggests that very few individual nucleosynthesis events were responsible for the synthesis of the light trans-Fe heavy elements in these cases, an unexpected result given that both are only moderately metal-poor.

  4. Metal-Poor Stars Observed with the Magellan Telescope I. Constraints on Progenitor Mass and Metallicity of AGB Stars Undergoing s-Process Nucleosynthesis

    CERN Document Server

    Placco, Vinicius M; Beers, Timothy C; Karakas, Amanda I; Kennedy, Catherine R; Rossi, Silvia; Christlieb, Norbert; Stancliffe, Richard J

    2013-01-01

    We present a comprehensive abundance analysis of two newly-discovered carbon-enhanced metal-poor (CEMP) stars. HE2138-3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if NLTE corrections are included ([Pb/Fe] = +3.84). HE2258-6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and followed up with medium-resolution (R ~ 2,000) spectroscopy with GEMINI/GMOS. We report here on derived abundances (or limits) for a total of 34 elements in each star, based on high-resolution (R ~ 30,000) spectroscopy obtained with Magellan-Clay/MIKE. Our results are compared to predictions from new theoretical AGB nucleosynthesis models of 1.3 Mo with [Fe/H] = -2.5 and -2.8, as well as to a set of AGB models of 1.0 to 6.0 Mo at [Fe/H] = -2.3. The agreement with the model predictions suggests that the neutron-capture materia...

  5. The Chemical Composition and Age of the Metal-Poor Halo Star BD +17^\\circ 3248

    CERN Document Server

    Cowan, J J; Burles, S M; Ivans, I I; Beers, T C; Truran, J W; Lawler, J E; Primas, F; Fuller, G M; Pfeiffer, B; Kratz, K L; Cowan, John J.; Sneden, Christopher; Burles, Scott; Ivans, Inese I.; Beers, Timothy C.; Truran, James W.; Lawler, James E.; Primas, Francesca; Fuller, George M.; Pfeiffer, Bernd; Kratz, Karl-Ludwig

    2002-01-01

    We have combined new high-resolution spectra obtained with the Hubble Space Telescope (HST) and ground-based facilities to make a comprehensive new abundance analysis of the metal-poor, halo star BD +17^\\circ 3248. We have detected the third r-process peak elements osmium, platinum, and (for the first time in a metal-poor star) gold, elements whose abundances can only be reliably determined using HST. Our observations illustrate a pattern seen in other similar halo stars with the abundances of the heavier neutron-capture elements, including the third r-process peak elements, consistent with a scaled solar system r-process distribution. The abundances of the lighter neutron-capture elements, including germanium and silver, fall below that same scaled solar r-process curve, a result similar to that seen in the ultra-metal-poor star CS 22892--052. A single site with two regimes or sets of conditions, or perhaps two different sites for the lighter and heavier neutron-capture elements, might explain the abundance ...

  6. Metal-poor stars towards the Galactic bulge: A population potpourri⋆

    Science.gov (United States)

    Koch, Andreas; McWilliam, Andrew; Preston, George W.; Thompson, Ian B.

    2016-03-01

    We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern edge of the Galactic bulge, at (l, b) ~ (0°,-11°). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H] = -2.52 dex, and another target is a moderately metal-poor ([Fe/H] = -1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe] = 1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning -2.0 to -2.6 dex, i.e., enhanced α-elements and solar Fe-peak and neutron-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with simulations of the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their highly uncertain proper motions prohibit a clear kinematic separation, the stars' chemical abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas

  7. The Synthetic-Oversampling Method: Using Photometric Colors to Discover Extremely Metal-poor Stars

    OpenAIRE

    Miller, A.A.

    2015-01-01

    Extremely metal-poor (EMP) stars ([Fe/H] ≤ −3.0 dex) provide a unique window into understanding the first generation of stars and early chemical enrichment of the universe. EMP stars are exceptionally rare, however, and the relatively small number of confirmed discoveries limits our ability to exploit these near-field probes of the first ~500 Myr after the Big Bang. Here, a new method to photometrically estimate [Fe/H] from only broadband photometric colors is presented. I show that the metho...

  8. Chemical Abundances in 35 Metal-Poor Stars. I. Basic Data

    CERN Document Server

    Lee, Jeong-Deok; Kim, Kang-Min

    2008-01-01

    We carried out a homogeneous abundance study for various elements, including $\\alpha$-elements, iron peak elements and $n$-capture elements for 35 metal-poor stars with a wide metallicity range ($-3.0\\lesssim$[Fe/H]$\\lesssim-0.5$). High-resolution ($R\\simeq30$k), high signal-to-noise($S/N\\geq110$) spectra with a wavelength range of 3800 to 10500 \\AA using the Bohyunsan Optical Echelle Spectrograph (BOES). Equivalent widths were measured by means of the Gaussian-fitting method for numerous isolated weak lines of elements. Atmospheric parameters were determined by a self-consistent LTE analysis technique using Fe I and Fe II lines. In this study, we present the EWs of lines and atmospheric parameters for 35 metal-poor stars.

  9. Bipolar Supernova Explosions: Nucleosynthesis & Implication on Abundances in Extremely Metal-Poor Stars

    OpenAIRE

    Maeda, K.; Nomoto, K.

    2003-01-01

    Hydrodynamics and explosive nucleosynthesis in bipolar supernova explosions are examined to account for some peculiar properties of hypernovae as well as peculiar abundance patterns of metal-poor stars. The explosion is supposed to be driven by bipolar jets which are powered by accretion onto a central remnant. We explore the features of the explosions with varying progenitors' masses and jet properties. The outcomes are different from conventional spherical models. (1) In the bipolar models,...

  10. Abundance Profiling of Extremely Metal-Poor Stars and Supernova Properties in the Early Universe

    CERN Document Server

    Tominaga, Nozomu; Nomoto, Ken'ichi

    2013-01-01

    The first metal enrichment in the universe was made by a supernova (SN) explosion of a population (Pop) III star and chemical evolution of the universe is recorded in abundance patterns of extremely metal-poor (EMP) stars. Increasing number of the EMP stars are now being discovered. This allows us to statistically constrain properties of SNe of Pop III stars (Pop III SNe). We investigate the properties of Pop III SNe by comparing their nucleosynthetic yields with the abundance patterns of the EMP stars. We focus on the most metal-poor stars with [Fe/H] $\\lsim-3.5$ and present Pop III SN models that reproduce well their individual abundance patterns. From these models we derive relations between abundance ratios and properties of Pop III SNe: [(C+N)/Fe] vs. an ejected Fe mass, and [(C+N)/Mg] vs. a remnant mass. Using fitting formulae, distribution of the abundance ratios of EMP stars is converted to those of the properties of Pop III SNe, which can be compared with SNe in the present day. Large samples of EMP ...

  11. Detailed abundances in extremely metal poor dwarf stars extracted from SDSS

    CERN Document Server

    Sbordone, Luca; Caffau, Elisabetta; Ludwig, Hans-Gunther

    2012-01-01

    We report on the result of an ongoing campaign to determine chemical abundances in extremely metal poor (EMP) turn-off (TO) stars selected from the Sloan Digital Sky Survey (SDSS) low resolution spectra. This contribution focuses principally on the largest part of the sample (18 stars out of 29), observed with UVES@VLT and analyzed by means of the automatic abundance analysis code MyGIsFOS to derive atmosphere parameters and detailed compositions. The most significant findings include i) the detection of a C-rich, strongly Mg-enhanced star ([Mg/Fe]=1.45); ii) a group of Mn-rich stars ([Mn/Fe]>-0.4); iii) a group of Ni-rich stars ([Ni/Fe]>0.2). Li is measured in twelve stars, while for three upper limits are derived.

  12. AN EXTREMELY CARBON-RICH, EXTREMELY METAL-POOR STAR IN THE SEGUE 1 SYSTEM

    International Nuclear Information System (INIS)

    We report the analysis of high-resolution, high signal-to-noise ratio, spectra of an extremely metal-poor, extremely C-rich red giant, Seg 1-7, in Segue 1-described in the literature alternatively as an unusually extended globular cluster or an ultra-faint dwarf galaxy. The radial velocity of Seg 1-7 coincides precisely with the systemic velocity of Segue 1, and its chemical abundance signature of [Fe/H] = -3.52, [C/Fe] = +2.3, [N/Fe] = +0.8, [Na/Fe] = +0.53, [Mg/Fe] = +0.94, [Al/Fe] = +0.23, and [Ba/Fe] < -1.0 is similar to that of the rare and enigmatic class of Galactic halo objects designated CEMP-no (carbon-rich, extremely metal-poor with no enhancement (over solar ratios) of heavy neutron-capture elements). This is the first star in a Milky Way 'satellite' that unambiguously lies on the metal-poor, C-rich branch of the Aoki et al. bimodal distribution of field halo stars in the ([C/Fe], [Fe/H])-plane. Available data permit us only to identify Seg 1-7 as a member of an ultra-faint dwarf galaxy or as debris from the Sgr dwarf spheroidal galaxy. In either case, this demonstrates that at extremely low abundance, [Fe/H ] <-3.0, star formation and associated chemical evolution proceeded similarly in the progenitors of both the field halo and satellite systems. By extension, this is consistent with other recent suggestions that the most metal-poor dwarf spheroidal and ultra-faint dwarf satellites were the building blocks of the Galaxy's outer halo.

  13. Stellar populations and Star Formation History of the Metal-Poor Dwarf Galaxy DDO 68

    CERN Document Server

    Sacchi, E; Cignoni, M; Aloisi, A; Sohn, T; Tosi, M; van der Marel, R P; Grocholski, A J; James, B

    2016-01-01

    We present the star formation history of the extremely metal-poor dwarf galaxy DDO~68, based on our $V-$ and $I-$ band photometry with the Advanced Camera for Surveys on board of the Hubble Space Telescope. With a metallicity of only $12+\\log(O/H)=7.15$ and an isolated location in the periphery of the nearby Lynx-Cancer void, DDO~68 is one of the most metal poor galaxies known. It has been argued in the past that DDO~68 is a young system that started forming stars only $\\sim 0.15$~Gyr ago. Our data provide a deep and uncontaminated optical color-magnitude diagram that now allows us to disprove this hypothesis, since we find a population of at least $\\sim 1$~Gyr old stars. The star formation activity has been fairly continuous over all the look-back time. The current rate is quite low, and the highest activity occurred between 10 and 100 Myr ago. The average star formation rate over the whole Hubble time is \\mbox{$\\simeq 0.01$ M$_{\\odot}$ yr$^{-1}$}, providing a total mass of formed stars of \\mbox{$\\simeq 1.3 ...

  14. r-Process Abundance Signatures in Metal-Poor Halo Stars

    CERN Document Server

    Cowan, John J; Sneden, Christopher; Lawler, James E

    2011-01-01

    Abundance observations indicate the presence of rapid-neutron capture (i.e., r-process) elements in old Galactic halo and globular cluster stars. Recent observations of the r-process-enriched star BD +17 3248 include new abundance determinations for the neutron-capture elements Cd I (Z=48), Lu II (Z = 71) and Os II (Z = 76), the first detections of these elements in metal-poor r-process-enriched halo stars. Combining these and previous observations, we have now detected 32 n-capture elements in BD +17 3248. This is the most of any metal-poor halo star to date. For the most r-process-rich (i.e. [Eu/Fe] ~= 1) halo stars, such as CS 22892-052 and BD +17 3248, abundance comparisons show that the heaviest stable n-capture elements (i.e., Ba and above, Z >= 56) are consistent with a scaled solar system r-process abundance distribution. The lighter n-capture element abundances in these stars, however, do not conform to the solar pattern. These comparisons, as well as recent observations of heavy elements in metal-po...

  15. VERY METAL-POOR OUTER-HALO STARS WITH ROUND ORBITS

    Energy Technology Data Exchange (ETDEWEB)

    Hattori, Kohei; Yoshii, Yuzuru [Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Beers, Timothy C. [National Optical Astronomy Observatories, Tucson, AZ 85719 (United States); Carollo, Daniela [Department of Physics and Astronomy, Macquarie University, Sydney, 2109 NSW (Australia); Lee, Young Sun, E-mail: khattori@ioa.s.u-tokyo.ac.jp [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States)

    2013-01-20

    The orbital motions of halo stars in the Milky Way reflect the orbital motions of the progenitor systems in which they formed, making it possible to trace the mass-assembly history of the Galaxy. Direct measurement of three-dimensional velocities, based on accurate proper motions and line-of-sight velocities, has revealed that the majority of halo stars in the inner-halo region move in eccentric orbits. However, our understanding of the motions of distant, in situ halo-star samples is still limited, due to the lack of accurate proper motions for these stars. Here we explore a model-independent analysis of the line-of-sight velocities and spatial distribution of a recent sample of 1865 carefully selected halo blue horizontal-branch (BHB) stars within 30 kpc of the Galactic center. We find that the mean rotational velocity of the very metal-poor ([Fe/H] < -2.0) BHB stars significantly lags behind that of the relatively more metal-rich ([Fe/H] > -2.0) BHB stars. We also find that the relatively more metal-rich BHB stars are dominated by stars with eccentric orbits, as previously observed for other stellar samples in the inner-halo region. By contrast, the very metal-poor BHB stars are dominated by stars on rounder, lower-eccentricity orbits. Our results indicate that the motion of the progenitor systems of the Milky Way that contributed to the stellar populations found within 30 kpc correlates directly with their metal abundance, which may be related to their physical properties such as gas fractions. These results are consistent with the existence of an inner/outer halo structure for the halo system, as advocated by Carollo et al.

  16. Galactic Cosmochronometry from Radioactive Elements in the Spectra of Very Old Metal-Poor Stars

    Energy Technology Data Exchange (ETDEWEB)

    Sneden, Christopher [Univ. of Texas, Austin, TX (United States). Dept. of Astronomy and McDonald Observatory; Lawler, James E. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Physics; Cowan, John J. [Univ. of Oklahoma, Norman, OK (United States). Dept. of Physics and Astronomy

    2002-08-01

    In a short review of neutron-capture elemental abundances in Galactic halo stars, emphasis is placed on the use of these elements to estimate the age of the Galactic halo. Two prominent characteristics of neutron-capture elements in halo stars are their large star-to-star scatter in the overall abundance level with respect to lighter elements, and the dominance of r-process abundance patterns at lowest stellar metallicities. The r-process abundance signature potentially allows the direct determination of the age of the earliest Galactic halo nucleosynthesis events, but further developments in r-process theory, high resolution spectroscopy of very metal-poor stars, and in basic atomic data are needed to narrow the uncertainties in age estimates. Attention is brought to the importance of accurate transition probabilities in neutron-capture element cosmochronometry Recent progress in the transition probabilities of rare earth elements is discussed, along with suggestions for future work on other species.

  17. Galactic Cosmochronometry from Radioactive Elements in the Spectra of Very Old Metal-Poor Stars

    CERN Document Server

    Sneden, C; Cowan, J J

    2001-01-01

    In a short review of neutron-capture elemental abundances in Galactic halo stars, emphasis is placed on the use of these elements to estimate the age of the Galactic halo. Two prominent characteristics of neutron-capture elements in halo stars are their large star-to-star scatter in the overall abundance level with respect to lighter elements, and the dominance of r-process abundance patterns at lowest stellar metallicities. The r-process abundance signature potentially allows the direct determination of the age of the earliest Galactic halo nucleosynthesis events, but further developments in r-process theory, high resolution spectroscopy of very metal-poor stars, and in basic atomic data are needed to narrow the uncertainties in age estimates. Attention is brought to the importance of accurate transition probabilities in neutron-capture element cosmochronometry. Recent progress in the transition probabilities of rare earth elements is discussed, along with suggestions for future work on other species.

  18. Galactic Cosmochronometry from Radioactive Elements in the Spectra of Very Old Metal-Poor Stars

    International Nuclear Information System (INIS)

    In a short review of neutron-capture elemental abundances in Galactic halo stars, emphasis is placed on the use of these elements to estimate the age of the Galactic halo. Two prominent characteristics of neutron-capture elements in halo stars are their large star-to-star scatter in the overall abundance level with respect to lighter elements, and the dominance of r-process abundance patterns at lowest stellar metallicities. The r-process abundance signature potentially allows the direct determination of the age of the earliest Galactic halo nucleosynthesis events, but further developments in r-process theory, high resolution spectroscopy of very metal-poor stars, and in basic atomic data are needed to narrow the uncertainties in age estimates. Attention is brought to the importance of accurate transition probabilities in neutron-capture element cosmochronometry Recent progress in the transition probabilities of rare earth elements is discussed, along with suggestions for future work on other species

  19. An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars

    CERN Document Server

    Hansen, T; Christlieb, N; Beers, T C; Yong, D; Bessell, M S; Frebel, A; Perez, A E Garcia; Placco, V M; Norris, J E; Asplund, M

    2015-01-01

    We present a high-resolution elemental-abundance analysis for a sample of 23 very metal-poor (VMP; [Fe/H] 0. The stars with [C/N] < 0 suggest a larger degree of mixing; the few CEMP-no stars that exhibit this signature are only found at [Fe/H] < -3.4, a metallicity below which we also find the CEMP-no stars with large enhancements in Na, Mg, and Al. We confirm the existence of two plateaus in the absolute carbon abundances of CEMP stars, as suggested by Spite et al. We also present evidence for a "floor" in the absolute Ba abundances of CEMP-no stars at A(Ba)~ -2.0.

  20. A Giant Planet Around a Metal-poor Star of Extragalactic Origin

    CERN Document Server

    Setiawan, Johny; Henning, Thomas; Rix, Hans-Walter; Rochau, Boyke; Rodmann, Jens; Schulze-Hartung, Tim; Heidelberg, MPIA; Noordwijk, ESTEC; 10.1126/science.1193342

    2010-01-01

    Stars in their late stage of evolution, such as Horizontal Branch stars, are still largely unexplored for planets. We report the detection of a planetary companion around HIP 13044, a very metal-poor star on the red Horizontal Branch, based on radial velocity observations with a high-resolution spectrograph at the 2.2-m MPG/ESO telescope. The star's periodic radial velocity variation of P=16.2 days caused by the planet can be distinguished from the periods of the stellar activity indicators. The minimum mass of the planet is 1.25 Jupiter masses and its orbital semi-major axis 0.116 AU. Because HIP 13044 belongs to a group of stars that have been accreted from a disrupted satellite galaxy of the Milky Way, the planet most likely has an extragalactic origin.

  1. Very Metal-poor Outer-halo Stars with Round Orbits

    Science.gov (United States)

    Hattori, Kohei; Yoshii, Yuzuru; Beers, Timothy C.; Carollo, Daniela; Lee, Young Sun

    2013-01-01

    The orbital motions of halo stars in the Milky Way reflect the orbital motions of the progenitor systems in which they formed, making it possible to trace the mass-assembly history of the Galaxy. Direct measurement of three-dimensional velocities, based on accurate proper motions and line-of-sight velocities, has revealed that the majority of halo stars in the inner-halo region move in eccentric orbits. However, our understanding of the motions of distant, in situ halo-star samples is still limited, due to the lack of accurate proper motions for these stars. Here we explore a model-independent analysis of the line-of-sight velocities and spatial distribution of a recent sample of 1865 carefully selected halo blue horizontal-branch (BHB) stars within 30 kpc of the Galactic center. We find that the mean rotational velocity of the very metal-poor ([Fe/H] -2.0) BHB stars. We also find that the relatively more metal-rich BHB stars are dominated by stars with eccentric orbits, as previously observed for other stellar samples in the inner-halo region. By contrast, the very metal-poor BHB stars are dominated by stars on rounder, lower-eccentricity orbits. Our results indicate that the motion of the progenitor systems of the Milky Way that contributed to the stellar populations found within 30 kpc correlates directly with their metal abundance, which may be related to their physical properties such as gas fractions. These results are consistent with the existence of an inner/outer halo structure for the halo system, as advocated by Carollo et al.

  2. The Synthetic-Oversampling Method: Using Photometric Colors to Discover Extremely Metal-poor Stars

    Science.gov (United States)

    Miller, A. A.

    2015-09-01

    Extremely metal-poor (EMP) stars ([Fe/H] ≤ ‑3.0 dex) provide a unique window into understanding the first generation of stars and early chemical enrichment of the universe. EMP stars are exceptionally rare, however, and the relatively small number of confirmed discoveries limits our ability to exploit these near-field probes of the first ∼500 Myr after the Big Bang. Here, a new method to photometrically estimate [Fe/H] from only broadband photometric colors is presented. I show that the method, which utilizes machine-learning algorithms and a training set of ∼170,000 stars with spectroscopically measured [Fe/H], produces a typical scatter of ∼0.29 dex. This performance is similar to what is achievable via low-resolution spectroscopy, and outperforms other photometric techniques, while also being more general. I further show that a slight alteration to the model, wherein synthetic EMP stars are added to the training set, yields the robust identification of EMP candidates. In particular, this synthetic-oversampling method recovers ∼20% of the EMP stars in the training set, at a precision of ∼0.05. Furthermore, ∼65% of the false positives from the model are very metal-poor stars ([Fe/H] ≤ ‑2.0 dex). The synthetic-oversampling method is biased toward the discovery of warm (∼F-type) stars, a consequence of the targeting bias from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding survey. This EMP selection method represents a significant improvement over alternative broadband optical selection techniques. The models are applied to >12 million stars, with an expected yield of ∼600 new EMP stars, which promises to open new avenues for exploring the early universe.

  3. Chemistry of the Most Metal-poor Stars in the Bulge and the z ≳ 10 Universe

    Science.gov (United States)

    Casey, Andrew R.; Schlaufman, Kevin C.

    2015-08-01

    Metal-poor stars in the Milky Way are local relics of the epoch of the first stars and the first galaxies. However, a low metallicity does not prove that a star formed in this ancient era, as metal-poor stars form over a range of redshift in different environments. Theoretical models of Milky Way formation have shown that at constant metallicity, the oldest stars are those closest to the center of the Galaxy on the most tightly bound orbits. For that reason, the most metal-poor stars in the bulge of the Milky Way provide excellent tracers of the chemistry of the high-redshift universe. We report the dynamics and detailed chemical abundances of three stars in the bulge with [{Fe}/{{H}}]≲ -2.7, two of which are the most metal-poor stars in the bulge in the literature. We find that with the exception of scandium, all three stars follow the abundance trends identified previously for metal-poor halo stars. These three stars have the lowest [Sc ii/Fe] abundances yet seen in α-enhanced giant stars in the Galaxy. Moreover, all three stars are outliers in the otherwise tight [Sc ii/Fe]-[Ti ii/Fe] relation observed among metal-poor halo stars. Theoretical models predict that there is a 30% chance that at least one of these stars formed at z≳ 15, while there is a 70% chance that at least one formed at 10≲ z≲ 15. These observations imply that by z˜ 10, the progenitor galaxies of the Milky Way had both reached [{Fe}/{{H}}]˜ -3.0 and established the abundance pattern observed in extremely metal-poor stars. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  4. Atomic diffusion in metal-poor stars II. Predictions for the Spite plateau

    CERN Document Server

    Salaris, M; Salaris, Maurizio; Weiss, Achim

    2001-01-01

    We have computed a grid of up-to-date stellar evolutionary models including atomic diffusion, in order to study the evolution with time of the surface Li abundance in low-mass metal-poor stars. We discuss in detail the dependence of the surface Li evolution on the initial metallicity and stellar mass, and compare the abundances obtained from our models with the available Li measurements in Pop II stars. While it is widely accepted that the existence of the Spite Li-plateau for these stars is a strong evidence that diffusion is inhibited, we show that, when taking into account observational errors, uncertainties in the Li abundance determinations, in the effective temperature scale, and in particular the size of the observed samples of stars, the Spite plateau and the Li abundances in subgiant branch stars can be reproduced also by models including fully efficient diffusion, provided that the most metal-poor field halo objects are between 13.5 and 14 Gyr old. We provide the value of the minimum number of plate...

  5. S-process in low-mass extremely metal-poor stars

    CERN Document Server

    Cruz, Monique A; Weiss, Achim

    2013-01-01

    Extremely metal-poor low-mass stars experience an ingestion of protons into the helium-rich layer during the core He-flash, resulting in the production of neutrons through the reactions ^{12}C(p,\\gamma)^{13}N(\\beta)^{13}C(\\alpha,n)^{16}O. This is a potential site for the production of s-process elements in extremely metal-poor stars not occurring in more metal-rich counterparts. Observationally, the signatures of s-process elements in the two most iron deficient stars observed to date, HE1327-2326 & HE0107-5240, still await for an explanation. We investigate the possibility that low-mass EMP stars could be the source of s-process elements observed in extremely iron deficient stars, either as a result of self-enrichment or in a binary scenario as the consequence of a mass transfer episode. We present evolutionary and post-processing s-process calculations of a 1Msun stellar model with metallicities Z=0, 10^{-8} and 10^{-7}. We assess the sensitivity of nucleosynthesis results to uncertainties in the input ...

  6. Lithium abundances in extremely metal-poor turn-off stars

    CERN Document Server

    Sbordone, L; Caffau, E

    2012-01-01

    We discuss the current status of the sample of Lithium abundances in extremely metal poor (EMP) turn-off (TO) stars collected by our group, and compare it with the available literature results. In the last years, evidences have accumulated of a progressive disruption of the Spite plateau in stars of extremely low metallicity. What appears to be a flat, thin plateau above [Fe/H]\\sim-2.8 turns, at lower metallicities, into a broader distribution for which the plateau level constitutes the upper limit, but more and more stars show lower Li abundances. The sample we have collected currently counts abundances or upper limits for 44 EMP TO stars between [Fe/H]=-2.5 and -3.5, plus the ultra-metal poor star SDSS J102915+172927 at [Fe/H]=-4.9. The "meltdown" of the Spite plateau is quite evident and, at the current status of the sample, does not appear to be restricted to the cool end of the effective temperature distribution. SDSS J102915+172927 displays an extreme Li depletion that contrasts with its otherwise quite...

  7. A new sample of extremely/ultra metal-poor stars

    Energy Technology Data Exchange (ETDEWEB)

    GarcIa Perez, A E; Ryan, S G [Department of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB (United Kingdom); Christlieb, N [Center for Astronomy, Landessternwarte, Koenigstuhl 12, University of Heidelberg, Heidelberg 69177 (Germany); Beers, T C [Department of Physics and Astronomy and JINA (Joint Institute for Nuclear Astrophysics), Michigan State University, East Lansing, MI 48824 (United States); Aoki, W [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Asplund, M [Max-Planck Institute for Astrophysics, Karl-Schwarzschild-Strasse 1, Postfach 1317, Garching b. Muenchen 8574 (Germany); Barklem, P S; Eriksson, K; Gustafsson, B; Korn, A J [Department of Physics and Astronomy, Uppsala University, Box 515, Uppsala 75120 (Sweden); Bessell, M S; Norris, J E [Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia); Frebel, A [McDonald Observatory, University of Texas, Austin, TX 78712-0259 (United States); Nordstroem, B [Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, Copenhagen 2100 (Denmark)], E-mail: a.e.garcia-perez@herts.ac.uk

    2008-12-15

    A sample of 30 very metal-poor stars from the Hamburg-European Southern Observatory (ESO) objective-prism survey have been observed at high spectral resolution at the Very Large Telescope (VLT) using the Ultraviolet and Visual Echelle Spectrograph (UVES). Two of the observed stars are very interesting not only because of their very low iron content, approximately four orders of magnitude lower than the solar value, but also because we detected the neutral lithium resonance line at 670.8 nm. Hydrogen lines suggest that the two observed stars have effective temperatures around 6000-6250 K and according to isochrones, they are either on the main-sequence or on the subgiant branch, in which case they would probably be the most metal-poor dwarfs or warm subgiants with lithium detections known. These detections would allow to determine more accurately the slope of the trend of the lithium abundance with [Fe/H] than was possible with samples of unevolved stars restricted to higher metallicities.

  8. THE MOST METAL-POOR STARS. I. DISCOVERY, DATA, AND ATMOSPHERIC PARAMETERS

    International Nuclear Information System (INIS)

    We report the discovery of 34 stars in the Hamburg/ESO Survey for metal-poor stars and the Sloan Digital Sky Survey that have [Fe/H] ∼eff), and surface gravity (log g), which are critical in the determination of the chemical abundances and the evolutionary status of these stars. Three techniques were used to derive these parameters. Spectrophotometric fits to model atmosphere fluxes were used to derive T eff, log g, and an estimate of E(B – V); Hα, Hβ, and Hγ profile fitting to model atmosphere results provided the second determination of T eff and log g; and finally, we used an empirical T eff-calibrated Hδ index, for the third, independent T eff determination. The three values of T eff are in good agreement, although the profile fitting may yield systematically cooler T eff values, by ∼100 K. This collective data set will be analyzed in future papers in the present series to utilize the most metal-poor stars as probes of conditions in the early universe.

  9. The IMF of Extremely Metal-Poor Stars and the Probe into the Star-Formation Process of the Milky Way

    CERN Document Server

    Komiya, Yutaka; Habe, Asao; Fujimoto, Masayuki Y

    2007-01-01

    We discuss the star formation history of the Galaxy, based on the observations of extremely metal-poor stars (EMP) in the Galactic halo, to gain an insight into the evolution and structure formation in the early universe. The initialmass function (IMF) of EMP stars is derived from the observed fraction of carbon-enhanced EXP (CEMP) stars among the EMP survivors, which are thought to originate from the evolution in the close binary systems with mass transfer. Relying upon the theory of the evolution of EMP stars and of their binary evolution, we find that stars of metallicity [Fe/H]<-2.5 were formed at typical mass of ~10M_sun. The top heavy IMF thus obtained is applied to study the early chemical evolution of the Galaxy. We construct the merging history of our Galaxy semi-analytically and derive the metallicity distribution function (MDF) of low-mass EMP stars that survive to date with taking into account the contribution of binary systems. It is shown that the resultant MDF can well reproduce the observed...

  10. The low Sr/Ba ratio on some extremely metal-poor stars

    CERN Document Server

    Spite, M; Bonifacio, P; Caffau, E; François, P; Sbordone, L

    2014-01-01

    It has been noted that, in classical extremely metal-poor (EMP) stars, the abundance ratio of Sr and Ba, is always higher than [Sr/Ba] = -0.5, the value of the solar r-only process; however, a handful of EMP stars have recently been found with a very low Sr/Ba ratio. We try to understand the origin of this anomaly by comparing the abundance pattern of the elements in these stars and in the classical EMP stars. Four stars with very low Sr/Ba ratios were observed and analyzed within LTE approximation through 1D (hydrostatic) model atmosphere, providing homogeneous abundances of nine neutron-capture elements. In CS 22950-173, the only turnoff star of the sample, the Sr/Ba ratio is, in fact, found to be higher than the r-only solar ratio, so the star is discarded. The remaining stars (CS 29493-090, CS 30322-023, HE 305-4520) are cool evolved giants. They do not present a clear carbon enrichment. The abundance patterns of the neutron-capture elements in the three stars are strikingly similar to a theoretical s-pro...

  11. The chemical imprint of silicate dust on the most metal-poor stars

    International Nuclear Information System (INIS)

    We investigate the impact of dust-induced gas fragmentation on the formation of the first low-mass, metal-poor stars (<1 M ☉) in the early universe. Previous work has shown the existence of a critical dust-to-gas ratio, below which dust thermal cooling cannot cause gas fragmentation. Assuming that the first dust is silicon-based, we compute critical dust-to-gas ratios and associated critical silicon abundances ([Si/H]crit). At the density and temperature associated with protostellar disks, we find that a standard Milky Way grain size distribution gives [Si/H]crit = –4.5 ± 0.1, while smaller grain sizes created in a supernova reverse shock give [Si/H]crit = –5.3 ± 0.1. Other environments are not dense enough to be influenced by dust cooling. We test the silicate dust cooling theory by comparing to silicon abundances observed in the most iron-poor stars ([Fe/H] < -4.0). Several stars have silicon abundances low enough to rule out dust-induced gas fragmentation with a standard grain size distribution. Moreover, two of these stars have such low silicon abundances that even dust with a shocked grain size distribution cannot explain their formation. Adding small amounts of carbon dust does not significantly change these conclusions. Additionally, we find that these stars exhibit either high carbon with low silicon abundances or the reverse. A silicate dust scenario thus suggests that the earliest low-mass star formation in the most metal-poor regime may have proceeded through two distinct cooling pathways: fine-structure line cooling and dust cooling. This naturally explains both the carbon-rich and carbon-normal stars at extremely low [Fe/H].

  12. Elemental abundances of metal poor carbon rich lead star: CS29497-030

    OpenAIRE

    Sivarani, T.; Bonifacio, P.; Molaro, P.; Cayrel, R.; Spite, M.; Spite, F.; Plez, B.; Andersen, J.; Barbuy, B.; Beers, T. C.; Depagne, E.; Hill, V.; Francois, P.; Nordstrom, B.; Primas, F.

    2002-01-01

    We present here the abundance analysis of a metal poor carbon rich lead star, CS29497-030. High resolution and high signal to noise spectra were obtained using the UVES spectrograph on the 8.2m VLT-Kueyen telescope. The observations were made as a part of the Large Programme 165.N-0276, P.I. R. Cayrel. Abundance analysis was done using the latest version of the MARCS model atmospheres (Plez et. al. 1992) and the turbospectrum spectrum synthesis code. We have derived Teff = 6650K from the FeI ...

  13. Follow-up observations of extremely metal-poor stars identified from SDSS

    CERN Document Server

    Aguado, D S; Hernández, J I González; Carrera, R; Rebolo, Rafael; Shetrone, M; Lambert, D L; Fernández-Alvar, E

    2016-01-01

    The most metal-poor stars in the Milky Way witnessed the early phases of formation of the Galaxy, and have chemical compositions that are close to the pristine mixture from Big Bang nucleosynthesis, polluted by one or few supernovae. Only two dozen stars with ([Fe/H]< -4) are known, and they show a wide range of abundance patterns. It is therefore important to enlarge this sample. We present the first results of an effort to identify new extremely metal-poor stars in the Milky Way halo. Our targets have been selected from low-resolution spectra obtained as part of the Sloan Digital Sky Survey, and followed-up with medium resolution spectroscopy on the 4.2 m William Herschel Telescope and, in a few cases, at high resolution on the the 9.2 m Hobby-Eberly Telescope. Stellar parameters and the abundances of magnesium, calcium, iron, and strontium have been inferred from the spectra using classical model atmospheres. We have also derived carbon abundances from the G band. We find consistency between the metalli...

  14. Chromospheres in Metal-Poor Stars Evidenced from the He I 10830A Line

    CERN Document Server

    Takeda, Yoichi

    2011-01-01

    Based on the near-IR spectra of 33 late-type stars in the wide metallicity range (mainly dwarfs and partly giants) obtained with IRCS+AO188 of the Subaru Telescope, we confirmed that He I 10830A line is seen in absorption in almost all moderately to extremely metal-poor stars of thick disk and halo population (from [Fe/H]~ -0.5 down to [Fe/H]~ -3.7), the strength of which is almost constant irrespective of the metallicity. This is an evidence that chromospheric activity at a basal level persists even for such old stars, despite that their rotations are considered to be slowed down and incapable of sustaining a dynamo, suggesting that some kind of chromospheric heating mechanism independent of rotation/magnetism (e.g., acoustic heating) may take place.

  15. METAL-POOR STARS OBSERVED WITH THE MAGELLAN TELESCOPE. I. CONSTRAINTS ON PROGENITOR MASS AND METALLICITY OF AGB STARS UNDERGOING s-PROCESS NUCLEOSYNTHESIS

    Energy Technology Data Exchange (ETDEWEB)

    Placco, Vinicius M.; Rossi, Silvia [Departamento de Astronomia-Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Sao Paulo, SP 05508-900 (Brazil); Frebel, Anna [Massachusetts Institute of Technology and Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Karakas, Amanda I.; Kennedy, Catherine R. [Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston, ACT 2611 (Australia); Christlieb, Norbert [Zentrum fuer Astronomie der Universitaet Heidelberg, Landessternwarte, Koenigstuhl 12, D-69117 Heidelberg (Germany); Stancliffe, Richard J. [Argelander-Institut fuer Astronomie der Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

    2013-06-20

    We present a comprehensive abundance analysis of two newly discovered carbon-enhanced metal-poor (CEMP) stars. HE 2138-3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if non-local thermodynamic equilibrium corrections are included ([Pb/Fe] = +3.84). HE 2258-6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and followed up with medium-resolution (R {approx} 2000) spectroscopy with GEMINI/GMOS. We report here on derived abundances (or limits) for a total of 34 elements in each star, based on high-resolution (R {approx} 30, 000) spectroscopy obtained with Magellan-Clay/MIKE. Our results are compared to predictions from new theoretical asymptotic giant branch (AGB) nucleosynthesis models of 1.3 M{sub Sun} with [Fe/H] = -2.5 and -2.8, as well as to a set of AGB models of 1.0 to 6.0 M{sub Sun} at [Fe/H] = -2.3. The agreement with the model predictions suggests that the neutron-capture material in HE 2138-3336 originated from mass transfer from a binary companion star that previously went through the AGB phase, whereas for HE 2258-6358, an additional process has to be taken into account to explain its abundance pattern. We find that a narrow range of progenitor masses (1.0 {<=} M(M{sub Sun }) {<=} 1.3) and metallicities (-2.8 {<=} [Fe/H] {<=}-2.5) yield the best agreement with our observed elemental abundance patterns.

  16. METAL-POOR STARS OBSERVED WITH THE MAGELLAN TELESCOPE. I. CONSTRAINTS ON PROGENITOR MASS AND METALLICITY OF AGB STARS UNDERGOING s-PROCESS NUCLEOSYNTHESIS

    International Nuclear Information System (INIS)

    We present a comprehensive abundance analysis of two newly discovered carbon-enhanced metal-poor (CEMP) stars. HE 2138–3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if non-local thermodynamic equilibrium corrections are included ([Pb/Fe] = +3.84). HE 2258–6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and followed up with medium-resolution (R ∼ 2000) spectroscopy with GEMINI/GMOS. We report here on derived abundances (or limits) for a total of 34 elements in each star, based on high-resolution (R ∼ 30, 000) spectroscopy obtained with Magellan-Clay/MIKE. Our results are compared to predictions from new theoretical asymptotic giant branch (AGB) nucleosynthesis models of 1.3 M☉ with [Fe/H] = –2.5 and –2.8, as well as to a set of AGB models of 1.0 to 6.0 M☉ at [Fe/H] = –2.3. The agreement with the model predictions suggests that the neutron-capture material in HE 2138–3336 originated from mass transfer from a binary companion star that previously went through the AGB phase, whereas for HE 2258–6358, an additional process has to be taken into account to explain its abundance pattern. We find that a narrow range of progenitor masses (1.0 ≤ M(M☉) ≤ 1.3) and metallicities (–2.8 ≤ [Fe/H] ≤–2.5) yield the best agreement with our observed elemental abundance patterns.

  17. Very Metal-Poor Outer-Halo Stars with Round Orbits

    CERN Document Server

    Hattori, Kohei; Beers, Timothy C; Carollo, Daniela; Lee, Young Sun

    2012-01-01

    The orbital motions of halo stars in the Milky Way reflect the orbital motions of the progenitor systems in which they formed, making it possible to trace the mass-assembly history of the Galaxy. Direct measurement of three-dimensional velocities, based on accurate proper motions and line-of-sight velocities, has revealed that the majority of halo stars in the inner-halo region move on eccentric orbits. However, our understanding of the motions of distant, in-situ halo-star samples is still limited, due to the lack of accurate proper motions for these stars. Here we explore a model-independent analysis of the line-of-sight velocities and spatial distribution of a recent sample of 1865 carefully selected halo blue horizontal-branch (BHB) stars within 30 kpc of the Galactic center. We find that the mean rotational velocity of the very metal-poor ([Fe/H] -2.0) BHB stars. We also find that the relatively more metal-rich BHB stars are dominated by stars with eccentric orbits, as previously observed for other stel...

  18. Detailed Abundances for 28 Metal-poor Stars: Stellar Relics in the Milky Way

    CERN Document Server

    Lai, David K; Johnson, Jennifer A; Lucatello, Sara; Heger, Alexander; Woosley, S E

    2008-01-01

    We present the results of an abundance analysis for a sample of stars with $-4<$[Fe/H]$<-2$. The data were obtained with the HIRES spectrograph at Keck Observatory. The set includes 28 stars, with effective temperature ranging from 4800 K to 6600 K. For 13 stars with [Fe/H]$<-2.6$, including nine of with [Fe/H]$<-3.0$, and one with [Fe/H]$=-4.0$, these are the first reported detailed abundances. For the most metal-poor star in our sample, CS 30336-049, we measure an abundance pattern that is very similar to stars in the range [Fe/H]$\\sim-3.5$, including a normal C+N abundance. We also find that it has very low but measurable Sr and Ba, indicating some neutron-capture activity even at this low of a metallicity. We explore this issue further by examining other very neutron-capture-deficient stars, and find that at the lowest levels, [Ba/Sr] exhibits the ratio of the main r-process. We also report on a new r-process enhanced star, CS 31078-018. This star has [Fe/H]$=-2.85$, [Eu/Fe]$=1.23$, and [Ba/Eu...

  19. High-resolution abundance analysis of very metal-poor R-I stars

    International Nuclear Information System (INIS)

    The moderately r-process enriched stars (r-I; +0.3 ≤ [Eu/Fe] ≤ +1.0) are, at least, four times as common as those that are greatly enriched in r-process elements (r-II; [Eu/Fe] > +1.0), and the abundances in their atmospheres are important tools for obtaining better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak. In this contribution, we derived abundances for a sample of 7 metal-poor stars with -3.4 ≤ [Fe/H] ≤ -2.4 classified as r-I stars, in order to understand the role of such stars for constraining the astrophysical nucleosynthesis event(s) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars. Based on high resolution spectra obtained with the VLT/UVES spectrograph, we have obtained abundances of the light elements Li, C and N, the alpha-elements Mg, Si, S, Ca and Ti, the odd-Z elements Al, K, and Sc, the iron-peak elements V, Cr, Mn, Fe, Co, and Ni, and the trans-iron elements from the first peak (Sr, Y, Zr, Mo, Ru, and Pd), the second peak (Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), the third peak (Os and Ir, as upper limits), and the actinides (Th) regions. The results are compared with values for these elements for r-II and 'normal' very and extremely metal-poor stars reported in the literature, ages based on radioactive chronometry are explored using different models, and a number of conclusions about the r-process and the r-I stars are presented. Hydrodynamical models were used for some elements and general behaviors for the 3D corrections were presented. Although the abundance ratios of the second r-process peak elements (usually associated with the main r-process) appear nearly identical for r-I and r-II stars, the first r-process peak abundance ratios (probably associated with the weak r-process) appear enhanced in r-I stars compared with r-II stars, suggesting that differing

  20. New Keck Observations of Lithium in Very Metal-poor Stars

    CERN Document Server

    Boesgaard, A M; Stephens, A; Boesgaard, Ann Merchant; Novicki, Megan C.

    2005-01-01

    Lithium abundances have been determined in more than 100 metal-poor halo stars both in the field and in clusters. From these data we find trends of Li with both temperature and metallicity and a real dispersion in Li abundances in the Spite Li plateau. We attribute this dispersion primarily to Li depletion (presumably due to extra mixing induced by stellar rotation) and to Galactic chemical evolution. We derive a primordial Li of 2.44 $\\pm$0.18 for A(Li)$_p$ = log N(Li/H) + 12.00. This agrees with the Li abundances predicted by the $WMAP$ results. For stars cooler than the Li plateau we have evidence that Li depletion sets in at hotter temperatures for the higher metallicity stars than for the low-metal stars. This is the opposite sense of predictions from stellar models. The smooth transition of the Li content from the Li plateau stars to the cool stars adds weight to the inference of Li depletion in the plateau stars.

  1. TESTING THE ASTEROSEISMIC MASS SCALE USING METAL-POOR STARS CHARACTERIZED WITH APOGEE AND KEPLER

    International Nuclear Information System (INIS)

    Fundamental stellar properties, such as mass, radius, and age, can be inferred using asteroseismology. Cool stars with convective envelopes have turbulent motions that can stochastically drive and damp pulsations. The properties of the oscillation frequency power spectrum can be tied to mass and radius through solar-scaled asteroseismic relations. Stellar properties derived using these scaling relations need verification over a range of metallicities. Because the age and mass of halo stars are well-constrained by astrophysical priors, they provide an independent, empirical check on asteroseismic mass estimates in the low-metallicity regime. We identify nine metal-poor red giants (including six stars that are kinematically associated with the halo) from a sample observed by both the Kepler space telescope and the Sloan Digital Sky Survey-III APOGEE spectroscopic survey. We compare masses inferred using asteroseismology to those expected for halo and thick-disk stars. Although our sample is small, standard scaling relations, combined with asteroseismic parameters from the APOKASC Catalog, produce masses that are systematically higher (<ΔM > =0.17 ± 0.05 M ☉) than astrophysical expectations. The magnitude of the mass discrepancy is reduced by known theoretical corrections to the measured large frequency separation scaling relationship. Using alternative methods for measuring asteroseismic parameters induces systematic shifts at the 0.04 M ☉ level. We also compare published asteroseismic analyses with scaling relationship masses to examine the impact of using the frequency of maximum power as a constraint. Upcoming APOKASC observations will provide a larger sample of ∼100 metal-poor stars, important for detailed asteroseismic characterization of Galactic stellar populations

  2. Europium, Samarium, and Neodymium Isotopic Fractions in Metal-Poor Stars

    Science.gov (United States)

    Roederer, Ian U.; Lawler, James E.; Sneden, Christopher; Cowan, John J.; Sobeck, Jennifer S.; Pilachowski, Catherine A.

    2008-03-01

    We have derived isotopic fractions of europium (Eu), samarium (Sm), and neodymium (Nd) in two metal-poor giants with differing neutron-capture nucleosynthetic histories. These isotopic fractions were measured from new very high resolution (R~120,000), high signal-to-noise (S/N~160-1000) spectra obtained with the 2dCoudé spectrograph of McDonald Observatory's 2.7 m Smith telescope. Synthetic spectra were generated using recent high-precision laboratory measurements of hyperfine and isotopic subcomponents of several transitions of these elements and matched quantitatively to the observed spectra. We interpret our isotopic fractions by the nucleosynthesis predictions of the stellar model, which models s-process nucleosynthesis in the physical conditions expected in a low-mass, thermally-pulsing star on the AGB, and the classical method, which assumes that s-process nucleosynthesis can be approximated by a steady neutron flux impinging upon Fe-peak seed nuclei. These two approaches predict the relative contributions to the Solar System n-capture abundances from the s- and r-processes and, by extension, the relative contributions of these two process to material in metal-poor stars. Our Eu isotopic fraction in HD 175305 is consistent with an r-process origin by the classical method and is consistent with both an r-process and s-process origin by the stellar model. Our Sm isotopic fraction in HD 175305 is consistent with a predominantly r-process origin by both methods, and our Sm isotopic fraction in HD 196944 is consistent with a pure s-process origin by both methods as well. Our Nd isotopic fractions in both stars are consistent with either r-process and s-process origins by both methods. The Eu and Sm isotopic fraction estimates argue for an r-process origin for the rare-earth elements in HD 175305 and an s-process origin for them in HD 196944, in excellent agreement with previous studies of the elemental abundance distributions in these stars. This study for the

  3. DETECTION OF THE SECOND r-PROCESS PEAK ELEMENT TELLURIUM IN METAL-POOR STARS ,

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U. [Carnegie Observatories, Pasadena, CA 91101 (United States); Lawler, James E. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Cowan, John J. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Frebel, Anna [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States); Ivans, Inese I. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Schatz, Hendrik [Department of Physics and Astronomy, Michigan State University, E. Lansing, MI 48824 (United States); Sobeck, Jennifer S. [Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Sneden, Christopher [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States)

    2012-03-15

    Using near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, we detect neutral tellurium in three metal-poor stars enriched by products of r-process nucleosynthesis, BD +17 3248, HD 108317, and HD 128279. Tellurium (Te, Z = 52) is found at the second r-process peak (A Almost-Equal-To 130) associated with the N = 82 neutron shell closure, and it has not been detected previously in Galactic halo stars. The derived tellurium abundances match the scaled solar system r-process distribution within the uncertainties, confirming the predicted second peak r-process residuals. These results suggest that tellurium is predominantly produced in the main component of the r-process, along with the rare earth elements.

  4. Detection of the Second r-process Peak Element Tellurium in Metal-Poor Stars

    CERN Document Server

    Roederer, Ian U; Cowan, John J; Beers, Timothy C; Frebel, Anna; Ivans, Inese I; Schatz, Hendrik; Sobeck, Jennifer S; Sneden, Christopher

    2012-01-01

    Using near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope, we detect neutral tellurium in three metal-poor stars enriched by products of r-process nucleosynthesis, BD+17 3248, HD 108317, and HD 128279. Tellurium (Te, Z=52) is found at the second r-process peak (A=130) associated with the N=82 neutron shell closure, and it has not been detected previously in Galactic halo stars. The derived tellurium abundances match the scaled solar system r-process distribution within the uncertainties, confirming the predicted second peak r-process residuals. These results suggest that tellurium is predominantly produced in the main component of the r-process, along with the rare earth elements.

  5. The r-Process in Metal Poor Stars and Black Hole Formation

    International Nuclear Information System (INIS)

    Nucleosynthesis of heavy nuclei in metal-poor stars is generally ascribed to the r-process, as the abundance pattern in many such stars agrees with the inferred Solar r-process abundances. Nonetheless, a significant number of these stars do not share this r-process template. they suggest that many such stars have begun an r-process, but it was prevented from running to completion in more massive stars by collapse to black holes, creating a 'truncated r-process,' or 'tr-process'. The observed fraction of tr-process stars is found to be consistent with expectations from the initial mass function (IMF), and they suggest that an apparent sharp truncation observed at around mass 160 could result from a combination of collapses to black holes and the difficulty of observing the higher mass rare earths. They test the tr-process hypothesis with calculations that are terminated before all r-process trajectories have been ejected. These produce qualitative agreement with observation when both black hole collapse and observational realities are taken into account.

  6. The r-Process in Metal Poor Stars and Black Hole Formation

    Energy Technology Data Exchange (ETDEWEB)

    Boyd, R N; Famiano, M A; Meyer, B S; Motizuki, Y; Kajino, T; Roederer, I U

    2011-11-30

    Nucleosynthesis of heavy nuclei in metal-poor stars is generally ascribed to the r-process, as the abundance pattern in many such stars agrees with the inferred Solar r-process abundances. Nonetheless, a significant number of these stars do not share this r-process template. they suggest that many such stars have begun an r-process, but it was prevented from running to completion in more massive stars by collapse to black holes, creating a 'truncated r-process,' or 'tr-process'. The observed fraction of tr-process stars is found to be consistent with expectations from the initial mass function (IMF), and they suggest that an apparent sharp truncation observed at around mass 160 could result from a combination of collapses to black holes and the difficulty of observing the higher mass rare earths. They test the tr-process hypothesis with calculations that are terminated before all r-process trajectories have been ejected. These produce qualitative agreement with observation when both black hole collapse and observational realities are taken into account.

  7. Metal-poor stars towards the Galactic bulge - a population potpourri

    CERN Document Server

    Koch, Andreas; Preston, George W; Thompson, Ian B

    2015-01-01

    We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern Galactic bulge, at (l,b)$\\sim$(0$^{\\rm o}$,-11$^{\\rm o}$). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H]=-2.52 dex, and another one is a moderately metal-poor ([Fe/H]=-1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe]=1.35). These individuals provide the first contenders of these classes of stars ...

  8. NEW HUBBLE SPACE TELESCOPE OBSERVATIONS OF HEAVY ELEMENTS IN FOUR METAL-POOR STARS

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U.; Thompson, Ian B. [Carnegie Observatories, Pasadena, CA 91101 (United States); Lawler, James E. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Sobeck, Jennifer S. [Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Cowan, John J. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Frebel, Anna [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139 (United States); Ivans, Inese I. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Schatz, Hendrik [Department of Physics and Astronomy, Michigan State University, E. Lansing, MI 48824 (United States); Sneden, Christopher [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States)

    2012-12-15

    Elements heavier than the iron group are found in nearly all halo stars. A substantial number of these elements, key to understanding neutron-capture nucleosynthesis mechanisms, can only be detected in the near-ultraviolet. We report the results of an observing campaign using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to study the detailed heavy-element abundance patterns in four metal-poor stars. We derive abundances or upper limits from 27 absorption lines of 15 elements produced by neutron-capture reactions, including seven elements (germanium, cadmium, tellurium, lutetium, osmium, platinum, and gold) that can only be detected in the near-ultraviolet. We also examine 202 heavy-element absorption lines in ground-based optical spectra obtained with the Magellan Inamori Kyocera Echelle Spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the High Resolution Echelle Spectrometer on the Keck I Telescope on Mauna Kea. We have detected up to 34 elements heavier than zinc. The bulk of the heavy elements in these four stars are produced by r-process nucleosynthesis. These observations affirm earlier results suggesting that the tellurium found in metal-poor halo stars with moderate amounts of r-process material scales with the rare earth and third r-process peak elements. Cadmium often follows the abundances of the neighboring elements palladium and silver. We identify several sources of systematic uncertainty that must be considered when comparing these abundances with theoretical predictions. We also present new isotope shift and hyperfine structure component patterns for Lu II and Pb I lines of astrophysical interest.

  9. CARMA CO Observations of Three Extremely Metal-Poor, Star-Forming Galaxies

    CERN Document Server

    Warren, Steven R; Cannon, John M; Bolatto, Alberto D; Adams, Elizabeth A K; Bernstein-Cooper, Elijah Z; Giovanelli, Riccardo; Haynes, Martha P; Herrera-Camus, Rodrigo; Jameson, Katie; McQuinn, Kristen B W; Rhode, Katherine L; Salzer, John J; Skillman, Evan D

    2015-01-01

    We present sensitive CO (J = 1 - 0) emission line observations of three metal-poor dwarf irregular galaxies Leo P (Z ~ 3% Z_Solar), Sextans A (Z ~ 7.5% Z_Solar), and Sextans B (Z ~ 7.5% Z_Solar), all obtained with the Combined Array for Millimeter-wave Astronomy (CARMA) interferometer. While no CO emission was detected, the proximity of the three systems allows us to place very stringent (4 sigma) upper limits on the CO luminosity (L_CO) in these metal-poor galaxies. We find the CO luminosities to be L_CO < 2900 K km/s pc^2 for Leo P, L_CO < 12400 K km/s pc^2 for Sextans A, and L_CO < 9700 K km/s pc^2 for Sextans B. Comparison of our results with recent observational estimates of the factor for converting between L_CO and the mass of molecular hydrogen, as well as theoretical models, provides further evidence that either the CO-to-H_2 conversion factor increases sharply as metallicity decreases, or that stars are forming in these three galaxies very efficiently, requiring little molecular hydrogen.

  10. Possible evidence for metal accretion onto the surfaces of metal-poor main-sequence stars

    International Nuclear Information System (INIS)

    The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f(x, v, [X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (e.g., G- or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way's formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parameterized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the same mass-assembly and star-formation histories. By analyzing a sample of nearby metal-poor halo and thick-disk stars on the main sequence, taken from Data Release 8 of the Sloan Digital Sky Survey, we find that the median metallicity of G-type dwarfs is systematically higher (by about 0.2 dex) than that of K-type dwarfs having the same median rotational velocity about the Galactic center. If it can be confirmed, this finding may invalidate the long-accepted assumption that the atmospheric metallicities of long-lived stars are conserved over time.

  11. Estimating R-Process Yields from Abundances of the Metal-Poor Stars

    CERN Document Server

    Li, Hongjie; Cui, Wenyuan; Zhang, Bo

    2014-01-01

    The chemical abundances of metal-poor stars provide important clues to explore stellar formation history and set significant constraints on models of the r-process. In this work, we find that the abundance patterns of the light and iron group elements of the main r-process stars are very close to those of the weak r-process stars. Based on a detailed abundance comparison, we find that the weak r-process occurs in supernovae with a progenitor mass range of $\\sim11-26M_{\\odot}$. Using the SN yields given by Heger & Woosley and the abundances of the weak r-process stars, the weak r-process yields are derived. The SNe with a progenitor mass range of $15M_{\\odot}

  12. New Detections of Arsenic, Selenium, and Other Heavy Elements in Two Metal-Poor Stars

    CERN Document Server

    Roederer, Ian U; Lawler, James E; Beers, Timothy C; Cowan, John J; Frebel, Anna; Ivans, Inese I; Sneden, Christopher; Sobeck, Jennifer S

    2014-01-01

    We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 to 2360 Angstrom wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu II, Zn II, As I, Se I, Mo II, and Cd II, which have not been detected previously in either star. Abundances derived for Ge I, Te I, Os II, and Pt I confirm those derived from lines at longer wavelengths. We also derive upper limits from the non-detection of W II, Hg II, Pb II, and Bi I. The mean [As/Fe] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range -2.8 = +0.28 +/- 0.14 (std. dev. = 0.36 dex). The mean [Se/Fe] ratio derived from these two stars and six others in the literature is also constant, = +0.16 +/- 0.09 (std. dev. = 0.26 dex). The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses, suggesting that this mass region (75 = +0.56 +/- ...

  13. Abundances in Metal-Poor Stars and Chemical Evolution of the Early Galaxy

    CERN Document Server

    Wasserburg, G J

    2008-01-01

    We have attributed the elements from Sr through Ag in stars of low metallicities ([Fe/H] -0.32 for all metal-poor stars. This is in direct conflict with the high-resolution data now available, which show that there is a great shortfall of Sr relative to Fe in many stars with [Fe/H] < -3. The same conflict also exists for the CPR elements Y and Zr. We show that the data require a stellar source leaving behind black holes and that hypernovae (HNe) from progenitors of ~ 25 to 50 M_sun are the most plausible candidates. If we expand our previous model to include three components (low-mass and normal SNe and HNe), we find that essentially all of the data are very well described by the new model. The HN yield pattern for the low-A elements from Na through Zn (including Fe) is inferred from the stars deficient in Sr, Y, and Zr. We estimate that HNe contributed ~ 24% of the bulk solar Fe inventory while normal SNe contributed only ~ 9% (not the usually assumed ~ 33%). This implies a greatly reduced role of normal...

  14. Extremely Metal-Poor Stars and a Hierarchical Chemical Evolution Model

    CERN Document Server

    Komiya, Yutaka

    2011-01-01

    Early phases of the chemical evolution and formation history of extremely metal poor (EMP) stars are investigated using hierarchical galaxy formation models. We build a merger tree of the Galaxy according to the extended Press-Schechter theory. We follow the chemical evolution along the tree, and compare the model results to the metallicity distribution function (MDF) and abundance ratio distribution of the Milky Way halo. We adopt three different initial mass functions (IMFs). In a previous studies, we argue that typical mass of EMP stars should be high-mass(~10Msun) based on studies of binary origin carbon-rich EMP stars. In this study, we show that only the high-mass IMF can explain a observed small number of EMP stars. For relative element abundances, the high-mass IMF and the Salpeter IMF predict similar distributions. We also investigate dependence on nucleosynthetic yields of supernovae (SNe). The theoretical SN yields by Kobayashi et al.(2006) and Chieffi & Limonge (2004) show reasonable agreement...

  15. A Planetary Companion around a Metal-Poor Star with Extragalactic Origin

    CERN Document Server

    Setiawan, J; Henning, T; Rix, H -W; Rochau, B; Schulze-Hartung, T; Rodmann, J

    2011-01-01

    We report the detection of a planetary companion around HIP 13044, a metal-poor star on the red Horizontal Branch. The detection is based on radial velocity observations with FEROS, a high-resolution spectrograph at the 2.2-m MPG/ESO telescope, located at ESO La Silla observatory in Chile. The periodic radial velocity variation of P = 16.2 days can be distinguished from the periods of the stellar activity indicators. We computed a minimum planetary mass of 1.25 MJup and an orbital semi-major axis of 0.116 AU for the planet. This discovery is unique in three aspects: First, it is the first planet detection around a star with a metallicity much lower than few percent of the solar value; second, the planet host star resides in a stellar evolutionary stage that is still unexplored in the exoplanet surveys; third, the star HIP 13044 belongs to one of the most significant stellar halo streams in the solar neighborhood, implying an extragalactic origin of the planetary system HIP 13044 in a disrupted former satellit...

  16. HST Observations of Heavy Elements in Metal-Poor Galactic Halo Stars

    CERN Document Server

    Cowan, J J; Beers, T C; Lawler, J E; Simmerer, J; Truran, J W; Primas, F; Collier, J L; Burles, S; Cowan, John J.; Sneden, Christopher; Beers, Timothy C.; Lawler, James E.; Simmerer, Jennifer; Truran, James W.; Primas, Francesca; Collier, Jason; Burles, Scott

    2005-01-01

    We present new abundance determinations of neutron-capture elements Ge, Zr, Os, Ir, and Pt in a sample of 11 metal-poor (-3.1 56) elements. However, the large (and correlated) scatters of [Eu,Os,Ir,Pt/Fe] suggests that the heaviest neutron-capture r-process elements are not formed in all supernovae. In contrast, the Ge abundances of all program stars track their Fe abundances, very well. An explosive process on iron-peak nuclei (e.g., the alpha-rich freeze-out in supernovae), rather than neutron capture, appears to have been the dominant synthesis mechanism for this element at low metallicities -- Ge abundances seem completely uncorrelated with Eu.

  17. X-Shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars

    CERN Document Server

    Caffau, E; Francois, P; Sbordone, L; Spite, M; Monaco, L; Plez, B; Spite, F; Zaggia, S; Ludwig, H -G; Cayrel, R; Molaro, P; Randich, S; Hammer, F; Hill, V

    2013-01-01

    The extremely metal-poor stars are the direct descendants of the first generation stars. They carry the chemical signature of the pristine Universe at the time they formed, shortly after the Big Bang. We aim to derive information about extremely metal-poor stars from their observed spectra. Four extremely metal-poor stars were selected from the Sloan Digital Sky Survey (SDSS) and observed during the guaranteed observing time of X-Shooter. The X-Shooter spectra were analysed using an automatic code, MyGIsFOS, which is based on a traditional analysis method. It makes use of a synthetic grid computed from one-dimensional, plane-parallel, hydrostatic model atmospheres. The low metallicity derived from the SDSS spectra is confirmed here. Two kinds of stars are found. Two stars are confirmed to be extremely metal-poor, with no evidence of any enhancement in carbon. The two other stars are strongly enhanced in carbon. We could not derive iron abundance for one of them, while [Ca/H] is below -4.5. Two of the stars ar...

  18. Looking for imprints of the first stellar generations in metal-poor bulge field stars

    CERN Document Server

    Siqueira-Mello, C; Barbuy, B; Freeman, K; Ness, M; Depagne, E; Cantelli, E; Pignatari, M; Hirschi, R; Frischknecht, U; Meynet, G; Maeder, A

    2016-01-01

    Context. Efforts to look for signatures of the first stars have concentrated on metal-poor halo objects. However, the low end of the bulge metallicity distribution has been shown to host some of the oldest objects in the Milky Way and hence this Galactic component potentially offers interesting targets to look at imprints of the first stellar generations. As a pilot project, we selected bulge field stars already identified in the ARGOS survey as having [Fe/H] ~ -1 and oversolar [alpha/Fe] ratios, and we used FLAMES-UVES to obtain detailed abundances of key elements that are believed to reveal imprints of the first stellar generations. Aims. The main purpose of this study is to analyse selected ARGOS stars using new high-resolution (R~45,000) and high-signal-to-noise (S/N >100) spectra. We aim to derive their stellar parameters and elemental ratios, in particular the abundances of C, N, the alpha-elements O, Mg, Si, Ca, and Ti, the odd-Z elements Na and Al, the neutron-capture s-process dominated elements Y, Z...

  19. High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey

    CERN Document Server

    Jacobson, Heather R; Frebel, Anna; Casey, Andrew R; Asplund, Martin; Bessell, Michael S; Da Costa, Gary S; Lind, Karin; Marino, Anna F; Norris, John E; Pena, Jose M; Schmidt, Brian P; Tisserand, Patrick; Walsh, Jennifer M; Yong, David; Yu, Qinsi

    2015-01-01

    The SkyMapper Southern Sky Survey is carrying out a search for the most metal-poor stars in the Galaxy. It identifies candidates by way of its unique filter set that allows for estimation of stellar atmospheric parameters. The set includes a narrow filter centered on the Ca II K 3933A line, enabling a robust estimate of stellar metallicity. Promising candidates are then confirmed with spectroscopy. We present the analysis of Magellan-MIKE high-resolution spectroscopy of 122 metal-poor stars found by SkyMapper in the first two years of commissioning observations. 41 stars have [Fe/H] 2. Only one other star is known to have a comparable value. Seven stars are "CEMP-no" stars ([C/Fe] > 0.7, [Ba/Fe] = 1.0. These results demonstrate the ability to identify extremely metal-poor stars from SkyMapper photometry, pointing to increased sample sizes and a better characterization of the metal-poor tail of the halo metallicity distribution function in the future.

  20. EXTREMELY METAL-POOR STARS AND A HIERARCHICAL CHEMICAL EVOLUTION MODEL

    International Nuclear Information System (INIS)

    Early phases of the chemical evolution of the Galaxy and formation history of extremely metal-poor (EMP) stars are investigated using hierarchical galaxy formation models. We build a merger tree of the Galaxy according to the extended Press-Schechter theory. We follow the chemical evolution along the tree and compare the model results to the metallicity distribution function and abundance ratio distribution of the Milky Way halo. We adopt three different initial mass functions (IMFs). In a previous study, we argued that the typical mass, Mmd, of EMP stars should be high, Mmd ∼ 10 Msun, based on studies of binary origin carbon-rich EMP stars. In this study, we show that only the high-mass IMF can explain an observed small number of EMP stars. For relative element abundances, the high-mass IMF and the Salpeter IMF predict similar distributions. We also investigate dependence on nucleosynthetic yields of supernovae (SNe). The theoretical SN yields by Kobayashi et al. and Chieffi and Limongi show reasonable agreement with observations for α-elements. Our model predicts a significant scatter of element abundances at [Fe/H] < -3. We adopted the stellar yields derived in the work of Francois et al., which produce the best agreement between the observational data and the one-zone chemical evolution model. Their yields well reproduce a trend of the averaged abundances of EMP stars but predict much larger scatter than do the observations. The model with hypernovae predicts Zn abundance, in agreement with the observations, but other models predict lower [Zn/Fe]. Ejecta from the hypernovae with large explosion energy is mixed in large mass and decreases the scatter of the element abundances.

  1. New detections of arsenic, selenium, and other heavy elements in two metal-poor stars

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Schatz, Hendrik; Beers, Timothy C. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Lawler, James E. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Cowan, John J. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Frebel, Anna [Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Ivans, Inese I. [Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112 (United States); Sneden, Christopher [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Sobeck, Jennifer S. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States)

    2014-08-10

    We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 ≤λ ≤ 2360 Å wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu II, Zn II, As I, Se I, Mo II, and Cd II, which have not been detected previously in either star. Abundances derived for Ge I, Te I, Os II, and Pt I confirm those derived from lines at longer wavelengths. We also derive upper limits from the non-detection of W II, Hg II, Pb II, and Bi I. The mean [As/Fe] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range –2.8 < [Fe/H] <–0.6, ([As/Fe]) = +0.28 ± 0.14 (σ = 0.36 dex). The mean [Se/Fe] ratio derived from these two stars and six others in the literature is also constant, ([Se/Fe]) = +0.16 ± 0.09 (σ = 0.26 dex). The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses, suggesting that this mass region (75 ≤A ≤ 82) may be the point at which a different nucleosynthetic mechanism begins to dominate the quasi-equilibrium α-rich freezeout of the iron peak. ([Cu II/Cu I]) = +0.56 ± 0.23 in HD 108317 and HD 128279, and we infer that lines of Cu I may not be formed in local thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and [Os/Fe] ratios are also derived from neutral and ionized species, and each ratio pair agrees within the mutual uncertainties, which range from 0.15 to 0.52 dex.

  2. New Hubble Space Telescope Observations of Heavy Elements in Four Metal-Poor Stars

    CERN Document Server

    Roederer, Ian U; Sobeck, Jennifer S; Beers, Timothy C; Cowan, John J; Frebel, Anna; Ivans, Inese I; Schatz, Hendrik; Sneden, Christopher; Thompson, Ian B

    2012-01-01

    Elements heavier than the iron group are found in nearly all halo stars. A substantial number of these elements, key to understanding neutron-capture nucleosynthesis mechanisms, can only be detected in the near-ultraviolet. We report the results of an observing campaign using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to study the detailed heavy element abundance patterns in four metal-poor stars. We derive abundances or upper limits from 27 absorption lines of 15 elements produced by neutron-capture reactions, including seven elements (germanium, cadmium, tellurium, lutetium, osmium, platinum, and gold) that can only be detected in the near-ultraviolet. We also examine 202 heavy element absorption lines in ground-based optical spectra obtained with the Magellan Inamori Kyocera Echelle Spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the High Resolution Echelle Spectrometer on the Keck I Telescope on Mauna Kea. We have detected up to 34 elements hea...

  3. A search for stars of very low metal abundance. VI. Detailed abundances of 313 metal-poor stars

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U.; Preston, George W.; Thompson, Ian B.; Shectman, Stephen A.; Burley, Gregory S.; Kelson, Daniel D. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Sneden, Christopher, E-mail: iur@umich.edu [Department of Astronomy, University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712 (United States)

    2014-06-01

    We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10 yr observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coudé Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by ≈0.25 dex for red giants and ≈0.04 dex for subgiants. Our sample contains 19 stars with [Fe/H] ≤–3.5, 84 stars with [Fe/H] ≤–3.0, and 210 stars with [Fe/H] ≤–2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H] ≤–2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers.

  4. uvby(-$\\beta$) photometry of high-velocity and metal-poor stars X. Stars of very low metal abundance: observations, reddenings, metallicities, classifications, distances, and relative ages

    CERN Document Server

    Schuster, W J; Michel, R; Nissen, P E; García, G

    2004-01-01

    uvby(--$\\beta$) photometry has been obtained for an additional 411 very metal-poor stars selected from the HK survey, and used to derive basic parameters such as interstellar reddenings, metallicities, photometric classifications, distances, and relative ages... These very metal-poor stars are compared to M92 in the c_0,(b-y)_0 diagram, and evidence is seen for field stars 1-3 Gyrs younger than this globular cluster. The significance of these younger very metal-poor stars is discussed in the context of Galactic evolution, mentioning such possibilities as hierarchical star-formation/mass-infall of very metal-poor material and/or accretion events whereby this material has been acquired from other (dwarf) galaxies with different formation and chemical-enrichment histories

  5. Estimation of Carbon Abundances in Metal-Poor Stars. I. Application to the "Strong G-band" stars of Beers, Preston, & Shectman

    CERN Document Server

    Rossi, S; Sneden, C; Sevastyanenko, T; Rhee, J; Marsteller, B; Rossi, Silvia; Beers, Timothy C.; Sneden, Chris; Sevastyanenko, Tatiana; Rhee, Jaehyon; Marsteller, Brian

    2005-01-01

    We develop and test a method for the estimation of metallicities ([Fe/H]) and carbon abundance ratios ([C/Fe]) for carbon-enhanced metal-poor (CEMP) stars, based on application of artificial neural networks, regressions, and synthesis models to medium-resolution (1-2 A) spectra and J-K colors. We calibrate this method by comparison with metallicities and carbon abundance determinations for 118 stars with available high-resolution analyses reported in the recent literature. The neural network and regression approaches make use of a previously defined set of line-strength indices quantifying the strength of the CaII K line and the CH G-band, in conjuction with J-K colors from the 2MASS Point Source Catalog. The use of near-IR colors, as opposed to broadband B-V colors, is required because of the potentially large affect of strong molecular carbon bands on bluer color indices. Using these methods we are able to reproduce the previously-measured [Fe/H] and [C/Fe] determinations with an accuracy of ~ 0.25 dex for ...

  6. 2MASS J18082002-5104378: The brightest (V=11.9) ultra metal-poor star

    CERN Document Server

    Melendez, Jorge; Tucci-Maia, Marcelo; Ramirez, Ivan; Li, Ting S; Perez, Gabriel

    2016-01-01

    Context. The most primitive metal-poor stars are important for studying the conditions of the early galaxy and are also relevant to big bang nucleosynthesis. Aims. Our objective is to find the brightest (V<14) most metal-poor stars. Methods. Candidates were selected using a new method, which is based on the mismatch between spectral types derived from colors and observed spectral types. They were observed first at low resolution with EFOSC2 at the NTT/ESO to obtain an initial set of stellar parameters. The most promising candidate, 2MASS J18082002-5104378 (V=11.9), was observed at high resolution (R=50 000) with UVES at the VLT/ESO, and a standard abundance analysis was performed. Results. We found that 2MASS J18082002-5104378 is an ultra metal-poor star with stellar parameters Teff = 5440 K, log g = 3.0 dex, vt = 1.5 km/s, [Fe/H] = -4.1 dex. The star has [C/Fe]<+0.9 in a 1D analysis, or [C/Fe]<=+0.5 if 3D effects are considered; its abundance pattern is typical of normal (non-CEMP) ultra metal-poor ...

  7. Europium, Samarium, and Neodymium Isotopic Fractions in Metal-Poor Stars

    CERN Document Server

    Roederer, Ian U; Sneden, Christopher; Cowan, John J; Sobeck, Jennifer S; Pilachowski, Catherine A

    2007-01-01

    We have derived isotopic fractions of europium, samarium, and neodymium in two metal-poor giants with differing neutron-capture nucleosynthetic histories. These isotopic fractions were measured from new high resolution (R ~ 120,000), high signal-to-noise (S/N ~ 160-1000) spectra obtained with the 2dCoude spectrograph of McDonald Observatory's 2.7m Smith telescope. Synthetic spectra were generated using recent high-precision laboratory measurements of hyperfine and isotopic subcomponents of several transitions of these elements and matched quantitatively to the observed spectra. We interpret our isotopic fractions by the nucleosynthesis predictions of the stellar model, which reproduces s-process nucleosynthesis from the physical conditions expected in low-mass, thermally-pulsing stars on the AGB, and the classical method, which approximates s-process nucleosynthesis by a steady neutron flux impinging upon Fe-peak seed nuclei. Our Eu isotopic fraction in HD 175305 is consistent with an r-process origin by the ...

  8. The Barium Isotopic Abundance in the Metal-Poor Star HD140283

    CERN Document Server

    Collet, R; Nissen, P E

    2008-01-01

    We derive the mixture of odd to even barium isotopes in the atmosphere of the metal-poor subgiant HD140283 from the analysis of the Ba II transition at 455.4 nm in a high-resolution high signal-to-noise spectrum of the star. The detailed shape of this spectral line depends on the relative contributions of odd and even isotopes via isotopic and hyperfine splitting. We measure the fractional abundance of odd Ba isotopes by modelling the formation of the Ba II 455.4 nm line profile with the use of both a classical 1D hydrostatic and a 3D hydrodynamical model atmosphere of HD140283. We interpret the results in terms of contributions by the slow (s-) and rapid (r-) neutron-capture processes to the isotopic mix. While the result of the 1D analysis of the Ba II feature indicates a (64 +/- 36)% contribution of the r-process to the isotopic mix, the 3D analysis points toward a mere (15 +/- 34)% contribution from this process, that is consistent with a solar-like mixture of barium isotopes.

  9. Bipolar Supernova Explosions Nucleosynthesis & Implication on Abundances in Extremely Metal-Poor Stars

    CERN Document Server

    Maeda, K

    2003-01-01

    Hydrodynamics and explosive nucleosynthesis in bipolar supernova explosions are examined to account for some peculiar properties of hypernovae as well as peculiar abundance patterns of metal-poor stars. The explosion is supposed to be driven by bipolar jets which are powered by accretion onto a central remnant. We explore the features of the explosions with varying progenitors' masses and jet properties. The outcomes are different from conventional spherical models. (1) In the bipolar models, Fe-rich materials are ejected at high velocities along the jet axis, while O-rich materials occupy the central region whose density becomes very high as a consequence of continuous accretion from the side. This configuration can explain some peculiar features in the light curves and the nebular spectra of hypernovae. (2) Production of $^{56}$Ni tends to be smaller than in spherical thermal bomb models. To account for a large amount of $^{56}$Ni observed in hypernovae, the jets should be initiated when the compact remnant...

  10. Beryllium and Alpha-Element Abundances in a Large Sample of Metal-Poor Stars

    CERN Document Server

    Boesgaard, Ann Merchant; Levesque, Emily M; Bowler, Brendan P

    2011-01-01

    The light elements, Li, Be, and B, provide tracers for many aspects of astronomy including stellar structure, Galactic evolution, and cosmology. We have taken spectra of Be in 117 metal-poor stars ranging in metallicity from [Fe/H] = -0.5 to -3.5 with Keck I + HIRES at a resolution of 42,000 and signal-to-noise ratios of near 100. We have determined the stellar parameters spectroscopically from lines of Fe I, Fe II, Ti I and Ti II. The abundances of Be and O were derived by spectrum synthesis techniques, while abundances of Fe, Ti, and Mg were found from many spectral line measurements. There is a linear relationship between [Fe/H] and A(Be) with a slope of +0.88 +-0.03 over three orders of magnitude in [Fe/H]. We fit the relationship between A(Be) and [O/H] with both a single slope and with two slopes. The relationship between [Fe/H] and [O/H] seems robustly linear and we conclude that the slope change in Be vs. O is due to the Be abundance. Although Be is a by-product of CNO, we have used Ti and Mg abundanc...

  11. Clear evidence for the presence of second-generation asymptotic giant branch stars in metal-poor Galactic globular clusters

    CERN Document Server

    Garcia-Hernandez, D A; Monelli, M; Cassisi, S; Stetson, P B; Zamora, O; Shetrone, M; Lucatello, S

    2015-01-01

    Galactic globular clusters (GCs) are known to host multiple stellar populations: a first generation with a chemical pattern typical of halo field stars and a second generation (SG) enriched in Na and Al and depleted in O and Mg. Both stellar generations are found at different evolutionary stages (e.g., the main-sequence turnoff, the subgiant branch, and the red giant branch). The non detection of SG asymptotic giant branch (AGB) stars in several metal-poor ([Fe/H] < -1) GCs suggests that not all SG stars ascend the AGB phase, and that failed AGB stars may be very common in metal-poor GCs. This observation represents a serious problem for stellar evolution and GC formation/evolution theories. We report fourteen SG-AGB stars in four metal-poor GCs (M 13, M 5, M 3, and M 2) with different observational properties: horizontal branch (HB) morphology, metallicity, and age. By combining the H-band Al abundances obtained by the APOGEE survey with ground-based optical photometry, we identify SG Al-rich AGB stars in...

  12. Fe-Group Elements in the Metal-Poor Star HD 84937: Abundances and their Implications

    Science.gov (United States)

    Sneden, Chris; Cowan, John J.; Kobayashi, Chiaki; Pignatari, Marco; Lawler, James E.; Den Hartog, Elizabeth; Wood, Michael P.

    2016-01-01

    We have derived accurate relative abundances of the Fe-group elements Sc through Zn in the very metal-poor main-sequence turnoff star HD 84937. For this study we analyzed high resolution, high signal-to-noise HST/STIS and VLT/UVES spectra over a total wavelength range 2300-7000 Å. We employed only recent or newly-applied reliable laboratory transition data for all species. Abundances from more than 600 lines of non-Fe species were combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. From parallel analyses of solar photospheric spectra we also derived new solar abundances of these elements. This in turn yielded internally-consistent relative HD 84937 abundances with respect to the Sun. For seven of the ten Fe-group elements the HD 84937 abundances were from both neutral and ionized transitions. In all of these cases the neutral and ionized species yield the same abundances within the measurement uncertainties. Therefore standard Saha ionization balance appears to hold in the HD 84937 atmosphere. We derived metallicity [Fe/H] = -2.32 with sample standard deviation of 0.06. Solid evidence is seen for departures from the solar abundance mix in HD 84937, for example [Co/Fe] = +0.14, [Cu/Fe] = -0.83, and = +0.31. Combining our Sc, Ti, and V abundances for this star with those from large-sample spectroscopic surveys suggests that these elements are positively correlated in stars with [Fe/H] analysis strongly suggests that different types of supernovae with a large scatter of explosion energies and asymmetries contributed to the creation of the Fe-group elements early in the Galaxy's history.This work has been supported in part by NASA grant NNX10AN93G (J.E.L.), by NSF grants AST-1211055 (J.E.L.), AST-1211585 (C.S.), PHY-1430152 (through JINA, J.J.C. and M.P.), EU MIRGCT-2006-046520 (M.P.), and by the ``Lendlet-2014'' Programme of the Hungarian Academy of Sciences (M.P.) and from SNF (Switzerland, M.P.).

  13. First stars XII. Abundances in extremely metal-poor turnoff stars,and comparison with the giants

    CERN Document Server

    Bonifacio, P; Cayrel, R; Hill, V; Spite, F; François, P; Plez, B; Ludwig, H -G; Caffau, E; Molaro, P; Depagne, E; Andersen, J; Barbuy, B; Beers, T C; Nordström, B; Primas, F

    2009-01-01

    CONTEXT:The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data are, however, for giant stars which may have experienced internal mixing later. AIMS: We aim to compare the results for giants with new, accurate abundances for all observable elements in 18 EMP turnoff stars. METHODS:VLT/UVES spectra at R ~45,000 and S/N~ 130 per pixel (330-1000 nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba. RESULTS: For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are ~0.2 dex larger than in giants of similar metallicity. Mg and Si abundances are ~0.2 dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again ~0.4 dex higher than in giants of similar [Fe/H] (6 stars only). CONCLUSIO...

  14. Far-ultraviolet energy distributions of the metal-poor A stars HD 109995 and HD 161817

    Science.gov (United States)

    Boehm-Vitense, E.

    1981-01-01

    Low-resolution IUE spectra at wavelengths between 1300 and 3400 A of the metal-poor stars HD 109995 (A1p) and HD 161817 (A4p) have been compared with model-atmosphere energy distributions computed by Kurucz (1979). Good overall agreement is found. Effective temperatures, metal abundances, and angular diameters could be determined. Assuming an absolute visual magnitude of 0.7, the previously determined gravity log = 3 yields masses of 0.5 solar masses for both stars. It is found that the theoretical UBV colors calculated earlier agree reaonably well with the ones observed for these stars.

  15. The HARPS search for southern extra-solar planets. XL. Searching for Neptunes around metal-poor stars

    Science.gov (United States)

    Faria, J. P.; Santos, N. C.; Figueira, P.; Mortier, A.; Dumusque, X.; Boisse, I.; Lo Curto, G.; Lovis, C.; Mayor, M.; Melo, C.; Pepe, F.; Queloz, D.; Santerne, A.; Ségransan, D.; Sousa, S. G.; Sozzetti, A.; Udry, S.

    2016-04-01

    Context. As a probe of the metallicity of proto-planetary disks, stellar metallicity is an important ingredient for giant planet formation, most likely through its effect on the timescales in which rocky or icy planet cores can form. Giant planets have been found to be more frequent around metal-rich stars, in agreement with predictions based on the core-accretion theory. In the metal-poor regime, however, the frequency of planets, especially low-mass planets, and the way it depends on metallicity are still largely unknown. Aims: As part of a planet search programme focused on metal-poor stars, we study the targets from this survey that were observed with HARPS on more than 75 nights. The main goals are to assess the presence of low-mass planets and provide a first estimate of the frequency of Neptunes and super-Earths around metal-poor stars. Methods: We performed a systematic search for planetary companions, both by analysing the periodograms of the radial-velocities and by comparing, in a statistically meaningful way, models with an increasing number of Keplerians. Results: A first constraint on the frequency of planets in our metal-poor sample is calculated considering the previous detection (in our sample) of a Neptune-sized planet around HD 175607 and one candidate planet (with an orbital period of 68.42 d and minimum mass Mpsini = 11.14 ± 2.47 M⊕) for HD 87838, announced in the present study. This frequency is determined to be close to 13% and is compared with results for solar-metallicity stars. Based on observations collected at ESO facilities under programs 082.C-0212, 085.C-0063, 086.C-0284, and 190.C-0027 (with the HARPS spectrograph at the ESO 3.6-m telescope, La Silla-Paranal Observatory).

  16. The HARPS search for southern extra-solar planets XL. Searching for Neptunes around metal-poor stars

    CERN Document Server

    Faria, J P; Figueira, P; Mortier, A; Dumusque, X; Boisse, I; Curto, G Lo; Lovis, C; Mayor, M; Melo, C; Pepe, F; Queloz, D; Santerne, A; Ségransan, D; Sousa, S G; Sozzetti, A; Udry, S

    2016-01-01

    Stellar metallicity -- as a probe of the metallicity of proto-planetary disks -- is an important ingredient for giant planet formation, likely through its effect on the timescales in which rocky/icy planet cores can form. Giant planets have been found to be more frequent around metal-rich stars, in agreement with predictions based on the core-accretion theory. In the metal-poor regime, however, the frequency of planets, especially low-mass planets, and how it depends on metallicity are still largely unknown. As part of a planet search programme focused on metal-poor stars, we study the targets from this survey that were observed with HARPS on more than 75 nights. The main goals are to assess the presence of low-mass planets and provide a first estimate of the frequency of Neptunes and super-Earths around metal-poor stars. We perform a systematic search for planetary companions, both by analysing the periodograms of the radial-velocities and by comparing, in a statistically-meaningful way, models with an incre...

  17. Searches for Metal-Poor Stars from the Hamburg/ESO Survey using the CH G-band

    CERN Document Server

    Placco, Vinicius M; Beers, Timothy C; Christlieb, Norbert; Rossi, Silvia; Sivarani, Thirupathi; Lee, Young Sun; Reimers, Dieter; Wisotzki, Lutz

    2011-01-01

    We describe a new method to search for metal-poor candidates from the Hamburg/ESO objective-prism survey (HES) based on identifying stars with apparently strong CH G-band strengths for their colors. The hypothesis we exploit is that large over-abundances of carbon are common among metal-poor stars. The selection was made by considering two line indices in the 4300A region, applied directly to the low-resolution prism spectra. This work also extends a previously published method by adding bright sources to the sample. The spectra of these stars suffer from saturation effects, compromising the index calculations and leading to an undersampling of the brighter candidates. Visual inspection and classification of the spectra from the HES plates yielded a list of 5,288 new metal-poor candidates, which are presently being used as targets for medium-resolution spectroscopic follow-up. Estimates of the stellar atmospheric parameters, as well as carbon abundances, are now available for 117 of the first candidates, base...

  18. New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars

    CERN Document Server

    Sneden, Christopher; Cowan, John J; Ivans, Inese I; Hartog, Elizabeth A Den

    2009-01-01

    We have derived new abundances of the rare-earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally-consistent Ba, rare-earth, and Hf (56<= Z <= 72) element distributions. These have been used in a critical comparison between stellar and solar r-process abundance mixes.

  19. New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars

    OpenAIRE

    Sneden, Christopher; Lawler, James E.; Cowan, John J.; Ivans, Inese I.; Hartog, Elizabeth A. Den

    2009-01-01

    We have derived new abundances of the rare-earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally-consistent Ba, rar...

  20. Abundances of light elements in metal-poor stars; 1, atmospheric parameters and a new T$_{eff}$ scale

    CERN Document Server

    Gratton, R G; Castelli, F

    1996-01-01

    We present atmospheric parameters for about 300 stars of different chemical composition, whose spectra will be used to study the galactic enrichment of Fe and light elements. These parameters were derived using an homogenous iterative procedure, which considers new calibrations of colour-\\teff\\ relations for F, G and K-type stars based on Infrared Flux Method (IRFM) and interferometric diameters for population~I stars, and the Kurucz (1992) model atmospheres. We found that these calibrations yield a self-consistent set of atmospheric parameters for \\teff>4400~K, representing a clear improvement over results obtained with older model atmospheres. Using this \\teff-scale and Fe equilibrium of ionization, we obtained very low gravities (implying luminosities incompatible with that expected for RGB stars) for metal-poor stars cooler than 4400~K; this might be due either to a moderate Fe overionization (expected from statistical equilibrium calculations) or to inadequacy of Kurucz models to describe the atmospheres...

  1. NLTE strontium abundance in a sample of extremely metal poor stars and the Sr/Ba ratio in the early Galaxy

    CERN Document Server

    Andrievsky, S M; Korotin, S A; Francois, P; Spite, M; Bonifacio, P; Cayrel, R; Hill, V

    2011-01-01

    Heavy element abundances in extremely metal-poor stars provide strong constraints on the processes of forming these elements in the first stars. We attempt to determine precise abundances of strontium in a homogeneous sample of extremely metal-poor stars. The abundances of strontium in 54 very or extremely metal-poor stars, was redetermined by abandoning the local thermodynamic equilibrium (LTE) hypothesis, and fitting non-LTE (NLTE) profiles to the observed spectral lines. The corrected Sr abundances and previously obtained NLTE Ba abundances are compared to the predictions of several hypothetical formation processes for the lighter neutron-capture elements. Our NLTE abundances confirm the previously determined huge scatter of the strontium abundance in low metallicity stars. This scatter is also found (and is even larger) at very low metallicities (i. e. early in the chemical evolution). The Sr abundance in the extremely metal-poor (EMP) stars is compatible with the main r-process involved in other processe...

  2. Molybdenum, Ruthenium, and the Heavy r-process Elements in Moderately Metal-Poor Main-Sequence Turnoff Stars

    CERN Document Server

    Peterson, Ruth C

    2013-01-01

    The ratios of elemental abundances observed in metal-poor stars of the Galactic halo provide a unique present-day record of the nucleosynthesis products of its earliest stars. While the heaviest elements were synthesized by the r- and s-processes, dominant production mechanisms of light trans-ironic elements were obscure until recently. This work investigates further our 2011 conclusion that the low-entropy regime of a high-entropy wind (HEW) produced molybdenum and ruthenium in two moderately metal-poor turnoff stars that showed extreme overabundances of those elements with respect to iron. Only a few, rare nucleosynthesis events may have been involved. Here we determine abundances for Mo, Ru, and other trans-Fe elements for 28 similar stars by matching spectral calculations to well-exposed near-UV Keck HIRES spectra obtained for beryllium abundances. In each of the 26 turnoff stars with Mo or Ru line detections and no evidence for s-process production (therefore old), we find Mo and Ru to be three to six ti...

  3. Carbon Abundances of Metal-Poor Star Determined from the C I 1.068-1.069 micron Lines

    CERN Document Server

    Takeda, Yoichi

    2013-01-01

    A non-LTE analysis of C I lines at 1.068-1.069 micron was carried out for selected 46 halo/disk stars covering a wide metallicity range (-3.7 <[Fe/H]< +0.3), based on the spectral data collected with IRCS+AO188 of the Subaru Telescope, in order to examine whether and how these strong neutral carbon lines of multiplet 1 can be exploited for establishing stellar carbon abundances, especially for very metal-poor stars where CH molecular lines have been commonly used. These C I lines were confirmed to be clearly visible for all stars down to [Fe/H] ~ -3.7, from which C abundances could be successfully determined. The resulting [C/Fe] vs. [Fe/H] diagram revealed almost the same trend established from previous studies. When the results for individual stars are compared with the published data collected from various literature, while a reasonable agreement is seen as a whole, a tendency is observed that our abundances are appreciably higher than those from CH lines especially for very metal-poor giants of low ...

  4. Chemical abundances of the metal-poor horizontal-branch stars CS 22186-005 and CS 30344-033

    CERN Document Server

    Caliskan, S; Bonifacio, P; Christlieb, N; Monaco, L; Beers, T C; Albayrak, B; Sbordone, L

    2014-01-01

    We report on a chemical-abundance analysis of two very metal-poor horizontal-branch stars in the Milky Way halo: CS 22186-005 ([Fe/H]=-2.70) and CS 30344-033 ([Fe/H]=-2.90). The analysis is based on high-resolution spectra obtained at ESO, with the spectrographs HARPS at the 3.6 m telescope, and UVES at the VLT. We adopted one-dimensional, plane-parallel model atmospheres assuming local thermodynamic equilibrium. We derived elemental abundances for 13 elements for CS 22186-005 and 14 elements for CS 30344-033. This study is the first abundance analysis of CS 30344-033. CS 22186-005 has been analyzed previously, but we report here the first measurement of nickel (Ni; Z = 28) for this star, based on twenty-two NiI lines ([Ni/Fe]=-0.21$\\pm$0.02); the measurement is significantly below the mean found for most metal-poor stars. Differences of up to 0.5 dex in [Ni/Fe] ratios were determined by different authors for the same type of stars in the literature, which means that it is not yet possible to conclude that th...

  5. Mass Fraction of 13C-Pocket in Metal-Poor AGB Stars and the Primary Nature of Neutron Source

    Institute of Scientific and Technical Information of China (English)

    CUI Dong-Nuan; GENG Yuan-Yuan; CUI Wen-Yuan; ZHANG Bo

    2009-01-01

    Chemical abundances of very metal-poor s-rich stars contain excellent information to set new constraints on models of neutron-capture processes at low metalficity.Using the parametric approach based on the radiative s-process nucleosynthesis model,we obtain the mass fraction q of 13 C-pocket,the overlap factor r,the neutron exposure per interpulse △r,and the component coefficients of the s-process and the r-process for 25 s-rich stars,respectively. We find that q deduced for the lead stars is comparable to the overlap factor r,which is larger than the standard case (hereafter ST case) of the AGB model (q~0.05) about 10 times,and △r are about 10 times smaller than the ST case (△r = 7.0 mbarn-1).Although the two parameters obtained for the lead stars are very different from the ST case of the AGB stellar model,it is worth noting that the total amounts of 13C in metal-poor condition are close to the ST case.The above relation is a significant evidence for the primary nature of the neutron source and the lead stars could be polluted by low-mass AGB stars.Because interpulse period declines with increasing stellar mass,for high-mass A GB star,the neutron irradiation may be terminated due to their shorter interpulse period.Thus the neutron exposure per interpulse of the larger AGB stars should be about 10 times smaller than the ST case.In this case,the primary nature of the neutron source also exists.

  6. Europium, Samarium, and Neodymium Isotopic Fractions in Metal-Poor Stars

    OpenAIRE

    Roederer, Ian U.; Lawler, James E.; Sneden, Christopher; Cowan, John J.; Sobeck, Jennifer S.; Pilachowski, Catherine A.

    2007-01-01

    We have derived isotopic fractions of europium, samarium, and neodymium in two metal-poor giants with differing neutron-capture nucleosynthetic histories. These isotopic fractions were measured from new high resolution (R ~ 120,000), high signal-to-noise (S/N ~ 160-1000) spectra obtained with the 2dCoude spectrograph of McDonald Observatory's 2.7m Smith telescope. Synthetic spectra were generated using recent high-precision laboratory measurements of hyperfine and isotopic subcomponents of se...

  7. Deep SDSS Optical Spectroscopy of Distant Halo Stars. III. Chemical analysis of extremely metal-poor stars

    CERN Document Server

    Fernandez-Alvar, E; Beers, T C; Lee, Y S; Masseron, T; Schneider, D P

    2016-01-01

    We present the results of an analysis for 107 extremely metal-poor (EMP) stars with metallicities less than [Fe/H] = -3.0, identified from medium-resolution spectra in SDSS. We follow a methodology based on comparisons of the observed spectra with synthetic spectra. The abundances of Fe, Ca, and Mg are determined by fitting spectral regions dominated by lines of each element. In addition, we present a technique to determine upper limits for elements whose features are not detected in a given spectrum. We also analyse our sample with the SEGUE Stellar Parameter Pipeline, in order to obtain additional determinations of the atmospheric parameters, iron and alpha-element abundances, to compare with ours, and to infer [C/Fe] ratios. We find that, in these moderate to low signal-to-noise and medium-resolution spectra in this metallicity regime, Ca is usually the only element that exhibits lines that are sufficiently strong to reliably measure its abundance. Fe and Mg exhibit weaker features that, in most cases, onl...

  8. Discovery of a strongly r-process enhanced extremely metal-poor star LAMOST J110901.22+075441.8

    CERN Document Server

    Li, Haining; Honda, Satoshi; Zhao, Gang; Christlieb, Norbert; Suda, Takuma

    2015-01-01

    We report the discovery of an extremely metal-poor (EMP) giant, LAMOST J110901.22+075441.8, which exhibits large excess of r-process elements with [Eu/Fe] ~ +1.16. The star is one of the newly discovered EMP stars identified from LAMOST low-resolution spectroscopic survey and the high-resolution follow-up observation with the Subaru Telescope. Stellar parameters and elemental abundances have been determined from the Subaru spectrum. Accurate abundances for a total of 23 elements including 11 neutron-capture elements from Sr through Dy have been derived for LAMOST J110901.22+075441.8. The abundance pattern of LAMOST J110901.22+075441.8 in the range of C through Zn is in line with the "normal" population of EMP halo stars, except that it shows a notable underabundance in carbon. The heavy element abundance pattern of LAMOST J110901.22+075441.8 is in agreement with other well studied cool r-II metal-poor giants such as CS 22892-052 and CS 31082-001. The abundances of elements in the range from Ba through Dy well...

  9. High-resolution Spectroscopy of Extremely Metal-poor Stars in the Least-evolved Galaxies: Bootes II

    Science.gov (United States)

    Ji, Alexander P.; Frebel, Anna; Simon, Joshua D.; Geha, Marla

    2016-01-01

    We present high-resolution Magellan/MIKE spectra of the four brightest confirmed red giant stars in the ultra-faint dwarf galaxy Boötes II (Boo II). These stars all inhabit the metal-poor tail of the Boo II metallicity distribution function. The chemical abundance pattern of all detectable elements in these stars is consistent with that of the Galactic halo. However, all four stars have undetectable amounts of neutron-capture elements Sr and Ba, with upper limits comparable to the lowest ever detected in the halo or in other dwarf galaxies. One star exhibits significant radial velocity variations over time, suggesting it to be in a binary system. Its variable velocity has likely increased past determinations of the Boo II velocity dispersion. Our four stars span a limited metallicity range, but their enhanced α-abundances and low neutron-capture abundances are consistent with the interpretation that Boo II has been enriched by very few generations of stars. The chemical abundance pattern in Boo II confirms the emerging trend that the faintest dwarf galaxies have neutron-capture abundances distinct from the halo, suggesting the dominant source of neutron-capture elements in halo stars may be different than in ultra-faint dwarfs. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  10. High-resolution spectroscopy of extremely metal-poor stars in the least evolved galaxies: Bootes II

    CERN Document Server

    Ji, Alexander P; Simon, Joshua D; Geha, Marla

    2015-01-01

    We present high-resolution Magellan/MIKE spectra of the four brightest confirmed red giant stars in the ultra-faint dwarf galaxy Bootes II (Boo II). These stars all inhabit the metal-poor tail of the Boo II metallicity distribution function. The chemical abundance pattern of all detectable elements in these stars is consistent with that of the Galactic halo. However, all four stars have undetectable amounts of neutron-capture elements Sr and Ba, with upper limits comparable to the lowest ever detected in the halo or in other dwarf galaxies. One star exhibits significant radial velocity variations over time, suggesting it to be in a binary system. Its variable velocity has likely increased past determinations of the Boo II velocity dispersion. Our four stars span a limited metallicity range, but their enhanced {\\alpha}-abundances and low neutron-capture abundances are consistent with the interpretation that Boo II has been enriched by very few generations of stars. The chemical abundance pattern in Boo II conf...

  11. HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: LEO IV

    International Nuclear Information System (INIS)

    We present high-resolution Magellan/MIKE spectroscopy of the brightest star in the ultra-faint dwarf galaxy Leo IV. We measure an iron abundance of [Fe/H] = -3.2, adding to the rapidly growing sample of extremely metal-poor (EMP) stars being identified in Milky Way satellite galaxies. The star is enhanced in the α elements Mg, Ca, and Ti by ∼0.3 dex, very similar to the typical Milky Way halo abundance pattern. All of the light and iron-peak elements follow the trends established by EMP halo stars, but the neutron-capture elements Ba and Sr are significantly underabundant. These results are quite similar to those found for stars in the ultra-faint dwarfs Ursa Major II, Coma Berenices, Booetes I, and Hercules, suggesting that the chemical evolution of the lowest-luminosity galaxies may be universal. The abundance pattern we observe is consistent with predictions for nucleosynthesis from a Population III supernova explosion. The extremely low metallicity of this star also supports the idea that a significant fraction (∼>10%) of the stars in the faintest dwarfs have metallicities below [Fe/H] = -3.0.

  12. Discovery of a strongly r-process enhanced extremely metal-poor star LAMOST J110901.22+075441.8

    Science.gov (United States)

    Li, Hai-Ning; Aoki, Wako; Honda, Satoshi; Zhao, Gang; Christlieb, Norbert; Suda, Takuma

    2015-08-01

    We report the discovery of an extremely metal-poor (EMP) giant, LAMOST J110901.22+075441.8, which exhibits a large excess of r-process elements with [Eu/Fe] ˜ +1.16. The star is one of the newly discovered EMP stars identified from the LAMOST low-resolution spectroscopic survey and a high-resolution follow-up observation with the Subaru Telescope. Stellar parameters and elemental abundances have been determined from the Subaru spectrum. Accurate abundances for a total of 23 elements including 11 neutron-capture elements from Sr through Dy have been derived for LAMOST J110901.22+075441.8. The abundance pattern of LAMOST J110901.22+075441.8 in the range of C through Zn is in line with the “normal” population of EMP halo stars, except that it shows a notable underabundance in carbon. The heavy element abundance pattern of LAMOST J110901.22+075441.8 is in agreement with other well studied cool r-II metal-poor giants such as CS 22892-052 and CS 31082-001. The abundances of elements in the range from Ba through Dy match the scaled solar r-process pattern well. LAMOST J110901.22+075441.8 provides the first detailed measurements of neutron-capture elements among r-II stars at such low metallicity with [Fe/H] ≲ -3.4, and exhibits similar behavior as other r-II stars in the abundance ratio of Zr/Eu as well as Sr/Eu and Ba/Eu.

  13. Exploring the [S/Fe] Behavior of Metal-Poor Stars with the S I 1.046 micron Lines

    CERN Document Server

    Takeda, Yoichi

    2010-01-01

    In an attempt of clarifying the [S/Fe] behavior with the run of [Fe/H] in the metal-poor regime which has been a matter of debate, an extensive non-LTE analysis of near-IR S I triplet lines (multiplet 3) at 1.046 micron was carried out for selected 33 halo/disk stars in a wide metallicity range of [Fe/H] ~-3.7 to ~+0.3, based on the spectral data collected with IRCS+AO188 of the Subaru Telescope. We found an evidence of considerably large [S/Fe] ratio amounting to ~+0.7-0.8 dex at very low metallicity of [Fe/H] ~-3, which makes marked contrast with other alpha-elements (Mg, Si, Ca, Ti) flatly showing moderately supersolar [alpha/Fe] of ~0.3 dex. Meanwhile, a locally-flat tendency of [S/Fe] at ~+0.3 is seen at -2.5 <[Fe/H]< -1.5. These results may suggest that the nature of [S/Fe] in metal-poor halo stars is not so simple as has been argued (i.e., neither being globally flat independent of [Fe/H] nor monotonically increasing with a decrease in [Fe/H]), but rather complicated with a local plateau around [...

  14. Abundances of Sr, Y, and Zr in Metal-Poor Stars and Implications for Chemical Evolution in the Early Galaxy

    CERN Document Server

    Qian, Y -Z

    2008-01-01

    Studies of nucleosynthesis in neutrino-driven winds from nascent neutron stars show that the elements from Sr through Ag with mass numbers A~88-110 are produced by charged-particle reactions (CPR) during the alpha-process in the winds. Accordingly, we have attributed all these elements in stars of low metallicities ([Fe/H]-0.32 for all metal-poor stars. The high-resolution data now available on Sr abundances in Galactic halo stars show that there is a great shortfall of Sr relative to Fe in many stars with [Fe/H]<-3. This is in direct conflict with the above prediction. The same conflict also exists for two other CPR elements Y and Zr. The very low abundances of Sr, Y, and Zr observed in stars with [Fe/H]<-3 thus require a stellar source that cannot be low-mass or normal SNe. We show that this observation requires a stellar source leaving behind black holes and that hypernovae (HNe) from progenitors of ~25-50M_sun are the most plausible candidates. (Abridged)

  15. Very metal poor stars in the Milky Way: constraints on stellar nucleosynthesis

    International Nuclear Information System (INIS)

    Recently Cayrel et al. [Cayrel, R., Depagne, E., Spite, M. et al. 2004, AfeA 416, 1117] have derived the abundances of several a and Fe-peak elements for a sample of very metal poor giants ([Fe/H] from -4.0 to -3.0 dex) thus allowing us to test chemical evolution models in a metallicity range never reached before. Moreover, the small spread in the [el/Fe] ratios in the metallicity range from [Fe/H]=-4.0 up to -3.0 dex [Cayrel, R., Depagne, E., Spite, M. et al. 2004, AfeA 416, 1117] is a clear sign that the halo of the Milky Way was well mixed even in the earliest phases of its evolution. We computed the evolution of the abundances of O, Mg, Si, Ca, K, Ti, Sc, Ni, Mn, Co, Fe and Zn in the Milky Way. We made use of the most widely adopted nucleosynthesis calculations and compared the model results with observational data with the aim of imposing constraints upon stellar yields

  16. The dust content of the most metal-poor star-forming galaxies

    CERN Document Server

    Schneider, Raffaella; Valiante, Rosa

    2016-01-01

    Although dust content is usually assumed to depend uniquely on metallicity, recent observations of two extremely metal-poor dwarf galaxies have suggested that this may not always be true. At a similar oxygen abundance of ~ 3% Zsun, the dust-to-gas and dust-to-stellar mass ratios in SBS 0335-052 and IZw 18 differ by a factor 40-70 according to including molecular gas or excluding it. Here we investigate a possible reason for this dramatic difference through models based on a semi-analytical formulation of chemical evolution including dust. Results suggest that the greater dust mass in SBS 0335-052 is due to the more efficient grain growth allowed by the high density in the cold interstellar medium (ISM), observationally inferred to be almost 20 times higher than in IZw 18. Our models are able to explain the difference in dust masses, suggesting that efficient dust formation and dust content in galaxies, including those with the highest measured redshifts, depend sensitively on the ISM density, rather than only...

  17. The dust content of the most metal-poor star-forming galaxies

    Science.gov (United States)

    Schneider, Raffaella; Hunt, Leslie; Valiante, Rosa

    2016-04-01

    Although dust content is usually assumed to depend uniquely on metallicity, recent observations of two extremely metal-poor dwarf galaxies have suggested that this may not always be true. At a similar oxygen abundance of ˜3 per cent Z⊙, the dust-to-gas and dust-to-stellar mass ratios in SBS 0335-052 and I Zw 18 differ by a factor of 40-70 according to including molecular gas or excluding it. Here, we investigate a possible reason for this dramatic difference through models based on a semi-analytical formulation of chemical evolution including dust. Results suggest that the greater dust mass in SBS 0335-052 is due to the more efficient grain growth allowed by the high density in the cold interstellar medium (ISM), observationally inferred to be almost 20 times higher than in I Zw 18. Our models are able to explain the difference in dust masses, suggesting that efficient dust formation and dust content in galaxies, including those with the highest measured redshifts, depend sensitively on the ISM density, rather than only on metallicity.

  18. Stellar Archaeology a Keck Pilot Program on Extremely Metal-Poor Stars From the Hamburg\\/ESO Survey. I Stellar Parameters

    CERN Document Server

    Cohen, J G; Beers, T C; Carretta, R; Gratton, E; Cohen, Judith G.; Christlieb, Norbert; Beers, Timothy C.

    2002-01-01

    In this series of two papers we present a high dispersion spectroscopic analysis of 8 candidate extremely metal poor stars selected from the Hamburg/ESO Survey and of 6 additional very metal poor stars. We demonstrate that with suitable vetting using moderate-resolution spectra the yield of this survey for stars with [Fe/H] $\\le -3.0$ dex is very high; three out of the eight stars observed thus far at high resolution from the HES are actually that metal poor, three more have [Fe/H] $\\le -2.8$ dex, and the remainder are only slightly more metal rich. In preparation for a large scale effort to mine the Hamburg/ESO Survey database for such stars about to get underway, we lay out in this paper the basic principles we intend to use to determine in a uniform way the stellar parameters Teff, surface grav, and reddening.

  19. High-Resolution Spectroscopy of Extremely Metal-Poor Stars from SDSS/SEGUE: I. Atmospheric Parameters and Chemical Compositions

    CERN Document Server

    Aoki, Wako; Lee, Young Sun; Honda, Satoshi; Ito, Hiroko; Takada-Hidai, Masahide; Frebel, Anna; Suda, Takuma; Fujimoto, Masatuki Y; Carollo, Daniela; Sivarani, Thirupathi

    2012-01-01

    Chemical compositions are determined based on high-resolution spectroscopy for 137 candidate extremely metal-poor (EMP) stars selected from the Sloan Digital Sky Survey (SDSS) and its first stellar extension, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). High-resolution spectra with moderate signal-to-noise (S/N) ratios were obtained with the High Dispersion Spectrograph of the Subaru Telescope. Most of the sample (approximately 80%) are main-sequence turn-off stars, including dwarfs and subgiants. Four cool main-sequence stars, the most metal-deficient such stars known, are included in the remaining sample. Good agreement is found between effective temperatures estimated by the SEGUE stellar parameter pipeline, based on the SDSS/SEGUE medium-resolution spectra, and those estimated from the broadband $(V-K)_0$ and $(g-r)_0$ colors. Our abundance measurements reveal that 70 stars in our sample have [Fe/H] $ +0.7$) among the 25 giants in our sample is as high as 36%, while only a lowe...

  20. Chemical compositions of six metal-poor stars in the ultra-faint dwarf spheroidal galaxy Bo\\"otes I

    CERN Document Server

    Ishigaki, Miho N; Arimoto, Nobuo; Okamoto, Sakurako

    2014-01-01

    Ultra-faint dwarf galaxies recently discovered around the Milky Way (MW) contain extremely metal-poor stars, and might represent the building blocks of low-metallicity components of the MW. Among them, the Bo\\"otes I dwarf spheroidal galaxy is of particular interest because of its exclusively old stellar population. We determine chemical compositions of six red giant stars in Bo\\"otes I, based on the high-resolution spectra obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of 12 elements, including C, Na, alpha, Fe-peak, and neutron capture elements, were determined for the sample stars. The abundance results were compared to those in field MW halo stars previously obtained using an abundance analysis technique similar to the present study. We confirm the low metallicity of Boo-094 ([Fe/H]=-3.4). Except for this star, the abundance ratios ([X/Fe]) of elements lighter than zinc are generally homogeneous with small scatter around the mean values in the metallicities span...

  1. The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars

    CERN Document Server

    Christlieb, N; Frebel, A; Beers, T C; Wisotzki, L; Reimers, D

    2008-01-01

    We present the quantitative methods used for selecting candidate metal-poor stars in the Hamburg/ESO objective-prism survey (HES). The selection is based on the strength of the Ca II K line, B-V colors (both measured directly from the digital HES spectra), as well as J-K colors from the 2 Micron All Sky Survey. The KP index for Ca II K can be measured from the HES spectra with an accuracy of 1.0 Angstrom, and a calibration of the HES B-V colors, using CCD photometry, yields a 1-sigma uncertainty of 0.07 mag for stars in the color range 0.3 -2.0 without sacrificing completeness at the lowest metallicities. A test of the selection using 1121 stars of the HK survey of Beers, Preston, and Shectman present on HES plates suggests that the completeness at [Fe/H] -2.5 and 97% of all stars with [Fe/H] > -2.0 are rejected. The selection was applied to 379 HES fields, covering a nominal area of 8853 square degrees of the southern high Galactic latitude sky. The candidate sample consists of 20,271 stars in the magnitud...

  2. BOO-1137-AN EXTREMELY METAL-POOR STAR IN THE ULTRA-FAINT DWARF SPHEROIDAL GALAXY BOOeTES I

    International Nuclear Information System (INIS)

    We present high-resolution (R ∼ 40,000), high-signal-to-noise ratio (20-90) spectra of an extremely metal-poor giant star Boo-1137 in the 'ultra-faint' dwarf spheroidal galaxy (dSph) Booetes I, absolute magnitude MV ∼ -6.3. We derive an iron abundance of [Fe/H] = -3.7, making this the most metal-poor star as yet identified in an ultra-faint dSph. Our derived effective temperature and gravity are consistent with its identification as a red giant in Booetes I. Abundances for a further 15 elements have also been determined. Comparison of the relative abundances, [X/Fe], with those of the extremely metal-poor red giants of the Galactic halo shows that Boo-1137 is 'normal' with respect to C and N, the odd-Z elements Na and Al, the iron-peak elements, and the neutron-capture elements Sr and Ba, in comparison with the bulk of the Milky Way halo population having [Fe/H] ∼<-3.0. The α-elements Mg, Si, Ca, and Ti are all higher by Δ[X/Fe] ∼ 0.2 than the average halo values. Monte Carlo analysis indicates that Δ[α/Fe] values this large are expected with a probability ∼0.02. The elemental abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution, consistent with the wide internal spread in iron abundances we previously reported. The similarity of most of the Boo-1137 relative abundances with respect to halo values, and the fact that the α-elements are all offset by a similar small amount from the halo averages, points to the same underlying galaxy-scale stellar initial mass function, but that Boo-1137 likely originated in a star-forming region where the abundances reflect either poor mixing of supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or both.

  3. Possible Evidence for Metal Accretion onto the Surfaces of Metal-Poor Main-Sequence Stars

    CERN Document Server

    Hattori, Kohei; Beers, Timothy C; Carollo, Daniela; Lee, Young Sun

    2014-01-01

    The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f(x, v, [X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (e.g., G- or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way's formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parametrized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the ...

  4. VizieR Online Data Catalog: Metal-poor stars towards the Galactic bulge (Koch+, 2016)

    Science.gov (United States)

    Koch, A.; McWilliam, A.; Preston, G. W.; Thompson, I. B.

    2015-11-01

    The stars studied here were identified in a search for EMP stars in the Galactic bulge (Preston et al. unpublished), near b=-10°, employing the 2.5-m du Pont and 1-m Swope telescopes at Las Campanas Observatory. Observations of seven EMP candidates presented here were taken spread over six nights in July 2007 with a median seeing of 0.95", while individual exposures reached as high as 2" and notably better conditions (~0.6") during several nights. Our chosen set-up included a 0.5" slit, 2x1 binning in spectral and spatial dimensions and resulted in a resolving power of R~45000. An observing log is given in Table 1. (3 data files).

  5. Star cluster formation and evolution in Mrk 930: properties of a metal-poor starburst

    CERN Document Server

    Adamo, A; Zackrisson, E; Papaderos, P; Bergvall, N; Rich, R M; Micheva, G

    2011-01-01

    We present a HST multiband analysis of the large population of star clusters in the blue compact galaxy (BCG) Mrk 930. We have reconstructed the spectral energy distributions of the star clusters and estimated age, mass, and extinction for a representative sample. We observe a very young cluster population with 70% of the systems formed less than 10 Myr ago. The peak in the star cluster age distribution at 4 Myr is corroborated by the presence of Wolf-Rayet spectral features, and by the observed optical and IR lines ratios [OIII]/H_beta and [NeIII]/[NeII]. The recovered extinction in these very young clusters shows large variations, with a decrease at older ages. It is likely that our analysis is limited to the optically brightest objects (i.e. systems only partially embedded in their natal cocoons). We map the extinction across the galaxy using low-resolution spectra and the H_alpha/H_beta ratio, as obtained from ground-based narrow band imaging. We find that the mean optical extinction derived in the starbu...

  6. Iron-Group Abundances in the Metal-Poor Main Sequence Turnoff Star HD~84937

    CERN Document Server

    Sneden, Christopher; Kobayashi, Chiaki; Pignatari, Marco; Lawler, James E; Hartog, Elizabeth A Den; Wood, Michael P

    2015-01-01

    We have derived new very accurate abundances of the Fe-group elements Sc through Zn (Z = 21-30) in the bright main-sequence turnoff star HD 84937, based on high-resolution spectra covering the visible and ultraviolet spectral regions. New or recent laboratory transition data for 14 species of seven elements have been used. Abundances from more than 600 lines of non-Fe species have been combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. The abundances have been determined from both neutral and ionized transitions, which generally are in agreement with each other. We find no substantial departures from standard LTE Saha ionization balance in this [Fe/H] = -2.32 star. Noteworthy among the abundances are: [Co/Fe] = 0.14 and [Cu/Fe] = -0.83, in agreement with past studies abundance trends in this and other low metallicity stars; and = 0.31, which has not been noted previously. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic...

  7. An astrometric companion to the nearby metal-poor, low-mass star LHS 1589

    CERN Document Server

    Lepine, S; Shara, M M; Cruz, K L; Skemer, A; Lepine, Sebastien; Shara, Michael M.; Cruz, Kelle L.; Skemer, Andrew

    2007-01-01

    We report the discovery of a companion to the high proper motion star LHS 1589, a nearby high-velocity, low-mass subdwarf. The companion (LHS 1589B) is located 0.220"+/-0.004" to the southwest of the primary (LHS 1589A), and is 0.5 magnitude fainter than the primary in the K_s band. The pair was resolved with the IRCAL infrared camera at Lick Observatory, operating with the Laser Guide Star Adaptive Optics system. A low-resolution spectrum obtained at MDM observatory confirms that the system consists of a pair of low-mass subdwarfs, with a composite spectral type sdK7.5. A photometric distance estimate places the system at a distance d=78+/-18 parsecs from the Sun. We also measure a radial velocity V_rad=75+/-25 km/s which, together with the proper motion and estimated distance, suggests that the star is roaming the inner Galactic halo on a highly eccentric orbit. With a projected orbital separation s=17.2+/-4.8 AU, we estimate the orbital period of the system to be in the range 95 yr < P < 370 yr. This...

  8. Homogeneous photometry and metal abundances for a large sample of Hipparcos metal-poor stars

    CERN Document Server

    Clementini, G; Carretta, E; Sneden, C

    1998-01-01

    Homogeneous photometric data (Johnson V, B-V, V-K, Cousins V-I and Stromgren b-y), radial velocities, and abundances of Fe, O, Mg, Si, Ca, Ti, Cr and Ni are presented for 99 stars with high precision parallaxes measured by the Hipparcos satellite. These data have been previously used to assist the derivation of accurate distances and ages of galactic globular clusters. Magnitudes and colours for the programme stars were obtained combining and standardizing carefully selected literature data available in the Simbad data-base and V and B-V values measured by the Hipparcos/Tycho mission. Comparison of colours for our targets suggests: (i) ground-based and Tycho B-V's agree well for colours bluer than 0.75 mag, but have a lot of scatter for redder colours; (ii) the Hipparcos V-I colours have a very large scatter and a zero point offset of +0.02 mag compared to the literature values. The programme stars have metal abundances in the range -2.5200) spectra obtained at the Asiago and McDonald Observatories for 66 sta...

  9. Detection of Elements at All Three r-process Peaks in the Metal-Poor Star HD 160617

    CERN Document Server

    Roederer, Ian U; 10.1088/0004-637X/750/1/76

    2012-01-01

    We report the first detection of elements at all three r-process peaks in the metal-poor halo star HD 160617. These elements include arsenic and selenium, which have not been detected previously in halo stars, and the elements tellurium, osmium, iridium, and platinum, which have been detected previously. Absorption lines of these elements are found in archive observations made with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. We present up-to-date absolute atomic transition probabilities and complete line component patterns for these elements. Additional archival spectra of this star from several ground-based instruments allow us to derive abundances or upper limits of 45 elements in HD 160617, including 27 elements produced by neutron-capture reactions. The average abundances of the elements at the three r-process peaks are similar to the predicted solar system r-process residuals when scaled to the abundances in the rare earth element domain. This result for arsenic and selen...

  10. DETECTION OF ELEMENTS AT ALL THREE r-PROCESS PEAKS IN THE METAL-POOR STAR HD 160617

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U. [Carnegie Observatories, Pasadena, CA 91101 (United States); Lawler, James E., E-mail: iur@obs.carnegiescience.edu, E-mail: jelawler@wisc.edu [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States)

    2012-05-01

    We report the first detection of elements at all three r-process peaks in the metal-poor halo star HD 160617. These elements include arsenic and selenium, which have not been detected previously in halo stars, and the elements tellurium, osmium, iridium, and platinum, which have been detected previously. Absorption lines of these elements are found in archive observations made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We present up-to-date absolute atomic transition probabilities and complete line component patterns for these elements. Additional archival spectra of this star from several ground-based instruments allow us to derive abundances or upper limits of 45 elements in HD 160617, including 27 elements produced by neutron-capture reactions. The average abundances of the elements at the three r-process peaks are similar to the predicted solar system r-process residuals when scaled to the abundances in the rare earth element domain. This result for arsenic and selenium may be surprising in light of predictions that the production of the lightest r-process elements generally should be decoupled from the heavier r-process elements.

  11. Non-LTE Analysis for the Sodium Abundances of Metal-Poor Stars in the Galactic Disk and Halo

    CERN Document Server

    Takeda, Y; Takada-Hidai, M; Chen, Y Q; Saitô, Y; Zhang, H W; Takeda, Yoichi; Zhao, Gang; Takada-Hidai, Masahide; Chen, Yu-Qin; Saito, Yu-ji; Zhang, Hua-Wei

    2003-01-01

    We performed an extensive non-LTE analysis of the neutral sodium lines of Na {\\sc i} 5683/5688, 5890/5896, 6154/6161, and 8183/8195 for disk/halo stars of F--K type covering a wide metallicity range ($-4 \\la$ [Fe/H] $\\la 0.4$), based on our own data as well as those collected from the literature. For comparatively metal-rich disk stars ($-1 \\la$ [Fe/H] $\\la 0$) where the weaker 6154/6161 lines are best abundance indicators, we confirmed [Na/Fe] $\\sim$ 0 with an ``upturn'' (i.e., a shallow/broad dip around $-0.5 \\la$ [Fe/H] $\\la 0$) as already reported by previous studies. Regarding the metal-deficient halo stars, where the much stronger 5890/5896 or 8183/8195 lines suffering considerable (negative) non-LTE corrections amounting to 0.5 dex have to be used, our analysis suggests mildly ``subsolar'' [Na/Fe] values down to $\\sim -0.4$ (with a somewhat large scatter of $\\sim \\pm 0.2$ dex) on the average at the typical halo metallicity of [Fe/H] $\\sim -2$, while they appear to rise again toward a very metal-poor re...

  12. The visitor from an ancient galaxy: A planetary companion around an old, metal-poor red horizontal branch star

    CERN Document Server

    Klement, Rainer J; Henning, Thomas; Rix, Hans-Walter; Rochau, Boyke; Rodmann, Jens; Schulze-Hartung, Tim; Heidelberg, MPIA; ESTEC,

    2010-01-01

    We report the detection of a planetary companion around HIP 13044, a metal-poor red horizontal branch star belonging to a stellar halo stream that results from the disruption of an ancient Milky Way satellite galaxy. The detection is based on radial velocity observations with FEROS at the 2.2-m MPG/ESO telescope. The periodic radial velocity variation of P=16.2 days can be distinguished from the periods of the stellar activity indicators. We computed a minimum planetary mass of 1.25 Jupiter masses and an orbital semimajor axis of 0.116 AU for the planet. This discovery is unique in three aspects: First, it is the first planet detection around a star with a metallicity much lower than few percent of the solar value; second, the planet host star resides in a stellar evolutionary stage that is still unexplored in the exoplanet surveys; third, the planetary system HIP 13044 most likely has an extragalactic origin in a disrupted former satellite of the Milky Way.

  13. Iron-Group Abundances in the Metal-Poor Main Sequence Turnoff Star HD~84937

    OpenAIRE

    Sneden, Christopher; Cowan, John J.; Kobayashi, Chiaki; Pignatari, Marco; Lawler, James E.; Hartog, Elizabeth A. Den; Wood, Michael P.

    2015-01-01

    We have derived new very accurate abundances of the Fe-group elements Sc through Zn (Z = 21-30) in the bright main-sequence turnoff star HD 84937, based on high-resolution spectra covering the visible and ultraviolet spectral regions. New or recent laboratory transition data for 14 species of seven elements have been used. Abundances from more than 600 lines of non-Fe species have been combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. The abundances hav...

  14. WASP-37b: A 1.8 MJ EXOPLANET TRANSITING A METAL-POOR STAR

    International Nuclear Information System (INIS)

    We report on the discovery of WASP-37b, a transiting hot Jupiter orbiting an mv = 12.7 G2-type dwarf, with a period of 3.577469 ± 0.000011 d, transit epoch T0 = 2455338.6188 ± 0.0006 (HJD; dates throughout the paper are given in Coordinated Universal Time (UTC)), and a transit duration 0.1304+0.0018-0.0017 d. The planetary companion has a mass Mp = 1.80 ± 0.17 MJ and radius Rp = 1.16+0.07-0.06 RJ, yielding a mean density of 1.15+0.12-0.15 ρJ. From a spectral analysis, we find that the host star has M* = 0.925 ± 0.120 Msun, R* = 1.003 ± 0.053 Rsun, Teff = 5800 ± 150 K, and [Fe/H] = -0.40 ± 0.12. WASP-37 is therefore one of the lowest metallicity stars to host a transiting planet.

  15. Origins of the thick disk of the galaxy as traced by metal-poor stars selected from RAVE

    Directory of Open Access Journals (Sweden)

    Ruchti G.R.

    2012-02-01

    Full Text Available Models of the formation of the thick disk of the Milky Way Galaxy make specific predictions about the chemical abundance properties of the metal-weak (and oldest stellar population in the thick disk. We have undertaken the study of the elemental abundances and kinematic properties of a sample of 319 candidate metal-poor thick-disk stars selected from the RAVE spectroscopic survey of bright stars. Our aim is to differentiate among the present scenarios of the formation of the thick disk. In this study, we measured the abundances of several alpha-elements and found that the thick-disk [alpha/Fe] ratios are enhanced, implying that enrichment proceeded by purely core-collapse supernovae. Further, the sample probes distances ranging out to about 2 kpc from the Sun, allowing for the investigation of the gradients in the thick disk. I will discuss the results from these investigations and how they compare to the predictions made by present models of the formation of the thick disk.

  16. The Extremely Metal-Poor, Neutron-Capture-Rich Star CS 22892-052: A Comprehensive Abundance Analysis

    CERN Document Server

    Sneden, C; Lawler, J E; Ivans, I I; Burles, S; Beers, T C; Primas, F; Hill, V; Truran, J W; Fuller, G M; Pfeiffer, B; Kratz, K L

    2003-01-01

    High-resolution spectra obtained with three ground-based facilities and the Hubble Space Telescope (HST) have been combined to produce a new abundance analysis of CS 22892-052, an extremely metal-poor giant with large relative enhancements of neutron-capture elements. A revised model stellar atmosphere has been derived with the aid of a large number of Fe-peak transitions, including both neutral and ionized species of six elements.Several elements, including Mo, Lu, Au, Pt and Pb, have been detected for the first time in CS 22892-052, and significant upper limits have been placed on the abundances of Ga, Ge, Cd, Sn, and U in this star. In total, abundance measurements or upper limits have been determined for 57 elements, far more than previously possible. New Be and Li detections in CS 22892-052 indicate that the abundances of both these elements are significantly depleted compared to unevolved main-sequence turnoff stars of similar metallicity. Abundance comparisons show an excellent agreement between the he...

  17. The Chemical Compositions of Very Metal-Poor Stars HD 122563 and HD 140283; A View From the Infrared

    CERN Document Server

    Afşar, Melike; Frebel, Anna; Kim, Hwihyun; Mace, Gregory N; Kaplan, Kyle F; Lee, Hye-In; Oh, Hee-Young; Oh, Jae Sok; Pak, Soojong; Park, Chan; Pavel, Michael D; Yuk, In-Soo; Jaffe, Daniel T

    2016-01-01

    From high resolution (R = 45,000), high signal-to-noise (S/N > 400) spectra gathered with the Immersion Grating Infrared Spectrograph (IGRINS) in the H and K photometric bands, we have derived elemental abundances of two bright, well-known metal-poor halo stars: the red giant HD 122563 and the subgiant HD 140283. Since these stars have metallicities approaching [Fe/H] = -3, their absorption features are generally very weak. Neutral-species lines of Mg, Si, S and Ca are detectable, as well as those of the light odd-Z elements Na and Al. The derived IR-based abundances agree with those obtained from optical-wavelength spectra. For Mg and Si the abundances from the infrared transitions are improvements to those derived from shorter wavelength data. Many useful OH and CO lines can be detected in the IGRINS HD 122563 spectrum, from which derived O and C abundances are consistent to those obtained from the traditional [O I] and CH features. IGRINS high resolutions H- and K-band spectroscopy offers promising ways to...

  18. 6Li detection in metal-poor stars: can 3D model atmospheres solve the second lithium problem?

    CERN Document Server

    Steffen, M; Caffau, E; Bonifacio, P; Ludwig, H -G; Spite, M

    2012-01-01

    The presence of 6Li in the atmospheres of metal-poor halo stars is usually inferred from the detection of a subtle extra depression in the red wing of the 7Li doublet line at 670.8 nm. However, the intrinsic line asymmetry caused by convective flows in the photospheres of cool stars is almost indistinguishable from the asymmetry produced by a weak 6Li blend on a (presumed) symmetric 7Li profile. Previous determinations of the 6Li/ 7Li isotopic ratio based on 1D model atmospheres, ignoring the convection-induced line asymmetry, must therefore be considered as upper limits. By comparing synthetic 1D LTE and 3D non-LTE line profiles of the Li 670.8 nm feature, we quantify the differential effect of the convective line asymmetry on the derived 6Li abundance as a function of effective temperature, gravity, and metallicity. As expected, we find that the asymmetry effect systematically reduces the resulting 6Li/7Li ratios. Depending on the stellar parameters, the 3D-1D offset in 6Li/7Li ranges between -0.005 and -0....

  19. A Statistical Model for Predicting the Average Abundance Patterns of Heavier Elements in Metal-Poor Stars

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    We have collected nearly all the available observed data of the elements from Ba to Dy in halo and disk stars in the metallicity range -4.0 <[Fe/H]< 0.5.Based on the observed data of Ba and Eu, we evaluated the least-squares regressions of [Ba/Fe] on [Fe/H], and [Eu/H] on [Ba/H]. Assuming that the heavy elements (heavier than Ba) are produced by a combination of the main components of s- and r-processes in metal-poor stars, and choosing Ba and Eu as respective representative elements of the main s- and the main r-processes, a statistical model for predicting the Galactic chemical evolution of the heavy elements is presented. With this model,we calculate the mean abundance trends of the heavy elements La, Ce, Pr, Nd,Sm, and Dy with the metallicity. We compare our results with the observed data at various metallicities, showing that the predicted trends are in good agreement with the observed trends, at least for the metallicity range [Fe/H]≥ -2.5. Finally,we discuss our results and deduce some important information about the Galactic chemical evolution.

  20. HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: URSA MAJOR II and COMA BERENICES

    International Nuclear Information System (INIS)

    We present spectra of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way (MW), Ursa Major II, and Coma Berenices obtained with the Keck/High Resolution Echelle Spectrometer (HIRES). These observations include the first high-resolution spectroscopic observations of extremely metal-poor ([Fe/H] -3.0. Not only are our results broadly consistent with a galaxy formation model that predicts that massive dwarf galaxies are the source of the metal-rich component ([Fe/H]> - 2.5) of the MW halo, but they also suggest that the faintest known dwarfs may be the primary contributors to the metal-poor end of the MW halo metallicity distribution.

  1. New Analyses of Star-to-Star Abundance Variations Among Bright Giants in the Mildly Metal-Poor Globular Cluster M5

    CERN Document Server

    Ivans, I I; Sneden, C; Smith, G H; Rich, R M; Shetrone, M; Ivans, Inese I.; Kraft, Robert P.; Sneden, Christopher; Smith, Graeme H.; Shetrone, Matthew

    2001-01-01

    We present a chemical composition analysis of 36 giant stars in the mildly metal-poor globular cluster M5 (NGC 5904). The analysis makes use of high resolution data acquired at the Keck I telescope as well as a re-analysis of high resolution spectra acquired for an earlier study at Lick Observatory. We employed two analysis techniques: one, adopting standard spectroscopic constraints, and two, adopting an analysis consistent with the non-LTE precepts as recently described by Thevenin & Idiart. The abundance ratios we derive for magnesium, silicon, calcium, scandium, titanium, vanadium, nickel, barium and europium in M5 show no significant abundance variations and the ratios are comparable to those of halo field stars. However, large variations are seen in the abundances of oxygen, sodium and aluminum, the elements that are sensitive to proton-capture nucleosynthesis. In comparing the abundances of M5 and M4 (NGC 6121), another mildly metal-poor globular cluster, we find that silicon, aluminum, barium and ...

  2. CAN THE GROWTH OF DUST GRAINS IN LOW-METALLICITY STAR-FORMING CLOUDS AFFECT THE FORMATION OF METAL-POOR LOW-MASS STARS?

    International Nuclear Information System (INIS)

    The discovery of a low-mass star with such a low metallicity as ≤4.5 × 10–5 Z☉ reveals the critical role of dust in the formation of extremely metal-poor stars. In this Letter, we explore the effect of the growth of dust grains through accretion of gaseous refractory elements in very low metallicity pre-stellar cores on cloud fragmentation induced by dust emission cooling. Employing a simple model of grain growth in a gravitationally collapsing gas, we show that Fe and Si grains can grow efficiently at hydrogen densities of ≅ 1010-1014 cm–3 in the clouds with metal abundances of –5 ∼crit ≅ 10–9-10–8, unless the initial grain radius is too large (∼>1 μm) or the sticking probability is too small (∼–5 Z☉.

  3. Dependence of the Sr-to-Ba and Sr-to-Eu Ratio on the Nuclear Equation of State in Metal Poor Halo Stars

    CERN Document Server

    Famiano, M A; Aoki, W; Suda, T

    2016-01-01

    A model is proposed in which the light r-process element enrichment in metal-poor stars is explained via enrichment from a truncated r-process, or "tr-process." The truncation of the r-process from a generic core-collapse event followed by a collapse into an accretion-induced black hole is examined in the framework of a galactic chemical evolution model. The constraints on this model imposed by observations of extremely metal-poor stars are explained, and the upper limits in the [Sr/Ba] distributions are found to be related to the nuclear equation of state in a collapse scenario. The scatter in [Sr/Ba] and [Sr/Eu] as a function of metallicity has been found to be consistent with turbulent ejection in core collapse supernovae. Adaptations of this model are evaluated to account for the scatter in isotopic observables. This is done by assuming mixing in ejecta in a supernova event.

  4. METAL-POOR, COOL GAS IN THE CIRCUMGALACTIC MEDIUM OF A z = 2.4 STAR-FORMING GALAXY: DIRECT EVIDENCE FOR COLD ACCRETION?

    International Nuclear Information System (INIS)

    In our current galaxy formation paradigm, high-redshift galaxies are predominantly fueled by accretion of cool, metal-poor gas from the intergalactic medium. Hydrodynamical simulations predict that this material should be observable in absorption against background sightlines within a galaxy's virial radius, as optically thick Lyman limit systems (LLSs) with low metallicities. Here we report the discovery of exactly such a strong metal-poor absorber at an impact parameter R = 58 kpc from a star-forming galaxy at z = 2.44. Besides strong neutral hydrogen (NH0=1019.50±0.16 cm-2) we detect neutral deuterium and oxygen, allowing a precise measurement of the metallicity: log10(Z/Z ☉) = –2.0 ± 0.17, or (7-15) × 10–3 solar. Furthermore, the narrow deuterium linewidth requires a cool temperature 0.1 solar, 10 times larger than the metal-poor component. We conclude that the photoionized circumgalactic medium (CGM) of this galaxy is highly inhomogeneous: the majority of the gas is in a cool, metal-poor and predominantly neutral phase, but the majority of the metals are in a highly ionized phase exhibiting weak neutral hydrogen absorption but strong metal absorption. If such inhomogeneity is common, then high-resolution spectra and detailed ionization modeling are critical to accurately appraise the distribution of metals in the high-redshift CGM

  5. The Diverse Origins of Neutron-Capture Elements in the Metal-Poor Star HD 94028: Possible Detection of Products of i-process Nucleosynthesis

    OpenAIRE

    Roederer, Ian U.; Karakas, Amanda I.; Pignatari, Marco; Herwig, Falk

    2016-01-01

    We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metal-poor ([Fe/H]=-1.62+/-0.09) star HD94028. Previous studies revealed that this star is mildly enhanced in elements produced by the slow neutron-capture process (s-process; e.g., [Pb/Fe]=+0.79+/-0.32) and rapid neutron-capture process (r-process; e.g., [Eu/Fe]=+0.22+/-0.12), including unusually large molybdenum ([Mo/Fe]=+0.97+/-0.16) and ruthenium ([Ru/Fe]=+0.69+/-0.17) enhancements. ...

  6. Abundance analysis of SDSS J134338.67+484426.6; an extremely metal-poor star from the MARVELS pre-survey

    Science.gov (United States)

    Susmitha Rani, A.; Sivarani, T.; Beers, T. C.; Fleming, S.; Mahadevan, S.; Ge, J.

    2016-05-01

    We present an elemental-abundance analysis of an extremely metal-poor (EMP; [Fe/H] carbon and no enhancement of neutron-capture abundances. Strontium is underabundant, [Sr/Fe] = -0.47, but the derived lower limit on [Sr/Ba] indicates that Sr is likely enhanced relative to Ba. This star belongs to the sparsely populated class of α-poor EMP stars that exhibit low ratios of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar metallicity. The observed variations in radial velocity from several epochs of (low- and high-resolution) spectroscopic follow-up indicate that SDSS J134338.67+484426.6 is a possible long-period binary. We also discuss the abundance trends in EMP stars for r-process elements, and compare with other magnesium-poor stars.

  7. AN INFRARED CENSUS OF DUST IN NEARBY GALAXIES WITH SPITZER (DUSTiNGS). II. DISCOVERY OF METAL-POOR DUSTY AGB STARS

    Energy Technology Data Exchange (ETDEWEB)

    Boyer, Martha L.; Sonneborn, George [Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); McQuinn, Kristen B. W.; Gehrz, Robert D.; Skillman, Evan [Minnesota Institute for Astrophysics, School of Physics and Astronomy, 116 Church Street SE, University of Minnesota, Minneapolis, MN 55455 (United States); Barmby, Pauline [Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7 (Canada); Bonanos, Alceste Z. [IAASARS, National Observatory of Athens, GR-15236 Penteli (Greece); Gordon, Karl D.; Meixner, Margaret [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Groenewegen, M. A. T. [Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels (Belgium); Lagadec, Eric [Laboratoire Lagrange, UMR7293, Univ. Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d' Azur, F-06300 Nice (France); Lennon, Daniel [ESA-European Space Astronomy Centre, Apdo. de Correo 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Marengo, Massimo [Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); McDonald, Iain; Zijlstra, Albert [Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Manchester M13 9PL (United Kingdom); Sloan, G. C. [Astronomy Department, Cornell University, Ithaca, NY 14853-6801 (United States); Van Loon, Jacco Th., E-mail: martha.boyer@nasa.gov [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom)

    2015-02-10

    The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6 and 4.5 μm imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing asymptotic giant branch (AGB) stars and massive stars. Using two epochs, spaced approximately six months apart, we identify a total of 526 dusty variable AGB stars (sometimes called ''extreme'' or x-AGB stars; [3.6]-[4.5] > 0.1 mag). Of these, 111 are in galaxies with [Fe/H] < –1.5 and 12 are in galaxies with [Fe/H] < –2.0, making them the most metal-poor dust-producing AGB stars known. We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables, with the exception of ≈30 stars in NGC 185 and NGC 147, 1 star in IC 1613, and 1 star in Phoenix. The chemical abundances of the x-AGB variables are unknown, but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirm that 70 of the x-AGB variables are confirmed or likely carbon stars. We see an increase in the pulsation amplitude with increased dust production, supporting previous studies suggesting that dust production and pulsation are linked. We find no strong evidence linking dust production with metallicity, indicating that dust can form in very metal-poor environments.

  8. AN INFRARED CENSUS OF DUST IN NEARBY GALAXIES WITH SPITZER (DUSTiNGS). II. DISCOVERY OF METAL-POOR DUSTY AGB STARS

    International Nuclear Information System (INIS)

    The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6 and 4.5 μm imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing asymptotic giant branch (AGB) stars and massive stars. Using two epochs, spaced approximately six months apart, we identify a total of 526 dusty variable AGB stars (sometimes called ''extreme'' or x-AGB stars; [3.6]-[4.5] > 0.1 mag). Of these, 111 are in galaxies with [Fe/H] < –1.5 and 12 are in galaxies with [Fe/H] < –2.0, making them the most metal-poor dust-producing AGB stars known. We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables, with the exception of ≈30 stars in NGC 185 and NGC 147, 1 star in IC 1613, and 1 star in Phoenix. The chemical abundances of the x-AGB variables are unknown, but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirm that 70 of the x-AGB variables are confirmed or likely carbon stars. We see an increase in the pulsation amplitude with increased dust production, supporting previous studies suggesting that dust production and pulsation are linked. We find no strong evidence linking dust production with metallicity, indicating that dust can form in very metal-poor environments

  9. Explaining the Ba, Y, Sr, and Eu abundance scatter in metal-poor halo stars: constraints to the r-process

    CERN Document Server

    Cescutti, Gabriele

    2014-01-01

    Context. Thanks to the heroic observational campaigns carried out in recent years we now have large samples of metal-poor stars for which measurements of detailed abundances exist. [...] These data hold important clues on the nature of the contribution of the first stellar generations to the enrichment of our Galaxy. Aims. We aim to explain the scatter in Sr, Ba, Y, and Eu abundance ratio diagrams unveiled by the metal-poor halo stars. Methods. We computed inhomogeneous chemical evolution models for the Galactic halo assuming different scenarios for the r-process site: the electron-capture supernovae (EC) and the magnetorotationally driven (MRD) supernovae scenario. We also considered models with and without the contribution of fast-rotating massive stars (spinstars) to an early enrichment by the s-process. A detailed comparison with the now large sample of stars with measured abundances of Sr, Ba, Y, Eu, and Fe is provided (both in terms of scatter plots and number distributions for several abundance ratios)...

  10. Metal-Poor, Cool Gas in the Circumgalactic Medium of a z = 2.4 Star-Forming Galaxy: Direct Evidence for Cold Accretion?

    CERN Document Server

    Crighton, Neil H M; Prochaska, J Xavier

    2013-01-01

    In our current galaxy formation paradigm, high-redshift galaxies are predominantly fuelled by accretion of cool, metal-poor gas from the intergalactic medium. Hydrodynamical simulations predict that this material should be observable in absorption against background sightlines within a galaxy's virial radius, as optically thick Lyman-limit systems (LLSs) with low metallicities. Here we report the discovery of exactly such a strong metal-poor absorber at an impact parameter R_perp = 58 kpc from a star-forming galaxy at z = 2.44. Besides strong neutral hydrogen [N(HI) = 10^(19.50 +/- 0.16) cm^-2] we detect neutral deuterium and oxygen, allowing a precise measurement of the metallicity: log10(Z / Zsolar) = -2.0 +/- 0.17, or (7-15) x 10^-3 solar. Furthermore, the narrow deuterium linewidth requires a cool temperature 0.1 solar, ten times larger than the metal-poor component. We conclude that the photoionized circumgalactic medium (CGM) of this galaxy is highly inhomogeneous: the majority of the gas is in a cool,...

  11. Abundance analysis of SDSS J134338.67+484426.6; an extremely metal-poor star from the MARVELS pre-survey

    CERN Document Server

    Rani, A Susmitha; Beers, T C; Fleming, S; Mahadevan, S; Ge, J

    2016-01-01

    We present an elemental-abundance analysis of an extremely metal-poor (EMP; [Fe/H] < -3.0) star, SDSS J134338.67+484426.6, identified during the course of the MARVELS spectroscopic pre-survey of some 20000 stars to identify suitable candidates for exoplanet searches. This star, with an apparent magnitude V = 12.14, is the lowest metallicity star found in the pre-survey, and is one of only ~20 known EMP stars that are this bright or brighter. Our high-resolution spectroscopic analysis shows that this star is a subgiant with [Fe/H] = -3.42, having "normal" carbon and no enhancement of neutron-capture abundances. Strontium is under-abundant, [Sr/Fe] =-0.47, but the derived lower limit on [Sr/Ba] indicates that Sr is likely enhanced relative to Ba. This star belongs to the sparsely populated class of alpha-poor EMP stars that exhibit low ratios of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar metallicity. The observed variations in radial velocity from several epochs of (low- and high...

  12. Improved Co I log(gf) & hfs data and Abundance Determinations in the Photospheres of the Sun & Metal-poor Star HD 84937

    Science.gov (United States)

    Lawler, James E.; Sneden, Chris; Cowan, John J.

    2016-01-01

    New emission branching fraction measurements for 898 lines of the first spectrum of cobalt (Co I) from hollow cathode lamp spectra recorded with a 1m Fourier transform spectrometer (FTS) and a high resolution echelle spectrometer are reported. Radiative lifetimes from laser induced fluorescence measurements are combined with the branching fractions to determine accurate log(gf)s for the 898 lines. Selected published hyperfine structure (hfs) constants for levels of neutral Co are used to generate complete hfs component patterns for 195 transitions of Co I. These new laboratory data are applied to determine the Co abundance in the Sun and metal-poor star HD 84937, yielding log eps(Co) = 4.955 ± 0.007 (sigma = 0.059) based on 82 Co I lines and log eps(Co) = 2.785 ± 0.008 (sigma = 0.065) based on 66 Co I lines respectively. A Saha balance test on the photosphere of HD 84937 is performed using 16 UV lines of Co II, and good agreement is found with the Co I result in this metal-poor ([Fe I /H] = -2.32, [Fe II /H] = -2.32) dwarf star. The resulting value of [Co/Fe] = +0.14 supports a rise of Co/Fe at low metallicity that has been suggested in other studies. These new Co I data are part of a continuing effort to explore the limits of 1D/LTE photospheric models in metal-poor stars and to determine the relative abundance of Fe-group elements at low metallicity. This work is supported in part by NASA grant NNX10AN93G (J.E.L.), by NSF grant AST-1211055 (J.E.L.), and by NSF grant AST-1211585 (C.S.).

  13. HST/STIS abundances in the uranium rich metal poor star CS 31082-001: Constraints on the r-Process

    Science.gov (United States)

    Siqueira-Mello, C.; Spite, M.; Barbuy, B.; Spite, F.; Caffau, E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.; Andersen, J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio, P.; François, P.; Molaro, P.

    2016-01-01

    As a brief revision, the origin of heavy elements and the role of abundances in extremely metal-poor (EMP) stars are presented. Heavy element abundances in the EMP uranium-rich star CS 31082-001 based mainly on near-UV spectra from STIS/HST are presented. These results should be useful for a better characterisation of the neutron exposure(s) that produced the r-process elements in this star, as well as a guide for improving nuclear data and astrophysical site modelling, given that the new element abundances not available in previous works (Ge, Mo, Lu, Ta, W, Re, Pt, Au, and Bi) make CS 31082-001 the most completely well studied r-II object, with a total of 37 detections of n-capture elements.

  14. A search for metal-poor stars pre-enriched by pair-instability supernovae I. A pilot study for target selection from Sloan Digital Sky Survey

    International Nuclear Information System (INIS)

    We report on a pilot study on identifying metal-poor stars pre-enriched by Pair-Instability Supernovae (PISNe). Very massive, first generation (Population III) stars (140 M☉ ≤ M ≤ 260 M☉) end their lives as PISNe, which have been predicted by theories, but no relics of PISNe have been observed yet. Among the distinct characteristics of the yields of PISNe, as predicted by theoretical calculations, are a strong odd-even effect, and a strong overabundance of Ca with respect to iron and the solar ratio. We use the latter characteristic to identify metal-poor stars in the Galactic halo that have been pre-enriched by PISNe, by comparing metallicites derived from strong, co-added Fe lines detected in low-resolution (i.e., R = λ/Δλ ∼ 2000) spectra of the Sloan Digital Sky Survey (SDSS), with metallicities determined by the SDSS Stellar Parameters Pipeline (SSPP). The latter are based on the strength of the Ca II K line and assumptions on the Ca/Fe abundance ratio. Stars are selected as candidates if their metallicity derived from Fe lines is significantly lower than the SSPP metallicities. In a sample of 12 300 stars for which SDSS spectroscopy is available, we have identified 18 candidate stars. Higher resolution and signal-to-noise ratio spectra of these candidates are being obtained with the Very Large Telescope of the European Southern Observatory and the XSHOOTER spectrograph, to determine their abundance patterns, and to verify our selection method. We plan to apply our method to the database of several million stellar spectra to be acquired with the Guo Shou Jing Telescope (LAMOST) in the next five years. (research papers)

  15. Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars

    CERN Document Server

    Amarsi, A M; Asplund, M; Barklem, P S; Collet, R

    2016-01-01

    As one of the most important elements in astronomy, iron abundance determinations need to be as accurate as possible. We investigate the accuracy of spectroscopic iron abundance analyses using archetypal metal-poor stars. We perform detailed 3D non-LTE radiative transfer calculations based on 3D hydrodynamic Stagger model atmospheres, and employ a new model atom that includes new quantum-mechanical neutral hydrogen collisional rate coefficients. With the exception of the red giant HD122563, we find that the 3D non-LTE models achieve Fe i/Fe ii excitation and ionization balance as well as not having any trends with equivalent width to within modelling uncertainties of 0.05 dex, all without having to invoke any microturbulent broadening; for HD122563 we predict that the current best parallax-based surface gravity is over-estimated by 0.5 dex. Using a 3D non-LTE analysis, we infer iron abundances from the 3D model atmospheres that are roughly 0.1 dex higher than corresponding abundances from 1D MARCS model atmos...

  16. First stars. XVI. HST/STIS abundances of heavy elements in the uranium-rich metal-poor star CS 31082-001

    Science.gov (United States)

    Siqueira Mello, C.; Spite, M.; Barbuy, B.; Spite, F.; Caffau, E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.; Andersen, J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio, P.; François, P.; Molaro, P.

    2013-02-01

    Context. The origin and site(s) of the r-process nucleosynthesis is(are) still not known with certainty, but complete, detailed r-element abundances offer our best clues. The few extremely metal-poor (EMP) stars with large r-element excesses allow us to study the r-process signatures in great detail, with minimal interference from later stages of Galactic evolution. CS 31082-001 is an outstanding example of the information that can be gathered from these exceptional stars. Aims: Here we aim to complement our previous abundance determinations for third-peak r-process elements with new and improved results for elements of the first and second r-process peaks from near-UV HST/STIS and optical UVES spectra. These results should provide new insight into the nucleosynthesis of the elements beyond iron. Methods: The spectra were analyzed by a consistent approach based on an OSMARCS LTE model atmosphere and the Turbospectrum spectrum synthesis code to derive abundances of heavy elements in CS 31082-001, and using updated oscillator strengths from the recent literature. Synthetic spectra were computed for all lines of the elements of interest to check for proper line intensities and possible blends in these crowded spectra. Our new abundances were combined with the best previous results to provide reliable mean abundances for the first and second-peak r-process elements. Results: We present new abundances for 23 neutron-capture elements, 6 of which - Ge, Mo, Lu, Ta, W, and Re - have not been reported before. This makes CS 31082-001 the most completely studied r-II star, with abundances for a total of 37 neutron-capture elements. We also present the first NLTE+3D abundance of lead in this star, further constraining the nature of the r-process. Based on observations made with the NASA/ESA Hubble Space Telescope (HST) through the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555; and

  17. Behavior of [S/Fe] in Very Metal-Poor Stars from the S I 1.046 µm Lines Revisited

    Science.gov (United States)

    Takeda, Yoichi; Takada-Hidai, Masahide

    2012-04-01

    With an aim to establish how the [S/Fe] ratios behave in the very low metallicity regime down to [Fe/H] ˜ -3, we conducted a non-LTE analysis of near-IR S I triplet lines (multiplet 3) at 10455-10459 Å for a dozen very metal-poor stars (-3.2 ≲ [Fe/H] ≲ -1.9) based on new observational data obtained with IRCS+AO188 of the Subaru Telescope. It turned out that the resulting [S/ Fe] values are only moderately supersolar at [S/Fe] ˜ +0.2-0.5, irrespective of the metallicity. While this ``flat'' tendency is consistent with a trend recently corroborated by Spite et al. (2011, A&A, 528, A9) based on the S I 9212/9228/9237 lines (multiplet 1), it disaffirms the possibility of a conspicuously large [S/Fe] (up to ˜ +0.8) at [Fe/H] ˜ -3 that we once suggested in our first report on the S abundances of disk/halo stars using S I 10455-10459 lines (Takeda & Takada-Hidai 2011, PASJ, 63, S537). Given these new observational facts, we withdraw our previous argument, since we consider that [S/Fe]'s of some most metal-poor objects were overestimated in that paper; the likely cause for this failure is also discussed.

  18. Improved Co I log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    Science.gov (United States)

    Lawler, J. E.; Sneden, C.; Cowan, J. J.

    2015-09-01

    New emission branching fraction measurements for 898 lines of the first spectrum of cobalt (Co i) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer on Kitt Peak, AZ and a high-resolution echelle spectrometer. Published radiative lifetimes from laser induced fluorescence measurements are combined with the branching fractions to determine accurate absolute atomic transition probabilities for the 898 lines. Hyperfine structure (hfs) constants for levels of neutral Co in the literature are surveyed and selected values are used to generate complete hfs component patterns for 195 transitions of Co i. These new laboratory data are applied to determine the Co abundance in the Sun and metal-poor star HD 84937, yielding log ɛ(Co) = 4.955 ± 0.007 (σ = 0.059) based on 82 Co i lines and log ɛ(Co) = 2.785 ± 0.008 (σ = 0.065) based on 66 Co i lines, respectively. A Saha or ionization balance test on the photosphere of HD 84937 is performed using 16 UV lines of Co ii, and good agreement is found with the Co i result in this metal-poor ([Fe i/H] = -2.32, [Fe ii/H] = -2.32) dwarf star. The resulting value of [Co/Fe] = +0.14 supports a rise of Co/Fe at low metallicity that has been suggested in other studies.

  19. First stars IX -Mixing in extremely metal-poor giants. Variation of the 12C/13C, [Na/Mg] and [Al/Mg] ratios

    CERN Document Server

    Spite, M; Hill, V; Spite, F; François, P; Plez, B; Bonifacio, P; Molaro, P; Depagne, E; Andersen, J; Barbuy, B; Beers, T C; Nordström, B; Primas, F

    2006-01-01

    Extremely metal-poor (EMP) stars preserve a fossil record of the composition of the ISM when the Galaxy formed. It is crucial, however, to verify whether internal mixing has modified their surface. We aim to understand the CNO abundance variations found in some, but not all EMP field giants analysed earlier. Mixing beyond the first dredge-up of standard models is required, and its origin needs clarification.The 12C/13C ratio is the most robust diagnostic of deep mixing, because it is insensitive to the adopted stellar parameters and should be uniformly high in near-primordial gas. We have measured 12C and 13C abundances in 35 EMP giants from high-quality VLT/UVES spectra. Correlations with other abundance data are used to study the depth of mixing.The 12C/13C ratio is found to correlate with [C/Fe] (and Li/H), and clearly anti-correlate with [N/Fe]. Evidence for such deep mixing is observed in giants above log L/Lsolar = 2.6, brighter than in less metal-poor stars, but matching the bump in the luminosity func...

  20. Improved Ti II log(gf) Values and Abundance Determinations in the Photospheres of the Metal-Poor Star HD 84937

    CERN Document Server

    Wood, M P; Sneden, C; Cowan, J J

    2013-01-01

    Atomic transition probability measurements for 364 lines of Ti II in the UV through near IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrometer are combined with published radiative lifetimes to determine these transition probabilities. The new results are in generally good agreement with previously reported FTS measurements. Use of the new echelle spectrometer, independent radiometric calibration methods, and independent data analysis routines enables a reduction of systematic errors and overall improvement in transition probability accuracy over previous measurements. The new Ti II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ti abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. The Ti abundances derived using Ti II for these two stars match those derived using Ti I and support the relative Ti/...

  1. On the necessity of composition-dependent low-temperature opacity in metal-poor AGB stars

    CERN Document Server

    Constantino, Thomas; Gil-Pons, Pilar; Lattanzio, John

    2014-01-01

    The vital importance of composition-dependent low-temperature opacity in low-mass (M 0.001 has recently been demonstrated (e.g. Marigo 2002; Ventura & Marigo 2010). Its significance to more metal-poor, intermediate mass (M > 2.5Msun) models has yet to be investigated. We show that its inclusion in lower-metallicity models ([Fe/H] < -2) is essential, and that there exists no threshold metallicity below which composition-dependent molecular opacity may be neglected. We find it to be crucial in all intermediate-mass models investigated ([Fe/H] < -2 and 2.5 < M/Msun < 5), because of the evolution of the surface chemistry, including the orders of magnitude increase in the abundance of molecule-forming species. Its effect on these models mirrors that previously reported for higher-metallicity models - increase in radius, decrease in Teff, faster mass loss, shorter thermally pulsing AGB lifetime, reduced enrichment in third dredge-up products (by a factor of three to ten), and an increase in the mas...

  2. Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. IV. Oxygen diagnostics in extremely metal-poor red giants with infrared OH lines

    CERN Document Server

    Dobrovolskas, V; Bonifacio, P; Caffau, E; Ludwig, H -G; Steffen, M; Spite, M

    2015-01-01

    Context. Although oxygen is an important tracer of Galactic chemical evolution, measurements of its abundance in the atmospheres of the oldest Galactic stars are still scarce and rather imprecise. At the lowest end of the metallicity scale, oxygen can only be measured in giant stars and in most of cases such measurements rely on a single forbidden [O I] 630 nm line that is very weak and frequently blended with telluric lines. Although molecular OH lines located in the ultraviolet and infrared could also be used for the diagnostics, oxygen abundances obtained from the OH lines and the [O I] 630 nm line are usually discrepant to a level of ~0.3-0.4 dex. Aims. We study the influence of convection on the formation of the infrared (IR) OH lines and the forbidden [O I] 630 nm line in the atmospheres of extremely metal-poor (EMP) red giant stars. Methods. We used high-resolution and high signal-to-noise ratio spectra of four EMP red giant stars obtained with the VLT CRIRES spectrograph. For each EMP star, 4-14 IR OH...

  3. High resolution study of the abundance pattern of the heavy elements in very metal-poor field stars

    CERN Document Server

    Spite, Monique

    2013-01-01

    The abundances of heavy elements in EMP stars are not well explained by the simple view of an initial basic "rapid" process. In a careful and homogeneous analysis of the "First stars" sample (eighty per cent of the stars have a metallicity [Fe/H]=-3.1$\\pm$0.4), it has been shown that at this metallicity [Eu/Ba] is constant, and therefore the Eu-rich stars (generally called "r-rich") are also Ba-rich. The very large variation of [Ba/Fe] (existence of "r-poor" and "r-rich" stars) induces that the early matter was not perfectly mixed. On the other hand, the distribution of the values of [Sr/Ba] vs. [Ba/Fe] appears with well defined upper and lower envelopes. No star was found with [Sr/Ba]<-0.5 and the scatter of [Sr/Ba] increases regularly when [Ba/Fe] decreases. To explain this behavior, we suggest that an early "additional" process forming mainly first peak elements would affect the initial composition of the matter. For a same quantity of accreted matter, this additional Sr production would barely affect t...

  4. The Diverse Origins of Neutron-capture Elements in the Metal-poor Star HD 94028: Possible Detection of Products of i-Process Nucleosynthesis

    Science.gov (United States)

    Roederer, Ian U.; Karakas, Amanda I.; Pignatari, Marco; Herwig, Falk

    2016-04-01

    We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metal-poor ([Fe/H] = ‑1.62 ± 0.09) star HD 94028. Previous studies revealed that this star is mildly enhanced in elements produced by the slow neutron-capture process (s process; e.g., [Pb/Fe] = +0.79 ± 0.32) and rapid neutron-capture process (r process; e.g., [Eu/Fe] = +0.22 ± 0.12), including unusually large molybdenum ([Mo/Fe] = +0.97 ± 0.16) and ruthenium ([Ru/Fe] = +0.69 ± 0.17) enhancements. However, this star is not enhanced in carbon ([C/Fe] = ‑0.06 ± 0.19). We analyze an archival near-ultraviolet spectrum of HD 94028, collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, and other archival optical spectra collected from ground-based telescopes. We report abundances or upper limits derived from 64 species of 56 elements. We compare these observations with s-process yields from low-metallicity AGB evolution and nucleosynthesis models. No combination of s- and r-process patterns can adequately reproduce the observed abundances, including the super-solar [As/Ge] ratio (+0.99 ± 0.23) and the enhanced [Mo/Fe] and [Ru/Fe] ratios. We can fit these features when including an additional contribution from the intermediate neutron-capture process (i process), which perhaps operated through the ingestion of H in He-burning convective regions in massive stars, super-AGB stars, or low-mass AGB stars. Currently, only the i process appears capable of consistently producing the super-solar [As/Ge] ratios and ratios among neighboring heavy elements found in HD 94028. Other metal-poor stars also show enhanced [As/Ge] ratios, hinting that operation of the i process may have been common in the early Galaxy. These data are associated with Program 072.B-0585(A), PI. Silva. Some data presented in this paper were obtained from the Barbara A. Mikulski Archive for Space Telescopes (MAST). The Space Telescope Science Institute

  5. The Diverse Origins of Neutron-capture Elements in the Metal-poor Star HD 94028: Possible Detection of Products of i-Process Nucleosynthesis

    Science.gov (United States)

    Roederer, Ian U.; Karakas, Amanda I.; Pignatari, Marco; Herwig, Falk

    2016-04-01

    We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metal-poor ([Fe/H] = -1.62 ± 0.09) star HD 94028. Previous studies revealed that this star is mildly enhanced in elements produced by the slow neutron-capture process (s process; e.g., [Pb/Fe] = +0.79 ± 0.32) and rapid neutron-capture process (r process; e.g., [Eu/Fe] = +0.22 ± 0.12), including unusually large molybdenum ([Mo/Fe] = +0.97 ± 0.16) and ruthenium ([Ru/Fe] = +0.69 ± 0.17) enhancements. However, this star is not enhanced in carbon ([C/Fe] = -0.06 ± 0.19). We analyze an archival near-ultraviolet spectrum of HD 94028, collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, and other archival optical spectra collected from ground-based telescopes. We report abundances or upper limits derived from 64 species of 56 elements. We compare these observations with s-process yields from low-metallicity AGB evolution and nucleosynthesis models. No combination of s- and r-process patterns can adequately reproduce the observed abundances, including the super-solar [As/Ge] ratio (+0.99 ± 0.23) and the enhanced [Mo/Fe] and [Ru/Fe] ratios. We can fit these features when including an additional contribution from the intermediate neutron-capture process (i process), which perhaps operated through the ingestion of H in He-burning convective regions in massive stars, super-AGB stars, or low-mass AGB stars. Currently, only the i process appears capable of consistently producing the super-solar [As/Ge] ratios and ratios among neighboring heavy elements found in HD 94028. Other metal-poor stars also show enhanced [As/Ge] ratios, hinting that operation of the i process may have been common in the early Galaxy. These data are associated with Program 072.B-0585(A), PI. Silva. Some data presented in this paper were obtained from the Barbara A. Mikulski Archive for Space Telescopes (MAST). The Space Telescope Science Institute is

  6. KELT-6b: A P ~ 7.9 Day Hot Saturn Transiting a Metal-poor Star with a Long-period Companion

    Science.gov (United States)

    Collins, Karen A.; Eastman, Jason D.; Beatty, Thomas G.; Siverd, Robert J.; Gaudi, B. Scott; Pepper, Joshua; Kielkopf, John F.; Johnson, John Asher; Howard, Andrew W.; Fischer, Debra A.; Manner, Mark; Bieryla, Allyson; Latham, David W.; Fulton, Benjamin J.; Gregorio, Joao; Buchhave, Lars A.; Jensen, Eric L. N.; Stassun, Keivan G.; Penev, Kaloyan; Crepp, Justin R.; Hinkley, Sasha; Street, Rachel A.; Cargile, Phillip; Mack, Claude E.; Oberst, Thomas E.; Avril, Ryan L.; Mellon, Samuel N.; McLeod, Kim K.; Penny, Matthew T.; Stefanik, Robert P.; Berlind, Perry; Calkins, Michael L.; Mao, Qingqing; Richert, Alexander J. W.; DePoy, Darren L.; Esquerdo, Gilbert A.; Gould, Andrew; Marshall, Jennifer L.; Oelkers, Ryan J.; Pogge, Richard W.; Trueblood, Mark; Trueblood, Patricia

    2014-02-01

    We report the discovery of KELT-6b, a mildly inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was established using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V = 10.38 host star (BD+31 2447) is a mildly evolved, late-F star with T eff = 6102 ± 43 K, log g_\\star =4.07_{-0.07}^{+0.04}, and [Fe/H] = -0.28 ± 0.04, with an inferred mass M sstarf = 1.09 ± 0.04 M ⊙ and radius R_\\star =1.58_{-0.09}^{+0.16} \\,R_\\odot. The planetary companion has mass MP = 0.43 ± 0.05 M Jup, radius R_{P}=1.19_{-0.08}^{+0.13} \\,R_Jup, surface gravity log g_{P}=2.86_{-0.08}^{+0.06}, and density \\rho _{P}=0.31_{-0.08}^{+0.07}\\,g\\,cm^{-3}. The planet is on an orbit with semimajor axis a = 0.079 ± 0.001 AU and eccentricity e=0.22_{-0.10}^{+0.12}, which is roughly consistent with circular, and has ephemeris of T c(BJDTDB) = 2456347.79679 ± 0.00036 and P = 7.845631 ± 0.000046 days. Equally plausible fits that employ empirical constraints on the host-star parameters rather than isochrones yield a larger planet mass and radius by ~4}-7}. KELT-6b has surface gravity and incident flux similar to HD 209458b, but orbits a host that is more metal poor than HD 209458 by ~0.3 dex. Thus, the KELT-6 system offers an opportunity to perform a comparative measurement of two similar planets in similar environments around stars of very different metallicities. The precise radial velocity data also reveal an acceleration indicative of a longer-period third body in the system, although the companion is not detected in Keck adaptive optics images. KELT is a joint project of The Ohio State University, Vanderbilt University, and Lehigh University.

  7. Investigation for the puzzling abundance pattern of the neutron-capture elements in the ultra metal-poor star: CS 30322-023

    CERN Document Server

    Cui, W Y; Ma, K; Zhang, L

    2007-01-01

    The s-enhanced and very metal-poor star CS 30322-023 shows a puzzling abundance pattern of the neutron-capture elements, i.e. several neutron-capture elements such as Ba, Pb etc. show enhancement, but other neutron-capture elements such as Sr, Eu etc. exhibit deficient with respect to iron. The study to this sample star could make people gain a better understanding of s- and r-process nucleosynthesis at low metallicity. Using a parametric model, we find that the abundance pattern of the neutron-capture elements could be best explained by a star that was polluted by an AGB star and the CS 30322-023 binary system formed in a molecular cloud which had never been polluted by r-process material. The lack of r-process material also indicates that the AGB companion cannot have undergone a type-1.5 supernova, and thus must have had an initial mass below 4.0M$_\\odot$, while the strong N overabundance and the absence of a strong C overabundance indicate that the companion's initial mass was larger than 2.0M$_\\odot$. Th...

  8. The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars

    CERN Document Server

    Hansen, T T; Nordstrøm, B; Beers, T C; Yoon, J; Buchhave, L A

    2015-01-01

    The detailed chemical composition of most metal-poor halo stars has been found to be highly uniform, but a minority of stars exhibit dramatic enhancements in their abundances of heavy neutron-capture elements and/or of carbon. The key question for Galactic chemical evolution models is whether these peculiarities reflect the composition of the natal clouds, or if they are due to later mass transfer of processed material from a binary companion. If the former case applies, the observed excess of certain elements was implanted within selected clouds in the early ISM from a production site at interstellar distances. Our aim is to determine the frequency and orbital properties of binaries among these chemically peculiar stars. This information provides the basis for deciding whether mass transfer from a binary companion is necessary and sufficient to explain their unusual compositions. This paper discusses our study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element enhanced VMP and EMP stars. ...

  9. Exploring the \\alpha-enhancement of metal-poor planet-hosting stars. The Kepler + HARPS samples

    CERN Document Server

    Adibekyan, V Zh; Sousa, S G; Santos, N C; Israelian, G; Hernandez, J I Gonzalez; Mayor, M; Hakobyan, A A

    2012-01-01

    Recent studies showed that at low metallicities Doppler-detected planet-hosting stars have preferably high \\alpha-content and belong to the thick disk. We used the reconnaissance spectra of 87 Kepler planet candidates and data available from the HARPS planet search survey to explore this phenomena. Using the traditional spectroscopic abundance analysis methods we derived Ti, Ca, and Cr abundances for the Kepler stars. In the metallicity region -0.65 < [Fe/H] < -0.3 dex the fraction of Ti-enhanced thick-disk HARPS planet harboring stars is 12.3 +/- 4.1 % and for their thin-disk counterparts this fraction is 2.2 +/- 1.3 %. The binomial statistics gives a probability of 0.008 that this could have occurred by chance. Combining the two samples (HARPS + Kepler) reinforces the significance of this result (P ~ 99.97 %). Since most of these stars are harboring small-mass/size planets we can assume that, although terrestrial planets can be found at low-iron regime, they are mostly enhanced by \\alpha-elements. Thi...

  10. Improved V II log($gf$) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    CERN Document Server

    Wood, M P; Hartog, E A Den; Sneden, C; Cowan, J J

    2014-01-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Use of two spectrometers, independent radiometric calibration methods, and independent data analysis routines enables a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used t...

  11. IMPROVED Ni I log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    Energy Technology Data Exchange (ETDEWEB)

    Wood, M. P.; Lawler, J. E. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Sneden, C. [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Cowan, J. J., E-mail: mpwood@wisc.edu, E-mail: jelawler@wisc.edu, E-mail: chris@verdi.as.utexas.edu, E-mail: cowan@nhn.ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)

    2014-04-01

    Atomic transition probability measurements for 371 Ni I lines in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrograph are combined with published radiative lifetimes to determine these transition probabilities. Generally good agreement is found in comparisons to previously reported Ni I transition probability measurements. Use of the new echelle spectrograph, independent radiometric calibration methods, and independent data analysis routines enable a reduction of systematic errors and overall improvement in transition probability uncertainty over previous measurements. The new Ni I data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ni abundances. Lines covering a wide range of wavelength and excitation potential are used to search for non-LTE effects.

  12. Improved Ni I log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    CERN Document Server

    Wood, M P; Sneden, C; Cowan, J J

    2014-01-01

    Atomic transition probability measurements for 371 Ni I lines in the UV through near IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrograph are combined with published radiative lifetimes to determine these transition probabilities. Generally good agreement is found in comparisons to previously reported Ni I transition probability measurements. Use of the new echelle spectrograph, independent radiometric calibration methods, and independent data analysis routines enable a reduction of systematic errors and overall improvement in transition probability uncertainty over previous measurements. The new Ni I data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ni abundances. Lines covering a wide range of wavelength and excitation potential are used to search for non-LTE effects.

  13. Atomic diffusion in metal poor stars The influence on the Main Sequence fitting distance scale, subdwarfs ages and the value of Delta Y/DeltaZ

    CERN Document Server

    Salaris, M; Weiss, A

    2000-01-01

    The effect of atomic diffusion on the Main Sequence (MS) of metal-poor low mass stars is investigated. Since diffusion alters the stellar surface chemical abundances with respect to their initial values, one must ensure - by calibrating the initial chemical composition of the theoretical models - that the surface abundances of the models match the observed ones of the stellar population under scrutiny. Since the observed surface abundances of subdwarfs are different from the initial ones due to the effect of diffusion, while the globular clusters stellar abundances are measured in Red Giants, which have practically recovered their initial abundances after the dredge-up, the isochrones to be employed for studying globular clusters and Halo subdwarfs with the same observational value of [Fe/H] are different and do not coincide. We find, however,that the current MS-fitting distances derived from HIPPARCOS subdwarfs using colour corrections from standard isochrones are basically unaltered when diffusion is taken ...

  14. IMPROVED Ni I log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    International Nuclear Information System (INIS)

    Atomic transition probability measurements for 371 Ni I lines in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrograph are combined with published radiative lifetimes to determine these transition probabilities. Generally good agreement is found in comparisons to previously reported Ni I transition probability measurements. Use of the new echelle spectrograph, independent radiometric calibration methods, and independent data analysis routines enable a reduction of systematic errors and overall improvement in transition probability uncertainty over previous measurements. The new Ni I data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ni abundances. Lines covering a wide range of wavelength and excitation potential are used to search for non-LTE effects

  15. The role of non-gray model atmospheres in the evolution of low mass metal poor stars

    OpenAIRE

    Harris, G. J.; Lynas-Gray, A. E.; Tennyson, J.; Miller, S.

    2006-01-01

    Gray model atmospheres are generally considered a reasonable approximation to make upon stars of mass greater than about 0.6 M-circle dot. Here we show that non-gray atmospheres can significantly affect evolutionary models, with masses up to 0.9 M-circle dot. The effect of including a non-gray atmosphere is strongest in the pre-main and post-main Sequence. This may have implications for the ages of the oldest globular clusters.

  16. Scaling relations of metallicity, stellar mass, and star formation rate in metal-poor starbursts: I. A fundamental plane

    CERN Document Server

    Hunt, Leslie; Galli, Daniele; Schneider, Raffaella; Bianchi, Simone; Maiolino, Roberto; Romano, Donatella; Tosi, Monica; Valiante, Rosa

    2012-01-01

    Most galaxies follow well-defined scaling relations of metallicity (O/H), star formation rate (SFR), and stellar mass. However, low-metallicity starbursts, rare in the Local Universe but more common at high redshift, deviate significantly from these scaling relations. On the "main sequence" of star formation, these galaxies have high SFR for a given M*; and on the mass-metallicity relation, they have excess M* for their low metallicity. In this paper, we characterize O/H, M*, and SFR for these deviant "low-metallicity starbursts", selected from a sample of ~1100 galaxies, spanning almost two orders of magnitude in metal abundance, a factor of ~10^6 in SFR, and of ~10^5 in stellar mass. Our sample includes quiescent star-forming galaxies and blue compact dwarfs at redshift 0, luminous compact galaxies at redshift 0.3, and Lyman Break galaxies at redshifts 1-3.4. Applying a Principal Component Analysis (PCA) to the galaxies in our sample with M*<10^{10} Msun gives a Fundamental Plane (FP) of scaling relation...

  17. The origins of light and heavy r-process elements identified by chemical tagging of metal-poor stars

    CERN Document Server

    Tsujimoto, Takuji

    2014-01-01

    Growing interests in neutron star (NS) mergers as the origin of r-process elements have sprouted since the discovery of evidence for the ejection of these elements from a short-duration gamma-ray burst. The hypothesis of a NS merger origin is reinforced by a theoretical update of nucleosynthesis in NS mergers successful in yielding r-process nuclides with A>130. On the other hand, whether the origin of light r-process elements are associated with nucleosynthesis in NS merger events remains unclear. We find a signature of nucleosynthesis in NS mergers from peculiar chemical abundances of stars belonging to the Galactic globular cluster M15. This finding combined with the recent nucleosynthesis results implies a potential diversity of nucleosynthesis in NS mergers. Based on these considerations, we are successful in the interpretation of an observed correlation between [light r-process/Eu] and [Eu/Fe] among Galactic halo stars and accordingly narrow down the role of supernova nucleosynthesis in the r-process pr...

  18. Low Energy Population III Supernovae and the Origin of the Extremely Metal-Poor Star SMSS J031300.36-670839.3

    CERN Document Server

    Chen, Ke-Jung; Whalen, Daniel J; Moriya, Takashi J; Bromm, Volker; Woosley, Stan; Almgren, Ann

    2016-01-01

    Ancient, dim metal-poor stars may have formed in the ashes of the first supernovae. If their chemical abundances can be reconciled with the nucleosynthetic yields of specific Pop III explosions, they could reveal the properties of primordial stars. But simulations of such explosions must be multidimensional because dynamical instabilities can dredge material up from deep in the ejecta that would be predicted to fall back onto the compact remnant and be lost in one-dimensional models. We have performed two-dimensional numerical simulations of two low-energy Pop III supernovae, a 12.4 Msun explosion and a 60 Msun explosion, and find that they have elemental yields that are a good fit to those measured in the most iron-poor star discovered to date, SMSS J031300.36-670839.3 (J031300). Fallback onto the compact remnant in these weak explosions accounts for the lack of measurable iron in J031300 and its low iron-group abundances in general. The low energies of these dim events will prevent their detection in the ne...

  19. The Diverse Origins of Neutron-Capture Elements in the Metal-Poor Star HD 94028: Possible Detection of Products of i-process Nucleosynthesis

    CERN Document Server

    Roederer, Ian U; Pignatari, Marco; Herwig, Falk

    2016-01-01

    We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metal-poor ([Fe/H]=-1.62+/-0.09) star HD94028. Previous studies revealed that this star is mildly enhanced in elements produced by the slow neutron-capture process (s-process; e.g., [Pb/Fe]=+0.79+/-0.32) and rapid neutron-capture process (r-process; e.g., [Eu/Fe]=+0.22+/-0.12), including unusually large molybdenum ([Mo/Fe]=+0.97+/-0.16) and ruthenium ([Ru/Fe]=+0.69+/-0.17) enhancements. However, this star is not enhanced in carbon ([C/Fe]=-0.06+/-0.19). We analyze an archival near-ultraviolet spectrum of HD94028, collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, and other archival optical spectra collected from ground-based telescopes. We report abundances or upper limits derived from 64 species of 56 elements. We compare these observations with s-process yields from low-metallicity AGB evolution and nucleosynthesis models. No combination of s- and r-process pa...

  20. Scaling relations of metallicity, stellar mass, and star formation rate in metal-poor starbursts: II. Theoretical models

    CERN Document Server

    Magrini, Laura; Galli, Daniele; Schneider, Raffaella; Bianchi, Simone; Maiolino, Roberto; Romano, Donatella; Tosi, Monica; Valiante, Rosa

    2012-01-01

    Scaling relations of metallicity (O/H), star formation rate (SFR), and stellar mass give important insight on galaxy evolution. They are obeyed by most galaxies in the Local Universe and also at high redshift. In a companion paper, we compiled a sample of ~1100 galaxies from redshift 0 to ~3, spanning almost two orders of magnitude in metal abundance, a factor of $\\sim10^6$ in SFR, and of ~10^5 in stellar mass. We have characterized empirically the star-formation "main sequence" (SFMS) and the mass-metallicity relation (MZR) for this sample, and also identified a class of low-metallicity starbursts, rare locally but more common in the distant universe. These galaxies deviate significantly from the main scaling relations, with high SFR and low metal content for a given M*. In this paper, we model the scaling relations and explain these deviations from them with a set of multi-phase chemical evolution models based on the idea that, independently of redshift, initial physical conditions in a galaxy's evolutionar...

  1. KELT-6b: A P ∼ 7.9 day hot Saturn transiting a metal-poor star with a long-period companion

    International Nuclear Information System (INIS)

    We report the discovery of KELT-6b, a mildly inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was established using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V = 10.38 host star (BD+31 2447) is a mildly evolved, late-F star with T eff = 6102 ± 43 K, log g⋆=4.07−0.07+0.04, and [Fe/H] = –0.28 ± 0.04, with an inferred mass M * = 1.09 ± 0.04 M ☉ and radius R⋆=1.58−0.09+0.16 R⊙. The planetary companion has mass MP = 0.43 ± 0.05 M Jup, radius RP=1.19−0.08+0.13 RJup, surface gravity log gP=2.86−0.08+0.06, and density ρP=0.31−0.08+0.07 g cm−3. The planet is on an orbit with semimajor axis a = 0.079 ± 0.001 AU and eccentricity e=0.22−0.10+0.12, which is roughly consistent with circular, and has ephemeris of T c(BJDTDB) = 2456347.79679 ± 0.00036 and P = 7.845631 ± 0.000046 days. Equally plausible fits that employ empirical constraints on the host-star parameters rather than isochrones yield a larger planet mass and radius by ∼4)-7). KELT-6b has surface gravity and incident flux similar to HD 209458b, but orbits a host that is more metal poor than HD 209458 by ∼0.3 dex. Thus, the KELT-6 system offers an opportunity to perform a comparative measurement of two similar planets in similar environments around stars of very different metallicities. The precise radial velocity data also reveal an acceleration indicative of a longer-period third body in the system, although the companion is not detected in Keck adaptive optics images.

  2. KELT-6b: A P ∼ 7.9 day hot Saturn transiting a metal-poor star with a long-period companion

    Energy Technology Data Exchange (ETDEWEB)

    Collins, Karen A.; Kielkopf, John F. [Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292 (United States); Eastman, Jason D. [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Santa Barbara, CA 93117 (United States); Beatty, Thomas G.; Gaudi, B. Scott [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Siverd, Robert J.; Pepper, Joshua; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Johnson, John Asher [Department of Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Howard, Andrew W.; Fulton, Benjamin J. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Fischer, Debra A. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Manner, Mark [Spot Observatory, Nunnelly, TN 37137 (United States); Bieryla, Allyson; Latham, David W. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gregorio, Joao [Atalaia Group and Crow-Observatory, Portalegre (Portugal); Buchhave, Lars A. [Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, DK-21S00 Copenhagen (Denmark); Jensen, Eric L. N. [Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA 19081 (United States); Penev, Kaloyan [Princeton University, Princeton, NJ 08544 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); and others

    2014-02-01

    We report the discovery of KELT-6b, a mildly inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was established using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V = 10.38 host star (BD+31 2447) is a mildly evolved, late-F star with T {sub eff} = 6102 ± 43 K, log g{sub ⋆}=4.07{sub −0.07}{sup +0.04}, and [Fe/H] = –0.28 ± 0.04, with an inferred mass M {sub *} = 1.09 ± 0.04 M {sub ☉} and radius R{sub ⋆}=1.58{sub −0.09}{sup +0.16} R{sub ⊙}. The planetary companion has mass M{sub P} = 0.43 ± 0.05 M {sub Jup}, radius R{sub P}=1.19{sub −0.08}{sup +0.13} R{sub Jup}, surface gravity log g{sub P}=2.86{sub −0.08}{sup +0.06}, and density ρ{sub P}=0.31{sub −0.08}{sup +0.07} g cm{sup −3}. The planet is on an orbit with semimajor axis a = 0.079 ± 0.001 AU and eccentricity e=0.22{sub −0.10}{sup +0.12}, which is roughly consistent with circular, and has ephemeris of T {sub c}(BJD{sub TDB}) = 2456347.79679 ± 0.00036 and P = 7.845631 ± 0.000046 days. Equally plausible fits that employ empirical constraints on the host-star parameters rather than isochrones yield a larger planet mass and radius by ∼4)-7). KELT-6b has surface gravity and incident flux similar to HD 209458b, but orbits a host that is more metal poor than HD 209458 by ∼0.3 dex. Thus, the KELT-6 system offers an opportunity to perform a comparative measurement of two similar planets in similar environments around stars of very different metallicities. The precise radial velocity data also reveal an acceleration indicative of a longer-period third body in the system, although the companion is not detected in Keck adaptive optics images.

  3. On the necessity of composition-dependent low-temperature opacity in models of metal-poor asymptotic giant branch stars

    International Nuclear Information System (INIS)

    The vital importance of composition-dependent low-temperature opacity in low-mass (M ≤ 3 M ☉) asymptotic giant branch (AGB) stellar models of metallicity Z ≥ 0.001 has recently been demonstrated. Its significance to more metal-poor, intermediate-mass (M ≥ 2.5 M ☉) models has yet to be investigated. We show that its inclusion in lower-metallicity models ([Fe/H] ≤–2) is essential and that there exists no threshold metallicity below which composition-dependent molecular opacity may be neglected. We find it to be crucial in all intermediate-mass models investigated ([Fe/H] ≤–2 and 2.5 ≤ M/M ☉ ≤ 5), because of the evolution of the surface chemistry, including the orders of magnitude increase in the abundance of molecule-forming species. Its effect on these models mirrors that previously reported for higher-metallicity models—increase in radius, decrease in T eff, faster mass loss, shorter thermally pulsing AGB lifetime, reduced enrichment in third dredge-up products (by a factor of 3-10), and an increase in the mass limit for hot bottom burning. We show that the evolution of low-metallicity models with composition-dependent low-temperature opacity is relatively independent of initial metal abundance because its contribution to the opacity is far outweighed by changes resulting from dredge-up. Our results imply a significant reduction in the expected number of nitrogen-enhanced metal-poor stars, which may help explain their observed paucity. We note that these findings are partially a product of the macrophysics adopted in our models, in particular, the Vassiliadis and Wood mass loss rate which is strongly dependent on radius.

  4. Evolution and nucleosynthesis of extremely metal-poor and metal-free low- and intermediate-mass stars II. s-process nucleosynthesis during the core He flash

    CERN Document Server

    Campbell, Simon W; Karakas, Amanda I

    2010-01-01

    Models of primordial and hyper-metal-poor stars with masses similar to the Sun experience an ingestion of protons into the hot core during the core helium flash phase at the end of their red giant branch evolution. This produces a concurrent secondary flash powered by hydrogen burning that gives rise to further nucleosynthesis in the core. We perform post-process nucleosynthesis calculations on a one-dimensional stellar evolution calculation of a star of 1 solar mass and metallicity [Fe/H] = -6.5 that suffers a proton ingestion episode. Our network includes 320 nuclear species and 2,366 reactions and treats mixing and burning simultaneously. The mixing and burning of protons into the hot convective core leads to the production of 13C, which then burns via the 13C(alpha,n)16O reaction releasing a large number of free neutrons. During the first two years of neutron production the neutron poison 14N abundance is low, allowing the prodigious production of heavy elements such as strontium, barium, and lead via slo...

  5. Behavior of [S/Fe] in Very Metal-Poor Stars from the S I 1.046 micron Lines Revisited

    CERN Document Server

    Takeda, Yoichi

    2011-01-01

    With an aim of establishing how the [S/Fe] ratios behave at the very low metallicity regime down to [Fe/H] ~ -3, we conducted a non-LTE analysis of near-IR S ~ {\\sc i} triplet lines (multiplet 3) at 10455-10459 A for a dozen of very metal-poor stars (-3.2 <[Fe/H] < -1.9) based on the new observational data obtained with IRCS+AO188 of the Subaru Telescope. It turned out that the resulting [S/Fe] values are only moderately supersolar at [S/Fe] ~ +0.2-0.5 irrespective of the metallicity. While this "flat" tendency is consistent with the trend recently corroborated by Spite et al. (2011, A&A, 528, A9) based on the S I 9212/9228/9237 lines (multiplet 1), it disaffirms the possibility of conspicuously large [S/Fe] (up to ~+0.8) at [Fe/H] ~ -3 that we once suggested in our first report on the S abundances of disk/halo stars using S I 10455-10459 lines (Takeda & Takada-Hidai 2011, PASJ, 63, S537). Given these new observational facts, we withdraw our previous argument, since we consider that [S/Fe]'s of ...

  6. KELT-6b: A P~7.9 d Hot Saturn Transiting a Metal-Poor Star with a Long-Period Companion

    CERN Document Server

    Collins, Karen A; Beatty, Thomas G; Siverd, Robert J; Gaudi, B Scott; Pepper, Joshua; Kielkopf, John F; Johnson, John Asher; Howard, Andrew W; Fischer, Debra A; Manner, Mark; Bieryla, Allyson; Latham, David W; Fulton, Benjamin J; Gregorio, Joao; Buchhave, Lars A; Jensen, Eric L N; Stassun, Keivan G; Penev, Kaloyan; Crepp, Justin R; Hinkley, Sasha; Street, Rachel A; Cargile, Phillip; Mack, Claude E; Oberst, Thomas E; Avril, Ryan L; Mellon, Samuel N; McLeod, Kim K; Penny, Matthew T; Stefanik, Robert P; Berlind, Perry; Calkins, Michael L; Mao, Qingqing; Richert, Alexander J W; DePoy, Darren L; Esquerdo, Gilbert A; Gould, Andrew; Marshall, Jennifer L; Oelkers, Ryan J; Pogge, Richard W; Trueblood, Mark; Trueblood, Patricia

    2013-01-01

    We report the discovery of KELT-6b, a mildly-inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was confirmed using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V=10.38 host star (TYC 2532-556-1) is a mildly evolved, late-F star with T_eff=6102 \\pm 43 K, log(g_*)=4.07_{-0.07}^{+0.04} and [Fe/H]=-0.28 \\pm 0.04, with an inferred mass M_*=1.09 \\pm 0.04 M_sun and radius R_*=1.58_{-0.09}^{+0.16} R_sun. The planetary companion has mass M_p=0.43 \\pm 0.05 M_Jup, radius R_p=1.19_{-0.08}^{+0.13} R_Jup, surface gravity log(g_p)=2.86_{-0.08}^{+0.06}, and density rho_p=0.31_{-0.08}^{+0.07} g cm^{-3}. The planet is on an orbit with semimajor axis a=0.079 \\pm 0.001 AU and eccentricity e=0.22_{-0.10}^{+0.12}, which is rough...

  7. Improved Laboratory Transition Probabilities for Er II and Applications to the Erbium Abundances of the Sun and Five r-Process Rich, Metal-Poor Stars

    CERN Document Server

    Lawler, J E; Cowan, J J; Wyart, J -F; Ivans, I I; Sobeck, J S; Stockett, M H; Hartog, E A Den

    2008-01-01

    Recent radiative lifetime measurements accurate to +/- 5% (Stockett et al. 2007, J. Phys. B 40, 4529) using laser-induced fluorescence (LIF) on 8 even-parity and 62 odd-parity levels of Er II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 418 lines of Er II. This work moves Er II onto the growing list of rare earth spectra with extensive and accurate modern transition probability measurements using LIF plus FTS data. This improved laboratory data set has been used to determine a new solar photospheric Er abundance, log epsilon = 0.96 +/- 0.03 (sigma = 0.06 from 8 lines), a value in excellent agreement with the recommended meteoric abundance, log epsilon = 0.95 +/- 0.03. Revised Er abundances have also been derived for the r-process-rich metal-poor giant stars CS 22892-052, BD+17 3248, HD 221170, HD 115444, and CS 31082-001. For these five stars the average Er/Eu abundance ratio, = 0.42, is in very good agreement ...

  8. IMPROVED Ti II log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    Energy Technology Data Exchange (ETDEWEB)

    Wood, M. P.; Lawler, J. E. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Sneden, C. [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Cowan, J. J., E-mail: mpwood@wisc.edu, E-mail: jelawler@wisc.edu, E-mail: chris@verdi.as.utexas.edu, E-mail: cowan@nhn.ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)

    2013-10-01

    Atomic transition probability measurements for 364 lines of Ti II in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer (FTS) and a new echelle spectrometer are combined with published radiative lifetimes to determine these transition probabilities. The new results are in generally good agreement with previously reported FTS measurements. Use of the new echelle spectrometer, independent radiometric calibration methods, and independent data analysis routines enables a reduction of systematic errors and overall improvement in transition probability accuracy over previous measurements. The new Ti II data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ti abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. The Ti abundances derived using Ti II for these two stars match those derived using Ti I and support the relative Ti/Fe abundance ratio versus metallicity seen in previous studies.

  9. The Abundance Evolution of Oxygen, Sodium and Magnesium in Extremely Metal-Poor Intermediate Mass Stars: Implications for the Self-Polution Scenario in Globular Clusters

    CERN Document Server

    Denissenkov, P A

    2003-01-01

    We present full stellar evolution and parametric models of the surface abundance evolution of O16, Ne22, Na23 and the magnesium isotopes in an extremely metal-poor intermediate mass star M_ZAMS=5M_sun, Z=0.0001. O16 and Ne22 are injected into the envelope by the third dredge-up following thermal pulses on the asymptotic giant branch. These species and the initially present Mg24 are depleted by hot bottom burning (HBB) during the interpulse phase. As a result, Na23, Mg25 and Mg26 are enhanced. If the HBB temperatures are sufficiently high for this process to deplete oxygen efficiently, Na23 is first produced and then depleted during the interpulse phase. Although the simultaneous depletion of O16 and enhancement of Na23 is possible, the required fine tuning of the dredge-up and HBB casts some doubt on the robustness of this process as the origin of the O-Na anti-correlation observed in globular cluster stars. However, a very robust prediction of our models are low Mg24/Mg25 and Mg24/Mg26 ratios whenever signif...

  10. IMPROVED Ti II log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    International Nuclear Information System (INIS)

    Atomic transition probability measurements for 364 lines of Ti II in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer (FTS) and a new echelle spectrometer are combined with published radiative lifetimes to determine these transition probabilities. The new results are in generally good agreement with previously reported FTS measurements. Use of the new echelle spectrometer, independent radiometric calibration methods, and independent data analysis routines enables a reduction of systematic errors and overall improvement in transition probability accuracy over previous measurements. The new Ti II data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ti abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. The Ti abundances derived using Ti II for these two stars match those derived using Ti I and support the relative Ti/Fe abundance ratio versus metallicity seen in previous studies

  11. The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars

    Science.gov (United States)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Yoon, J.; Buchhave, L. A.

    2015-11-01

    Context. The detailed chemical composition of most metal-poor halo stars has been found to be highly uniform, but a minority of stars exhibit dramatic enhancements in their abundances of heavy neutron-capture elements and/or of carbon. The key question for Galactic chemical evolution models is whether these peculiarities reflect the composition of the natal clouds, or if they are due to later (post-birth) mass transfer of chemically processed material from a binary companion. If the former case applies, the observed excess of certain elements was implanted within selected clouds in the early ISM from a production site at interstellar distances. Aims: Our aim is to determine the frequency and orbital properties of binaries among these chemically peculiar stars. This information provides the basis for deciding whether local mass transfer from a binary companion is necessary and sufficient to explain their unusual compositions. This paper discusses our study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element enhanced VMP and EMP stars. Methods: High-resolution, low signal-to-noise spectra of the stars were obtained at roughly monthly intervals over eight years with the FIES spectrograph at the Nordic Optical Telescope. From these spectra, radial velocities with an accuracy of ~100 m s-1 were determined by cross-correlation against an optimized template. Results: Fourteen of the programme stars exhibit no significant radial-velocity variation over this temporal window, while three are binaries with orbits of typical eccentricity for their periods, resulting in a normal binary frequency of ~18 ± 6% for the sample. Conclusions: Our results confirm our preliminary conclusion from 2011, based on partial data, that the chemical peculiarity of the r-I and r-II stars is not caused by any putative binary companions. Instead, it was imprinted on the natal molecular clouds of these stars by an external, distant source. Models of the ISM in early galaxies

  12. New high S/N observations of the (6Li) /(7) Li blend in HD 84937 and two other metal-poor stars

    Science.gov (United States)

    Cayrel, R.; Spite, M.; Spite, F.; Vangioni-Flam, E.; Cassé, M.; Audouze, J.

    1999-03-01

    High signal to noise ratio spectra have been obtained with the GECKO spectrograph at CFHT, at a spectral resolution of 100 000, for three metal-poor stars in order to obtain more accurate abundances of the very fragile element (6) Li. For two newly observed stars, BD +42 2667 and BD +36 2165 it appears that the first may have a detectable amount of (6) Li, whereas no (6) Li is found in the second one. The S/N ratio of only a few hundreds obtained for these two faint stars preclude however a firm conclusion. For the third star, the well known object HD84937, a very high S/N of 650 per pixel (over 1000 per resolved spectral element) was obtained, yielding greatly improved accuracy over previous determinations. A value of (6) Li / (7) Li = 0.052 +/- 0.019 (one sigma) is obtained. We also conclude that the no- (6) Li assumption is ruled out at the 95 per cent level, even in the most permissive case, when a variation of all the other free parameters (wavelength zero-point, continuum location, macroturbulent broadening, abundance of (7) Li) is allowed. The possibility that the (6) Li feature is an artifact due to a once suspected binarity of HD 84937 is discussed, with the conclusion that this assumption is ruled out by the extant data on the radial velocity of the object. The (6) Li abundance is compared with recent models of formation of the light elements Li, Be and B. This comparison shows that (6) Li is either undepleted, or only moderately depleted in HD 84937, from its initial value. Under the assumption that the atmospheric depletion of (6) Li and (7) Li in stars is by slow mixing with hot layers (underneath the convective zone), in which these elements can burn, we conclude that the depletion of (7) Li by this mechanism in HD 84937 is less than 0.1 dex. This new upper limit to the efficiency of the depletion of (7) Li by slow mixing burning, in a star located on the Spite plateau, leads to a more secure estimation of the primordial abundance of (7) Li. However

  13. IMPROVED V II log(gf) VALUES, HYPERFINE STRUCTURE CONSTANTS, AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    Energy Technology Data Exchange (ETDEWEB)

    Wood, M. P.; Lawler, J. E.; Den Hartog, E. A. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Sneden, C. [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Cowan, J. J., E-mail: mpwood@wisc.edu, E-mail: jelawler@wisc.edu, E-mail: eadenhar@wisc.edu, E-mail: chris@verdi.as.utexas.edu, E-mail: cowan@nhn.ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)

    2014-10-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ε(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = –2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.

  14. IMPROVED V I log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    Energy Technology Data Exchange (ETDEWEB)

    Lawler, J. E.; Wood, M. P.; Den Hartog, E. A.; Feigenson, T. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Sneden, C. [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Cowan, J. J., E-mail: jelawler@wisc.edu, E-mail: mpwood@wisc.edu, E-mail: eadenhar@wisc.edu, E-mail: tfeigenson@wisc.edu, E-mail: chris@verdi.as.utexas.edu, E-mail: cowan@nhn.ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)

    2015-01-01

    New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ε(V) = 3.956 ± 0.004 (σ = 0.037) based on 93 V I lines and log ε(V) = 1.89 ± 0.03 (σ = 0.07) based on nine V I lines, respectively, using the Holweger-Müller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.

  15. Improved V II Log(gf) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    Science.gov (United States)

    Wood, M. P.; Lawler, J. E.; Den Hartog, E. A.; Sneden, C.; Cowan, J. J.

    2014-10-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ɛ(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = -2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.

  16. IMPROVED V II log(gf) VALUES, HYPERFINE STRUCTURE CONSTANTS, AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    International Nuclear Information System (INIS)

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ε(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = –2.08 from 68 lines, leading to a value of [V/Fe] = 0.24

  17. Metal-Poor, Cool Gas in the Circumgalactic Medium of a z = 2.4 Star-Forming Galaxy: Direct Evidence for Cold Accretion?

    OpenAIRE

    Crighton, Neil H. M.; Hennawi, Joseph F.; Prochaska, J. Xavier

    2013-01-01

    In our current galaxy formation paradigm, high-redshift galaxies are predominantly fuelled by accretion of cool, metal-poor gas from the intergalactic medium. Hydrodynamical simulations predict that this material should be observable in absorption against background sightlines within a galaxy's virial radius, as optically thick Lyman-limit systems (LLSs) with low metallicities. Here we report the discovery of exactly such a strong metal-poor absorber at an impact parameter R_perp = 58 kpc fro...

  18. IMPROVED log(gf) VALUES FOR LINES OF Ti I AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937 (ACCURATE TRANSITION PROBABILITIES FOR Ti I)

    International Nuclear Information System (INIS)

    New atomic transition probability measurements for 948 lines of Ti I are reported. Branching fractions from Fourier transform spectra and from spectra recorded using a 3 m echelle spectrometer are combined with published radiative lifetimes from laser-induced fluorescence measurements to determine these transition probabilities. Generally good agreement is found in comparisons to the NIST Atomic Spectra Database. The new Ti I data are applied to re-determine the Ti abundance in the photospheres of the Sun and metal-poor star HD 84937 using many lines covering a range of wavelength and excitation potential to explore possible non-local thermal equilibrium effects. The variation of relative Ti/Fe abundance with metallicity in metal-poor stars observed in earlier studies is supported in this study.

  19. IMPROVED log(gf) VALUES FOR LINES OF Ti I AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937 (ACCURATE TRANSITION PROBABILITIES FOR Ti I)

    Energy Technology Data Exchange (ETDEWEB)

    Lawler, J. E.; Guzman, A.; Wood, M. P. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Sneden, C. [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Cowan, J. J., E-mail: jelawler@wisc.edu, E-mail: adrianaguzman2014@u.northwestern.edu, E-mail: mpwood@wisc.edu, E-mail: chris@verdi.as.utexas.edu, E-mail: cowan@nhn.ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)

    2013-04-01

    New atomic transition probability measurements for 948 lines of Ti I are reported. Branching fractions from Fourier transform spectra and from spectra recorded using a 3 m echelle spectrometer are combined with published radiative lifetimes from laser-induced fluorescence measurements to determine these transition probabilities. Generally good agreement is found in comparisons to the NIST Atomic Spectra Database. The new Ti I data are applied to re-determine the Ti abundance in the photospheres of the Sun and metal-poor star HD 84937 using many lines covering a range of wavelength and excitation potential to explore possible non-local thermal equilibrium effects. The variation of relative Ti/Fe abundance with metallicity in metal-poor stars observed in earlier studies is supported in this study.

  20. Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data

    CERN Document Server

    Lawler, J E; Cowan, J J; Ivans, I I; Hartog, E A Den

    2009-01-01

    Recent radiative lifetime measurements accurate to +/- 5% using laser-induced fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 921 lines of Ce II. This improved laboratory data set has been used to determine a new solar photospheric Ce abundance, log epsilon = 1.61 +/- 0.01 (sigma = 0.06 from 45 lines), a value in excellent agreement with the recommended meteoritic abundance, log epsilon = 1.61 +/- 0.02. Revised Ce abundances have also been derived for the r-process-rich metal-poor giant stars BD+17 3248, CS 22892-052, CS 31082-001, HD 115444 and HD 221170. Between 26 and 40 lines were used for determining the Ce abundance in these five stars, yielding a small statistical uncertainty of 0.01 dex similar to the Solar result. The relative abundances in the metal-poor stars of Ce and Eu, a nearly pure r-process element in the Sun, matches r-process ...

  1. The Hobby-Eberly Telescope Chemical Abundances of Stars in the Halo (CASH) Project. I. The Lithium-, s-, and r-enhanced Metal-poor Giant HKII 17435-00532

    Science.gov (United States)

    Roederer, Ian U.; Frebel, Anna; Shetrone, Matthew D.; Allende Prieto, Carlos; Rhee, Jaehyon; Gallino, Roberto; Bisterzo, Sara; Sneden, Christopher; Beers, Timothy C.; Cowan, John J.

    2008-06-01

    We present the first detailed abundance analysis of the metal-poor giant HKII 17435-00532. This star was observed as part of the University of Texas long-term project Chemical Abundances of Stars in the Halo (CASH). A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R ~ 15,000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H] = - 2.2) star has an unusually high lithium abundance [log ɛ (Li) = + 2.1], mild carbon ([C/Fe] = + 0.7) and sodium ([Na/Fe] = + 0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe] = + 0.8) and r-process ([Eu/Fe] = + 0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing that connects the convective envelope with the outer regions of the H-burning shell. If so, HKII 17435-00532 is the most metal-poor star in which this short-lived phase of Li enrichment has been observed. The Na and n-capture enrichment can be explained by mass transfer from a companion that passed through the thermally pulsing AGB phase of evolution with only a small initial enrichment of r-process material present in the birth cloud. Despite the current nondetection of radial velocity variations (over ~180 days), it is possible that HKII 17435-00532 is in a long-period or highly inclined binary system, similar to other stars with similar n-capture enrichment patterns. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

  2. The Abundances of Neutron Capture Species in the Very Metal-Poor Globular Cluster M15: An Uniform Analysis of RGB and RHB Stars

    CERN Document Server

    Sobeck, J S; Sneden, C; Preston, G W; Cowan, J J; Smith, G H; Thompson, I B; Shectman, S A; Burley, G S

    2011-01-01

    The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of $\\Delta(RHB-RGB) \\approx 0.1$ dex in the iron abundance was found. The anti-correlative behavior of the light neutron capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the {\\it s}...

  3. HAT-P-24b: An inflated hot-Jupiter on a 3.36d period transiting a hot, metal-poor star

    CERN Document Server

    Kipping, D M; Hartman, J; Torres, G; Shporer, A; Latham, D W; Kovacs, Geza; Noyes, R W; Howard, A W; Fischer, D A; Johnson, J A; Marcy, G W; Beky, B; Perumpilly, G; Esquerdo, G A; Sasselov, D D; Stefanik, R P; Lazar, J; Papp, I; Sari, P

    2010-01-01

    We report the discovery of HAT-P-24b, a transiting extrasolar planet orbiting the moderately bright V=11.818 F8 dwarf star GSC 0774-01441, with a period P = 3.3552464 +/- 0.0000071 d, transit epoch Tc = 2455216.97669 +/- 0.00024 (BJD_UTC), and transit duration 3.653 +/- 0.025 hours. The host star has a mass of 1.186 +/- 0.042 Msun , radius of 1.294 +/- 0.071 Rsun , effective temperature 6373 +/- 80 K, and a low metallicity of [Fe/H] = -0.16 +/- 0.08. The planetary companion has a mass of 0.681 +/- 0.031 MJ , and radius of 1.243 +/- 0.072 RJ yielding a mean density of 0.439 +/- 0.069 g cm-3 . By repeating our global fits with different parameter sets, we have performed a critical investigation of the fitting techniques used for previous HAT planetary discoveries. We find that the system properties are robust against the choice of priors. The effects of fixed versus fitted limb darkening are also examined. HAT-P-24b probably maintains a small eccentricity of e = 0.052 +0.022 -0.017, which is accepted over the c...

  4. Discovering extremely compact and metal-poor, star-forming dwarf galaxies out to z ~ 0.9 in the VIMOS Ultra-Deep Survey

    CERN Document Server

    Amorín, Ricardo; Castellano, M; Grazian, A; Tasca, L A M; Fontana, A; Pentericci, L; Cassata, P; Garilli, B; Brun, V Le; Fèvre, O Le; Maccagni, D; Thomas, R; Vanzella, E; Zamorani, G; Zucca, E; Bardelli, S; Capak, P; Cassará, L; Cimatti, A; Cuby, J G; Cucciati, O; de la Torre, S; Durkalec, A; Giavalisco, M; Hathi, N P; Ilbert, O; Lemaux, B C; Moreau, C; Paltani, S; Ribeiro, B; Salvato, M; Schaerer, D; Scodeggio, M; Talia, M; Taniguchi, Y; Tresse, L; Vergani, D; Wang, P W; Charlot, S; Contini, T; Fotopoulou, S; López-Sanjuan, C; Mellier, Y; Scoville, N

    2014-01-01

    We report the discovery of 31 low-luminosity (-14.5 < M_{AB}(B) < -18.8), extreme emission line galaxies (EELGs) at 0.3 < z < 0.9 identified by their unusually high rest-frame equivalent widths (100 < EW[OIII] < 1700 A) as part of the VIMOS Ultra Deep Survey (VUDS). VIMOS optical spectra of unprecedented sensitivity ($I_{AB}$ ~ 25 mag) along with multiwavelength photometry and HST imaging are used to investigate spectrophotometric properties of this unique sample and explore, for the first time, the very low stellar mass end (M* < 10^8 M$_{\\odot}$) of the luminosity-metallicity (LZR) and mass-metallicity (MZR) relations at z < 1. Characterized by their extreme compactness (R50 < 1 kpc), low stellar mass and enhanced specific star formation rates (SFR/M* ~ 10^{-9} - 10^{-7} yr^{-1}), the VUDS EELGs are blue dwarf galaxies likely experiencing the first stages of a vigorous galaxy-wide starburst. Using T_e-sensitive direct and strong-line methods, we find that VUDS EELGs are low-metall...

  5. Extremely Metal-Poor Galaxies: The Environment

    CERN Document Server

    Filho, M E; Muñoz-Tuñón, C; Nuza, S E; Kitaura, F; Heß, S

    2015-01-01

    We have analyzed bibliographical observational data and theoretical predictions, in order to probe the environment in which extremely metal-poor dwarf galaxies (XMPs) reside. We have assessed the HI component and its relation to the optical galaxy, the cosmic web type (voids, sheets, filaments and knots), the overdensity parameter and analyzed the nearest galaxy neighbours. The aim is to understand the role of interactions and cosmological accretion flows in the XMP observational properties, particularly the triggering and feeding of the star formation. We find that XMPs behave similarly to Blue Compact Dwarfs; they preferably populate low-density environments in the local Universe: ~60% occupy underdense regions, and ~75% reside in voids and sheets. This is more extreme than the distribution of irregular galaxies, and in contrast to those regions preferred by elliptical galaxies (knots and filaments). We further find results consistent with previous observations; while the environment does determine the frac...

  6. Global results from the HARPS metal-poor sample

    Directory of Open Access Journals (Sweden)

    Ségransan D.

    2011-02-01

    Full Text Available In this paper we present the global results of a HARPS-GTO program to search for planets orbiting a sample of metal-poor stars. The detection of several giant planets in long period orbits is discussed in the context of the metallicitygiant planet correlation.

  7. 贫金属星r过程核合成相关问题的研究进展%Progress of the Study About R-process Nucleosynthesis in Metal-poor Stars

    Institute of Scientific and Technical Information of China (English)

    张江; 崔文元; 张波

    2011-01-01

    快中子俘获过程(r过程)可以解释大约一半比铁重的稳定(和一些长寿命放射性的)富中子核素的产生,这已经被太阳系及各种金属丰度下恒星的观测结果所证实.为建立r过程模型,需要大量的核物理信息:涉及到β稳定谷与中子滴线之间的各种核素的稳定特性及β衰变分支等物理参数,实验和理论都面临巨大的挑战.综述了近年来贫金属星r过程核合成理论的研究情况,包括人们比较关注的主要r过程与弱r过程核合成、元素丰度分布规律及其产生场所等.%The rapid neutron-capture process (r-process) is traditionally believed to be responsible for the nucleosynthesis of approximately half of the heavy nuclei beyond the iron peak with long-decay half-lives in the solar material. In globular clusters and Galactic halo stars, the observed abundances show a nearly universal presence of r-process. With the rapid development of the abundance determinations, more elements (e.g., Lu, Z - 71) are firstly detected in metal-poor r-process-enriched halo stars, which can be used as the r-process indicators for the early Galaxy. Moreover, these r-rich stars provide a strong constraint on the models of the r-process nucleosynthesis, especially the early galaxy chemical evolution of neutron-capture elements.Based on new atomic lab data, recent neutron-capture abundance comparisons between six r-rich Galactic halo stars and the Solar System r-only abundance distribution indicate that the heavier stable neutron-capture elements beyond Ba (Z > 56) agree completely with a scaled solar system r-process abundance value. Nevertheless, the lighter neutron-capture elemental abundances in these stars are not in agreement with Solar-system r-only values. Although there is controversy over the origin of weak r-process, the neutron-capture elements are proposed to be formed possibly from multiple synthesis mechanisms, even if there exists little uncertainty. Whether the r

  8. New Abundansec From Very Old Stars

    CERN Document Server

    Hansen, T; Christlieb, N; Yong, D; Beers, T C; Andersen, J

    2015-01-01

    Metal-poor stars hold the fossil record of the Galactic chemical evolution and nucleosynthesis processes that took place at the earliest times in the history of our Galaxy. From detailed abundance studies of low mass, extremely metal-poor stars ([Fe/H] < -3), we can trace and help constrain the formation processes which created the first heavy elements in our Galaxy. Here we present the results of a ~20-star homogeneously analysed sample of metal-poor candidates from the Hamburg/ESO survey. We have derived abundances for a large number of elements ranging from Li to Ba, covering production processes from hydrostatic burning to neutron-capture. The sample includes some of the most metal-poor stars ([Fe/H] < -4) studied to date, containing neutron-capture elements, and also a number of stars enhanced in carbon. The so called CEMP (carbon enhanced metal-poor) stars, these stars make up ~20% of the stars with [Fe/H] < -3, and 80% of the stars with [Fe/H] < -4.5. The progenitors of CEMP stars is still ...

  9. Population studies. XIII. A new analysis of the Bidelman-Macconnell 'weak-metal' stars - confirmation of metal-poor stars in the thick disk of the galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Beers, Timothy C. [Department of Physics and JINA Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556 (United States); Norris, John E. [Research School of Astronomy and Astrophysics, The Australian National University, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia); Placco, Vinicius M. [Gemini Observatory, Hilo, HI 96720 (United States); Lee, Young Sun [Department of Astronomy and Space Science, Chungnam National University, Daejeon 305-764 (Korea, Republic of); Rossi, Silvia [Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Departamento de Astronomia, Universidade de São Paulo, Rua do Matão 1226, 05508-900 São Paulo (Brazil); Carollo, Daniela [Department of Physics and Astronomy, Astronomy, Astrophysics and Astrophotonic Research Center, Macquarie University, North Ryde 2019, NSW (Australia); Masseron, Thomas, E-mail: tbeers@nd.edu, E-mail: jen@mso.anu.edu.au, E-mail: vplacco@gemini.edu, E-mail: youngsun@cnu.ac.kr, E-mail: rossi@astro.iag.usp.br, E-mail: daniela.carollo@mq.edu.au, E-mail: tpm40@ast.cam.ac.uk [Institute of Astronomy, University of Cambridge, CB3 0HA (United Kingdom)

    2014-10-10

    A new set of very high signal-to-noise (S/N > 100/1), medium-resolution (R ∼ 3000) optical spectra have been obtained for 302 of the candidate 'weak-metal' stars selected by Bidelman and MacConnell. We use these data to calibrate the recently developed generalization of the Sloan Extension for Galactic Exploration and Understanding and Exploration (SEGUE) Stellar Parameter Pipeline, and obtain estimates of the atmospheric parameters (T {sub eff}, log g, and [Fe/H]) for these non-Sloan Digital Sky Survey/SEGUE data; we also obtain estimates of [C/Fe]. The new abundance measurements are shown to be consistent with available high-resolution spectroscopic determinations, and represent a substantial improvement over the accuracies obtained from the previous photometric estimates reported in Paper I of this series. The apparent offset in the photometric abundances of the giants in this sample noted by several authors is confirmed by our new spectroscopy; no such effect is found for the dwarfs. The presence of a metal-weak thick-disk (MWTD) population is clearly supported by these new abundance data. Some 25% of the stars with metallicities –1.8 < [Fe/H] ≤–0.8 exhibit orbital eccentricities e < 0.4, yet are clearly separated from members of the inner-halo population with similar metallicities by their location in a Lindblad energy versus angular momentum diagram. A comparison is made with recent results for a similar-size sample of Radial Velocity Experiment stars from Ruchti et al. We conclude, based on both of these samples, that the MWTD is real, and must be accounted for in discussions of the formation and evolution of the disk system of the Milky Way.

  10. Sulphur in the metal poor globular cluster NGC 6397

    CERN Document Server

    Koch, Andreas

    2011-01-01

    Sulphur (S) is a non-refractory alpha-element that is not locked into dust grains in the interstellar medium. Thus no correction to the measured, interstellar sulphur abundance is needed and it can be readily compared to the S content in stellar photospheres. Here we present the first measurement of sulphur in the metal poor globular cluster (GC) NGC 6397, as detected in a MIKE/Magellan high signal-to-noise, high-resolution spectrum of one red giant star. While abundance ratios of sulphur are available for a larger number of Galactic stars down to an [Fe/H] of ~ -3.5 dex, no measurements in globular clusters more metal poor than -1.5 dex have been reported so far. We find a NLTE, 3-D abundance ratio of [S/Fe] = +0.52 +/- 0.20 (stat.) +/- 0.08 (sys.), based on the S I, Multiplet 1 line at 9212.8A. This value is consistent with a Galactic halo plateau as typical of other alpha-elements in GCs and field stars, but we cannot rule out its membership with a second branch of increasing [S/Fe] with decreasing [Fe/H],...

  11. Population Studies. XIII. A New Analysis of the Bidelman-MacConnell "Weak-Metal" Stars - Confirmation of Metal-Poor Stars in the Thick Disk of the Galaxy

    CERN Document Server

    Beers, Timothy C; Placco, Vinicius M; Lee, Young Sun; Rossi, Silvia; Carollo, Daniela; Masseron, Thomas

    2014-01-01

    A new set of very high signal-to-noise (S/N > 100/1), medium-resolution (R~3000) optical spectra have been obtained for 302 of the candidate "weak-metal" stars selected by Bidelman & MacConnell. We use these data to calibrate the recently developed generalization of the SEGUE Stellar Parameter Pipeline, and obtain estimates of the atmospheric parameters (Teff, log g , and [Fe/H]) for these non-SDSS/SEGUE data; we also obtain estimates of [C/Fe]. The new abundance measurements are shown to be consistent with available high-resolution spectroscopic determinations, and represent a substantial improvement over the accuracies obtained from the previous photometric estimates reported in Paper I of this series. The apparent offset in the photometric abundances of the giants in this sample noted by several authors is confirmed by our new spectroscopy; no such effect is found for the dwarfs. The presence of a metal-weak thick-disk (MWTD) population is clearly supported by these new abundance data. Some 25% of the ...

  12. Relative abundance determinations in extremely metal poor giants. II. Transition probabilities and the abundance determinations

    International Nuclear Information System (INIS)

    The abundances of Fe and other elements are determined for a star of intermediate metallicity and for nine extremely metal poor stars, including two members of the globular cluster M92 and CD -38 deg 245. The accuracy of the transition probabilities for Fe I and other elements is evaluated. The distribution of the abundances of other elements with respect to Fe is the same for most of the cases studied. Manganese is the only element that shows a different relative abundance in an extremely metal poor star. 120 refs

  13. The Abundances of Neutron-capture Species in the Very Metal-poor Globular Cluster M15: A Uniform Analysis of Red Giant Branch and Red Horizontal Branch Stars

    Science.gov (United States)

    Sobeck, Jennifer S.; Kraft, Robert P.; Sneden, Christopher; Preston, George W.; Cowan, John J.; Smith, Graeme H.; Thompson, Ian B.; Shectman, Stephen A.; Burley, Gregory S.

    2011-06-01

    The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Δ(RHB - RGB) ≈ 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.

  14. THE ABUNDANCES OF NEUTRON-CAPTURE SPECIES IN THE VERY METAL-POOR GLOBULAR CLUSTER M15: A UNIFORM ANALYSIS OF RED GIANT BRANCH AND RED HORIZONTAL BRANCH STARS

    International Nuclear Information System (INIS)

    The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Δ(RHB - RGB) ∼ 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.

  15. Spatially resolved dust emission of extremely metal-poor galaxies*

    Science.gov (United States)

    Zhou, Luwenjia; Shi, Yong; Diaz-Santos, Taino; Armus, Lee; Helou, George; Stierwalt, Sabrina; Li, Aigen

    2016-05-01

    We present infrared (IR) spectral energy distributions (SEDs) of individual star-forming regions in four extremely metal-poor (EMP) galaxies with metallicity Z ≲ Z⊙/10 as observed by the Herschel Space Observatory. With the good wavelength coverage of the SED, it is found that these EMP star-forming regions show distinct SED shapes as compared to those of grand design Spirals and higher metallicity dwarfs: they have on average much higher f70μm/f160 μm ratios at a given f160 μm/f250 μm ratio; single modified blackbody (MBB) fittings to the SED at λ ≥ 100 μm still reveal higher dust temperatures and lower emissivity indices compared to that of Spirals, while two MBB fittings to the full SED with a fixed emissivity index (β = 2) show that even at 100 μm, about half of the emission comes from warm (50 K) dust, in contrast to the cold (˜20 K) dust component. Our spatially resolved images furthermore reveal that the far-IR colours including f70 μm/f160 μm, f160 μm/f250 μm and f250 μm/f350 μm are all related to the surface densities of young stars as traced by far-UV, 24 μm and star formation rates (SFRs), but not to the stellar mass surface densities. This suggests that the dust emitting at wavelengths from 70 to 350 μm is primarily heated by radiation from young stars.

  16. Spatially resolved dust emission of extremely metal poor galaxies

    CERN Document Server

    Zhou, Luwenjia; Diaz-Santos, Taino; Armus, Lee; Helou, George; Stierwalt, Sabrina; Li, Aigen

    2016-01-01

    We present infrared (IR) spectral energy distributions (SEDs) of individual star-forming regions in four extremely metal poor (EMP) galaxies with metallicity Z around Zsun/10 as observed by the Herschel Space Observatory. With the good wavelength coverage of the SED, it is found that these EMP star-forming regions show distinct SED shapes as compared to those of grand design Spirals and higher metallicity dwarfs: they have on average much higher f70um/f160um ratios at a given f160um/f250um ratio; single modified black-body (MBB) fittings to the SED at \\lambda >= 100 um still reveal higher dust temperatures and lower emissivity indices compared to that of Spirals, while two MBB fittings to the full SED with a fixed emissivity index (beta = 2) show that even at 100 um about half of the emission comes from warm (50 K) dust, in contrast to the cold (~20 K) dust component. Our spatially resolved images further reveal that the far-IR colors including f70um/f160um, f160um/f250um and f250um/f350um are all related to ...

  17. Primordial r-process Dispersion in Metal-Poor Globular Clusters

    CERN Document Server

    Roederer, Ian U

    2011-01-01

    Heavy elements, those produced by neutron-capture reactions, have traditionally shown no star-to-star dispersion in all but a handful of metal-poor globular clusters (GCs). Recent detections of low [Pb/Eu] ratios or upper limits in several metal-poor GCs indicate that the heavy elements in these GCs were produced exclusively by an r-process. Reexamining GC heavy element abundances from the literature, we find unmistakable correlations between the [La/Fe] and [Eu/Fe] ratios in 4 metal-poor GCs (M5, M15, M92, and NGC 3201), only 2 of which were known previously. This indicates that the total r-process abundances vary star-to-star (by factors of 2-6) relative to Fe within each GC. We also identify potential dispersion in two other GCs (M3 and M13). Several GCs (M12, M80, and NGC 6752) show no evidence of r-process dispersion. The r-process dispersion is not correlated with the well-known light element dispersion, indicating it was present in the gas throughout the duration of star formation. The observations ava...

  18. METAL-POOR LITHIUM-RICH GIANTS IN THE RADIAL VELOCITY EXPERIMENT SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Ruchti, Gregory R.; Fulbright, Jon P.; Wyse, Rosemary F. G. [Bloomberg Center for Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Gilmore, Gerard F. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Grebel, Eva K. [Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg, Moenchhofstr. 12-14, D-69120 Heidelberg (Germany); Bienayme, Olivier; Siebert, Arnaud [Observatoire de Strasbourg, 11 Rue de l' Universite, F-67000 Strasbourg (France); Bland-Hawthorn, Joss [Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006 (Australia); Freeman, Ken C. [RSAA Australian National University, Mount Stromlo Observatory, Cotter Road, Weston Creek, Canberra, ACT 2611 (Australia); Gibson, Brad K. [Jeremiah Horrocks Institute for Astrophysics and Super-computing, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Munari, Ulisse [INAF Osservatorio Astronomico di Padova, Via dell' Osservatorio 8, I-36012 Asiago (Italy); Navarro, Julio F. [Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Station CSC, Victoria, BC V8W 3P6 (Canada); Parker, Quentin A.; Watson, Fred G. [Australian Astronomical Observatory, Coonabarabran, NSW 2357 (Australia); Reid, Warren [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Seabroke, George M. [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT (United Kingdom); Siviero, Alessandro [Department of Astronomy, Padova University, Vicolo dell' Osservatorio 2, I-35122 Padova (Italy); Steinmetz, Matthias; Williams, Mary [Leibniz-Institut fuer Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany); Zwitter, Tomaz, E-mail: gruchti@mpa-garching.mpg.de [Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SK-1000 Ljubljana (Slovenia)

    2011-12-20

    We report the discovery of eight lithium-rich field giants found in a high-resolution spectroscopic sample of over 700 metal-poor stars ([Fe/H] < -0.5) selected from the Radial Velocity Experiment survey. The majority of the Li-rich giants in our sample are very metal-poor ([Fe/H] {approx}< -1.9), and have a Li abundance (in the form of {sup 7}Li), A(Li) = log (n(Li)/n(H)) + 12, between 2.30 and 3.63, well above the typical upper red giant branch (RGB) limit, A(Li) < 0.5, while two stars, with A(Li) {approx} 1.7-1.8, show similar lithium abundances to normal giants at the same gravity. We further included two metal-poor, Li-rich globular cluster giants in our sample, namely the previously discovered M3-IV101 and newly discovered (in this work) M68-A96. This comprises the largest sample of metal-poor Li-rich giants to date. We performed a detailed abundance analysis of all stars, finding that the majority of our sample stars have elemental abundances similar to that of Li-normal halo giants. Although the evolutionary phase of each Li-rich giant cannot be definitively determined, the Li-rich phase is likely connected to extra mixing at the RGB bump or early asymptotic giant branch that triggers cool bottom processing in which the bottom of the outer convective envelope is connected to the H-burning shell in the star. The surface of a star becomes Li-enhanced as {sup 7}Be (which burns to {sup 7}Li) is transported to the stellar surface via the Cameron-Fowler mechanism. We discuss and discriminate among several models for the extra mixing that can cause Li production, given the detailed abundances of the Li-rich giants in our sample.

  19. MODELS FOR METAL-POOR STARS WITH ENHANCED ABUNDANCES OF C, N, O, Ne, Na, Mg, Si, S, Ca, AND Ti, IN TURN, AT CONSTANT HELIUM AND IRON ABUNDANCES

    Energy Technology Data Exchange (ETDEWEB)

    VandenBerg, Don A.; Dotter, Aaron [Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Victoria, B.C. V8W 3P6 (Canada); Bergbusch, Peter A. [Department of Physics, University of Regina, Regina, Saskatchewan S4S 0A2 (Canada); Ferguson, Jason W. [Department of Physics, Wichita State University, Wichita, KS 67260-0032 (United States); Michaud, Georges; Richer, Jacques [Departement de Physique, Universite de Montreal, Montreal, Quebec H3C 3J7 (Canada); Proffitt, Charles R., E-mail: vandenbe@uvic.ca, E-mail: Aaron.Dotter@gmail.com, E-mail: pbergbusch@accesscomm.ca, E-mail: proffitt@stsci.edu, E-mail: Jason.Ferguson@wichita.edu, E-mail: michaudg@astro.umontreal.ca, E-mail: jacques.richer@umontreal.ca [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2012-08-10

    Recent work has shown that most globular clusters have at least two chemically distinct components, as well as cluster-to-cluster differences in the mean [O/Fe], [Mg/Fe], and [Si/Fe] ratios at similar [Fe/H] values. In order to investigate the implications of variations in the abundances of these and other metals for H-R diagrams and predicted ages, grids of evolutionary sequences have been computed for scaled solar and enhanced {alpha}-element metal abundances, and for mixtures in which the assumed [m/Fe] value for each of the metals C, N, O, Ne, Na, Mg, Si, S, Ca, and Ti has been increased, in turn, by 0.4 dex at constant [Fe/H]. These tracks, together with isochrones for ages from Almost-Equal-To 5 to 14 Gyr, have been computed for -3.0 {<=} [Fe/H] {<=}-0.6, with helium abundances Y = 0.25, 0.29, and 0.33 at each [Fe/H] value, using upgraded versions of the Victoria stellar structure program and the Regina interpolation code, respectively. Turnoff luminosity versus age relations from isochrones are found to depend almost entirely on the importance of the CNO cycle, and thereby mainly on the abundance of oxygen. Since C, N, and O, as well as Ne and S, do not contribute significantly to the opacities at low temperatures and densities, variations in their abundances do not impact the predicted T{sub eff} scale of red giants. The latter is a strong function of the abundances of only Mg and Si (and Fe, possibly to a lesser extent) because they are so abundant and because they are strong sources of opacity at low temperatures. For these reasons, Mg and Si also have important effects on the temperatures of main-sequence stars. Due to their low abundances, Na, Ca, and Ti are of little consequence for stellar models. The effects of varying the adopted solar metals mixture and the helium abundance at a fixed [Fe/H] are also briefly discussed.

  20. MODELS FOR METAL-POOR STARS WITH ENHANCED ABUNDANCES OF C, N, O, Ne, Na, Mg, Si, S, Ca, AND Ti, IN TURN, AT CONSTANT HELIUM AND IRON ABUNDANCES

    International Nuclear Information System (INIS)

    Recent work has shown that most globular clusters have at least two chemically distinct components, as well as cluster-to-cluster differences in the mean [O/Fe], [Mg/Fe], and [Si/Fe] ratios at similar [Fe/H] values. In order to investigate the implications of variations in the abundances of these and other metals for H-R diagrams and predicted ages, grids of evolutionary sequences have been computed for scaled solar and enhanced α-element metal abundances, and for mixtures in which the assumed [m/Fe] value for each of the metals C, N, O, Ne, Na, Mg, Si, S, Ca, and Ti has been increased, in turn, by 0.4 dex at constant [Fe/H]. These tracks, together with isochrones for ages from ≈5 to 14 Gyr, have been computed for –3.0 ≤ [Fe/H] ≤–0.6, with helium abundances Y = 0.25, 0.29, and 0.33 at each [Fe/H] value, using upgraded versions of the Victoria stellar structure program and the Regina interpolation code, respectively. Turnoff luminosity versus age relations from isochrones are found to depend almost entirely on the importance of the CNO cycle, and thereby mainly on the abundance of oxygen. Since C, N, and O, as well as Ne and S, do not contribute significantly to the opacities at low temperatures and densities, variations in their abundances do not impact the predicted Teff scale of red giants. The latter is a strong function of the abundances of only Mg and Si (and Fe, possibly to a lesser extent) because they are so abundant and because they are strong sources of opacity at low temperatures. For these reasons, Mg and Si also have important effects on the temperatures of main-sequence stars. Due to their low abundances, Na, Ca, and Ti are of little consequence for stellar models. The effects of varying the adopted solar metals mixture and the helium abundance at a fixed [Fe/H] are also briefly discussed.

  1. THE TERZAN 5 PUZZLE: DISCOVERY OF A THIRD, METAL-POOR COMPONENT

    International Nuclear Information System (INIS)

    We report on the discovery of three metal-poor giant stars in Terzan 5, a complex stellar system in the Galactic bulge, known to have two populations at [Fe/H] = –0.25 and +0.3. For these three stars we present new echelle spectra obtained with NIRSPEC at Keck II, which confirm their radial velocity membership and provide an average [Fe/H] = –0.79 dex iron abundance and [α/Fe] = +0.36 dex enhancement. This new population extends the metallicity range of Terzan 5 to 0.5 dex more metal poor, and it has properties consistent with having formed from a gas polluted by core-collapse supernovae

  2. Before the Bar: Kinematic Detection of A Spheroidal Metal-Poor Bulge Component

    CERN Document Server

    Kunder, Andrea; Storm, J; Nataf, D M; De Propris, R; Walker, A R; Bono, G; Johnson, C I; Shen, J; Li, Z Y

    2016-01-01

    We present 947 radial velocities of RR Lyrae variable stars in four fields located toward the Galactic bulge, observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR). We show that these RR Lyrae stars exhibit hot kinematics and null or negligible rotation and are therefore members of a separate population from the bar/pseudobulge that currently dominates the mass and luminosity of the inner Galaxy. Our RR Lyrae stars predate these structures, and have metallicities, kinematics, and spatial distribution that are consistent with a "classical" bulge, although we cannot yet completely rule out the possibility that they are the metal-poor tail of a more metal rich ([Fe/H] ~ -1 dex) halo-bulge population. The complete catalog of radial velocities for the BRAVA-RR stars is also published electronically.

  3. The Chemical Evolution of Very Metal-Poor Damped Lyman-$\\alpha$ Systems

    CERN Document Server

    Webster, David; Sutherland, Ralph S

    2015-01-01

    In earlier work we showed that a dark matter halo with a virial mass of $10^7$ M$_\\odot$ can survive feedback from its own massive stars and form stars for $\\gtrsim100$ Myr. We also found that our modelled systems were consistent with observations of ultrafaint dwarfs (UFDs), the least massive known galaxies. Very metal-poor damped Lyman-$\\alpha$ systems (DLAs) recently identified at $z\\sim2$ may represent the gas that formed at least some of the observed stars in UFDs. We compare projected sightlines from our simulations to the observed metal-poor DLAs and find that our models can reach the densities of the observed sightlines; however the metallicities are inconsistent with the single supernova simulations, suggesting enrichment by multiple supernovae. We model two scenarios for the history of these systems. The first explains the gas abundances in DLAs by a single burst of star formation. This model can produce the observed DLA abundances, but does not provide an explanation as to why the DLAs show suppres...

  4. The Kennicutt-Schmidt Relation in Extremely Metal-Poor Dwarf Galaxies

    CERN Document Server

    Filho, M E; Amorín, R; Muñoz-Tuñón, C; Elmegreen, B G; Elmegreen, D M

    2016-01-01

    The Kennicutt-Schmidt (KS) relation between the gas mass and star formation rate (SFR) describes the star formation regulation in disk galaxies. It is a function of gas metallicity, but the low metallicity regime of the KS diagram is poorly sampled. We have analyzed data for a representative set of extremely metal-poor galaxies (XMPs), as well as auxiliary data, and compared these to empirical and theoretical predictions. The majority of the XMPs possess high specific SFRs, similar to high redshift star-forming galaxies. On the KS plot, the XMP HI data occupy the same region as dwarfs, and extend the relation for low surface brightness galaxies. Considering the HI gas alone, a considerable fraction of the XMPs already fall off the KS law. Significant quantities of 'dark' H$_2$ mass (i.e., not traced by CO) would imply that XMPs possess low star formation efficiencies (SFE$_{\\rm gas}$). Low SFE$_{\\rm gas}$ in XMPs may be the result of the metal-poor nature of the HI gas. Alternatively, the HI reservoir may be ...

  5. The helium abundance in the metal-poor globular clusters M30 and NGC6397

    CERN Document Server

    Mucciarelli, A; Lanzoni, B; Ferraro, F R

    2014-01-01

    We present the helium abundance of the two metal-poor clusters M30 and NGC6397. Helium estimates have been obtained by using the high-resolution spectrograph FLAMES at the ESO Very Large Telescope and by measuring the HeI line at 4471 A in 24 and 35 horizontal branch stars in M30 and NGC6397, respectively. This sample represents the largest dataset of He abundances collected so far in metal-poor clusters. The He mass fraction turns out to be Y=0.252+-0.003 (sigma=0.021) for M30 and Y=0.241+-0.004 (sigma=0.023) NGC6397. These values are fully compatible with the cosmological abundance, thus suggesting that the horizontal branch stars are not strongly enriched in He. The small spread of the Y distributions are compatible with those expected from the observed main sequence splitting. Finally, we find an hint of a weak anticorrelation between Y and [O/Fe] in NGC6397 in agreement with the prediction that O-poor stars are formed by (He-enriched) gas polluted by the products of hot proton-capture reactions.

  6. Near-Infrared Imaging of the Central Regions of Metal-Poor Inner Spheroid Globular Clusters

    CERN Document Server

    Davidge, T J

    2001-01-01

    JHK images obtained with the Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) are used to investigate the near-infrared photometric properties of red giant branch (RGB) and horizontal branch (HB) stars in eight metal-poor globular clusters with R_GC < 2 kpc. The slope of the RGB on the (K, J-K) CMDs confirms the metal-poor nature of these clusters, four of which appear to have metallicities comparable to M92. The luminosity functions of RGB stars in inner spheroid and outer halo clusters have similar slopes, although there is a tendency for core-collapsed clusters to have slightly flatter luminosity functions than non-collapsed clusters. The distribution of red HB stars on the (K, J-K) CMDs of inner spheroid clusters with [Fe/H] ~ -1.5 is very different from that of clusters with [Fe/H] ~ -2.2, suggesting that metallicity is the main parameter defining HB content among these objects. The RGB-bump is detected in four of the inner spheroid clusters, and this feature is used to compute dis...

  7. Before the Bar: Kinematic Detection of a Spheroidal Metal-poor Bulge Component

    Science.gov (United States)

    Kunder, Andrea; Rich, R. M.; Koch, A.; Storm, J.; Nataf, D. M.; De Propris, R.; Walker, A. R.; Bono, G.; Johnson, C. I.; Shen, Juntai; Li, Z.-Y.

    2016-04-01

    We present 947 radial velocities of RR Lyrae variable stars in four fields located toward the Galactic bulge, observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR). We show that these RR Lyrae stars (RRLs) exhibit hot kinematics and null or negligible rotation and are therefore members of a separate population from the bar/pseudobulge that currently dominates the mass and luminosity of the inner Galaxy. Our RRLs predate these structures and have metallicities, kinematics, and spatial distribution that are consistent with a “classical” bulge, although we cannot yet completely rule out the possibility that they are the metal-poor tail of a more metal-rich ([{Fe}/{{H}}]∼ -1 dex) halo–bulge population. The complete catalog of radial velocities for the BRAVA-RR stars is also published electronically.

  8. Preserving chemical signatures of primordial star formation in the first low-mass stars

    CERN Document Server

    Ji, Alexander P; Bromm, Volker

    2015-01-01

    We model early star forming regions and their chemical enrichment by Population III (Pop III) supernovae with nucleosynthetic yields featuring high [C/Fe] ratios and pair-instability supernova (PISN) signatures. We aim to test how well these chemical abundance signatures are preserved in the gas prior to forming the first long-lived low-mass stars (or second-generation stars). Our results show that second-generation stars can retain the nucleosynthetic signature of their Pop III progenitors, even in the presence of nucleosynthetically normal Pop III core-collapse supernovae. We find that carbon-enhanced metal-poor stars are likely second-generation stars that form in minihaloes. Furthermore, it is likely that the majority of Pop III supernovae produce high [C/Fe] yields. In contrast, metals ejected by a PISN are not concentrated in the first star forming haloes, which may explain the absence of observed PISN signatures in metal-poor stars. We also find that unique Pop III abundance signatures in the gas are q...

  9. The metal-poor Knee in the Fornax Dwarf Spheroidal Galaxy

    CERN Document Server

    Hendricks, Benjamin; Lanfranchi, Gustavo A; Boeche, Corrado; Walker, Matthew; Johnson, Christian I; Penarrubia, Jorge; Gilmore, Gerard

    2014-01-01

    We present alpha-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal galaxy (dSph), obtained with VLT/GIRAFFE (R~16,000). Due to the large fraction of metal-poor stars in our sample, we are able to follow the alpha-element evolution from [Fe/H]=-2.5 continuously to [Fe/H]=-0.7 dex. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, alpha-enhanced plateau down to subsolar [alpha/Fe] values due to the onset of SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an alpha-enhanced plateau at early epochs, followed by a well-defined "knee", caused by the onset of SNe Ia, and finally a second plateau with sub-solar [alpha/Fe] values. We find the position of this knee to be at [Fe/H]=-1.9 and therefore significantly more metal-poor than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value ...

  10. The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime

    DEFF Research Database (Denmark)

    Cooke, Ryan; Pettini, Max; Steidel, Charles C.;

    2011-01-01

    We present a high spectral resolution survey of the most metal-poor damped Lyα absorption systems (DLAs) aimed at probing the nature and nucleosynthesis of the earliest generations of stars. Our survey comprises 22 systems with iron abundance less than 1/100 solar; observations of seven of these...... confirm the near-solar values of C/O in DLAs at the lowest metallicities probed, and find that their distribution is in agreement with that seen in Galactic halo stars. We find that the O/Fe ratio in VMP DLAs is essentially constant, and shows very little dispersion, with a mean [〈O/Fe〉]=+0.39 ± 0.12, in...... good agreement with the values measured in Galactic halo stars when the oxygen abundance is measured from the [O i] λ6300 line. We speculate that such good agreement in the observed abundance trends points to a universal origin for these metals. In view of this agreement, we construct the abundance...

  11. Hubble Space Telescope Near-Ultraviolet Spectroscopy of Bright CEMP-s Stars

    OpenAIRE

    Placco, Vinicius M.; Beers, Timothy C.; Ivans, Inese I.; Filler, Dan; Imig, Julie A.; Roederer, Ian U.; Abate, Carlo; Hansen, Terese; Cowan, John J.; Frebel, Anna; Lawler, James E.; Schatz, Hendrik; Sneden, Christopher; Sobeck, Jennifer S.; Aoki, Wako

    2015-01-01

    We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the bright carbon-enhanced metal-poor (CEMP) stars HD196944 (V = 8.40, [Fe/H] = -2.41) and HD201626 (V = 8.16, [Fe/H] = -1.51), based on data acquired with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. Both of these stars belong to the sub-class CEMP-s, and exhibit clear over-abundances of heavy elements associated with production by the slow neutron-capture process. ...

  12. Discovery of a Metal-Poor Field Giant with a Globular Cluster Second-Generation Abundance Pattern

    OpenAIRE

    Fernandez-Trincado, J. G.; Robin, A. C.; Moreno, E; Schiavon, R. P.; Peréz, A. E. García; Vieira, K.; Cunha, K.; Zamora, O.; Sneden, C.; Carrera, R.; Johnson, J.A.; Shetrone, M.; Zasowski, G.; García-Hernándes, D. A.; Majewski, S. R.

    2016-01-01

    We report on the direct detection from observations obtained with the APOGEE survey of a metal-poor ([Fe/H]$=-1.3$) field giant star in the Milky Way, with an extreme Mg-Al abundance ([Mg/Fe]$=$-0.31; [Al/Fe]$=$1.49) seen only among the secondary population of globular clusters. This star, 2M16011638-1201525 found using SDSSIII/APOGEE data also shows particularly atypical light-element patterns not seen among Galactic disk field stars, indicating that it could have been born in a globular clu...

  13. The Gaia-ESO Survey: Detailed Abundances in the Metal-poor Globular Cluster NGC 4372

    CERN Document Server

    Roman, I San; Geisler, D; Villanova, S; Kacharov, N; Koch, A; Carraro, G; Tautvaišiene, G; Vallenari, A; Alfaro, E J; Bensby, T; Flaccomio, E; Francois, P; Korn, A J; Pancino, E; Recio-Blanco, A; Smiljanic, R; Bergemann, M; Costado, M T; Damiani, F; Heiter, U; Hourihane, A; Jofré, P; Lardo, C; de Laverny, P; Masseron, T; Morbidelli, L; Sbordone, L; Sousa, S G; Worley, C C; Zaggia, S

    2015-01-01

    We present the abundance analysis for a sample of 7 red giant branch stars in the metal-poor globular cluster NGC 4372 based on UVES spectra acquired as part of the Gaia-ESO Survey. This is the first extensive study of this cluster from high resolution spectroscopy. We derive abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Fe, Cr, Ni, Y, Ba, and La. We find a metallicity of [Fe/H] = -2.19 $\\pm$ 0.03 and find no evidence for a metallicity spread. This metallicity makes NGC 4372 one of the most metal-poor galactic globular clusters. We also find an {\\alpha}-enhancement typical of halo globular clusters at this metallicity. Significant spreads are observed in the abundances of light elements. In particular we find a Na-O anti-correlation. Abundances of O are relatively high compared with other globular clusters. This could indicate that NGC 4372 was formed in an environment with high O for its metallicity. A Mg-Al spread is also present which spans a range of more than 0.5 dex in Al abundances. Na is correlated wit...

  14. The Physical Nature of the Most Metal-Poor Damped Lyman Alpha Systems

    CERN Document Server

    Yuan, Sihan

    2015-01-01

    Utilizing the high-resolution, large-scale LAOZI cosmological simulations we investigate the nature of the metal-poor (${\\rm [Z/H]<-2}$) damped Lyman alpha systems (mpDLA) at $z=3$. The following physical picture of mpDLAs emerges. The majority of mpDLAs inhabit regions $\\ge 20$~kpc from the host galaxy center on infalling cold gas streams originating from the intergalactic medium, with infall velocity of $\\sim 100$ km/s and temperature of $\\sim 10^{4}$ K. For each host galaxy, on average, about $1\\%$ of the area within a radius $150$~kpc is covered by mpDLAs. The mpDLAs are relatively diffuse ($n_{\\rm{gas}} \\sim 10^{-2}$ cm$^{-3}$), Jeans quasi-stable, and have very low star formation rate ($\\dot{\\Sigma} \\le 10^{-4} \\msun \\rm{\\ yr}^{-1} \\rm{\\ kpc}^{-2}$). As mpDLAs migrate inward to the galaxy center, they mix with high metallicity gas and stellar outflows in the process, removing themselves from the metal-poor category and rendering the central ($\\le 5$ kpc) regions of galaxies devoid of mpDLAs. Thus, th...

  15. THE MOST METAL-POOR DAMPED Lyα SYSTEMS: AN INSIGHT INTO DWARF GALAXIES AT HIGH-REDSHIFT

    Energy Technology Data Exchange (ETDEWEB)

    Cooke, Ryan J. [Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, CA 95064 (United States); Pettini, Max [Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA (United Kingdom); Jorgenson, Regina A., E-mail: rcooke@ucolick.org [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

    2015-02-10

    In this paper we analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Lyα systems (DLAs), to uncover their links to modern-day galaxies. We present evidence that the DLA population as a whole exhibits a ''knee'' in the relative abundances of the α-capture and Fe-peak elements when the metallicity is [Fe/H] ≅ –2.0, assuming that Zn traces the buildup of Fe-peak elements. In this respect, the chemical evolution of DLAs is clearly different from that experienced by Milky Way halo stars, but resembles that of dwarf spheroidal galaxies in the Local Group. We also find a close correspondence between the kinematics of Local Group dwarf galaxies and of high-redshift metal-poor DLAs, which further strengthens this connection. On the basis of such similarities, we propose that the most metal-poor DLAs provide us with a unique opportunity to directly study the dwarf galaxy population more than ten billion years in the past, at a time when many dwarf galaxies were forming the bulk of their stars. To this end, we have measured some of the key physical properties of the DLA gas, including their neutral gas mass, size, kinetic temperature, density, and turbulence. We find that metal-poor DLAs contain a warm neutral medium with T {sub gas} ≅ 9600 K predominantly held up by thermal pressure. Furthermore, all of the DLAs in our sample exhibit a subsonic turbulent Mach number, implying that the gas distribution is largely smooth. These results are among the first empirical descriptions of the environments where the first few generations of stars may have formed in the universe.

  16. THE ACS NEARBY GALAXY SURVEY TREASURY. IX. CONSTRAINING ASYMPTOTIC GIANT BRANCH EVOLUTION WITH OLD METAL-POOR GALAXIES

    International Nuclear Information System (INIS)

    In an attempt to constrain evolutionary models of the asymptotic giant branch (AGB) phase at the limit of low masses and low metallicities, we have examined the luminosity functions and number ratios between AGB and red giant branch (RGB) stars from a sample of resolved galaxies from the ACS Nearby Galaxy Survey Treasury. This database provides Hubble Space Telescope optical photometry together with maps of completeness, photometric errors, and star formation histories for dozens of galaxies within 4 Mpc. We select 12 galaxies characterized by predominantly metal-poor populations as indicated by a very steep and blue RGB, and which do not present any indication of recent star formation in their color-magnitude diagrams. Thousands of AGB stars brighter than the tip of the RGB (TRGB) are present in the sample (between 60 and 400 per galaxy), hence, the Poisson noise has little impact in our measurements of the AGB/RGB ratio. We model the photometric data with a few sets of thermally pulsing AGB (TP-AGB) evolutionary models with different prescriptions for the mass loss. This technique allows us to set stringent constraints on the TP-AGB models of low-mass, metal-poor stars (with M sun, [Fe/H]∼sun. This is also in good agreement with recent observations of white dwarf masses in the M4 old globular cluster. These constraints can be added to those already derived from Magellanic Cloud star clusters as important mileposts in the arduous process of calibrating AGB evolutionary models.

  17. Detailed abundance analysis of a metal-poor giant in the Galactic Center

    CERN Document Server

    Ryde, N; Rich, R M; Thorsbro, B; Schultheis, M; Origlia, L; Chatzopoulos, S

    2016-01-01

    We report the first results from our program to examine the metallicity distribution of the Milky Way nuclear star cluster connected to SgrA*, with the goal of inferring the star formation and enrichment history of this system, as well as its connection and relationship with the central 100 pc of the bulge/bar system. We present the first high resolution (R~24,000), detailed abundance analysis of a K=10.2 metal-poor, alpha-enhanced red giant projected at 1.5 pc from the Galactic Center, using NIRSPEC on Keck II. A careful analysis of the dynamics and color of the star locates it at about 26 pc line-of-sight distance in front of the nuclear cluster. It probably belongs to one of the nuclear components (cluster or disk), not to the bar-bulge or classical disk. A detailed spectroscopic synthesis, using a new linelist in the K band, finds [Fe/H]~-1.0 and [alpha/Fe]~+0.4, consistent with stars of similar metallicity in the bulge. As known giants with comparable [Fe/H] and alpha enhancement are old, we conclude tha...

  18. Evidence for inhomogeneous reionization in the local Universe from metal-poor globular cluster systems

    CERN Document Server

    Spitler, Lee R; Diemand, Jürg; Strader, Jay; Forbes, Duncan A; Moore, Ben; Brodie, Jean P

    2011-01-01

    Exploiting a fundamental characteristic of galaxy assembly in the {\\Lambda}CDM paradigm, the observed spatial biasing and kinematics of metal-poor globular star clusters are used to constrain the local reionization epoch around individual galaxies. Selecting three galaxies located in different environments, the first attempt at constraining the environmental propagation of reionization in the local Universe is carried out. The joint constraint from the three galaxies (z_reion = 10.5^{+1.0}_{-0.9}) agrees remarkably well with the latest WMAP constraint on z_reion for a simple instantaneous reionization model. More importantly, the range of z_reion values found here are consistent with the global range of z_reion estimates from other observations. We furthermore find a 1.7{\\sigma} indication that reionization completed in low-density environments before the intergalactic medium in high-density environments was reionized. This is consistent with certain theoretical models that predict that reionization was globa...

  19. Detailed Chemical Abundances in NGC 5824: Another Metal-Poor Globular Cluster with Internal Heavy Element Abundance Variations

    CERN Document Server

    Roederer, Ian U; Bailey, John I; Spencer, Meghin; Crane, Jeffrey D; Shectman, Stephen A

    2015-01-01

    We present radial velocities, stellar parameters, and detailed abundances of 39 elements derived from high-resolution spectroscopic observations of red giant stars in the luminous, metal-poor globular cluster NGC 5824. We observe 26 stars in NGC 5824 using the Michigan/Magellan Fiber System (M2FS) and two stars using the Magellan Inamori Kyocera Echelle (MIKE) spectrograph. We derive a mean metallicity of [Fe/H]=-1.94+/-0.02 (statistical) +/-0.10 (systematic). The metallicity dispersion of this sample of stars, 0.08 dex, is in agreement with previous work and does not exceed the expected observational errors. Previous work suggested an internal metallicity spread only when fainter samples of stars were considered, so we cannot exclude the possibility of an intrinsic metallicity dispersion in NGC 5824. The M2FS spectra reveal a large internal dispersion in [Mg/Fe], 0.28 dex, which is found in a few other luminous, metal-poor clusters. [Mg/Fe] is correlated with [O/Fe] and anti-correlated with [Na/Fe] and [Al/F...

  20. A Search for Coronal Activity Among Two Metal-poor Subdwarfs and One Subgiant

    Science.gov (United States)

    Smith, Graeme H.; Dupree, Andrea K.; Günther, Hans Moritz

    2016-08-01

    A search has been made using the XMM-Newton satellite for coronal soft X-ray emission from HD 19445, HD 25329, and HD 140283, three Population II stars in the Galactic halo having metallicities of {{[Fe/H]}}˜ -2. The program stars, consisting of two subdwarfs and one metal-poor subgiant, were pre-selected from ground-based observations to have He i λ10830 absorption lines with an equivalent width (EW) of 30 mÅ or more. If such stars follow a relation between He i EW and soft X-ray flux applicable to Population I dwarf stars, then they would be expected to have X-ray luminosities ˜ 5× {10}-7 times their bolometric luminosity, and as such would yield detectable sources in 20 ks exposures with the XMM-Newton EPIC-PN and MOS cameras. No detections were found in such exposures made with XMM-Newton. Upper limits to soft X-ray emission from the two program stars that have effective temperatures most similar to that of the Sun, namely HD 19445 and HD 140283, are comparable to the level of the quiet Sun. The star HD 25329, a cooler subdwarf, exhibits an upper limit similar to the Sun at maximum activity. These measurements suggest that coronal activity appears to decrease with age among the oldest G dwarfs, but K-M subdwarfs possibly have maintained a solar-like level of activity. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

  1. A differential chemical element analysis of the metal poor Globular Cluster NGC 6397

    CERN Document Server

    Koch, Andreas

    2011-01-01

    We present chemical abundances in three red giants and two turn-off stars in the metal poor Galactic globular cluster (GC) NGC 6397 based on spectroscopy obtained with the MIKE high resolution spectrograph on the Magellan 6.5-m Clay telescope. Our results are based on a line-by-line differential abundance analysis relative to the well-studied red giant Arcturus and the Galactic halo field star Hip 66815. At a mean of -2.10 +/- 0.02 (stat.) +/- 0.07 (sys.) the differential iron abundance is in good agreement with other studies in the literature based on gf-values. As in previous, differential works we find a distinct departure from ionization equilibrium in that the abundances of Fe I and Fe II differ by ~0.1 dex, with opposite sign for the RGB and TO stars. The alpha-element ratios are enhanced to 0.4 (RGB) and 0.3 dex (TO), respectively, and we also confirm strong variations in the O, Na, and Al/Fe abundance ratios. Accordingly, the light-element abundance patterns in one of the red giants can be attributed ...

  2. Dust and hydrogen molecules in the extremely metal-poor dwarf galaxy SBS 0335-052

    CERN Document Server

    Hirashita, H; Ferrara, A

    2002-01-01

    During the early stages of galaxy evolution, the metallicity is generally low and nearby metal-poor star-forming galaxies may provide templates for primordial star formation. In particular, the dust content of such objects is of great importance since early molecular formation can take place on grains. To gain insight into primeval galaxies at high redshift, we examine the dust content of the nearby extremely low-metallicity galaxy SBS 0335-052 which hosts a very young starburst (< 10 Myr). In young galaxies, the dust formation rate in Type II supernovae governs the amount of dust, and by incorporating recent results on dust production in Type II supernovae we model the evolution of dust content. If the star-forming region is compact (< 100 pc), as suggested by observations of SBS 0335-052, our models consistently explain the quantity of dust, far-infrared luminosity, and dust temperature in this low-metallicity object. We also discuss the H_2 abundance. The compactness of the region is important to H_2...

  3. Tidal stripping stellar substructures around four metal-poor globular clusters in the Galactic bulge

    CERN Document Server

    Chun, Sang-Hyun; Jung, DooSeok; Sohn, Young-Jong

    2014-01-01

    We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642 and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the WFCAM near-infrared array on United Kingdom Infrared Telescope. Statistical weighted filtering algorithm for the stars on the color-magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all of the four globular clusters exhibit strong evidence of tidally stripping stellar features beyond tidal radius, in the form of tidal tail or small density lobes or chunk. The orientations of the extended stellar substructures are likely to be associated with the effect of the dynamic interaction with the Galaxy and the cluster space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from t...

  4. The extreme chemistry of multiple stellar populations in the metal-poor globular cluster NGC 4833

    CERN Document Server

    Carretta, E; Gratton, R G; D'Orazi, V; Lucatello, S; Momany, Y; Sollima, A; Bellazzini, M; Catanzaro, G; Leone, F

    2014-01-01

    Our FLAMES survey of Na-O anticorrelation in globular clusters (GCs) is extended to NGC 4833, a metal-poor GC with a long blue tail on the horizontal branch (HB). We present the abundance analysis for a large sample of 78 red giants based on UVES and GIRAFFE spectra acquired at the ESO-VLT. We derived abundances of Na, O, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Ba, La, Nd. This is the first extensive study of this cluster from high resolution spectroscopy. On the scale of our survey, the metallicity of NGC 4833 is [Fe/H]=-2.015+/-0.004+/-0.084 dex (rms=0.014 dex) from 12 stars observed with UVES, where the first error is from statistics and the second one refers to the systematic effects. The iron abundance in NGC 4833 is homogeneous at better than 6%. On the other hand, the light elements involved in proton-capture reactions at high temperature show the large star-to-star variations observed in almost all GCs studied so far. The Na-O anticorrelation in NGC 4833 is quite extended, as expecte...

  5. The Evolved Pulsating CEMP Star HD 112869

    Science.gov (United States)

    Začs, Laimons; Sperauskas, Julius; Grankina, Aija; Deveikis, Viktoras; Kaminskyi, Bogdan; Pavlenko, Yakiv; Musaev, Faig A.

    2015-04-01

    Radial velocity measurements, BVRC photometry, and high-resolution spectroscopy in the wavelength region from blue to near-infrared are employed in order to clarify the evolutionary status of the carbon-enhanced metal-poor star HD 112869 with a unique ratio of carbon isotopes in the atmosphere. An LTE abundance analysis was carried out using the method of spectral synthesis and new self-consistent 1D atmospheric models. The radial velocity monitoring confirmed semiregular variations with a peak-to-peak amplitude of about 10 km {{s}-1} and a dominating period of about 115 days. The light, color, and radial velocity variations are typical of the evolved pulsating stars. The atmosphere of HD 112869 appears to be less metal-poor than reported before, [Fe/H] = -2.3 ± 0.2 dex. Carbon-to-oxygen and carbon isotope ratios are found to be extremely high, C/O ≃ 12.6 and12C/13C ≳ 1500, respectively. The s-process elements yttrium and barium are not enhanced, but neodymium appears to be overabundant. The magnesium abundance seems to be lower than the average found for CEMP stars, [Mg/Fe] < +0.4 dex. HD 112869 could be a single low-mass halo star in the stage of asymptotic giant branch evolution.

  6. The first stars: a classification of CEMP-no stars

    CERN Document Server

    Maeder, Andre

    2015-01-01

    We propose and apply a new classification for the CEMP-no stars, which are "carbon-enhanced metal-poor" stars with no overabundance of s-elements and with [Fe/H] generally inferior or equal to -2.5. This classification is based on the changes in abundances for the elements and isotopes involved in the CNO, Ne-Na, and Mg-Al nuclear cycles. These abundances change very much owing to successive back and forth mixing motions between the He- and H-burning regions in massive stars (the "source stars" responsible for the chemical enrichment of the CEMP-no stars). The wide variety of the ratios [C/Fe], 12C/13C, [N/Fe], [O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe], [Sr/Fe], and [Ba/Fe], which are the main characteristics making the CEMP-no and low s stars so peculiar, is described well in terms of the proposed nucleosynthetic classification. We note that the [(C+N+O)/Fe] ratios significantly increase for lower values of [Fe/H]. The classification of CEMP-no stars and the behavior of [(C+N+O)/Fe] support the presence, in the firs...

  7. Hubble Space Telescope Near-Ultraviolet Spectroscopy of the Bright CEMP-no Star BD+44 493

    CERN Document Server

    Placco, Vinicius; Roederer, Ian; Cowan, John; Frebel, Anna; Filler, Dan; Ivans, Inese I; Lawler, James E; Schatz, Hendrik; Sneden, Christopher; Sobeck, Jennifer; Aoki, Wako; Smith, Verne

    2014-01-01

    We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the extremely metal-poor star BD+44 493, a 9th magnitude sub-giant with [Fe/H] = -3.8 and enhanced carbon, based on data acquired with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. This star is the brightest example of a class of objects that, unlike the great majority of carbon-enhanced metal-poor (CEMP) stars, does not exhibit over-abundances of heavy neutron-capture elements (CEMP-no). In this paper, we validate the abundance determinations for a number of species that were previously studied in the optical region, and obtain strong upper limits for beryllium and boron, as well as for neutron-capture elements from zirconium to platinum, many of which are not accessible from ground-based spectra. The boron upper limit we obtain for BD+44 493, logeps(B) < -0.70, the first such measurement for a CEMP star, is the lowest yet found for very and extremely metal-poor stars. In addition, we ob...

  8. Lithium abundance in the metal-poor open cluster NGC 2243

    CERN Document Server

    Francois, P; Biazzo, K; Bonifacio, P; Palsa, R

    2013-01-01

    Lithium is a fundamental element for studying the mixing mechanisms acting in the stellar interiors, for understanding the chemical evolution of the Galaxy and the Big Bang nucleosynthesis. The study of Li in stars of open clusters (hereafter OC) allows a detailed comparison with stellar evolutionary models and permits us to trace its galactic evolution. The OC NGC 2243 is particularly interesting because of its low metallicity ([Fe/H]=$-0.54 \\pm0.10$ dex). We measure the iron and lithium abundance in stars of the metal-poor OC NGC 2243. The first aim is to determine whether the Li dip extends to such low metallicities, the second is to compare the results of our Li analysis in this OC with those present in 47 Tuc, a globular cluster of similar metallicity. We performed a detailed analysis of high-resolution spectra obtained with the multi-object facility FLAMES at the ESO VLT 8.2m telescope. Lithium abundance was derived through line equivalent widths and the OSMARCS atmosphere models. We determine a Li dip ...

  9. A new L-dwarf member of the moderately metal-poor triple system HD 221356

    CERN Document Server

    Gauza, B; Rebolo, R; Ramírez, K Peña; Osorio, M R Zapatero; Pérez-Garrido, A; Lodieu, N; Pinfield, D J; McMahon, R G; González-Solares, E; Emerson, J P; Boudreault, S; Banerji, M

    2012-01-01

    We report on the discovery of a fourth component in the HD 221356 star system, previously known to be formed by an F8V, slightly metal-poor primary ([Fe/H]=-0.26), and a distant M8V+L3V pair. In our ongoing common proper motion search based on VISTA Hemisphere Survey (VHS) and 2MASS catalogues, we have detected a faint (J=13.76+/-0.04 mag) co-moving companion of the F8 star located at angular separation of 12.13+/-0.18 arcsec (position angle of 221.8+/-1.7), corresponding to a projected distance of ~312 AU at 26 pc. Near-infrared spectroscopy of the new companion, covering the 1.5-2.4 micron wavelength range with a resolving power of R~600, indicates an L1+/-1 spectral type. Using evolutionary models the mass of the new companion is estimated at ~0.08 solar masses, which places the object close to the stellar-substellar borderline. This multiple system provides an interesting example of objects with masses slightly above and below the hydrogen burning mass limit. The low mass companions of HD 221356 have slig...

  10. NGC 1252: a high altitude, metal poor open cluster remnant

    CERN Document Server

    Marcos, R de la Fuente; Bidin, C Moni; Carraro, G; Costa, E

    2013-01-01

    If stars form in clusters but most stars belong to the field, understanding the details of the transition from the former to the latter is imperative to explain the observational properties of the field. Aging open clusters are one of the sources of field stars. The disruption rate of open clusters slows down with age but, as an object gets older, the distinction between the remaining cluster or open cluster remnant (OCR) and the surrounding field becomes less and less obvious. As a result, finding good OCR candidates or confirming the OCR nature of some of the best candidates still remain elusive. One of these objects is NGC 1252, a scattered group of about 20 stars in Horologium. Here we use new wide-field photometry in the UBVI pass-bands, proper motions from the Yale/San Juan SPM 4.0 catalogue, and high resolution spectroscopy concurrently with results from N-body simulations to decypher NGC 1252's enigmatic character. Spectroscopy shows that most of the brightest stars in the studied area are chemically,...

  11. A wide-field photometric survey for extratidal tails around five metal-poor globular clusters in the Galactic halo

    CERN Document Server

    Chun, Sang-Hyun; Sohn, Sangmo T; Park, Jang-Hyun; Han, Wonyong; Kim, Ho-Il; Lee, Young-Wook; Lee, Myung Gyoon; Lee, Sang-Gak; Sohn, Young-Jong

    2009-01-01

    Wide-field deep gri images obtained with the Megacam of the Canada-France-Hawaii Telescope (CFHT) are used to investigate the spatial configuration of stars around five metal-poor globular cluster M15, M30, M53, NGC 5053, and NGC 5466, in a field-of-view ~3 degree. Applying a mask filtering algorithm to the color-magnitude diagrams of the observed stars, we sorted cluster's member star candidates that are used to examine the characteristics of the spatial stellar distribution surrounding the target clusters. The smoothed surface density maps and the overlaid isodensity contours indicate that all of the five metal-poor globular clusters exhibit strong evidence of extratidal overdensity features over their tidal radii, in the form of extended tidal tails around the clusters. The orientations of the observed extratidal features show signatures of tidal tails tracing the clusters' orbits, inferred from their proper motions, and effects of dynamical interactions with the Galaxy. Our findings include detections of ...

  12. The Distribution of Carbon Abundances in Stars in the Milky Way’s Satellite Galaxies

    Science.gov (United States)

    Guo, Michelle; Zhang, A.

    2013-01-01

    There is evidence that the Milky Way halo is comprised in part of disrupted dwarf satellite galaxies; however, the extent to which they contribute to the halo’s formation is unclear. To further examine the role of dwarf galaxies in building the halo, we compared the degrees of carbon enhancement of the dwarf spheroidal (dSph) galaxies and field halo populations. We generated a grid of high-resolution synthetic spectra for hypothetical stars of specific effective temperature, surface gravity, metallicity, alpha element abundance, and carbon abundance for comparison with medium-resolution observed spectra of dSph stars of unmeasured [C/Fe] but otherwise known properties. After smoothing, rebinning, and normalizing the two data sets, we varied carbon abundance to find the best carbon abundance by determining the synthetic spectrum that gave the minimal deviation. We found a lower Carbon-Enhanced Metal-Poor (CEMP) fraction in the dSph galaxies, which suggests that they have evolved over time. Whereas star formation and chemical evolution stopped for accreted galaxies, the surviving galaxies evolved to became less carbon enhanced and more metal rich. The variation in carbon abundances supports prior knowledge of dSph stars and provide a deeper understanding the formation of stars such as those of the Milky Way halo. We thank the US National Science Foundation, the UCSC Science Internship Program, and the W. M. Keck Observatory where the spectra were obtained.

  13. Chemical Enrichment in the Carbon-enhanced Damped Lyman $\\alpha$ System

    CERN Document Server

    Kobayashi, Chiaki; Nomoto, Ken'ich

    2011-01-01

    We show that the recently observed elemental abundance pattern of the carbon-rich metal-poor Damped Lyman $\\alpha$ (DLA) system is in excellent agreement with the nucleosynthesis yields of faint core-collapse supernovae of primordial stars. The observed abundance pattern is not consistent with the nucleosynthesis yields of pair-instability supernovae. The DLA abundance pattern is very similar to that of carbon-rich extremely metal-poor (EMP) stars, and the contributions from low-mass stars and/or binary effects should be very small in DLAs. This suggests that chemical enrichment by the first stars in the first galaxies is driven by core-collapse supernovae from $\\sim 20-50 M_\\odot$ stars, and also supports the supernova scenario as the enrichment source of EMP stars in the Milky Way Galaxy.

  14. The Extremely Metal-Poor Dwarf Galaxy AGC 198691

    Science.gov (United States)

    Hirschauer, Alec S.; Salzer, John Joseph; Cannon, John M.; Skillman, Evan D.; SHIELD II Team

    2016-01-01

    We present spectroscopic observations of the nearby dwarf irregular galaxy AGC 198691. This object is part of the Survey of HI in Extremely Low-Mass Dwarfs (SHIELD) sample, which consists of ultra-low HI mass galaxies discovered by the Arecibo Legacy Fast-Acting ALFA (ALFALFA) survey. SHIELD is a multi-configuration Expanded Very Large Array (EVLA) study of the neutral gas content and dynamics of galaxies with HI masses in the range of 106-107 M⊙. Our spectral data were obtained using the new high-throughput KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m telescope as part of a systematic study of the nebular abundances in the SHIELD galaxy sample. These observations enable measurement of the temperature sensitive [OIII]λ4363 line and hence the determination of a "direct" oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) galaxy with an oxygen abundance comparable to such objects as I Zw 18, SBS 0335-052W, Leo P, and DDO 68 - the lowest metallicity star-forming systems known. It is worth noting that two of the five lowest-abundance galaxies currently recognized were discovered via the ALFALFA blind HI survey. These XMD galaxies are potential analogues to the first star-forming systems, which through hierarchical accretion processes built up the large galaxies we observe today in the local Universe. Detailed analysis of such XMD systems offers observational constraint to models of galactic evolution and star formation histories to allow a better understanding of the processes that govern the chemical evolution of low-mass galaxies.

  15. Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68

    CERN Document Server

    Cannon, John M; McQuinn, Kristen B W; Alfvin, Erik D; Bailin, Jeremy; Ford, H Alyson; Girardi, Léo; Hirschauer, Alec S; Janowiecki, Steven; Salzer, John J; Van Sistine, Angela; Dolphin, Andrew; Elson, E C; Koribalski, Baerbel; Marigo, Paola; Rosenberg, Jessica L; Rosenfield, Philip; Skillman, Evan D; Venkatesan, Aparna; Warren, Steven R

    2014-01-01

    We present HI spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only 3% Z$_{\\odot}$, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival HI spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (M$_{\\rm HI}$ $=$ 2.8$\\times$10$^{7}$ M$_{\\odot}$), recently star-forming (SFR$_{\\rm FUV}$ $=$ 1.4$\\times$10$^{-3}$ M$_{\\odot}$ yr$^{-1}$, SFR$_{\\rm H\\alpha}$ $<$ 7$\\times$10$^{-5}$ M$_{\\...

  16. ALFALFA Discovery of the Most Metal-poor Gas-rich Galaxy Known: AGC 198691

    Science.gov (United States)

    Hirschauer, Alec S.; Salzer, John J.; Skillman, Evan D.; Berg, Danielle; McQuinn, Kristen B. W.; Cannon, John M.; Gordon, Alex J. R.; Haynes, Martha P.; Giovanelli, Riccardo; Adams, Elizabeth A. K.; Janowiecki, Steven; Rhode, Katherine L.; Pogge, Richard W.; Croxall, Kevin V.; Aver, Erik

    2016-05-01

    We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of H i in Extremely Low-Mass Dwarfs project, which is a multi-wavelength study of galaxies with H i masses in the range of 106–107.2 M ⊙, discovered by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We have obtained spectra of the lone H ii region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph on the Mayall 4 m, as well as with the Blue Channel spectrograph on the MMT 6.5 m telescope. These observations enable the measurement of the temperature-sensitive [O iii]λ4363 line and hence the determination of a “direct” oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) system with an oxygen abundance of 12+log(O/H) = 7.02 ± 0.03, making AGC 198691 the lowest-abundance star-forming galaxy known in the local universe. Two of the five lowest-abundance galaxies known have been discovered by the ALFALFA blind H i survey; this high yield of XMD galaxies represents a paradigm shift in the search for extremely metal-poor galaxies.

  17. An Infrared High Resolution Spectroscopic Abundance Study of the Metal-Poor Giant HD 122563

    Science.gov (United States)

    Sneden, Christopher; Afsar, Melike; Jaffe, Daniel Thomas; Kim, Hwiyun; Mace, Gregory

    2015-01-01

    A high resolution, high signal-to-noise spectrum of the very metal-poor giant star HD 122563 has been obtained with the newly commissioned IGRINS H- and K-band high resolution (R = 40,000) spectrograph on the McDonald Observatory 2.7m Smith telescope. With complete spectral coverage in the range 1.5-1.8 and 1.9-2.4 microns and high signal-to-noise (S/N > 200) in the reduced spectrum, we have so far detected about 50neutral-species transitions of elements Na, Mg, Al, Si, Ca, and Fe, as well as many transitions of OH and CO.Assuming atmosphere parameters from the literature of this well-studied bright giant (Teff~4600K, log(g)~1.3) we have derived a metallicity of [Fe/H] = -2.8, in agreement with past results. The alpha-elements are enhanced: [(Mg,Si,Ca)/Fe] = +0.3 to +0.4. The OH lines yield an O abundance in good accord with past claims from analyses of the [O I] lines in the visible part of the spectrum. Study of other features in the IGRINSspectrum is ongoing.Support for this research from the US National Science Foundation (AST-1211585) and the The Scientific and Technological Research Council of Turkey (TÜBITAK, project No. 112T929) are acknowledged with thanks.

  18. Is atomic carbon a good tracer of molecular gas in metal-poor galaxies?

    CERN Document Server

    Glover, Simon C O

    2015-01-01

    Carbon monoxide (CO) is widely used as a tracer of molecular hydrogen (H2) in metal-rich galaxies, but is known to become ineffective in low metallicity dwarf galaxies. Atomic carbon has been suggested as a superior tracer of H2 in these metal-poor systems, but its suitability remains unproven. To help us to assess how well atomic carbon traces H2 at low metallicity, we have performed a series of numerical simulations of turbulent molecular clouds that cover a wide range of different metallicities. Our simulations demonstrate that in star-forming clouds, the conversion factor between [CI] emission and H2 mass, $X_{\\rm CI}$, scales approximately as $X_{\\rm CI} \\propto Z^{-1}$. We recover a similar scaling for the CO-to-H2 conversion factor, $X_{\\rm CO}$, but find that at this point in the evolution of the clouds, $X_{\\rm CO}$ is consistently smaller than $X_{\\rm CI}$, by a factor of a few or more. We have also examined how $X_{\\rm CI}$ and $X_{\\rm CO}$ evolve with time. We find that $X_{\\rm CI}$ does not vary ...

  19. Chemical Abundances in NGC 5053: A Very Metal-Poor and Dynamically Complex Globular Cluster

    CERN Document Server

    Boberg, Owen M; Vesperini, Enrico

    2015-01-01

    NGC 5053 provides a rich environment to test our understanding of the complex evolution of globular clusters (GCs). Recent studies have found that this cluster has interesting morphological features beyond the typical spherical distribution of GCs, suggesting that external tidal effects have played an important role in its evolution and current properties. Additionally, simulations have shown that NGC 5053 could be a likely candidate to belong to the Sagittarius dwarf galaxy (Sgr dSph) stream. Using the Wisconsin-Indiana-Yale-NOAO-Hydra multi-object spectrograph, we have collected high quality (signal-to-noise ratio $\\sim$ 75-90), medium-resolution spectra for red giant branch stars in NGC 5053. Using these spectra we have measured the Fe, Ca, Ti, Ni, Ba, Na, and O abundances in the cluster. We measure an average cluster [Fe/H] abundance of -2.45 with a standard deviation of 0.04 dex, making NGC 5053 one of the most metal-poor GCs in the Milky Way (MW). The [Ca/Fe], [Ti/Fe], and [Ba/Fe] we measure are consist...

  20. The rarity of dust in metal-poor galaxies.

    Science.gov (United States)

    Fisher, David B; Bolatto, Alberto D; Herrera-Camus, Rodrigo; Draine, Bruce T; Donaldson, Jessica; Walter, Fabian; Sandstrom, Karin M; Leroy, Adam K; Cannon, John; Gordon, Karl

    2014-01-01

    Galaxies observed at redshift z > 6, when the Universe was less than a billion years old, thus far very rarely show evidence of the cold dust that accompanies star formation in the local Universe, where the dust-to-gas mass ratio is around one per cent. A prototypical example is the galaxy Himiko (z = 6.6), which--a mere 840 million years after the Big Bang--is forming stars at a rate of 30-100 solar masses per year, yielding a mass assembly time of about 150 × 10(6) years. Himiko is thought to have a low fraction (2-3 per cent of the Sun's) of elements heavier than helium (low metallicity), and although its gas mass cannot yet be determined its dust-to-stellar mass ratio is constrained to be less than 0.05 per cent. The local dwarf galaxy I Zwicky 18, which has a metallicity about 4 per cent that of the Sun's and is forming stars less rapidly (assembly time about 1.6 × 10(9) years) than Himiko but still vigorously for its mass, is also very dust deficient and is perhaps one of the best analogues of primitive galaxies accessible to detailed study. Here we report observations of dust emission from I Zw 18, from which we determine its dust mass to be 450-1,800 solar masses, yielding a dust-to-stellar mass ratio of about 10(-6) to 10(-5) and a dust-to-gas mass ratio of 3.2-13 × 10(-6). If I Zw 18 is a reasonable analogue of Himiko, then Himiko's dust mass must be around 50,000 solar masses, a factor of 100 below the current upper limit. These numbers are quite uncertain, but if most high-z galaxies are more like Himiko than like the very-high-dust-mass galaxy SDSS J114816.64 + 525150.3 at z ≈ 6, which hosts a quasar, then our prospects for detecting the gas and dust inside such galaxies are much poorer than hitherto anticipated. PMID:24317694

  1. A support vector machine to search for metal-poor galaxies

    Science.gov (United States)

    Shi, Fei; Liu, Yu-Yan; Kong, Xu; Chen, Yang; Li, Zhong-Hua; Zhi, Shu-Teng

    2014-10-01

    To develop a fast and reliable method for selecting metal-poor galaxies (MPGs), especially in large surveys and huge data bases, a support vector machine (SVM) supervized learning algorithms is applied to a sample of star-forming galaxies from the Sloan Digital Sky Survey data release 9 provided by the Max Planck Institute and the Johns Hopkins University (http://www.sdss3.org/dr9/spectro/spectroaccess.php). A two-step approach is adopted: (i) the SVM must be trained with a subset of objects that are known to be either MPGs or metal-rich galaxies (MRGs), treating the strong emission line flux measurements as input feature vectors in n-dimensional space, where n is the number of strong emission line flux ratios. (ii) After training on a sample of star-forming galaxies, the remaining galaxies are classified in the automatic test analysis as either MPGs or MRGs using a 10-fold cross-validation technique. For target selection, we have achieved an acquisition accuracy for MPGs of ˜96 and ˜95 per cent for an MPG threshold of 12 + log(O/H) = 8.00 and 12 + log(O/H) = 8.39, respectively. Running the code takes minutes in most cases under the MATLAB 2013a software environment. The code in the Letter is available on the web (http://fshi5388.blog.163.com). The SVM method can easily be extended to any MPGs target selection task and can be regarded as an efficient classification method particularly suitable for modern large surveys.

  2. The evolved pulsating CEMP star HD112869

    CERN Document Server

    Začs, L; Grankina, A; Deveikis, V; Kaminskyi, B; Pavlenko, Y; Musaev, F

    2015-01-01

    Radial velocity measurements, $BVR_C$ photometry, and high-resolution spectroscopy in the wavelength region from blue to near infrared are employed in order to clarify the evolutionary status of the carbon-enhanced metal-poor star HD112869 with unique ratio of carbon isotopes in the atmosphere. An LTE abundance analysis was carried out using the method of spectral synthesis and new self consistent 1D atmospheric models. The radial velocity monitoring confirmed semiregular variations with a peak-to-peak amplitude of about 10 km $s^{-1}$ and a dominating period of about 115 days. The light, color and radial velocity variations are typical of the evolved pulsating stars. The atmosphere of HD112869 appears to be less metal-poor than reported before, [Fe/H] = -2.3 $\\pm$0.2 dex. Carbon to oxygen and carbon isotope ratios are found to be extremely high, C/O $\\simeq$ 12.6 and $^{12}C/^{13}C \\gtrsim$ 1500, respectively. The s-process elements yttrium and barium are not enhanced, but neodymium appears to be overabundan...

  3. An Age Difference of 2 Gyr between a Metal-Rich and a Metal-Poor Globular Cluster

    CERN Document Server

    Hansen, B M S; Anderson, J; Dotter, A; Richer, H B; Rich, R M; Shara, M M; Fahlman, G G; Hurley, J R; King, I R; Reitzel, D; Stetson, P B

    2013-01-01

    Globular clusters trace the formation history of the spheroidal components of both our Galaxy and others, which represent the bulk of star formation over the history of the universe. They also exhibit a range of metallicities, with metal-poor clusters dominating the stellar halo of the Galaxy, and higher metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and later swallowed along with their original host galaxies, and which were formed in situ. Here we present an age determination of the metal-rich globular cluster 47 Tucanae by fitting the properties of the cluster white dwarf population, which implies an absolute age of 9.9 (0.7) Gyr at 95% confidence. This is about 2.0 Gyr younger than inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evi...

  4. Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of CEMP-no Stars

    CERN Document Server

    Yoon, Jinmi; Placco, Vinicius M; Rasmussen, Kaitlin C; Carollo, Daniela; He, Siyu; Hansen, Terese T; Roederer, Ian U

    2016-01-01

    We investigate anew the distribution of absolute carbon abundance, $A$(C) $= \\log\\,\\epsilon $(C), for carbon-enhanced metal-poor (CEMP) stars in the halo of the Milky Way, based on high-resolution spectroscopic data for a total sample of 301 CEMP stars. The sample includes 147 CEMP-$s$ (and CEMP-r/s) stars, 124 CEMP-no stars, and 30 CEMP stars that are unclassified, based on the currently employed [Ba/Fe] criterion. We confirm previous claims that the distribution of $A$(C) for CEMP stars is (at least) bimodal, with newly determined peaks centered on $A$(C)$=7.93$ (the high-C region) and $A$(C)$ =6.28$ (the low-C region). A very high fraction of CEMP-$s$ (and CEMP-r/s) stars belong to the high-C region, while the great majority of CEMP-no stars reside in the low-C region. However, there exists complexity in the morphology of the $A$(C)-[Fe/H] space for the CEMP-no stars, a first indication that more than one class of first-generation stellar progenitors may be required to account for their observed abundances...

  5. The metal-poor knee in the Fornax dwarf spheroidal galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Hendricks, Benjamin; Koch, Andreas [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117, Heidelberg (Germany); Lanfranchi, Gustavo A. [Núcleo de Astrofísica Teórica, Universidade Cruzeiro do Sul, R. Galvão Bueno 868, Liberdade, 01506-000, São Paulo, SP (Brazil); Boeche, Corrado [Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12-14, D-69120, Heidelberg (Germany); Walker, Matthew [McWilliams Center for Cosmology, Carnegie Mellon University, 5000 Forbes Ave., Pittsburgh, PA 15213 (United States); Johnson, Christian I. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-15, Cambridge, MA 02138 (United States); Peñarrubia, Jorge [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Gilmore, Gerard, E-mail: ben.hendricks@lsw.uni-heidelberg.de [Institute of Astronomy, Cambridge University, Madingley Rd, Cambridge CB3 OHA (United Kingdom)

    2014-04-20

    We present α-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal (dSph) galaxy, obtained with Very Large Telescope/GIRAFFE (R ∼ 16, 000). Due to the large fraction of metal-poor (MP) stars in our sample, we are able to follow the α-element evolution from [Fe/H] ≈ –2.5 continuously to [Fe/H] ≈ –0.7. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, α-enhanced plateau down to subsolar [α/Fe] values, due to the onset of SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an α-enhanced plateau at early epochs, followed by a well-defined 'knee' caused by the onset of SNe Ia, and finally a second plateau with sub-solar [α/Fe] values. We find the position of this knee to be at [Fe/H] ≈ –1.9 and therefore significantly more MP than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value is rather comparable to the knee in Sculptor, a dSph ∼10 times less luminous than Fornax. Using chemical evolution models, we find that the position of the knee and the subsequent plateau at the sub-solar level can hardly be explained unless the galaxy experienced several discrete star formation (SF) events with a drastic variation in SF efficiency, while a uniform SF can be ruled out. One possible evolutionary scenario is that Fornax experienced one or several major accretion events from gas-rich systems in the past, so that its current stellar mass is not indicative of the chemical evolution environment at ancient times. If Fornax is the product of several smaller buildings blocks, this may also have implications for the understanding of the formation process of dSphs in general.

  6. The metal-poor knee in the Fornax dwarf spheroidal galaxy

    International Nuclear Information System (INIS)

    We present α-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal (dSph) galaxy, obtained with Very Large Telescope/GIRAFFE (R ∼ 16, 000). Due to the large fraction of metal-poor (MP) stars in our sample, we are able to follow the α-element evolution from [Fe/H] ≈ –2.5 continuously to [Fe/H] ≈ –0.7. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, α-enhanced plateau down to subsolar [α/Fe] values, due to the onset of SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an α-enhanced plateau at early epochs, followed by a well-defined 'knee' caused by the onset of SNe Ia, and finally a second plateau with sub-solar [α/Fe] values. We find the position of this knee to be at [Fe/H] ≈ –1.9 and therefore significantly more MP than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value is rather comparable to the knee in Sculptor, a dSph ∼10 times less luminous than Fornax. Using chemical evolution models, we find that the position of the knee and the subsequent plateau at the sub-solar level can hardly be explained unless the galaxy experienced several discrete star formation (SF) events with a drastic variation in SF efficiency, while a uniform SF can be ruled out. One possible evolutionary scenario is that Fornax experienced one or several major accretion events from gas-rich systems in the past, so that its current stellar mass is not indicative of the chemical evolution environment at ancient times. If Fornax is the product of several smaller buildings blocks, this may also have implications for the understanding of the formation process of dSphs in general.

  7. DISCOVERY OF A GAS-RICH COMPANION TO THE EXTREMELY METAL-POOR GALAXY DDO 68

    International Nuclear Information System (INIS)

    We present H I spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only ∼3% Z ☉, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival H I spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (MH I = 2.8 × 107 M ☉), recently star-forming (SFRFUV = 1.4 × 10–3 M ☉ yr–1, SFRHα < 7 × 10–5 M ☉ yr–1) companion has the same systemic velocity as DDO 68 (V sys = 506 km s–1; D = 12.74 ± 0.27 Mpc) and is located at a projected distance of ∼42 kpc. New H I maps obtained with the 100 m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness H I gas forms a bridge between these objects

  8. DISCOVERY OF A GAS-RICH COMPANION TO THE EXTREMELY METAL-POOR GALAXY DDO 68

    Energy Technology Data Exchange (ETDEWEB)

    Cannon, John M.; Alfvin, Erik D. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Johnson, Megan; Koribalski, Baerbel [Australia Telescope National Facility, CSIRO Astronomy and Space Science, P.O. Box 76, NSW 1710, Epping (Australia); McQuinn, Kristen B. W.; Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455 (United States); Bailin, Jeremy [Department of Physics and Astronomy, University of Alabama, P.O. Box 870324, Tuscaloosa, AL 35487-0324 (United States); Ford, H. Alyson [National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944 (United States); Girardi, Léo [Osservatorio Astronomico di Padova—INAF, Vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Hirschauer, Alec S.; Janowiecki, Steven; Salzer, John J.; Van Sistine, Angela [Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405 (United States); Dolphin, Andrew [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Elson, E. C. [Astrophysics, Cosmology and Gravity Centre (ACGC), Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa); Marigo, Paola; Rosenfield, Philip [Dipartimento di Fisica e Astronomia Galileo Galilei, Universitá degli Studi di Padova, Vicolo dell' Osservatorio 3, I-35122 Padova (Italy); Rosenberg, Jessica L. [School of Physics, Astronomy, and Computational Science, George Mason University, Fairfax, VA 22030 (United States); Venkatesan, Aparna [Department of Physics and Astronomy, University of San Francisco, 2130 Fulton Street, San Francisco, CA 94117 (United States); Warren, Steven R., E-mail: jcannon@macalester.edu [Department of Astronomy, University of Maryland, CSS Bldg., Rm. 1024, Stadium Drive, College Park, MD 20742-2421 (United States)

    2014-05-20

    We present H I spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only ∼3% Z {sub ☉}, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival H I spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (M{sub H} {sub I} = 2.8 × 10{sup 7} M {sub ☉}), recently star-forming (SFR{sub FUV} = 1.4 × 10{sup –3} M {sub ☉} yr{sup –1}, SFR{sub Hα} < 7 × 10{sup –5} M {sub ☉} yr{sup –1}) companion has the same systemic velocity as DDO 68 (V {sub sys} = 506 km s{sup –1}; D = 12.74 ± 0.27 Mpc) and is located at a projected distance of ∼42 kpc. New H I maps obtained with the 100 m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness H I gas forms a bridge between these objects.

  9. The ACS Nearby Galaxy Survey Treasury IX. Constraining asymptotic giant branch evolution with old metal-poor galaxies

    CERN Document Server

    Girardi, Leo; Gilbert, Karoline M; Rosenfield, Philip; Dalcanton, Julianne J; Marigo, Paola; Boyer, Martha L; Dolphin, Andrew; Weisz, Daniel R; Melbourne, Jason; Olsen, Knut A G; Seth, Anil C; Skillman, Evan

    2010-01-01

    In an attempt to constrain evolutionary models of the asymptotic giant branch (AGB) phase at the limit of low masses and low metallicities, we have examined the luminosity functions and number ratio between AGB and red giant branch (RGB) stars from a sample of resolved galaxies from the ACS Nearby Galaxy Survey Treasury (ANGST). This database provides HST optical photometry together with maps of completeness, photometric errors, and star formation histories for dozens of galaxies within 4 Mpc. We select 12 galaxies characterized by predominantly metal-poor populations as indicated by a very steep and blue RGB, and which do not present any indication of recent star formation in their color--magnitude diagrams. Thousands of AGB stars brighter than the tip of the RGB (TRGB) are present in the sample (between 60 and 400 per galaxy), hence the Poisson noise has little impact in our measurements of the AGB/RGB ratio. We model the photometric data with a few sets of thermally pulsing AGB (TP-AGB) evolutionary models...

  10. Discovery of a Metal-Poor Field Giant with a Globular Cluster Second-Generation Abundance Pattern

    CERN Document Server

    Fernandez-Trincado, J G; Moreno, E; Schiavon, R P; Peréz, A E García; Vieira, K; Cunha, K; Zamora, O; Sneden, C; Carrera, R; Johnson, J A; Shetrone, M; Zasowski, G; García-Hernándes, D A; Majewski, S R; Reylé, C; Blanco-Cuaresma, S; Martinez-Medina, L A; Pérez-Villegas, A; Valenzuela, O; Pichardo, B; Meza, A; Mészáros, Sz; Sobeck, J; Geisler, D; Anders, F; Schultheis, M; Tang, B; Roman-Lopes, A; Mennickent, R E; Pan, K; Nitschelm, C; Allard, F

    2016-01-01

    We report on the direct detection from observations obtained with the APOGEE survey of a metal-poor ([Fe/H]$=-1.3$) field giant star in the Milky Way, with an extreme Mg-Al abundance ([Mg/Fe]$=$-0.31; [Al/Fe]$=$1.49) seen only among the secondary population of globular clusters. This star, 2M16011638-1201525 found using SDSSIII/APOGEE data also shows particularly atypical light-element patterns not seen among Galactic disk field stars, indicating that it could have been born in a globular cluster. We explore several explanations, in particular studying the orbit of the star to check the probability of it being related to known globular clusters. With the use of a Monte Carlo scheme, we performed simple orbital integrations assuming the estimated distance of 2M16011638-1201525 and the available six-dimensional phase-space coordinates of 63 globular clusters, looking for close encounters in the past with a minimum distance approach within the tidal radius for each cluster. We found a very low probability that 2...

  11. Characterizing the Chemistry of the Milky Way Stellar Halo: Detailed Chemical Analysis of a Metal-Poor Stellar Stream

    CERN Document Server

    Roederer, Ian U; Thompson, Ian B; Preston, George W; Shectman, Stephen A

    2010-01-01

    We present the results of a detailed abundance analysis of one of the confirmed building blocks of the Milky Way stellar halo, a kinematically-coherent metal-poor stellar stream. We have obtained high resolution and high S/N spectra of 12 probable stream members using the MIKE spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the 2dCoude spectrograph on the Smith Telescope at McDonald Observatory. We have derived abundances or upper limits for 51 species of 46 elements in each of these stars. The stream members show a range of metallicity (-3.4 < [Fe/H] < -1.5) but are otherwise chemically homogeneous, with the same star-to-star dispersion in [X/Fe] as the rest of the halo. This implies that, in principle, a significant fraction of the Milky Way stellar halo could have formed from accreted systems like the stream. The stream stars show minimal evolution in the alpha or Fe-group elements over the range of metallicity. This stream is enriched with material produced by the main an...

  12. The first stars: CEMP--no stars and signatures of spinstars

    CERN Document Server

    Maeder, Andre; Chiappini, Cristina

    2014-01-01

    (Abridged) The CEMP--no stars are "carbon-enhanced-metal-poor" stars that in principle show no evidence of s-- and r--elements from neutron captures. We try to understand the origin and nucleosynthetic site of their peculiar CNO, Ne--Na, and Mg--Al abundances. We compare the observed abundances to the nucleosynthetic predictions of AGB models and of models of rotating massive stars with internal mixing and mass loss. We also analyze the different behaviors of $\\alpha$-- and CNO--elements, as well the abundances of elements involved in the Ne--Na and Mg--Al cycles. We show that CEMP-no stars exhibit products of He--burning that have gone through partial mixing and processing by the CNO cycle, producing low $^{12}$C/$^{13}$C and a broad variety of [C/N] and [O/N] ratios. From a $^{12}$C/$^{13}$C vs. [C/N] diagram, we conclude that neither the yields of AGB stars (in binaries or not) nor the yields of classic supernovae can fully account for the observed CNO abundances in CEMP-no stars. Better agreement is obtai...

  13. Hubble space telescope near-ultraviolet spectroscopy of the bright cemp-no star BD+44°493

    Energy Technology Data Exchange (ETDEWEB)

    Placco, Vinicius M. [Gemini Observatory, Hilo, HI 96720 (United States); Beers, Timothy C.; Smith, Verne V. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Roederer, Ian U. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Cowan, John J. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Frebel, Anna [Kavli Institute for Astrophysics and Space Research and Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Filler, Dan; Ivans, Inese I. [Department of Physics and Astronomy, The University of Utah, Salt Lake City, UT 84112 (United States); Lawler, James E. [Department of Physics, University of Wisconsin, Madison, WI 53706 (United States); Schatz, Hendrik [JINA—Joint Institute for Nuclear Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, IN 46556-5670 (United States); Sneden, Christopher [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States); Sobeck, Jennifer S. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Aoki, Wako, E-mail: vplacco@gemini.edu [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2014-07-20

    We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the extremely metal-poor star BD+44°493 a ninth magnitude subgiant with [Fe/H] =–3.8 and enhanced carbon, based on data acquired with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. This star is the brightest example of a class of objects that, unlike the great majority of carbon-enhanced metal-poor (CEMP) stars, does not exhibit over-abundances of heavy neutron-capture elements (CEMP-no). In this paper, we validate the abundance determinations for a number of species that were previously studied in the optical region, and obtain strong upper limits for beryllium and boron, as well as for neutron-capture elements from zirconium to platinum, many of which are not accessible from ground-based spectra. The boron upper limit we obtain for BD+44°493, log ε (B) <–0.70, the first such measurement for a CEMP star, is the lowest yet found for very and extremely metal-poor stars. In addition, we obtain even lower upper limits on the abundances of beryllium, log ε (Be) <–2.3, and lead, log ε (Pb) <–0.23 ([Pb/Fe] <+1.90), than those reported by previous analyses in the optical range. Taken together with the previously measured low abundance of lithium, the very low upper limits on Be and B suggest that BD+44°493 was formed at a very early time, and that it could well be a bona-fide second-generation star. Finally, the Pb upper limit strengthens the argument for non-s-process production of the heavy-element abundance patterns in CEMP-no stars.

  14. Hubble space telescope near-ultraviolet spectroscopy of the bright cemp-no star BD+44°493

    International Nuclear Information System (INIS)

    We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the extremely metal-poor star BD+44°493 a ninth magnitude subgiant with [Fe/H] =–3.8 and enhanced carbon, based on data acquired with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. This star is the brightest example of a class of objects that, unlike the great majority of carbon-enhanced metal-poor (CEMP) stars, does not exhibit over-abundances of heavy neutron-capture elements (CEMP-no). In this paper, we validate the abundance determinations for a number of species that were previously studied in the optical region, and obtain strong upper limits for beryllium and boron, as well as for neutron-capture elements from zirconium to platinum, many of which are not accessible from ground-based spectra. The boron upper limit we obtain for BD+44°493, log ε (B) <–0.70, the first such measurement for a CEMP star, is the lowest yet found for very and extremely metal-poor stars. In addition, we obtain even lower upper limits on the abundances of beryllium, log ε (Be) <–2.3, and lead, log ε (Pb) <–0.23 ([Pb/Fe] <+1.90), than those reported by previous analyses in the optical range. Taken together with the previously measured low abundance of lithium, the very low upper limits on Be and B suggest that BD+44°493 was formed at a very early time, and that it could well be a bona-fide second-generation star. Finally, the Pb upper limit strengthens the argument for non-s-process production of the heavy-element abundance patterns in CEMP-no stars.

  15. The Weak Carbon Monoxide Emission In An Extremely Metal Poor Galaxy, Sextans A

    CERN Document Server

    Shi, Yong; Zhang, Zhi-Yu; Gao, Yu; Armus, Lee; Helou, George; Gu, Qiusheng; Stierwalt, Sabrina

    2015-01-01

    Carbon monoxide (CO) is one of the primary coolants of gas and an easily accessible tracer of molecular gas in spiral galaxies but it is unclear if CO plays a similar role in metal poor dwarfs. We carried out a deep observation with IRAM 30 m to search for CO emission by targeting the brightest far-IR peak in a nearby extremely metal poor galaxy, Sextans A, with 7% Solar metallicity. A weak CO J=1-0 emission is seen, which is already faint enough to place a strong constraint on the conversion factor (a_CO) from the CO luminosity to the molecular gas mass that is derived from the spatially resolved dust mass map. The a_CO is at least seven hundred times the Milky Way value. This indicates that CO emission is exceedingly weak in extremely metal poor galaxies, challenging its role as a coolant in these galaxies.

  16. Carbon-enhanced VRLA batteries.

    Energy Technology Data Exchange (ETDEWEB)

    Enos, David George; Hund, Thomas D.; Shane, Rod (East Penn Manufacturing, Lyon Station, PA)

    2010-10-01

    The addition of certain forms of carbon to the negative plate in valve regulated lead acid (VRLA) batteries has been demonstrated to increase the cycle life of such batteries by an order of magnitude or more under high-rate, partial-state-of-charge operation. Such performance will provide a significant impact, and in some cases it will be an enabling feature for applications including hybrid electric vehicles, utility ancillary regulation services, wind farm energy smoothing, and solar photovoltaic energy smoothing. There is a critical need to understnd how the carbon interacts with the negative plate and achieves the aforementioned benefits at a fundamental level. Such an understanding will not only enable the performance of such batteries to be optimzied, but also to explore the feasibility of applying this technology to other battery chemistries. In partnership with the East Penn Manufacturing, Sandia will investigate the electrochemical function of the carbon and possibly identify improvements to its anti-sulfation properties. Shiomi, et al. (1997) discovered that the addition of carbon to the negative active material (NAM) substantially reduced PbSO{sub 4} accumulation in high rate, partial state of charge (HRPSoC) cycling applications. This improved performance with a minimal cost. Cycling applications that were uneconomical for traditional VRLA batteries are viable for the carbon enhanced VRLA. The overall goal of this work is to quantitatively define the role that carbon plays in the electrochemistry of a VRLA battery.

  17. Explosive Nucleosynthesis of Weak R-Process Elements in Extremely Metal-Poor Core-Collapse Supernovae

    Science.gov (United States)

    Izutani, Natsuko; Umeda, Hideyuki; Tominaga, Nozomu

    2009-02-01

    There have been attempts to fit the abundance patterns of extremely metal-poor (EMP) stars with supernova (SN) nucleosynthesis models for the elements lighter than Zn. Observations have revealed the presence of EMP stars with a peculiarly high ratio of "weak r-process elements" Sr, Y, and Zr. Although several possible processes were suggested for the origin of these elements, a complete solution for reproducing those ratios has not yet been found. In order to reproduce the abundance patterns of such stars, we investigate a model with neutron-rich matter ejection from the inner region of the conventional mass-cut. We find that explosive nucleosynthesis in a high energy SN (or "hypernova") can reproduce the high abundances of Sr, Y, and Zr but that the enhancements of Sr, Y, and Zr are not achieved by nucleosynthesis in a normal SN. Our results imply that, if these elements are ejected from a normal SN, nucleosynthesis in higher entropy flow than that of the SN shock is required.

  18. Europium s-process signature at close-to-solar metallicity in stardust SiC grains from AGB stars

    CERN Document Server

    Avila, Janaina N; Lugaro, Maria; Gyngard, Frank; Zinner, Ernst; Cristallo, Sergio; Holden, Peter; Rauscher, Thomas

    2013-01-01

    Individual mainstream stardust silicon carbide (SiC) grains and a SiC-enriched bulk sample from the Murchison carbonaceous meteorite have been analyzed by the Sensitive High Resolution Ion Microprobe - Reverse Geometry (SHRIMP-RG) for Eu isotopes. The mainstream grains are believed to have condensed in the outflows of 1.5 to 3 Msun carbon-rich asymptotic giant branch (AGB) stars with close-to-solar metallicity. The 151Eu fractions [fr(151Eu) = 151Eu/(151Eu+153Eu)] derived from our measurements are compared with previous astronomical observations of carbon-enhanced metal-poor (CEMP) stars enriched in elements made by slow neutron captures (the s-process). Despite the difference in metallicity between the parent stars of the grains and the metal-poor stars, the fr(151Eu) values derived from our measurements agree well with fr(151Eu) values derived from astronomical observations. We have also compared the SiC data with theoretical predictions of the evolution of Eu isotopic ratios in the envelope of AGB stars. B...

  19. Searching for chemical relics of first stars with LAMOST and Subaru

    Science.gov (United States)

    Li, Haining; Aoki, Wako; Zhao, Gang; Honda, Satoshi; Christlieb, Norbert; Takuma, Suda

    2015-08-01

    Extremely Metal-Poor (EMP) stars ([Fe/H] EMP stars are rare, but provide basic information of first stars and supernova, as well as on the nucleosynthesis and chemical enrichment of the very beginning of the Universe. LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) plans to observe 6 million Galactic stars through a 5-year spectroscopic survey, and has already obtained more than 3 million stellar spectra during the first two years. Such huge database will provide an unprecedented chance to enlarge the EMP star sample. Since 2014, a joint project on searching for EMP stars has been initiated based on the LAMOST survey and Subaru follow-up observation. The first run with Subaru for 54 objects found by the LAMOST survey resulted in 40 EMP stars, indicating that the efficiency of the searches for EMP stars from LAMOST is as high as 80%. We already identified chemically interesting objects in our EMP sample: (1) Two UMP (ultra metal-poor) stars with [Fe/H] ~ -4.0 have been found, of which only a dozen have been discovered in the past 30 years. One of them is the second UMP turnoff star with Li detection. Both objects are carbon-enhanced stars with no excess of neutron-capture elements (i.e. CEMP-no stars). (2) A super Li-rich (A(Li)=+3) giant with extremely low metallicity has been discovered. This is the most metal-poor and most extreme example of Li enhancement in red giants known to date, and will shed light on production of Li during the evolution on the red giant branch. (3) A few EMP stars showing extreme enhancements in neutron-capture elements showing r-process or s-process abundance patterns have also been identified. Detailed chemical abundances of these extreme objects, as well as statistics obtained by the large sample of EMP stars, provides with important constraints on formation processes of the Milky Way halo.

  20. The origin of the most iron-poor star

    International Nuclear Information System (INIS)

    We investigate the origin of carbon-enhanced metal-poor (CEMP) stars starting from the recently discovered [Fe/H] < -7.1 star SMSS J031300. We show that the elemental abundances observed on the surface of SMSS J031300 can be well fit by the yields of faint, metal-free, supernovae (SNe). Using properly calibrated faint SN explosion models, we study, for the first time, the formation of dust grains in such carbon-rich, iron-poor SN ejecta. Calculations are performed assuming both unmixed and uniformly mixed ejecta and taking into account the partial destruction by the SN reverse shock. We find that, due to the paucity of refractory elements beside carbon, amorphous carbon is the only grain species to form, with carbon condensation efficiencies that range between (0.15 and 0.84), resulting in dust yields in the range (0.025-2.25) M ☉. We follow the collapse and fragmentation of a star-forming cloud enriched by the products of these faint SN explosions and we explore the role played by fine structure line cooling and dust cooling. We show that even if grain growth during the collapse has a minor effect of the dust-to-gas ratio, due to C depletion into CO molecules at an early stage of the collapse, the formation of CEMP low-mass stars, such as SMSS J031300, could be triggered by dust cooling and fragmentation. A comparison between model predictions and observations of a sample of C-normal and C-rich metal-poor stars supports the idea that a single common pathway may be responsible for the formation of the first low-mass stars.

  1. The Origin of the Metal-Poor Common Proper Motion Pair HD 134439/134440: Insights from New Elemental Abundances

    CERN Document Server

    Chen, Yu; Boesgaard, Ann M

    2014-01-01

    The low [alpha/Fe] ratio in the metal-poor ([Fe/H]= -1.50) common proper motion pair HD 134439 and HD 134440 has been variously attributed to chemical evolution in an extragalactic environment with an irregular star formation history, planetessimal accretion, and formation in an environment with an unusually high dust-to-gas ratio. We explore these various putative origins using CNO, Be, Ag, and Eu abundances derived from high-resolution near-UV Keck/HIRES spectroscopy. While we confirm a previously suggested correlation between elemental abundance ratios and condensation temperature at the 95% confidence level, these ratios lie within the continuum of values manifested by extant dSph data. We argue that the most plausible origin of our stars' distinctive abundance distribution relative to the Galactic halo field is formation in an environment chemically dominated by products of Type II SN of low progenitor mass; such a progenitor mass bias has been previously suggested as an explanation of low alpha-element ...

  2. An optical transmission spectrum of the transiting hot Jupiter in the metal-poor WASP-98 planetary system

    CERN Document Server

    Mancini, L; Molliere, P; Southworth, J; Brahm, R; Ciceri, S; Henning, Th

    2016-01-01

    The WASP-98 planetary system represents a rare case of a hot Jupiter hosted by a metal-poor main-sequence star. We present a follow-up study of this system based on multi-band photometry and high-resolution spectroscopy. Two new transit events of WASP-98b were simultaneously observed in four passbands (g,r,i,z), using the telescope-defocussing technique, yielding eight high-precision light curves with point-to-point scatters of less than 1 mmag. We also collected three spectra of the parent star with a high-resolution spectrograph, which we used to remeasure its spectral characteristics, in particular its metallicity. We found this to be very low, Fe/H]=-0.49, but larger than was previously reported, [Fe/H]=-0.60. We used these new photometric and spectroscopic data to refine the orbital and physical properties of this planetary system, finding that the stellar and planetary mass measurements are significantly larger than those in the discovery paper. In addition, the multi-band light curves were used to cons...

  3. The distribution of stars in space.

    Science.gov (United States)

    Gilmore, G.

    Contents: 1. A didactic ramble. 2. Star counts and galactic structure. 3. Integrated surface-brightness measurements. 4. Specific tracers of galactic structure. 5. The analysis of star-count data. 6. The shape of the metal-poor halo.

  4. Search for Extremely Metal-poor Galaxies in the Sloan Digital Sky Survey. (II). High Electron Temperature Objects

    Science.gov (United States)

    Sánchez Almeida, J.; Pérez-Montero, E.; Morales-Luis, A. B.; Muñoz-Tuñón, C.; García-Benito, R.; Nuza, S. E.; Kitaura, F. S.

    2016-03-01

    Extremely metal-poor (XMP) galaxies are defined to have a gas-phase metallicity smaller than a tenth of the solar value (12+{log}[{{O/H}}]k-means, we classify 788,677 spectra to select 1281 galaxies that have particularly intense [O III]λ4363 with respect to [O III]λ5007, which is a proxy for high electron temperature. The metallicity of these candidates was computed using a hybrid technique consistent with the direct method, rendering 196 XMPs. A less restrictive noise constraint provides a larger set with 332 candidates. Both lists are provided in electronic format. The selected XMP sample has a mean stellar mass around {10}8 {M}⊙ , with the dust mass ∼ {10}3{M}⊙ for typical star-forming regions. In agreement with previous findings, XMPs show a tendency to be tadpole-like or cometary. Their underlying stellar continuum corresponds to a fairly young stellar population (clusters. The puzzling 2%-solar low-metallicity threshold exhibited by XMPs remains.

  5. Molecular depletion times and the CO-to-H2 conversion factor in metal-poor galaxies

    CERN Document Server

    Hunt, L K; Casasola, V; Caselli, P; Combes, F; Henkel, C; Lundgren, A; Maiolino, R; Menten, K M; Testi, L; Weiss, A

    2015-01-01

    Tracing molecular hydrogen content with carbon monoxide in low-metallicity galaxies has been exceedingly difficult. Here we present a new effort, with IRAM 30-m observations of 12CO(1-0) of a sample of 8 dwarf galaxies having oxygen abundances ranging from 12+logO/H=7.7 to 8.4. CO emission is detected in all galaxies, including the most metal-poor galaxy of our sample (0.1 Zsun); to our knowledge this is the largest number of 12CO(1-0) detections ever reported for galaxies with 12+logO/H<=8 (0.2 Zsun) outside the Local Group. We calculate stellar masses (Mstar) and star-formation rates (SFRs), and analyze our results by combining our observations with galaxy samples from the literature. Extending previous results for a correlation of the molecular gas depletion time, tau(dep), with Mstar and specific SFR (sSFR), we find a variation in tau(dep) of a factor of 200 or more (from <50 Myr to 10 Gyr) over a spread of 1000 in sSFR and Mstar. We exploit the variation of tau(dep) to constrain the CO-to-H2 mass c...

  6. CEMP stars: possible hosts to carbon planets in the early universe

    Science.gov (United States)

    Mashian, Natalie; Loeb, Abraham

    2016-05-01

    We explore the possibility of planet formation in the carbon-rich protoplanetary disks of carbon-enhanced metal-poor (CEMP) stars, possible relics of the early Universe. The chemically anomalous abundance patterns ([C/Fe] ≥ 0.7) in this subset of low-mass stars suggest pollution by primordial core-collapsing supernovae (SNe) ejecta that are particularly rich in carbon dust grains. By comparing the dust-settling timescale in the protoplanetary disks of CEMP stars to the expected disk lifetime (assuming dissipation via photoevaporation), we determine the maximum distance rmax from the host CEMP star at which carbon-rich planetesimal formation is possible, as a function of the host star's [C/H] abundance. We then use our linear relation between rmax and [C/H], along with the theoretical mass-radius relation derived for a solid, pure carbon planet, to characterize potential planetary transits across host CEMP stars. Given that the related transits are detectable with current and upcoming space-based transit surveys, we suggest initiating an observational program to search for carbon planets around CEMP stars in hopes of shedding light on the question of how early planetary systems may have formed after the Big Bang.

  7. CEMP stars: possible hosts to carbon planets in the early Universe

    Science.gov (United States)

    Mashian, Natalie; Loeb, Abraham

    2016-08-01

    We explore the possibility of planet formation in the carbon-rich protoplanetary discs of carbon-enhanced metal-poor (CEMP) stars, possible relics of the early Universe. The chemically anomalous abundance patterns ([C/Fe] ≥ 0.7) in this subset of low-mass stars suggest pollution by primordial core-collapsing supernovae ejecta that are particularly rich in carbon dust grains. By comparing the dust-settling time-scale in the protoplanetary discs of CEMP stars to the expected disc lifetime (assuming dissipation via photoevaporation), we determine the maximum distance rmax from the host CEMP star at which carbon-rich planetesimal formation is possible, as a function of the host star's [C/H] abundance. We then use our linear relation between rmax and [C/H], along with the theoretical mass-radius relation derived for a solid, pure carbon planet, to characterize potential planetary transits across host CEMP stars. Given that the related transits are detectable with current and upcoming space-based transit surveys, we suggest initiating an observational programme to search for carbon planets around CEMP stars in hopes of shedding light on the question of how early planetary systems may have formed after the big bang.

  8. CEMP stars: possible hosts to carbon planets in the early Universe

    Science.gov (United States)

    Mashian, Natalie; Loeb, Abraham

    2016-08-01

    We explore the possibility of planet formation in the carbon-rich protoplanetary disks of carbon-enhanced metal-poor (CEMP) stars, possible relics of the early Universe. The chemically anomalous abundance patterns ([C/Fe] $\\geq$ 0.7) in this subset of low-mass stars suggest pollution by primordial core-collapsing supernovae (SNe) ejecta that are particularly rich in carbon dust grains. By comparing the dust-settling timescale in the protoplanetary disks of CEMP stars to the expected disk lifetime (assuming dissipation via photoevaporation), we determine the maximum distance $r_{max}$ from the host CEMP star at which carbon-rich planetesimal formation is possible, as a function of the host star's [C/H] abundance. We then use our linear relation between $r_{max}$ and [C/H], along with the theoretical mass-radius relation derived for a solid, pure carbon planet, to characterize potential planetary transits across host CEMP stars. Given that the related transits are detectable with current and upcoming space-based transit surveys, we suggest initiating an observational program to search for carbon planets around CEMP stars in hopes of shedding light on the question of how early planetary systems may have formed after the Big Bang.

  9. Current hot questions on the s process in AGB stars

    Science.gov (United States)

    Lugaro, M.; Campbell, S. W.; D'Orazi, V.; Karakas, A. I.; Garcia-Hernandez, D. A.; Stancliffe, R. J.; Tagliente, G.; Iliadis, C.; Rauscher, T.

    2016-01-01

    Asymptotic giant branch (AGB) stars are a main site of production of nuclei heavier than iron via the s process. In massive (>4 M⊙) AGB stars the operation of the 22Ne neutron source appears to be confirmed by observations of high Rb enhancements, while the lack of Tc in these stars rules out 13C as a main source of neutrons. The problem is that the Rb enhancements are not accompanied by Zr enhancements, as expected by s-process models. This discrepancy may be solved via a better understanding of the complex atmospheres of AGB stars. Second- generation stars in globular clusters (GCs), on the other hand, do not show enhancements in any s-process elements, not even Rb. If massive AGB stars are responsible for the composition of these GC stars, they may have evolved differently in GCs than in the field. In AGB stars of lower masses, 13C is the main source of neutrons and we can potentially constrain the effects of rotation and proton-ingestion episodes using the observed composition of post-AGB stars and of stardust SiC grains. Furthermore, independent asteroseismology observations of the rotational velocities of the cores of red giants and of white dwarves will play a fundamental role in helping us to better constrain the effect of rotation. Observations of carbon-enhanced metal-poor stars enriched in both Ba and Eu may require a neutron flux in-between the s and the r process, while the puzzling increase of Ba as function of the age in open clusters, not accompanied by increase in any other element heavier than iron, require further observational efforts. Finally, stardust SiC provides us high-precision constraints to test nuclear inputs such as neutron-capture cross sections of stable and unstable isotopes and the impact of excited nuclear states in stellar environments.

  10. Compact Binary Assembly in the First Nuclear Star Clusters and r-Process Synthesis in the Early Universe

    CERN Document Server

    Ramirez-Ruiz, Enrico; Roberts, Luke F; Lee, William H; Saladino-Rosas, Martha I

    2014-01-01

    Investigations of element abundances in the ancient and most metal deficient stars are extremely important because they serve as tests of variable nucleosynthesis pathways and can provide critical inferences of the type of stars that lived and died before them. The presence of r-process elements in a handful of carbon-enhanced metal-poor (CEMP) stars, which are assumed to be closely connected to the chemical yield from the first stars, is hard to reconcile with standard neutron star mergers. Here we show that the production rate of dynamically assembled compact binaries in high-z nuclear star clusters can attain a sufficient high value to be a potential viable source of heavy r-material in CEMP stars. The predicted frequency of such events in the early Galaxy, much lower than the frequency of Type II supernovae but with significantly higher mass ejected per event, can naturally lead to a high level of scatter of Eu as observed in CEMP stars.

  11. Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68

    OpenAIRE

    Cannon, John M.; Johnson, Megan; McQuinn, Kristen B W; Alfvin, Erik D.; Bailin, Jeremy; Ford, H. Alyson; Girardi, Léo; Hirschauer, Alec S.; Janowiecki, Steven; Salzer, John J.; Van Sistine, Angela; Dolphin, Andrew; Elson, E. C.; Koribalski, Baerbel; Marigo, Paola

    2014-01-01

    We present HI spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only 3% Z$_{\\odot}$, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of ...

  12. Near-Infrared Properties of Metal-poor Globular Clusters in the Galactic Bulge Direction

    OpenAIRE

    Chun, S. -H.; Kim, J. -W.; Shin, I. -G.; Chung, C.; Lim, D. -W.; Park, J. -H.; Kim, H. -I.; Han, W.; Sohn, Y. -J.

    2010-01-01

    Aims. J, H, and K' images obtained from the near-infrared imager CFHTIR on the Canada-France-Hawaii Telescope are used to derive the morphological parameters of the red giant branch (RGB) in the near-infrared color-magnitude diagrams for 12 metal-poor globular clusters in the Galactic bulge direction. Using the compiled data set of the RGB parameters for the observed 12 clusters, in addition to the previously studied 5 clusters, we discuss the properties of the RGB morphology for the clusters...

  13. HS 2134+0400 - new very metal-poor galaxy, a representative of void population?

    CERN Document Server

    Pustilnik, S A; Kniazev, A Yu; Pramsky, A G; Ugryumov, A V; Hagen, H J

    2005-01-01

    We present the SAO 6m telescope spectroscopy of a blue compact galaxy (BCG) HS 2134+0400 discovered in frame of the dedicated Hamburg/SAO survey for Low Metallicity BCGs (HSS-LM). Its very low abundance of oxygen (12+log(O/H) = 7.44), as well as other heavy elements (S, N, Ne, Ar), assigns this dwarf galaxy to the group of BCGs with the lowest metal content. There are only eight that low metallicity among several thousand known BCGs in the nearby Universe. The abundance ratios for the heavy elements (S/O, Ne/O, N/O, and Ar/O) are well consistent with the typical values of other very metal-poor BCGs. The global environment of HS 2134+0400 is atypical of the majority of BCGs. The object falls within the Pegasus void, the large volume with the very low density of galaxies with the normal (M_B* = -19.6) or high luminosity. Since we found in voids a dozen more the very metal-poor galaxies, we discuss the hypothesis that such objects can be representative of a substantial fraction of the void dwarf galaxy populatio...

  14. CEMP stars: possible hosts to carbon planets in the early universe

    CERN Document Server

    Mashian, Natalie

    2016-01-01

    We explore the possibility of planet formation in the carbon-rich protoplanetary disks of carbon-enhanced metal-poor (CEMP) stars, possible relics of the early Universe. The chemically anomalous abundance patterns ([C/Fe] $\\geq$ 0.7) in this subset of low-mass stars suggest pollution by primordial core-collapsing supernovae (SNe) ejecta that are particularly rich in carbon dust grains. By comparing the dust-settling timescale in the protoplanetary disks of CEMP stars to the expected disk lifetime (assuming dissipation via photoevaporation), we determine the maximum distance $r_{max}$ from the host CEMP star at which carbon-rich planetesimal formation is possible, as a function of the host star's [C/H] abundance. We then use our linear relation between $r_{max}$ and [C/H], along with the theoretical mass-radius relation derived for a solid, pure carbon planet, to characterize potential planetary transits across host CEMP stars. Given that the related transits are detectable with current and upcoming space-base...

  15. Scl-1013644: a CEMP-s star in the Sculptor Dwarf Spheroidal Galaxy

    CERN Document Server

    Salgado, C; Yong, D; Norris, J E

    2016-01-01

    Recent studies of the Milky Way and its satellites have paid special attention to the importance of carbon-enhanced metal-poor (CEMP) stars due to their involvement in Galactic formation history and their possible connection with the chemical elements originating in the first stellar generation. In an ongoing study of red giants in the Sculptor dwarf galaxy we have discovered a star with extremely strong CN and CH molecular bands. This star, Scl-1013644, has previously been identified by Geisler et al. (2005) as a star with an enrichment in the heavy elements. Spectrum synthesis has been used to derive the carbon, nitrogen and barium abundances for Scl-1013644. Our findings are [C/Fe] = +0.8, [N/Fe] = -0.3 and [Ba/Fe] = +2.1 with the latter result consistent with the value found by Geisler et al. (2005). These results reveal Scl-1013644 as a CEMP-s star, the third such star discovered in this dwarf galaxy.

  16. TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies

    CERN Document Server

    Bonifacio, P; Spite, M; Limongi, M; Chieffi, A; Klessen, R S; François, P; Molaro, P; Ludwig, H G; Zaggia, S; Spite, F; Plez, B; Cayrel, R; Christlieb, N; Clark, P C; Glover, S C O; Hammer, F; Koch, A; Monaco, L; Sbordone, L; Steffen, M

    2015-01-01

    In the course of the TOPoS (Turn Off Primordial Stars) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. We here present our analysis of six CEMP stars. Calcium and carbon are the only elements that can be measured in all six stars. The range is -5.0<=[Ca/H]< -2.1 and 7.12<=A(C)<=8.65. For star SDSS J1742+2531 we were able to detect three FeI lines from which we deduced [Fe/H]=-4.80, from four CaII lines we derived [Ca/H]=-4.56, and from synthesis of the G-band we derived A(C)=7.26. For SDSS J1035+0641 we were not able to detect any iron lines, yet we could place a robust (3sigma) upper limit of [Fe/H]< -5.0 and measure the Ca abundance, with [Ca/H]=-5.0, and carbon, A(C)=6.90. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li)<1.8 for both stars. Our measured carbon abundances confirm the bimodal distribution of carbon in CEMP stars, identifying a hi...

  17. WASP-36b: A NEW TRANSITING PLANET AROUND A METAL-POOR G-DWARF, AND AN INVESTIGATION INTO ANALYSES BASED ON A SINGLE TRANSIT LIGHT CURVE

    International Nuclear Information System (INIS)

    We report the discovery, from WASP and CORALIE, of a transiting exoplanet in a 1.54 day orbit. The host star, WASP-36, is a magnitude V = 12.7, metal-poor G2 dwarf (Teff = 5959 ± 134 K), with [Fe/H] =–0.26 ± 0.10. We determine the planet to have mass and radius, respectively, 2.30 ± 0.07 and 1.28 ± 0.03 times that of Jupiter. We have eight partial or complete transit light curves, from four different observatories, which allow us to investigate the potential effects on the fitted system parameters of using only a single light curve. We find that the solutions obtained by analyzing each of these light curves independently are consistent with our global fit to all the data, despite the apparent presence of correlated noise in at least two of the light curves.

  18. An optical transmission spectrum of the transiting hot Jupiter in the metal-poor WASP-98 planetary system

    Science.gov (United States)

    Mancini, L.; Giordano, M.; Mollière, P.; Southworth, J.; Brahm, R.; Ciceri, S.; Henning, Th.

    2016-09-01

    The WASP-98 planetary system represents a rare case of a hot Jupiter hosted by a metal-poor main-sequence star. We present a follow-up study of this system based on multiband photometry and high-resolution spectroscopy. Two new transit events of WASP-98 b were simultaneously observed in four passbands (g', r', i', z'), using the telescope-defocusing technique, yielding eight high-precision light curves with point-to-point scatters of less than 1 mmag. We also collected three spectra of the parent star with a high-resolution spectrograph, which we used to remeasure its spectral characteristics, in particular its metallicity. We found this to be very low, [Fe/H] = -0.49 ± 0.10, but larger than was previously reported, [Fe/H] = -0.60 ± 0.19. We used these new photometric and spectroscopic data to refine the orbital and physical properties of this planetary system, finding that the stellar and planetary mass measurements are significantly larger than those in the discovery paper. In addition, the multiband light curves were used to construct an optical transmission spectrum of WASP-98 b and probe the characteristics of its atmosphere at the terminator. We measured a lower radius at z' compared with the other three passbands. The maximum variation is between the r' and z' bands, has a confidence level of roughly 6σ and equates to 5.5 pressure scale heights. We compared this spectrum to theoretical models, investigating several possible types of atmospheres, including hazy, cloudy, cloud-free, and clear atmospheres with titanium and vanadium oxide opacities. We could not find a good fit to the observations, except in the extreme case of a clear atmosphere with TiO and VO opacities, in which the condensation of Ti and V was suppressed. As this case is unrealistic, our results suggest the presence of an additional optical-absorbing species in the atmosphere of WASP-98 b, of unknown chemical nature.

  19. An optical transmission spectrum of the transiting hot Jupiter in the metal-poor WASP-98 planetary system

    Science.gov (United States)

    Mancini, L.; Giordano, M.; Mollière, P.; Southworth, J.; Brahm, R.; Ciceri, S.; Henning, Th.

    2016-06-01

    The WASP-98 planetary system represents a rare case of a hot Jupiter hosted by a metal-poor main-sequence star. We present a follow-up study of this system based on multi-band photometry and high-resolution spectroscopy. Two new transit events of WASP-98 b were simultaneously observed in four passbands (g', r', i', z'), using the telescope-defocussing technique, yielding eight high-precision light curves with point-to-point scatters of less than 1 mmag. We also collected three spectra of the parent star with a high-resolution spectrograph, which we used to remeasure its spectral characteristics, in particular its metallicity. We found this to be very low, [Fe/H] = -0.49 ± 0.10, but larger than was previously reported, [Fe/H] = -0.60 ± 0.19. We used these new photometric and spectroscopic data to refine the orbital and physical properties of this planetary system, finding that the stellar and planetary mass measurements are significantly larger than those in the discovery paper. In addition, the multi-band light curves were used to construct an optical transmission spectrum of WASP-98 b and probe the characteristics of its atmosphere at the terminator. We measured a lower radius at z' compared with the other three passbands. The maximum variation is between the r' and z' bands, has a confidence level of roughly 6σ and equates to 5.5 pressure scale heights. We compared this spectrum to theoretical models, investigating several possible types of atmospheres, including hazy, cloudy, cloud-free, and clear atmospheres with titanium and vanadium oxide opacities. We could not find a good fit to the observations, except in the extreme case of a clear atmosphere with TiO and VO opacities, in which the condensation of Ti and V was suppressed. As this case is unrealistic, our results suggest the presence of an additional optical-absorbing species in the atmosphere of WASP-98 b, of unknown chemical nature.

  20. DETECTION OF A DISTINCT METAL-POOR STELLAR HALO IN THE EARLY-TYPE GALAXY NGC 3115

    Energy Technology Data Exchange (ETDEWEB)

    Peacock, Mark B.; Strader, Jay [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States); Romanowsky, Aaron J. [Department of Physics and Astronomy, San José State University, San Jose, CA 95192 (United States); Brodie, Jean P., E-mail: mpeacock@msu.edu [University of California Observatories/Lick Observatory, Santa Cruz, CA 95064 (United States)

    2015-02-10

    We present the resolved stellar populations in the inner and outer halo of the nearby lenticular galaxy NGC 3115. Using deep Hubble Space Telescope observations, we analyze stars 2 mag fainter than the tip of the red giant branch (TRGB). We study three fields along the minor axis of this galaxy, 19, 37, and 54 kpc from its center—corresponding to 7, 14, and 21 effective radii (r{sub e} ). Even at these large galactocentric distances, all of the fields are dominated by a relatively enriched population, with the main peak in the metallicity distribution decreasing with radius from [Z/H] ∼ –0.5 to –0.65. The fraction of metal-poor stars ([Z/H] < –0.95) increases from 17% at 16-37 kpc to 28% at ∼54 kpc. We observe a distinct low-metallicity population (peaked at [Z/H] ∼ –1.3 and with total mass 2 × 10{sup 10} M {sub ☉} ∼ 14% of the galaxy's stellar mass) and argue that this represents the detection of an underlying low-metallicity stellar halo. Such halos are generally predicted by galaxy formation theories and have been observed in several late-type galaxies, including the Milky Way and M31. The metallicity and spatial distribution of the stellar halo of NGC 3115 are consistent with the galaxy's globular cluster system, which has a similar low-metallicity population that becomes dominant at these large radii. This finding supports the use of globular clusters as bright chemodynamical tracers of galaxy halos. These data also allow us to make a precise measurement of the magnitude of the TRGB, from which we derive a distance modulus of NGC 3115 of 30.05 ± 0.05 ± 0.10{sub sys} (10.2 ± 0.2 ± 0.5{sub sys} Mpc)

  1. The Evolution of Pristine Gas: Implications for Milky Way Halo Stars

    Science.gov (United States)

    Sarmento, Richard J.; Scannapieco, Evan; Pan, Liubin

    2016-06-01

    We implement a new subgrid model for turbulent mixing to accurately follow the cosmological evolution of the first stars, the mixing of their supernova ejecta and the impact on the chemical composition of the Galactic Halo. Using the cosmological adaptive mesh refinement code RAMSES, we implement a model for the pollution of pristine gas as described in Pan et al. (2013). This allows us to account for the fraction of Z evolution of the “primordial metals” generated by Pop III supernovae. These metals are taken up by second-generation stars and are likely to lead to unique abundance signatures characteristic of carbon enhanced, metal poor (CEMP) stars. As an illustrative example, we associate primordial metals with abundance ratios used by Keller at al (2014) to explain the source of metals in the star SMSS J031300.36- 670839.3, finding good agreement with the observed [Fe/H], [C/H], [O/H] and [Mg/Ca] ratios in CEMP Milky Way (MW) halo stars.

  2. The HARPS search for southern extra-solar planets. XXXIX. HD175607 b, the most metal-poor G dwarf with an orbiting sub-Neptune

    CERN Document Server

    Mortier, A; Santos, N C; Rajpaul, V; Figueira, P; Boisse, I; Cameron, A Collier; Dumusque, X; Curto, G Lo; Lovis, C; Mayor, M; Melo, C; Pepe, F; Queloz, D; Santerne, A; Ségransan, D; Sousa, S G; Sozzetti, A; Udry, S

    2016-01-01

    Context. The presence of a small-mass planet (M$_p<$0.1\\,M$_{Jup}$) seems, to date, not to depend on metallicity, however, theoretical simulations have shown that stars with subsolar metallicities may be favoured for harbouring smaller planets. A large, dedicated survey of metal-poor stars with the HARPS spectrograph has thus been carried out to search for Neptunes and super-Earths. Aims. In this paper, we present the analysis of \\object{HD175607}, an old G6 star with metallicity [Fe/H] = -0.62. We gathered 119 radial velocity measurements in 110 nights over a time span of more than nine years. Methods. The radial velocities were analysed using Lomb-Scargle periodograms, a genetic algorithm, a Markov chain Monte Carlo analysis, and a Gaussian processes analysis. The spectra were also used to derive stellar properties. Several activity indicators were analysed to study the effect of stellar activity on the radial velocities. Results. We find evidence for the presence of a small Neptune-mass planet (M$_{p}\\s...

  3. The primordial deuterium abundance of the most metal-poor damped Lyman-alpha system

    CERN Document Server

    Cooke, Ryan; Nollett, Kenneth M; Jorgenson, Regina

    2016-01-01

    We report the discovery and analysis of the most metal-poor damped Lyman-alpha (DLA) system currently known, which also displays the Lyman series absorption lines of neutral deuterium. The average [O/H] abundance of this system is [O/H] = -2.804 +/- 0.015, which includes an absorption component with [O/H] = -3.07 +/- 0.03. Despite the unfortunate blending of many weak D I absorption lines, we report a precise measurement of the deuterium abundance of this system. Using the six highest quality and self-consistently analyzed measures of D/H in DLAs, we report tentative evidence for a subtle decrease of D/H with increasing metallicity. This trend must be confirmed with future high precision D/H measurements spanning a range of metallicity. A weighted mean of these six independent measures provides our best estimate of the primordial abundance of deuterium, 10^5 (D/H)_P = 2.547 +/- 0.033 (log_10 (D/H)_P = -4.5940 +/- 0.0056). We perform a series of detailed Monte Carlo calculations of Big Bang nucleosynthesis (BB...

  4. Systematic search for extremely metal poor galaxies in the Sloan Digital Sky Survey

    CERN Document Server

    Morales-Luis, A B; Aguerri, J A L; Munoz-Tunon, C

    2011-01-01

    We carry out a systematic search for extremely metal poor (XMP) galaxies in the spectroscopic sample of Sloan Digital Sky Survey (SDSS) data release 7 (DR7). The XMP candidates are found by classifying all the galaxies according to the form of their spectra in a region 80AA wide around Halpha. Due to the data size, the method requires an automatic classification algorithm. We use k-means. Our systematic search renders 32 galaxies having negligible [NII] lines, as expected in XMP galaxy spectra. Twenty one of them have been previously identified as XMP galaxies in the literature -- the remaining eleven are new. This was established after a thorough bibliographic search that yielded only some 130 galaxies known to have an oxygen metallicity ten times smaller than the Sun (explicitly, with 12+log(O/H) <= 7.65). XMP galaxies are rare; they represent 0.01% of the galaxies with emission lines in SDSS/DR7. Although the final metallicity estimate of all candidates remains pending, strong-line empirical calibration...

  5. DUST-TO-GAS RATIO IN THE EXTREMELY METAL-POOR GALAXY I Zw 18

    International Nuclear Information System (INIS)

    The blue compact dwarf galaxy I Zw 18 is one of the most metal-poor systems known in the local universe (12+log(O/H) = 7.17). In this work we study I Zw 18 using data from Spitzer, Herschel Space Telescope, and IRAM Plateau de Bure Interferometer. Our data set includes the most sensitive maps of I Zw 18, to date, in both the far-infrared and the CO J = 1 → 0 transition. We use dust emission models to derive a dust mass upper limit of only Mdust ≤ 1.1 × 104 M☉ (3σ limit). This upper limit is driven by the non-detection at 160 μm, and it is a factor of 4-10 times smaller than previous estimates (depending on the model used). We also estimate an upper limit to the total dust-to-gas mass ratio of MDust/Mgas ≤ 5.0 × 10–5. If a linear correlation between the dust-to-gas mass ratio and metallicity (measured as O/H) were to hold, we would expect a ratio of 3.9 × 10–4. We also show that the infrared spectral energy distribution is similar to that of starbursting systems.

  6. The Gaia-ESO Survey: Separating disk chemical substructures with cluster models. Evidence of a separate evolution in the metal-poor thin disk

    Science.gov (United States)

    Rojas-Arriagada, A.; Recio-Blanco, A.; de Laverny, P.; Schultheis, M.; Guiglion, G.; Mikolaitis, Š.; Kordopatis, G.; Hill, V.; Gilmore, G.; Randich, S.; Alfaro, E. J.; Bensby, T.; Koposov, S. E.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.; Chiappini, C.

    2016-02-01

    Context. Recent spectroscopic surveys have begun to explore the Galactic disk system on the basis of large data samples, with spatial distributions sampling regions well outside the solar neighborhood. In this way, they provide valuable information for testing spatial and temporal variations of disk structure kinematics and chemical evolution. Aims: The main purposes of this study are to demonstrate the usefulness of a rigorous mathematical approach to separate substructures of a stellar sample in the abundance-metallicity plane, and provide new evidence with which to characterize the nature of the metal-poor end of the thin disk sequence. Methods: We used a Gaussian mixture model algorithm to separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample (essentially at RGC -0.25 dex) highlight a change in the slope at solar metallicity. This holds true at different radial regions of the Milky Way. The distribution of Galactocentric radial distances of the metal-poor part of the thin disk ([Fe/H] levels might be due to their origin from gas pre-enriched by outflows from the thick disk or the inner halo. The smooth trends of their properties (their spatial distribution with respect to the plane, in particular) with [Fe/H] and [Mg/Fe] suggested by the data indicates a quiet dynamical evolution, with no relevant merger events. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002. These data products have been processed by the Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council.

  7. Beryllium in the Ultra-Lithium-Deficient,Metal-Poor Halo Dwarf, G186-26

    CERN Document Server

    Boesgaard, A M; Boesgaard, Ann Merchant; Novicki, Megan C.

    2005-01-01

    The vast majority of low-metal halo dwarfs show a similar amount of Li; this has been attributed to the Li that was produced in the Big Bang. However, there are nine known halo stars with T $>$ 5900 K and [Fe/H] $<$ $-$1.0 that are ultra-Li-deficient. We have looked for Be in the very low metallicity star, G 186-26 at [Fe/H] = $-$2.71, which is one of the ultra-Li-deficient stars. This star is also ultra-Be deficient. Relative to Be in the Li-normal stars at [Fe/H] = $-$2.7, G 182-26 is down in Be by more than 0.8 dex. Of two potential causes for the Li-deficiency -- mass-transfer in a pre-blue straggler or extra rotationally-induced mixing in a star that was initially a very rapid rotator -- the absence of Be favors the blue-straggler hypothesis, but the rotation model cannot be ruled-out completely.

  8. FAST WINDS AND MASS LOSS FROM METAL-POOR FIELD GIANTS

    International Nuclear Information System (INIS)

    Echelle spectra of the infrared He I λ10830 line were obtained with NIRSPEC on the Keck 2 telescope for 41 metal-deficient field giant stars including those on the red giant branch (RGB), asymptotic giant branch (AGB), and red horizontal branch (RHB). The presence of this He I line is ubiquitous in stars with T eff∼> 4500 K and MV fainter than -1.5, and reveals the dynamics of the atmosphere. The line strength increases with effective temperature for T eff∼> 5300 K in RHB stars. In AGB and RGB stars, the line strength increases with luminosity. Fast outflows (∼> 60 km s-1) are detected from the majority of the stars and about 40% of the outflows have sufficient speed as to allow escape of material from the star as well as from a globular cluster. Outflow speeds and line strengths do not depend on metallicity for our sample ([Fe/H]= -0.7 to -3.0), suggesting the driving mechanism for these winds derives from magnetic and/or hydrodynamic processes. Gas outflows are present in every luminous giant, but are not detected in all stars of lower luminosity indicating possible variability. Mass loss rates ranging from ∼3 x 10-10 to ∼6 x 10-8 M sun yr-1 estimated from the Sobolev approximation for line formation represent values with evolutionary significance for red giants and RHB stars. We estimate that 0.2 M sun will be lost on the RGB, and the torque of this wind can account for observations of slowly rotating RHB stars in the field. About 0.1-0.2 M sun will be lost on the RHB itself. This first empirical determination of mass loss on the RHB may contribute to the appearance of extended horizontal branches in globular clusters. The spectra appear to resolve the problem of missing intracluster material in globular clusters. Opportunities exist for 'wind smothering' of dwarf stars by winds from the evolved population, possibly leading to surface pollution in regions of high stellar density.

  9. THE SPLASH SURVEY: A SPECTROSCOPIC ANALYSIS OF THE METAL-POOR, LOW-LUMINOSITY M31 dSph SATELLITE ANDROMEDA X ,

    International Nuclear Information System (INIS)

    Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal galaxy (dSph) found by Zucker et al. in the Sloan Digital Sky Survey (SDSS; York et al.). In this paper, we present the first spectroscopic study of individual red giant branch stars in And X, as a part of the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) Survey. Using the Keck II telescope and multiobject DEIMOS spectrograph, we target two spectroscopic masks over the face of the galaxy and measure radial velocities for ∼100 stars with a median accuracy of σ v ∼ 3 km s-1. The velocity histogram for this field confirms three populations of stars along the sight line: foreground Milky Way dwarfs at small negative velocities, M31 halo red giants over a broad range of velocities, and a very cold velocity 'spike' consisting of 22 stars belonging to And X with v rad = -163.8 ± 1.2 km s-1. By carefully considering both the random and systematic velocity errors of these stars (e.g., through duplicate star measurements), we derive an intrinsic velocity dispersion of just σ v = 3.9 ± 1.2 km s-1 for And X, which for its size, implies a minimum mass-to-light ratio of M/LV = 37+26-19 assuming that the mass traces the light. Based on the clean sample of member stars, we measure the median metallicity of And X to be [Fe/H] = -1.93 ± 0.11, with a slight radial metallicity gradient. The dispersion in metallicity is large, σ([Fe/H]phot) = 0.48, possibly hinting that the galaxy retained much of its chemical enrichment products. And X has a total integrated luminosity (MV = -8.1 ± 0.5) that straddles the classical Local Group dSphs and the new SDSS ultra-low luminosity galaxies. The galaxy is among the most metal-poor dSphs known, especially relative to those with MV < -8, and has the second lowest intrinsic velocity dispersion of the entire sample. Our results suggest that And X is less massive by a factor of 4 when compared to Milky Way dSphs of comparable

  10. Oxygen in the early Galaxy: OH lines as tracers of oxygen abundance in extremely metal-poor giant stars

    CERN Document Server

    Kucinskas, A; Bonifacio, P; Caffau, E; Ludwig, H -G; Steffen, M; Spite, M

    2014-01-01

    Oxygen is a powerful tracer element of Galactic chemical evolution. Unfortunately, only a few oxygen lines are available in the ultraviolet-infrared stellar spectra for the reliable determination of its abundance. Moreover, oxygen abundances obtained using different spectral lines often disagree significantly. In this contribution we therefore investigate whether the inadequate treatment of convection in 1D hydrostatic model atmospheres used in the abundance determinations may be responsible for this disagreement. For this purpose, we used VLT CRIRES spectra of three EMP giants, as well as 3D hydrodynamical CO$^5$BOLD and 1D hydrostatic LHD model atmospheres, to investigate the role of convection in the formation of infrared (IR) OH lines. Our results show that the presence of convection leads to significantly stronger IR OH lines. As a result, the difference in the oxygen abundance determined from IR OH lines with 3D hydrodynamical and classical 1D hydrostatic model atmospheres may reach -0.2 ... -0.3 dex. I...

  11. Hubble Space Telescope Near-Ultraviolet Spectroscopy of Bright CEMP-s Stars

    CERN Document Server

    Placco, Vinicius M; Ivans, Inese I; Filler, Dan; Imig, Julie A; Roederer, Ian U; Abate, Carlo; Hansen, Terese; Cowan, John J; Frebel, Anna; Lawler, James E; Schatz, Hendrik; Sneden, Christopher; Sobeck, Jennifer S; Aoki, Wako; Smith, Verne V; Bolte, Michael

    2015-01-01

    We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the bright carbon-enhanced metal-poor (CEMP) stars HD196944 (V = 8.40, [Fe/H] = -2.41) and HD201626 (V = 8.16, [Fe/H] = -1.51), based on data acquired with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. Both of these stars belong to the sub-class CEMP-s, and exhibit clear over-abundances of heavy elements associated with production by the slow neutron-capture process. HD196944 has been well-studied in the optical region, but we are able to add abundance results for six species (Ge, Nb, Mo, Lu, Pt, and Au) that are only accessible in the NUV. In addition, we provide the first determination of its orbital period, P=1325 days. HD201626 has only a limited number of abundance results based on previous optical work -- here we add five new species from the NUV, including Pb. We compare these results with models of binary-system evolution and s-process element production in stars on the asympt...

  12. HE 0017+0055 : A probable pulsating CEMP-rs star and long-period binary

    CERN Document Server

    Jorissen, A; Van Eck, S; Andersen, J; Nordstroem, B; Siess, L; Torres, G; Masseron, T; Van Winckel, H

    2015-01-01

    A radial-velocity monitoring of the Carbon-Enhanced Metal-Poor (CEMP) star HE 0017+0055 over 8 years with the Nordic Optical Telescope and Mercator telescopes reveals variability with a period of 384 d and amplitude of 540$\\pm27$ m s$^{-1}$, superimposed on a nearly linear long-term decline of $\\sim$1 m s$^{-1}$ day$^{-1}$. High-resolution HERMES/Mercator and Keck/HIRES spectra have been used to derive elemental abundances using 1-D LTE MARCS models. A metallicity of [Fe/H] $\\sim -2.4$ is found, along with s-process overabundances on the order of 2 dex (with the exception of [Y/Fe] $\\sim+0.5$), and most notably overabundances of r-process elements like Sm, Eu, Dy, and Er in the range 0.9 - 2.0 dex. With [Ba/Fe] $ > 1.9$ dex and [Eu/Fe] = 2.3 dex, HE 0017+0055 is a CEMP-rs star. It appears to be a giant star below the tip of the red giant branch (RGB). The s-process pollution must therefore originate from mass transfer from a companion formerly on the AGB, now a carbon-oxygen white dwarf (WD). If the 384 d vel...

  13. VI Photometry of Globular Clusters NGC6293 and NGC6541: The Formation of the Metal-Poor Inner Halo Globular Clusters

    CERN Document Server

    Lee, J W; Lee, Jae-Woo; Carney, Bruce W.

    2006-01-01

    We present VI photometry of the metal-poor inner halo globular clusters NGC6293 and NGC6541 using the planetary camera of the WFPC2 on board HST. Our color-magnitude diagrams of the clusters show well-defined BHB populations, consistent with their low metallicities and old ages. NGC6293 appears to have blue straggler stars in the cluster's central region. We discuss the interstellar reddening and the distance modulus of NGC6293 and NGC6541 and obtain E(B-V) = 0.40 and (m-M)_0 = 14.61 for NGC6293 and E(B-V) = 0.14 and (m-M)_0 = 14.19 for NGC6541. Our results confirm that NGC6293 and NGC6541 are clearly located in the Galaxy's central regions (R_{GC} < 3 kpc). We also discuss the differential reddening across NGC6293. The interstellar reddening value of NGC6293 appears to vary by Delta E(B-V) ~ 0.02 -- 0.04 mag within our small field of view. The most notable result of our study is that the inner halo clusters NGC6293 and NGC6541 essentially have the same ages as M92, confirming the previous result from the ...

  14. The Mass Distribution of Population III Stars

    CERN Document Server

    Fraser, M; Gilmore, G; Heger, A; Chan, C

    2015-01-01

    Extremely metal-poor stars are uniquely informative on the nature of massive Population III stars. Modulo a few elements that vary with stellar evolution, the present-day photospheric abundances observed in extremely metal-poor stars are representative of their natal gas cloud composition. For this reason, the detailed chemistry of extremely metal-poor stars closely reflects the nucleosynthetic yields of supernovae from massive Population III stars. Here we collate detailed chemical abundances of 53 extremely metal-poor stars from the literature and infer the masses of their Population III progenitors. We fit a simple initial mass function to the ensemble of inferred Population III star masses, and find that the mass distribution is well-represented by a powerlaw IMF with an exponent of \\$\\alpha=2.35^{+0.29}_{-0.24}\\$. The inferred maximum progenitor mass for supernovae from massive Population III stars is \\$M=87^{+13}_{-33}M_\\odot\\$, and we find no evidence for a contribution from stars with masses above \\$\\...

  15. The Second Stars

    CERN Document Server

    Herwig, Falk

    2005-01-01

    The ejecta of the first probably very massive stars polluted the Big Bang primordial element mix with the first heavier elements. The resulting ultra metal-poor abundance distribution provided the initial conditions for the second stars of a wide range of initial masses reaching down to intermediate and low masses. The importance of these second stars for understanding the origin of the elements in the early universe are manifold. While the massive first stars have long vanished the second stars are still around and currently observed. They are the carriers of the information about the first stars, but they are also capable of nuclear production themselves. For example, in order to use ultra or extremely metal-poor stars as a probe for the r-process in the early universe a reliable model of the s-process in the second stars is needed. Eventually, the second stars may provide us with important clues on questions ranging from structure formation to how the stars actually make the elements, not only in the early...

  16. ALFALFA Discovery of the Most Metal-Poor Gas-Rich Galaxy Known: AGC 198691

    CERN Document Server

    Hirschauer, Alec S; Skillman, Evan D; Berg, Danielle; McQuinn, Kristen B W; Cannon, John M; Gordon, Alex J R; Haynes, Martha P; Giovanelli, Riccardo; Adams, Elizabeth A K; Janowiecki, Steven; Rhode, Katherine L; Pogge, Richard W; Croxall, Kevin V; Aver, Erik

    2016-01-01

    We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part of the Survey of HI in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength study of galaxies with HI masses in the range of 10$^{6}$-10$^{7.2}$~M$_{\\odot}$ discovered by the ALFALFA survey. We have obtained spectra of the lone HII region in AGC 198691 with the new high-throughput KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the temperature-sensitive [OIII]$\\lambda$4363 line and hence the determination of a "direct" oxygen abundance for AGC 198691. We find this system to be an extremely metal-deficient (XMD) system with an oxygen abundance of 12+log(O/H) = 7.02 $\\pm$ 0.03, making AGC 198691 the lowest-abundance star-forming galaxy known in the local universe. Two of the five lowest-abundance galaxies known have been discovered by the ALFALFA blind HI surv...

  17. HS 0822+3542 a New Nearby Extremely Metal-Poor Galaxy

    CERN Document Server

    Kniazev, A Yu; Merlino, S; Hopp, U; Brosch, N; Pustilnik, S A; Masegosa, J; Márquez, I; Izotov, Yu I; Ugryumov, A V; Martin, J M; Engels, D

    2000-01-01

    We present the results of spectrophotometry and BVR CCD photometry, as well as integrated HI radio measurements of a new blue compact galaxy (BCG) HS 0822+3542 with extremely low oxygen abundance: 12+log(O/H) = 7.35, or 1/36 of solar value. The galaxy is the third most metal-deficient BCG after I Zw 18 and SBS 0335-052. Its very high mass fraction of gas (~950f all visible mass) and blue colours of underlying nebulosity are also similar to those of SBS 0335-052. This suggests that HS 0822+3542 is one of the nearest and dimmest galaxies experiencing a recently-started first star formation (SF) episode. Its properties imply that for such galaxies there is a linear scaling of the main parameters, at least for the baryon mass range (0.3-20)x10^8 M_sun. The total mass estimate indicates that the galaxy is dynamically dominated by a dark matter (DM) halo, which itself is one of the least massive for galaxies.

  18. First stars in Damped Lyman Alpha systems

    NARCIS (Netherlands)

    Salvadori, Stefania; Ferrara, Andrea

    2011-01-01

    In order to characterize Damped Lyman Alpha systems (DLAs) potentially host- ing first stars, we present a novel approach to investigate DLAs in the context of Milky Way (MW) formation, along with their connection with the most metal-poor stars and local dwarf galaxies. The merger tree method previo

  19. ON THE USE OF THE INDEX N2 TO DERIVE THE METALLICITY IN METAL-POOR GALAXIES

    International Nuclear Information System (INIS)

    The N2 index ([N II] λ6584/Hα) is used to determine emission line galaxy metallicities at all redshifts, including high redshift, where galaxies tend to be metal-poor. The initial aim of this work was to improve the calibrations used to infer oxygen abundance from N2 by employing updated low-metallicity galaxy databases. We compare N2 and the metallicity determined using the direct method for the set of extremely metal-poor galaxies compiled by Morales-Luis et al. To our surprise, the oxygen abundance presents a tendency to be constant with N2, with a very large scatter. Consequently, we find that the existing N2 calibrators overestimate the oxygen abundance for most low-metallicity galaxies, and can therefore only be used to set upper limits to the true metallicity in low-metallicity galaxies. An explicit expression for this limit is given. In addition, we try to explain the observed scatter using photoionization models. It is mostly due to the different evolutionary state of the H II regions producing the emission lines, but it also arises due to differences in N/O among the galaxies

  20. Search for Extremely Metal-poor Galaxies in the Sloan Digital Sky Survey (II): high electron temperature objects

    CERN Document Server

    Almeida, J Sanchez; Morales-Luis, A B; Munoz-Tunon, C; Garcia-Benito, R; Nuza, S E; Kitaura, F S

    2016-01-01

    Extremely metal-poor (XMP) galaxies are defined to have gas-phase metallicity smaller than a tenth of the solar value (12 + log[O/H] < 7.69). They are uncommon, chemically and possibly dynamically primitive, with physical conditions characteristic of earlier phases of the Universe. We search for new XMPs in the Sloan Digital Sky Survey (SDSS) in a work that complements Paper I. This time high electron temperature objects are selected; since metals are a main coolant of the gas, metal- poor objects contain high-temperature gas. Using the algorithm k-means, we classify 788677 spectra to select 1281 galaxies having particularly intense [OIII]4363 with respect to [OIII]5007, which is a proxy for high electron temperature. The metallicity of these candidates was computed using a hybrid technique consistent with the direct method, rendering 196 XMPs. A less restrictive noise constraint provides a larger set with 332 candidates. Both lists are provided in electronic format. The selected XMP sample have mean stell...

  1. ON THE USE OF THE INDEX N2 TO DERIVE THE METALLICITY IN METAL-POOR GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Morales-Luis, A. B.; Almeida, J. Sánchez; Muñoz-Tuñón, C. [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain); Pérez-Montero, E., E-mail: anabelen1516@gmail.com, E-mail: cmt@iac.es, E-mail: jos@iac.es, E-mail: epm@iaa.es [Instituto de Astrofísica de Andalucía-CSIC, Apdo. de correos 3004, E-18080 Granada (Spain)

    2014-12-20

    The N2 index ([N II] λ6584/Hα) is used to determine emission line galaxy metallicities at all redshifts, including high redshift, where galaxies tend to be metal-poor. The initial aim of this work was to improve the calibrations used to infer oxygen abundance from N2 by employing updated low-metallicity galaxy databases. We compare N2 and the metallicity determined using the direct method for the set of extremely metal-poor galaxies compiled by Morales-Luis et al. To our surprise, the oxygen abundance presents a tendency to be constant with N2, with a very large scatter. Consequently, we find that the existing N2 calibrators overestimate the oxygen abundance for most low-metallicity galaxies, and can therefore only be used to set upper limits to the true metallicity in low-metallicity galaxies. An explicit expression for this limit is given. In addition, we try to explain the observed scatter using photoionization models. It is mostly due to the different evolutionary state of the H II regions producing the emission lines, but it also arises due to differences in N/O among the galaxies.

  2. MUSE searches for galaxies near very metal-poor gas clouds at z~3: new constraints for cold accretion models

    CERN Document Server

    Fumagalli, Michele; Dekel, Avishai; Morris, Simon L; O'Meara, John M; Prochaska, J Xavier; Theuns, Tom

    2016-01-01

    We report on the search for galaxies in the proximity of two very metal-poor gas clouds at z~3 towards the quasar Q0956+122. With a 5-hour MUSE integration in a ~500x500 kpc^2 region centred at the quasar position, we achieve a >80% complete spectroscopic survey of continuum-detected galaxies with m3e41 erg/s. We do not identify galaxies at the redshift of a z~3.2 Lyman limit system (LLS) with log Z/Zsun = -3.35 +/- 0.05, placing this gas cloud in the intergalactic medium or circumgalactic medium of a galaxy below our sensitivity limits. Conversely, we detect five Ly{\\alpha} emitters at the redshift of a pristine z~3.1 LLS with log Z/Zsun < -3.8, while ~0.4 sources were expected given the z~3 Ly{\\alpha} luminosity function. Both this high detection rate and the fact that at least three emitters appear aligned in projection with the LLS suggest that this pristine cloud is tracing a gas filament that is feeding one or multiple galaxies. Our observations uncover two different environments for metal-poor LLSs,...

  3. Stellar Archaeology: New Science with Old Stars

    Science.gov (United States)

    Frebel, Anna

    2011-01-01

    The early chemical evolution of the Galaxy and the Universe is vital to our understanding of a host of astrophysical phenomena. Since the most metal-poor Galactic stars are relics from the high-redshift Universe, they probe the chemical and dynamical conditions as the Milky Way began to form, the origin and evolution of the elements, and the physics of nucleosynthesis. They also provide constraints on the nature of the first stars, their associated supernovae and initial mass function, and early star and galaxy formation. I will present exemplary metal-poor stars with which these different topics can be addressed. Those are the most metal-poor stars in the Galaxy ([Fe/H] thorium, which can be used to radioactively date the stars to be 13 Gyr old. I will then transition to recent discoveries of metal-poor ([Fe/H] -3.0) stars in the least luminous dwarf satellites orbiting the Milky Way. Their stellar chemical signatures support the concept that small systems, analogous to the surviving dwarf galaxies, were the building blocks of the Milky Way's low-metallicity halo. This opens a new window for studying galaxy formation through stellar chemistry.

  4. THE FIRST STARS

    Directory of Open Access Journals (Sweden)

    Daniel J. Whalen

    2013-12-01

    Full Text Available Pop III stars are the key to the character of primeval galaxies, the first heavy elements, the onset of cosmological reionization, and the seeds of supermassive black holes. Unfortunately, in spite of their increasing sophistication, numerical models of Pop III star formation cannot yet predict the masses of the first stars. Because they also lie at the edge of the observable universe, individual Pop III stars will remain beyond the reach of observatories for decades to come, and so their properties are unknown. However, it will soon be possible to constrain their masses by direct detection of their supernovae, and by reconciling their nucleosynthetic yields to the chemical abundances measured in ancient metal-poor stars in the Galactic halo, some of which may bear the ashes of the first stars. Here, I review the state of the art in numerical simulations of primordial stars and attempts to directly and indirectly constrain their properties.

  5. The Most Ancient Stars in the Milky Way's Halo

    Science.gov (United States)

    Schlaufman, Kevin C.; Casey, Andrew R.

    2015-08-01

    The earliest phase of the assembly of the Milky Way's stellar halo is encoded in the detailed abundances of its oldest stars. It is tempting to assert that extremely metal-poor stars in the halo are the direct descendants of the first stars. This is not necessarily the case though, as metal-poor stars form over a range of redshift in halos of varying mass and environment. Since halos form from the inside out, the oldest stars at a given metallicity are found near the center of a halo on the most tightly-bound orbits. The oldest stars in the Milky Way are therefore the most metal-poor stars in -- but not necessarily of -- the bulge. We have developed a new selection that uses only public infrared photometry to identify metal-poor star candidates through their lack of molecular absorption near 4.6 microns. A pilot high-resolution follow-up program has verified that our selection is as efficient as previous techniques, yet is capable of finding bright metal-poor stars in areas of high reddening. Our pilot survey has already identified three of the most metal-poor stars known in the bulge. We find that with the exception of scandium, all three stars follow the abundance trends identified previously for metal-poor halo stars. These three stars have the lowest [Sc/Fe] abundances yet seen in alpha-enhanced giant stars in the Galaxy. The only place that a similar abundance pattern has been observed is the ultra-faint dwarf spheroidal galaxy Coma Berenices, which is thought to have an age of 13.9 +/- 0.3 Gyr. Theoretical models predict that there is a 30% chance that at least one of these stars formed at z > 15, while there is a 70% chance that at least one formed at 10 < z < 15. These observations imply that by z ˜ 10, the progenitor galaxies of the Milky Way had both reached [Fe/H] ˜ -3.0 and established the abundance pattern observed in extremely metal-poor stars.

  6. TOPoS . II. On the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies

    Science.gov (United States)

    Bonifacio, P.; Caffau, E.; Spite, M.; Limongi, M.; Chieffi, A.; Klessen, R. S.; François, P.; Molaro, P.; Ludwig, H.-G.; Zaggia, S.; Spite, F.; Plez, B.; Cayrel, R.; Christlieb, N.; Clark, P. C.; Glover, S. C. O.; Hammer, F.; Koch, A.; Monaco, L.; Sbordone, L.; Steffen, M.

    2015-07-01

    Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. Aims: We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns. Methods: We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D local thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum line formation code. Results: Calcium and carbon are the only elements that can be measured in all six stars. The range is -5.0 ≤ [Ca/H] UIP) stars. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li) UIP stars shows a large star-to-star scatter in the [X/Ca] ratios for all elements up to aluminium (up to 1 dex), but this scatter drops for heavier elements and is at most of the order of a factor of two. We propose that this can be explained if these stars are formed from gas that has been chemically enriched by several SNe, that produce the roughly constant [X/Ca] ratios for the heavier elements, and in some cases the gas has also been polluted by the ejecta of a faint SN that contributes the lighter elements in variable amounts. The absence of lithium in four of the five known unevolved UIP stars can be explained by a dominant role of fragmentation in the formation of these stars. This would result either in a destruction of lithium in the pre-main-sequence phase, through rotational mixing or to a lack of late accretion from a reservoir of fresh gas. The phenomenon should have varying degrees of efficiency. Based on observations obtained at ESO Paranal

  7. The most iron-deficient stars as the polluted population III stars

    CERN Document Server

    Komiya, Yutaka; Fujimoto, Masayuki Y

    2015-01-01

    We investigate the origin of the most iron-poor stars including SMSS J031300.36-670839.3 with [Fe/H] < -7.52. We compute the change of surface metallicity of stars with the accretion of interstellar matter (ISM) after their birth using the chemical evolution model within the framework of the hierarchical galaxy formation. The predicted metallicity distribution function agrees very well with that observed from extremely metal-poor stars. In particular, the lowest metallicity tail is well reproduced by the Population III stars whose surfaces are polluted with metals through ISM accretion. This suggests that the origin of iron group elements is explained by ISM accretion for the stars with [Fe/H]$\\lesssim -5$. The present results give new insights into the nature of the most metal-poor stars and the search for Population III stars with pristine abundances.

  8. Stellar Archaeology: New Science with Old Stars

    OpenAIRE

    Frebel, Anna

    2010-01-01

    The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of cosmic chemical evolution. In particular, these stars allow us to study the formation and evolution of the elements, and the involved nucleosynthesis processes. This knowledge is invaluable for our understanding of the nature and condition of the early Universe, and the associated processes of early star- and galaxy formation. This proceeding summarizes the astrophysical topics and q...

  9. s-process production in rotating massive stars at solar and low metallicities

    Science.gov (United States)

    Frischknecht, Urs; Hirschi, Raphael; Pignatari, Marco; Maeder, André; Meynet, George; Chiappini, Cristina; Thielemann, Friedrich-Karl; Rauscher, Thomas; Georgy, Cyril; Ekström, Sylvia

    2016-02-01

    Rotation was shown to have a strong impact on the structure and light element nucleosynthesis in massive stars. In particular, models including rotation can reproduce the primary nitrogen observed in halo extremely metal poor (EMP) stars. Additional exploratory models showed that rotation may enhance s-process production at low metallicity. Here we present a large grid of massive star models including rotation and a full s-process network to study the impact of rotation on the weak s-process. We explore the possibility of producing significant amounts of elements beyond the strontium peak, which is where the weak s-process usually stops. We used the Geneva stellar evolution code coupled to an enlarged reaction network with 737 nuclear species up to bismuth to calculate 15-40 M⊙ models at four metallicities (Z = 0.014, 10-3, 10-5 and 10-7) from the main sequence up to the end of oxygen burning. We confirm that rotation-induced mixing between the convective H-shell and He-core enables an important production of primary 14N and 22Ne and s-process at low metallicity. At low metallicity, even though the production is still limited by the initial number of iron seeds, rotation enhances the s-process production, even for isotopes heavier than strontium, by increasing the neutron-to-seed ratio. The increase in this ratio is a direct consequence of the primary production of 22Ne. Despite nuclear uncertainties affecting the s-process production and stellar uncertainties affecting the rotation-induced mixing, our results show a robust production of s-process at low metallicity when rotation is taken into account. Considering models with a distribution of initial rotation rates enables us to reproduce the observed large range of the [Sr/Ba] ratios in (carbon-enhanced and normal) EMP stars.

  10. The youngest massive star clusters in the Magellanic Clouds

    CERN Document Server

    Heydari-Malayeri, M; Deharveng, L; Rosa, M R; Schärer, D; Zinnecker, H

    2001-01-01

    High resolution observations with HST have recently allowed us to resolve and study several very tight clusters of newly born massive stars in the Magellanic Clouds. Situated in an extremely rare category of HII regions, being only 5 to 10 arcsecs across and of high excitation and extinction, these stars are just hatching from their natal molecular clouds. Since the SMC is the most metal-poor galaxy observable with very high angular resolution, this work may provide valuable templates for addressing issues of star formation in the very distant metal-poor galaxies of the early Universe.

  11. The SLUGGS survey: inferring the formation epochs of metal-poor and metal-rich globular clusters

    CERN Document Server

    Forbes, Duncan A; Romanowsky, Aaron J; Usher, Christopher; Brodie, Jean P; Strader, Jay

    2015-01-01

    We present a novel, observationally-based framework for the formation epochs and sites of globular clusters (GCs) in a cosmological context. Measuring directly the mean ages of the metal-poor and metal-rich GC subpopulations in our own Galaxy, and in other galaxies, is observationally challenging. Here we apply an alternative approach utilising the property that the galaxy mass-metallicity relation is a strong function of redshift (or look-back age) but is relatively insensitive to galaxy mass for massive galaxies. Assuming that GCs follow galaxy mass-metallicity relations that evolve with redshift, one can estimate the mean formation epochs of the two GC subpopulations by knowing their mean metallicities and the growth in host galaxy mass with redshift. Recently, the SLUGGS survey has measured the spectroscopic metallicities for over 1000 GCs in a dozen massive early-type galaxies. Here we use these measurements, and our new metallicity matching method, to infer a mean age for metal-rich GCs of 11.5 Gyr (z =...

  12. Deuterium Abundance in the Most Metal-Poor Damped Lyman alpha System: Converging on Omega_baryons

    CERN Document Server

    Pettini, Max; Murphy, Michael T; Lewis, Antony; Steidel, Charles C

    2008-01-01

    The most metal-poor DLA known to date, at z = 2.61843 in the spectrum of the QSO Q0913+072, with an oxygen abundance only about 1/250 of the solar value, shows six well resolved D I Lyman series transitions in high quality echelle spectra recently obtained with the ESO VLT. We deduce a value of the deuterium abundance log (D/H) = -4.56+/-0.04 which is in good agreement with four out of the six most reliable previous determinations of this ratio in QSO absorbers. We find plausible reasons why in the other two cases the 1 sigma errors may have been underestimated by about a factor of two. The addition of this latest data point does not change significantly the mean value of the primordial abundance of deuterium, suggesting that we are now converging to a reliable measure of this quantity. We conclude that = -4.55+/-0.03 and Omega_b h^2 (BBN) = 0.0213+/-0.0010 (68% confidence limits). Including the latter as a prior in the analysis of the five year data of WMAP leads to a revised best-fitting value of the power...

  13. Kinematic Evidence for Superbubbles in I Zw 18: Constraints on the Star Formation History and Chemical Evolution

    OpenAIRE

    Martin, Crystal L.

    1996-01-01

    We have combined measurements of the kinematics, morphology, and oxygen abundance of the ionized gas in \\IZw18, one of the most metal-poor galaxies known, to examine the star formation history and chemical mixing processes.

  14. Structure in the motions of the fastest halo stars

    NARCIS (Netherlands)

    Fiorentin, PR; Helmi, A; Lattanzi, MG; Spagna, A

    2005-01-01

    We analyzed the catalog published by Beers et al. ( 2000, ApJ, 119, 2866) of 2106 non-kinematically selected metal poor stars in the solar neighborhood, with the goal of quantifying the amount of substructure in the motions of the fastest halo stars. We computed the two-point velocity correlation fu

  15. A holistic abundance analysis of r-rich stars

    CERN Document Server

    Zhang, Jiang; Zhang, Bo; 10.1111/j.1365-2966.2010.17374.x

    2010-01-01

    The chemical abundances of metal-poor stars are an excellent test bed by which to set new constraints on models of neutron-capture processes at low metallicity. Some r-process-rich (hereafter r-rich) metal-poor stars, such as HD221170, show an overabundance of the heavier neutron-capture elements and excesses of lighter neutron-capture elements. The study of these r-rich stars could give us a better understanding of weak and main r-process nucleosynthesis at low metallicity. Based on conclusions from the observation of metal-poor stars and neutron-capture element nucleosynthesis theory, we set up a model to determine the relative contributions from weak and main r-processes to the heavy-element abundances in metal-poor stars. Using this model, we find that the abundance patterns of light elements for most sample stars are close to the pattern of weak r-process stars, and those of heavier neutron-capture elements very similar to the pattern of main r-process stars, while the lighter neutron-capture elements ca...

  16. The ACS Nearby Galaxy Survey Treasury IX. Constraining asymptotic giant branch evolution with old metal-poor galaxies

    OpenAIRE

    Girardi, Leo; Williams, Benjamin F.; Gilbert, Karoline M.; Rosenfield, Philip; Dalcanton, Julianne J.; Marigo, Paola; Boyer, Martha L.; Dolphin, Andrew; Weisz, Daniel R.; Melbourne, Jason; Olsen, Knut A. G.; Seth, Anil C; Skillman, Evan

    2010-01-01

    In an attempt to constrain evolutionary models of the asymptotic giant branch (AGB) phase at the limit of low masses and low metallicities, we have examined the luminosity functions and number ratios between AGB and red giant branch (RGB) stars from a sample of resolved galaxies from the ACS Nearby Galaxy Survey Treasury. This database provides Hubble Space Telescope optical photometry together with maps of completeness, photometric errors, and star formation histories for dozens of galaxies ...

  17. High Angular Resolution JHK Imaging of the Centers of the Metal-Poor Globular Clusters NGC5272 (M3), NGC6205 (M13), NGC6287, and NGC6341 (M92)

    CERN Document Server

    Davidge, T J

    1998-01-01

    The Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) has been used to obtain high angular resolution JHK images of the centers of the metal-poor globular clusters NGC5272 (M3), NGC6205 (M13), NGC6287, and NGC6341 (M92). The color-magnitude diagrams (CMDs) derived from these data include the upper main sequence and most of the red giant branch (RGB), and the cluster sequences agree with published photometric measurements of bright stars in these clusters. The photometric accuracy is limited by PSF variations, which introduce systematic errors of a few hundredths of a magnitude near the AO reference star. The clusters are paired according to metallicity, and the near-infrared CMDs and luminosity functions are used to investigate the relative ages within each pair. The near-infrared CMDs provide the tightest constraints on the relative ages of the classical second parameter pair NGC5272 and NGC6205, and indicate that these clusters have ages that differ by no more than +/- 1 Gyr. These result...

  18. Stellar yields of rotating first stars

    International Nuclear Information System (INIS)

    First stars, also called population III stars, are born in the earliest universe without any heavy elements. These stars are the first nuclear reactor in the universe and affect their circumstances emitting synthesized materials. Not only the stellar evolution, but also their chemical yields have many distinctive characteristics. We have modeled evolution of population III stars including effect of stellar rotation. Internal mixing induced by rotation naturally results in primary nitrogen production. Evolution of rotating massive stars is followed until the core collapse phase. The new Pop III yield model will consistently explain the observed abundances of metal-poor systems

  19. The infrared spectral properties of Magellanic carbon stars

    CERN Document Server

    Sloan, G C; McDonald, I; Groenewegen, M A T; Wood, P R; Zijlstra, A A; Lagadec, E; Boyer, M L; Kemper, F; Matsuura, M; Sahai, R; Sargent, B A; Srinivasan, S; van Loon, J Th; Volk, K

    2016-01-01

    The Infrared Spectrograph on the Spitzer Space Telescope observed 184 carbon stars in the Magellanic Clouds. This sample reveals that the dust-production rate (DPR) from carbon stars generally increases with the pulsation period of the star. The composition of the dust grains follows two condensation sequences, with more SiC condensing before amorphous carbon in metal-rich stars, and the order reversed in metal-poor stars. MgS dust condenses in optically thicker dust shells, and its condensation is delayed in more metal-poor stars. Metal-poor carbon stars also tend to have stronger absorption from C2H2 at 7.5 um. The relation between DPR and pulsation period shows significant apparent scatter, which results from the initial mass of the star, with more massive stars occupying a sequence parallel to lower-mass stars, but shifted to longer periods. Accounting for differences in the mass distribution between the carbon stars observed in the Small and Large Magellanic Clouds reveals a hint of a subtle decrease in ...

  20. On the properties of the interstellar medium in extremely metal-poor blue compact dwarf galaxies: GMOS-IFU spectroscopy and SDSS photometry of the double-knot galaxy HS 2236+1344

    CERN Document Server

    Lagos, P; Gomes, J M; Castelli, A V Smith; Vega, L R; .,

    2014-01-01

    The main goal of this study is to carry out a spatially resolved investigation of the warm interstellar medium (ISM) in the extremely metal-poor Blue Compact Dwarf (BCD) galaxy HS 2236+1344. Special emphasis is laid on the analysis of the spatial distribution of chemical abundances, emission-line ratios and kinematics of the ISM, and to the recent star-forming activity in this galaxy. This study is based on optical integral field unit spectroscopy data from Gemini Multi-Object Spectrograph at the Gemini North telescope and archival Sloan Digital Sky Survey images. The data were obtained in two different positions across the galaxy, obtaining a total 4 arcsec X 8 arcsec field which encompasses most of its ISM. Emission-line maps and broad-band images obtained in this study indicate that HS 2236+1344 hosts three Giant HII regions. Our data also reveal some faint curved features in the BCD periphery that might be due to tidal perturbations or expanding ionized-gas shells. The ISM velocity field shows systematic ...

  1. An extremely primitive halo star

    CERN Document Server

    Caffau, E; François, P; Sbordone, L; Monaco, L; Spite, M; Spite, F; Ludwig, H -G; Cayrel, R; Zaggia, S; Hammer, F; Randich, S; Molaro, P; Hill, V; 10.1038/nature10377

    2012-01-01

    The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium1, almost all other elements were created in stars and supernovae. The mass fraction, Z, of elements more massive than helium, is called "metallicity". A number of very metal poor stars have been found some of which, while having a low iron abundance, are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with metallicities lower than Z=1.5E-5, it has been suggested that low mass stars (M<0.8M\\odot, the ones that survive to the present day) cannot form until the interstellar medium has been enriched above a critical value, estimated to lie in the range 1.5E-8\\leqZ\\leq1.5E-6, although competing theories claiming the contrary do exist. Here we report the chemical composition of a star with a very low Z\\leq6.9E-7 (4.5E-5 of that of the Sun) and a chemical pattern typical of classical extremely metal poor stars, meaning without the enrichment of carbon, nitroge...

  2. High-resolution abundance analysis of red giants in the metal-poor bulge globular cluster HP~1

    CERN Document Server

    Barbuy, B; Vemado, A; Ernandes, H; Ortolani, S; Saviane, I; Bica, E; Minniti, D; Dias, B; Momany, Y; Hill, V; Zoccali, M; Siqueira-Mello, C

    2016-01-01

    The globular cluster HP~1 is projected at only 3.33 degrees from the Galactic center. Together with its distance, this makes it one of the most central globular clusters in the Milky Way. It has a blue horizontal branch (BHB) and a metallicity of [Fe/H]~-1.0. This means that it probably is one of the oldest objects in the Galaxy. Abundance ratios can reveal the nucleosynthesis pattern of the first stars as well as the early chemical enrichment and early formation of stellar populations. High-resolution spectra obtained for six stars were analyzed to derive the abundances of the light elements C, N, O, Na, and Al, the alpha-elements Mg, Si, Ca, and Ti, and the heavy elements Sr, Y , Zr, Ba, La, and Eu.} High-resolution spectra of six red giants that are confirmed members of the bulge globular cluster HP~1 were obtained with the 8m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. The spectroscopic parameter derivation was based on the excitation and ionization equilibrium of FeI...

  3. Improved V II log($gf$) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    OpenAIRE

    Wood, M. P.; Lawler, J. E.; Hartog, E.A. den; Sneden, C.; Cowan, J. J.

    2014-01-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Use of two spectrometers, independent radiometric ...

  4. Improved Laboratory Transition Probabilities for Er II and Applications to the Erbium Abundances of the Sun and Five r-Process Rich, Metal-Poor Stars

    OpenAIRE

    Lawler, J. E.; Sneden, C.; Cowan, J. J.; Wyart, J. -F.; Ivans, I. I.; Sobeck, J. S.; Stockett, M. H.; Hartog, E.A. den

    2008-01-01

    Recent radiative lifetime measurements accurate to +/- 5% (Stockett et al. 2007, J. Phys. B 40, 4529) using laser-induced fluorescence (LIF) on 8 even-parity and 62 odd-parity levels of Er II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 418 lines of Er II. This work moves Er II onto the growing list of rare earth spectra with extensive and accurate modern transition probability measurements usin...

  5. Lyman `bump' galaxies - II. A possible signature of massive extremely metal-poor or metal-free stars in z=3.1 Ly-alpha emitters

    CERN Document Server

    Inoue, Akio K; Iwata, I; Matsuda, Y; Nakamura, E; Horie, M; Hayashino, T; Tapken, C; Akiyama, M; Noll, S; Yamada, T; Burgarella, D

    2010-01-01

    (Abridged) Deep NB359 imaging with Subaru by Iwata et al. have detected surprisingly strong Lyman continuum (LyC; ~900A in the rest-frame) from some LAEs at z=3.1. However, the redshifts might be misidentified due to a narrow wavelength coverage in previous spectroscopy. We here present new deep spectroscopy covering the observed 4,000-7,000A with VLT/VIMOS and Subaru/FOCAS of 8 LAEs detected in NB359. All the 8 objects have only one detectable emission line around 4,970A which is most likely to be Ly-A at z=3.1, and thus, the objects are certainly LAEs at the redshift. However, 5 of them show a ~0.''8 spatial offset between the Ly-A emission and the source detected in NB359. No indications of the redshifts of the NB359 sources are found although it is statistically difficult that all the 5 LAEs have a foreground object accounting for the NB359 flux. The rest 3 LAEs show no significant offset from the NB359 position. Therefore, they are truly LyC emitting LAEs at z=3.1. We also examine the stellar population ...

  6. An in-depth spectroscopic examination of molecular bands from 3D hydrodynamical model atmospheres I. Formation of the G-band in metal-poor dwarf stars

    CERN Document Server

    Gallagher, A J; Bonifacio, P; Ludwig, H -G; Steffen, M; Spite, M

    2016-01-01

    Recent developments in the three-dimensional (3D) spectral synthesis code Linfor3D have meant that, for the first time, large spectral wavelength regions, such as molecular bands, can be synthesised with it in a short amount of time. A detailed spectral analysis of the synthetic G-band for several dwarf turn-off-type 3D atmospheres (5850 <= T_eff [K] <= 6550, 4.0 <= log g <= 4.5, -3.0 <= [Fe/H] <= -1.0) was conducted, under the assumption of local thermodynamic equilibrium. We also examine carbon and oxygen molecule formation at various metallicity regimes and discuss the impact it has on the G-band. Using a qualitative approach, we describe the different behaviours between the 3D atmospheres and the traditional one-dimensional (1D) atmospheres and how the different physics involved inevitably leads to abundance corrections, which differ over varying metallicities. Spectra computed in 1D were fit to every 3D spectrum to determine the 3D abundance correction. Early analysis revealed that the ...

  7. The assembly of the halo system of the Milky Way as revealed by SDSS/SEGUE – The CEMP star connection

    Directory of Open Access Journals (Sweden)

    Carollo D.

    2012-02-01

    Full Text Available In recent years, massive new spectroscopic data sets, such as the over half million stellar spectra obtained during the course of SDSS (in particular its sub-survey SEGUE, have provided the quantitative detail required to formulate a coherent story of the assembly and evolution of the Milky Way. The disk and halo systems of our Galaxy have been shown to be both more complex, and more interesting, than previously thought. Here we concentrate on the halo system of the Milky Way. New data from SDSS/SEGUE has revealed that the halo system comprises at least two components, the inner halo and the outer halo, with demonstrably different characteristics (metallicity distributions, density distributions, kinematics, etc.. In addition to suggesting new ways to examine these data, the inner/outer halo dichotomy has enabled an understanding of at least one long-standing observational result, the increase of the fraction of carbon-enhanced metal-poor (CEMP stars with decreasing metallicity.

  8. Cosmic chemical evolution with intermediate mass pop III stars

    International Nuclear Information System (INIS)

    We explore the consequences of an early population of intermediate mass stars (IMS) in the 2 – 8 Msun range on cosmic chemical evolution. We discuss the implications of this population as it pertains to several cosmological and astrophysical observables. Some very metal-poor galactic stars show large enhancements of carbon, typical of the C-rich ejecta of IMS; moreover, halo star carbon and oxygen abundances show a scatter, which imply a wide range of star-formation and nucleosynthetic histories contributed to the first generations of stars. Also, recent analyses of the He abundance in metal-poor extragalactic H II regions suggest an elevated primitive abundance of Helium, Yp ≅ 0.256 by mass, higher than the predicted result from big bang nucleosynthesis assuming the baryon density determined by WMAP, Yp ≅ 0.249. This offset suggests a prompt initial enrichment of He in early metal-poor structures, and IMS Pop III stars are again good candidates. We also discuss the effect of these Pop III stars on global cosmic evolution for example the reionization of the Universe. We conclude that if IMS are to be associated with some Population III stars, their relevance is limited to low mass structures involving a little fraction of the total baryon content of the Universe typical at redshift 10 [1].

  9. A study of rotating globular clusters - the case of the old, metal-poor globular cluster NGC 4372

    CERN Document Server

    Kacharov, N; Koch, A; Frank, M J; Martin, N F; van de Ven, G; Puzia, T H; McDonald, I; Johnson, C I; Zijlstra, A A

    2014-01-01

    Aims: We present the first in-depth study of the kinematic properties and derive the structural parameters of NGC 4372 based on the fit of a Plummer profile and a rotating, physical model. We explore the link between internal rotation to different cluster properties and together with similar studies of more GCs, we put these in the context of globular cluster formation and evolution. Methods: We present radial velocities for 131 cluster member stars measured from high-resolution FLAMES/GIRAFFE observations. Their membership to the GC is additionally confirmed from precise metallicity estimates. Using this kinematic data set we build a velocity dispersion profile and a systemic rotation curve. Additionally, we obtain an elliptical number density profile of NGC 4372 based on optical images using a MCMC fitting algorithm. From this we derive the cluster's half-light radius and ellipticity as r_h=3.4'+/-0.04' and e=0.08+/-0.01. Finally, we give a physical interpretation of the observed morphological and kinematic...

  10. PS1-10bzj: A Fast, Hydrogen-Poor Superluminous Supernova in a Metal Poor Host Galaxy

    CERN Document Server

    Lunnan, R; Berger, E; Milisavljevic, D; Drout, M; Sanders, N E; Challis, P M; Czekala, I; Foley, R J; Fong, W; Huber, M E; Kirshner, R P; Leibler, C; Marion, G H; McCrum, M; Narayan, G; Rest, A; Roth, K C; Scolnic, D; Smartt, S J; Smith, K; Soderberg, A M; Stubbs, C W; Tonry, J L; Burgett, W S; Chambers, K C; Kudritzki, R -P; Magnier, E A; Price, P A

    2013-01-01

    We present observations and analysis of PS1-10bzj, a superluminous supernova (SLSN) discovered in the Pan-STARRS Medium Deep Survey at a redshift z = 0.650. Spectroscopically, PS1-10bzj is similar to the hydrogen-poor SLSNe 2005ap and SCP 06F6, though with a steeper rise and lower peak luminosity (M_bol = -21.4 mag) than previous events. We construct a bolometric light curve, and show that while PS1-10bzj's energetics were less extreme than previous events, its luminosity still cannot be explained by radioactive nickel decay alone. We explore both a magnetar spin-down and circumstellar interaction scenario and find that either can fit the data. PS1-10bzj is located in the Extended Chandra Deep Field South (ECDF-S) and the host galaxy is imaged in a number of surveys, including with the Hubble Space Telescope. The host is a compact dwarf galaxy (M_B ~ -18 mag, diameter < 800 pc), with a low stellar mass (M_* ~ 2.4 * 10^7 M_sun), young stellar population (\\tau_* ~ 5 Myr), and a star formation rate of ~ 2-3 M...

  11. The absolute magnitudes of RR Lyrae stars: Pt. 1

    International Nuclear Information System (INIS)

    A Baade-Wesselink method has been developed based on the Infrared Flux Method of previous authors. The method requires extensive photometry. However, if the data are available it can give accurate results. We have applied the method to the metal-poor RR Lyrae star X Arietis for which we also present new ultraviolet, optical and infrared photometry. (author)

  12. Absolute magnitudes of RR Lyrae stars: Pt. 1. X Arietis

    Energy Technology Data Exchange (ETDEWEB)

    Fernley, J.A.; Lynas-Gray, A.E.; Skillen, I.; Jameson, R.F.; Marang, F.; Kilkenny, D.; Longmore, A.J.

    1989-01-15

    A Baade-Wesselink method has been developed based on the Infrared Flux Method of previous authors. The method requires extensive photometry. However, if the data are available it can give accurate results. We have applied the method to the metal-poor RR Lyrae star X Arietis for which we also present new ultraviolet, optical and infrared photometry.

  13. KECK OBSERVATIONS OF THE YOUNG METAL-POOR HOST GALAXY OF THE SUPER-CHANDRASEKHAR-MASS TYPE Ia SUPERNOVA SN 2007if

    International Nuclear Information System (INIS)

    We present Keck LRIS spectroscopy and g-band photometry of the metal-poor, low-luminosity host galaxy of the super-Chandrasekhar-mass Type Ia supernova SN 2007if. Deep imaging of the host reveals its apparent magnitude to be mg = 23.15 ± 0.06, which at the spectroscopically measured redshift of zhelio = 0.07450 ± 0.00015 corresponds to an absolute magnitude of Mg = -14.45 ± 0.06. Galaxy g - r color constrains the mass-to-light ratio, giving a host stellar mass estimate of log(M*/Msun) = 7.32 ± 0.17. Balmer absorption in the stellar continuum, along with the strength of the 4000 A break, constrains the age of the dominant starburst in the galaxy to be tburst = 123+165-77 Myr, corresponding to a main-sequence turnoff mass of M/Msun = 4.6+2.6-1.4. Using the R23 method of calculating metallicity from the fluxes of strong emission lines, we determine the host oxygen abundance to be 12 + log(O/H)KK04 = 8.01 ± 0.09, significantly lower than any previously reported spectroscopically measured Type Ia supernova host galaxy metallicity. Our data show that SN 2007if is very likely to have originated from a young, metal-poor progenitor.

  14. Massive Star Clusters in Dwarf Galaxies

    CERN Document Server

    Larsen, Soeren S

    2015-01-01

    Dwarf galaxies can have very high globular cluster specific frequencies, and the GCs are in general significantly more metal-poor than the bulk of the field stars. In some dwarfs, such as Fornax, WLM, and IKN, the fraction of metal-poor stars that belong to GCs can be as high as 20%-25%, an order of magnitude higher than the 1%-2% typical of GCs in halos of larger galaxies. Given that chemical abundance anomalies appear to be present also in GCs in dwarf galaxies, this implies severe difficulties for self-enrichment scenarios that require GCs to have lost a large fraction of their initial masses. More generally, the number of metal-poor field stars in these galaxies is today less than what would originally have been present in the form of low-mass clusters if the initial cluster mass function was a power-law extending down to low masses. This may imply that the initial GC mass function in these dwarf galaxies was significantly more top-heavy than typically observed in present-day star forming environments.

  15. Gaia FGK benchmark stars: new candidates at low metallicities

    Science.gov (United States)

    Hawkins, K.; Jofré, P.; Heiter, U.; Soubiran, C.; Blanco-Cuaresma, S.; Casagrande, L.; Gilmore, G.; Lind, K.; Magrini, L.; Masseron, T.; Pancino, E.; Randich, S.; Worley, C. C.

    2016-07-01

    Context. We have entered an era of large spectroscopic surveys in which we can measure, through automated pipelines, the atmospheric parameters and chemical abundances for large numbers of stars. Calibrating these survey pipelines using a set of "benchmark stars" in order to evaluate the accuracy and precision of the provided parameters and abundances is of utmost importance. The recent proposed set of Gaia FGK benchmark stars has up to five metal-poor stars but no recommended stars within -2.0 http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A70

  16. Five Planets Transiting a Ninth Magnitude Star

    OpenAIRE

    Vanderburg, Andrew; Becker, Juliette C.; Kristiansen, Martti H.; Bieryla, Allyson; Duev, Dmitry A.; Jensen-Clem, Rebecca; Morton, Timothy D.; Latham, David W.; Adams, Fred C.; Baranec, Christoph; Berlind, Perry; Calkins, Michael L.; Esquerdo, Gilbert A.; Kulkarni, Shrinivas; Law, Nicholas M.

    2016-01-01

    The Kepler mission has revealed a great diversity of planetary systems and architectures, but most of the planets discovered by Kepler orbit faint stars. Using new data from the K2 mission, we present the discovery of a five planet system transiting a bright (V = 8.9, K = 7.7) star called HIP 41378. HIP 41378 is a slightly metal-poor late F-type star with moderate rotation (v sin(i) = 7 km/s) and lies at a distance of 116 +/- 18 from Earth. We find that HIP 41378 hosts two sub-Neptune sized p...

  17. Five Planets Transiting a Ninth Magnitude Star

    OpenAIRE

    Vanderburg, Andrew; Becker, Juliette C.; Kristiansen, Martti H.; Bieryla, Allyson; Duev, Dmitry A.; Jensen-Clem, Rebecca; Morton, Timothy D.; Latham, David W.; Adams, Fred C.; Baranec, Christoph; Berlind, Perry; Calkins, Michael L.; Esquerdo, Gilbert A.; Kulkarni, Shrinivas; Law, Nicholas M.

    2016-01-01

    The Kepler mission has revealed a great diversity of planetary systems and architectures, but most of the planets discovered by Kepler orbit faint stars. Using new data from the K2 mission, we present the discovery of a five-planet system transiting a bright (V = 8.9, K = 7.7) star called HIP 41378. HIP 41378 is a slightly metal-poor late F-type star with moderate rotation (v sin i ≃7 km s^(-1)) and lies at a distance of 116 ± 18 pc from Earth. We find that HIP 41378 hosts two sub-Neptune-siz...

  18. Is HE0107-5240 A Primordial Star?

    CERN Document Server

    Suda, T; Fujimoto, M Y; Machida, M N

    2004-01-01

    We discuss the origin of HE0107-5240 which is the most metal poor star yet observed ([Fe/H] = -5.3). Its discovery has an important bearing on the question of the observability of "first generation" stars. In common with other metal-poor stars (-4 < [Fe/H] < -2.5), HE0107-5240 shows a peculiar abundance pattern (CNO rich, moderate Na rich). The observed abundance pattern can be explained by nucleosynthesis and mass transfer in a first generation binary star, which, after birth, accretes matter from a primordial cloud mixed with the ejectum of a supernova. We elaborate the binary scenario on the basis of the evolution and nucleosynthesis of extremely metal-poor, low-mass model stars and discuss the possibility of discriminating this scenario from others. In our picture, iron peak elements arise in surface layers of the component stars by accretion of gas from the polluted primordial cloud. To explain the observed C, N, O, and Na enhancements, we suppose that the currently observed star, once the secondar...

  19. The Na-O anticorrelation in horizontal branch stars. IV. M22

    CERN Document Server

    Gratton, R G; Sollima, A; Carretta, E; Bragaglia, A; Momany, Y; D'Orazi, V; Cassisi, S; Salaris, M

    2014-01-01

    We obtained high-resolution spectra for 94 candidate stars belonging to the HB of M22 with FLAMES. The HB stars we observed span a restricted temperature range (7,800stars of M22 are. Within our sample, we can distinguish three groups of stars segregated (though contiguous) in colours: Group 1 (49 stars) is metal-poor, N-normal, Na-poor and O-rich with abundances that match those determined for the primordial group of RGB stars from previous studies. Group 2 (23 stars) is still metal-poor, but it is N- and Na-rich, though only very mildly depleted in O. We can identify this intermediate group as the progeny of the metal-poor RGB stars that occupy an intermediate location along the Na-O anti-correlation. The third group (20 stars) is metal-rich, Na-rich, and O-rich and likely corresponds to the most O-rich component of the previously found metal-rich RGB population. We did not observe any severely O-depleted stars and we think that the progeny of these stars fal...

  20. Imprints of fast-rotating massive stars in the Galactic Bulge.

    Science.gov (United States)

    Chiappini, Cristina; Frischknecht, Urs; Meynet, Georges; Hirschi, Raphael; Barbuy, Beatriz; Pignatari, Marco; Decressin, Thibaut; Maeder, André

    2011-04-28

    The first stars that formed after the Big Bang were probably massive, and they provided the Universe with the first elements heavier than helium ('metals'), which were incorporated into low-mass stars that have survived to the present. Eight stars in the oldest globular cluster in the Galaxy, NGC 6522, were found to have surface abundances consistent with the gas from which they formed being enriched by massive stars (that is, with higher α-element/Fe and Eu/Fe ratios than those of the Sun). However, the same stars have anomalously high abundances of Ba and La with respect to Fe, which usually arises through nucleosynthesis in low-mass stars (via the slow-neutron-capture process, or s-process). Recent theory suggests that metal-poor fast-rotating massive stars are able to boost the s-process yields by up to four orders of magnitude, which might provide a solution to this contradiction. Here we report a reanalysis of the earlier spectra, which reveals that Y and Sr are also overabundant with respect to Fe, showing a large scatter similar to that observed in extremely metal-poor stars, whereas C abundances are not enhanced. This pattern is best explained as originating in metal-poor fast-rotating massive stars, which might point to a common property of the first stellar generations and even of the 'first stars'. PMID:21525928

  1. Hubble Space Telescope Near-Ultraviolet Spectroscopy of Bright CEMP-s Stars

    Science.gov (United States)

    Placco, Vinicius M.; Beers, Timothy C.; Ivans, Inese I.; Filler, Dan; Imig, Julie A.; Roederer, Ian U.; Abate, Carlo; Hansen, Terese; Cowan, John J.; Frebel, Anna; Lawler, James E.; Schatz, Hendrik; Sneden, Christopher; Sobeck, Jennifer S.; Aoki, Wako; Smith, Verne V.; Bolte, Michael

    2015-10-01

    We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the bright carbon-enhanced metal-poor (CEMP) stars HD 196944 (V=8.40, [Fe/H] = -2.41) and HD 201626 (V=8.16, [Fe/H] = -1.51), based on data acquired with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. Both of these stars belong to the sub-class CEMP-s, and exhibit clear over-abundances of heavy elements associated with production by the slow neutron-capture process. HD 196944 has been well-studied in the optical region, but we add abundance results for six species (Ge, Nb, Mo, Lu, Pt, and Au) that are only accessible in the NUV. In addition, we provide the first determination of its orbital period, P = 1325 days. HD 201626 has only a limited number of abundance results based on previous optical work—here we add five new species from the NUV, including Pb. We compare these results with models of binary-system evolution and s-process element production in stars on the asymptotic giant branch, with the goal of explaining their origin and evolution. Our best-fitting models for HD 196944 ({M}1,i=0.9{M}⊙ , {M}2,i=0.86{M}⊙ , for [Fe/H] = -2.2), and HD 201626 ({M}1,i=0.9{M}⊙ , {M}2,i=0.76{M}⊙ , for [Fe/H] = -2.2; {M}1,i=1.6{M}⊙ , {M}2,i=0.59{M}⊙ , for [Fe/H] = -1.5) are consistent with the current accepted scenario for the formation of CEMP-s stars. The data presented herein were obtained with the (i) NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. (These observations are associated with program GO-12554, data sets OBQ601010-30 and OBQ602010-30.); and (ii) W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. (The Observatory was made

  2. On the properties of the interstellar medium in extremely metal-poor blue compact dwarf galaxies. GMOS-IFU spectroscopy and SDSS photometry of the double-knot galaxy HS 2236+1344

    Science.gov (United States)

    Lagos, P.; Papaderos, P.; Gomes, J. M.; Smith Castelli, A. V.; Vega, L. R.

    2014-09-01

    Aims: The main goal of this study is to carry out a spatially resolved investigation of the warm interstellar medium (ISM) in the extremely metal-poor blue compact dwarf (BCD) galaxy HS 2236+1344. Special emphasis is laid on analysis of the spatial distribution of chemical abundances, emission-line ratios, and the kinematics of the ISM, and to the recent star-forming (SF) activity in this galaxy. Methods: This study is based on optical integral field unit spectroscopy data from Gemini Multi-Object Spectrograph (GMOS) at the Gemini North telescope and archival Sloan Digital Sky Survey (SDSS) images. The galaxy was observed at medium spectral resolution over the spectral range from ~4300 Å to 7300 Å. The data were obtained in two different positions across the galaxy, obtaining a total 4″ × 8″ field that encompasses most of its ISM. Results: Emission-line maps and broad-band images obtained in this study indicate that HS 2236+1344 hosts three giant H ii regions (GH iiRs). Our data also reveal some faint curved features in the BCD periphery that might be due to tidal perturbations or expanding ionized-gas shells. The ISM velocity field shows systematic gradients along the major axis of the BCD, with its southeastern and northwestern half differing by ~80 km s-1 in their recessional velocity over the field of view. The Hα and Hβ equivalent-width distribution in the central part of HS 2236+1344 is consistent with a very young (~3 Myr) burst. Our surface photometry analysis reveals an underlying low surface brightness component with moderately red colors, which suggest that the galaxy has undergone previous star formation. We derive an integrated oxygen abundance of 12 + log (O / H) = 7.53 ± 0.06 and a nitrogen-to-oxygen ratio of log (N / O) = -1.57 ± 0.19. Our results are consistent, within the uncertainties, with a homogeneous distribution of oxygen and nitrogen within the ISM of the galaxy. The high-ionization He ii λ4686 emission line is detected only in

  3. How plausible are the proposed formation scenarios of CEMP-r/s stars?

    OpenAIRE

    Abate, Carlo; Stancliffe, Richard J.; Liu, Zheng-Wei

    2016-01-01

    CEMP-$r/s$ stars are metal-poor stars with enhanced abundances of carbon and heavy elements associated with the slow ($s$-) and rapid ($r$-) neutron-capture process. It is believed that carbon and $s$-elements were accreted from the wind of an AGB primary star, a scenario that is generally accepted to explain the formation of CEMP stars that are only enhanced in $s$-elements (CEMP-$s$ stars). The origin of $r$-element-enrichment in CEMP-$r/s$ stars is debated and many formation scenarios have...

  4. The Hamburg/ESO R-process Enhanced Star survey (HERES). I. Project description, and discovery of two stars with strong enhancements of neutron-capture elements

    CERN Document Server

    Christlieb, N; Barklem, P S; Bessell, M; Hill, V; Holmberg, J; Korn, A J; Marsteller, B; Mashonkina, L I; Qian, Y Z; Rossi, S; Wasserburg, G J; Zickgraf, F J; Kratz, K L; Nordström, B; Pfeiffer, B; Rhee, J; Ryan, S G

    2004-01-01

    We report on a dedicated effort to identify and study metal-poor stars strongly enhanced in r-process elements ([r/Fe] > 1 dex; hereafter r-II stars), the Hamburg/ESO R-process Enhanced Star survey (HERES). Moderate-resolution (~2A) follow-up spectroscopy has been obtained for metal-poor giant candidates selected from the Hamburg/ESO objective-prism survey (HES) as well as the HK survey to identify sharp-lined stars with [Fe/H] < -2.5dex. For several hundred confirmed metal-poor giants brighter than B~16.5mag (most of them from the HES), ``snapshot'' spectra (R~20,000; S/N~30 per pixel) are being obtained with VLT/UVES, with the main aim of finding the 2-3% r-II stars expected to be among them. These are studied in detail by means of higher resolution and higher S/N spectra. In this paper we describe a pilot study based on a set of 35 stars, including 23 from the HK survey, 8 from the HES, and 4 comparison stars. We discovered two new r-II stars, CS29497-004 ([Eu/Fe] = 1.64 +/- 0.22) and CS29491-069 ([Eu/F...

  5. Neutron-capture nucleosynthesis in the first stars

    International Nuclear Information System (INIS)

    Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly rotating massive stars and pair instability supernovae did not contribute substantial amounts of neutron-capture elements to the regions where the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor stars with low levels of neutron-capture elements were enriched by products of zero-metallicity supernovae only, then the presence of these heavy elements indicates that at least one form of neutron-capture reaction operated in some of the first stars.

  6. Spitzer spectra of evolved stars in omega Centauri and their low-metallicity dust production

    CERN Document Server

    McDonald, Iain; Sloan, Gregory C; Dupree, Andrea K; Zijlstra, Albert A; Boyer, Martha L; Gehrz, Robert D; Evans, Aneurin; Woodward, Charles E; Johnson, Christian I

    2011-01-01

    Dust production is explored around 14 metal-poor ([Fe/H] = -1.91 to -0.98) giant stars in the Galactic globular cluster omega Centauri using new Spitzer IRS spectra. This sample includes the cluster's post-AGB and carbon stars and is thus the first representative spectral study of dust production in a metal-poor ([Fe/H] < -1) population. Only the more metal rich stars V6 and V17 ([Fe/H] = -1.08, -1.06) exhibit silicate emission, while the five other stars with mid-infrared excess show only a featureless continuum which we argue is caused by metallic iron dust grains. We examine the metallicity of V42, and find it is likely part of the metal-rich population ([Fe/H] ~ -0.8). Aside from the post-AGB star V1, we find no star from the cluster's bulk, metal-poor ([Fe/H] < -1.5) population - including the carbon stars - to be producing detectable amounts of dust. We compare the dust production to the stars' H-alpha line profiles obtained at the Magellan/Clay telescope at Las Campanas Observatory, finding pulsa...

  7. HE 0017+0055: A probable pulsating CEMP-rs star and long-period binary

    Science.gov (United States)

    Jorissen, A.; Hansen, T.; Van Eck, S.; Andersen, J.; Nordström, B.; Siess, L.; Torres, G.; Masseron, T.; Van Winckel, H.

    2016-02-01

    Context. A large fraction of the carbon-enhanced, extremely metal-poor halo giants ([Fe/H] Nordic Optical Telescope and Mercator telescopes exhibits variability, with a period of 384 d and amplitude of 540 ± 27 m s-1 superimposed on a nearly linear long-term decline of ~1 m s-1 day-1. We used high-resolution HERMES/Mercator and Keck/HIRES spectra to derive elemental abundances with 1D LTE MARCS models. A metallicity of [Fe/H] ~ -2.4 is found, along with s-process overabundances of the order of 2 dex (with the exception of [Y/Fe] ~ + 0.5), and most notably overabundances of r-process elements like Sm, Eu, Dy, and Er in the range 0.9-2.0 dex. With [Ba/Fe] > 1.9 dex and [Eu/Fe] = 2.3 dex, HE 0017+0055 is a CEMP-rs star. We used the derived atmospheric parameters and abundances to infer HE 0017+0055 evolutionary status from a comparison with evolutionary tracks. Results: HE 0017+0055 appears to be a giant star below the tip of the red giant branch. The s-process pollution must therefore originate from mass transfer from a companion formerly on the AGB, which is now a carbon-oxygen white dwarf (WD). If the 384 d velocity variations are attributed to the WD companion, its orbit must be seen almost face-on, with i ~ 2.3°, because the mass function is very small: f(M1,M2) = (6.1 ± 1.1) × 10-6M⊙. Alternatively, the WD orbital motion could be responsible for the long-term velocity variations, with a period of several decades. The 384 d variations should then be attributed either to a low-mass inner companion (perhaps a brown dwarf, depending on the orbital inclination), or to stellar pulsations. The latter possibility is made likely by the fact that similar low-amplitude velocity variations, with periods close to 1 yr, have been reported for other CEMP stars in a companion paper. A definite conclusion about the origin of the 384 d velocity variations should however await the detection of synchronous low-amplitude photometric variations. Based on observations performed

  8. Carbon Stars in the Hamburg/ESO Survey: Abundances

    CERN Document Server

    Cohen, J G; McWilliam, A; Melendez, J; Ramírez, S; Shectman, S; Swensson, A; Thompson, I; Zickgraf, F J; Christlieb, Norbert; Cohen, Judith G.; Melendez, Jorge; Ramirez, Solange; Shectman, Stephen; Swensson, Amber; Thompson, Ian; William, Andrew Mc; Zickgraf, Franz-Josef

    2006-01-01

    We have carried out a detailed abundance analysis for a sample of 16 carbon stars found among candidate extremely metal-poor (EMP) stars from the Hamburg/ESO Survey. We find that the Fe-metallicities for the cooler C-stars (Teff ~ 5100K) have been underestimated by a factor of ~10 by the standard HES survey tools. The results presented here provided crucial supporting data used by Cohen et al (2006) to derive the frequency of C-stars among EMP stars. C-enhancement in these EMP C-stars appears to be independent of Fe-metallicity and approximately constant at ~1/5 the solar C/H. The mostly low C12/C13 ratios (~4) and the high N abundances in many of these stars suggest that material which has been through proton burning via the CN cycle comprises most of the stellar envelope. C-enhancement is associated with strong enrichment of heavy nuclei beyond the Fe-peak for 12 of the 16 stars. The remaining C-stars from the HES, which tend to be the most Fe-metal poor, show no evidence for enhancement of the heavy elemen...

  9. The calcium isotopic anomaly in magnetic CP stars

    OpenAIRE

    Cowley, Ch. R.; Hubrig, S.

    2005-01-01

    Chemically peculiar stars in the magnetic sequence can show the same isotopic anomaly in calcium previously discovered for mercury-manganese stars in the non-magnetic sequence. In extreme cases, the dominant isotope is the exotic 48^Ca. Measurements of Ca II lines arising from 3d-4p transitions reveal the anomaly by showing shifts up to 0.2 AA for the extreme cases - too large to be measurement errors. We report measurements of miscellaneous objects, including two metal-poor stars, two appare...

  10. Gaia FGK Benchmark Stars: New Candidates At Low-Metallicities

    CERN Document Server

    Hawkins, Keith; Heiter, Ulrike; Soubiran, Caroline; Blanco-Cuaresma, Sergi; Casagrande, Luca; Gilmore, Gerry; Lind, Karin; Magrini, Laura; Masseron, Thomas; Pancino, Elena; Randich, Sofia; Worley, Clare C

    2016-01-01

    We have entered an era of large spectroscopic surveys in which we can measure, through automated pipelines, the atmospheric parameters and chemical abundances for large numbers of stars. Calibrating these survey pipelines using a set of "benchmark stars" in order to evaluate the accuracy and precision of the provided parameters and abundances is of utmost importance. The recent proposed set of Gaia FGK benchmark stars of Heiter et al. (2015) has no recommended stars within the critical metallicity range of $-2.0 <$ [Fe/H] $< -1.0$ dex. In this paper, we aim to add candidate Gaia benchmark stars inside of this metal-poor gap. We began with a sample of 21 metal-poor stars which was reduced to 10 stars by requiring accurate photometry and parallaxes, and high-resolution archival spectra. The procedure used to determine the stellar parameters was similar to Heiter et al. (2015) and Jofre et al. (2014) for consistency. The effective temperature (T$_{\\mathrm{eff}}$) of all candidate stars was determined using...

  11. A Correlation Between the Eclipse Depths of Kepler Gas Giant Candidates and the Metallicities of their Parent Stars

    CERN Document Server

    Dodson-Robinson, Sarah

    2012-01-01

    Previous studies of the interior structure of transiting exoplanets have shown that the heavy element content of gas giants increases with host star metallicity. Since metal-poor planets are less dense and have larger radii than metal-rich planets of the same mass, one might expect that metal-poor stars host a higher proportion of gas giants with large radii than metal-rich stars. Here I present evidence for a negative correlation at the 2.3-sigma level between eclipse depth and stellar metallicity in the Kepler gas giant candidates. Based on Kendall's tau statistics, the probability that eclipse depth depends on star metallicity is 0.981. The correlation is consistent with planets orbiting low-metallicity stars being, on average, larger in comparison with their host stars than planets orbiting metal-rich stars. Furthermore, since metal-rich stars have smaller radii than metal-poor stars of the same mass and age, a uniform population of planets should show a rise in median eclipse depth with [M/H]. The fact t...

  12. The SPLASH Survey: A Spectroscopic Analysis of the Metal-Poor, Low-Luminosity M31 dSph Satellite Andromeda X

    CERN Document Server

    Kalirai, Jason S; Guhathakurta, Puragra; Geha, Marla; Kniazev, Alexei Y; Martinez-Delgado, David; Bell, Eric F; Grebel, Eva K; Gilbert, Karoline M

    2009-01-01

    Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal galaxy (dSph) found by Zucker et al. (2007) in the Sloan Digital Sky Survey (SDSS - York et al. 2000). In this paper, we present the first spectroscopic study of individual red giant branch stars in And X, as a part of the SPLASH Survey (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo). Using the Keck II telescope and multiobject DEIMOS spectrograph, we target two spectroscopic masks over the face of the galaxy and measure radial velocities for ~100 stars with a median accuracy of sigma_v ~ 3 km/s. The velocity histogram for this field confirms three populations of stars along the sight line: foreground Milky Way dwarfs at small negative velocities, M31 halo red giants over a broad range of velocities, and a very cold velocity ``spike'' consisting of 22 stars belonging to And X with v_rad = -163.8 +/- 1.2 km/s. By carefully considering both the random and systematic velocity errors of these stars (e.g., through d...

  13. An extremely primitive star in the Galactic halo.

    Science.gov (United States)

    Caffau, Elisabetta; Bonifacio, Piercarlo; François, Patrick; Sbordone, Luca; Monaco, Lorenzo; Spite, Monique; Spite, François; Ludwig, Hans-G; Cayrel, Roger; Zaggia, Simone; Hammer, François; Randich, Sofia; Molaro, Paolo; Hill, Vanessa

    2011-09-01

    The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as 'metallicity'. A number of very metal-poor stars has been found, some of which have a low iron abundance but are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with Z theories claiming the contrary do exist. (We use 'low-mass' here to mean a stellar mass of less than 0.8 solar masses, the stars that survive to the present day.) Here we report the chemical composition of a star in the Galactic halo with a very low Z (≤ 6.9 × 10(-7), which is 4.5 × 10(-5) times that of the Sun) and a chemical pattern typical of classical extremely metal-poor stars--that is, without enrichment of carbon, nitrogen and oxygen. This shows that low-mass stars can be formed at very low metallicity, that is, below the critical value of Z. Lithium is not detected, suggesting a low-metallicity extension of the previously observed trend in lithium depletion. Such lithium depletion implies that the stellar material must have experienced temperatures above two million kelvin in its history, given that this is necessary to destroy lithium. PMID:21886158

  14. Stars Too Old to be Trusted?

    Science.gov (United States)

    2006-08-01

    Analysing a set of stars in a globular cluster with ESO's Very Large Telescope, astronomers may have found the solution to a critical cosmological and stellar riddle. Until now, an embarrassing question was why the abundance of lithium produced in the Big Bang is a factor 2 to 3 times higher than the value measured in the atmospheres of old stars. The answer, the researchers say, lies in the fact that the abundances of elements measured in a star's atmosphere decrease with time. ESO PR Photo 30/06 ESO PR Photo 30/06 Globular cluster NGC 6397, with some of the FLAMES-UVES target stars highlighted "Such trends are predicted by models that take into account the diffusion of elements in a star", said Andreas Korn, lead-author of the paper reporting the results in this week's issue of the journal Nature [1,2]. "But an observational confirmation was lacking. That is, until now." Lithium is one of the very few elements to have been produced in the Big Bang. Once astronomers know the amount of ordinary matter present in the Universe [3], it is rather straightforward to derive how much lithium was created in the early Universe. Lithium can also be measured in the oldest, metal-poor stars, which formed from matter similar to the primordial material. But the cosmologically predicted value is too high to reconcile with the measurements made in the stars. Something is wrong, but what? Diffusive processes altering the relative abundances of elements in stars are well known to play a role in certain classes of stars. Under the force of gravity, heavy elements will tend to sink out of visibility into the star over the course of billions of years. "The effects of diffusion are expected to be more pronounced in old, very metal-poor stars", said Korn. "Given their greater age, diffusion has had more time to produce sizeable effects than in younger stars like the Sun." The astronomers thus set up an observational campaign to test these model predictions, studying a variety of stars in

  15. Population III stars around the Milky Way

    CERN Document Server

    Komiya, Yutaka; Fujimoto, Masayuki Y

    2016-01-01

    We explore the possibility of observing Population III (Pop~III) stars, born of the primordial gas. Pop~III stars with masses below $0.8 M_\\odot$ should survive to date though are not observed yet, but the existence of stars with low metallicity as [Fe/H]$ < -5$ in the Milky Way halo suggests the surface pollution of Pop~III stars with accreted metals from the interstellar gas after birth. In this paper, we investigate the runaway of Pop~III stars from their host mini-halos, considering the ejection of secondary members from binary systems when their massive primaries explode as supernovae. These stars save them from the surface pollution. By computing the star formation and chemical evolution along with the hierarchical structure formation based on the extended Press--Schechter merger trees, we demonstrate that several hundreds to tens of thousands of low-mass Pop~III stars escape from the building blocks of the Milky Way. The second and later generations of extremely metal-poor (EMP) stars are also escap...

  16. Discovery of the Earliest-Type Oe Stars in the Small Magellanic Cloud

    OpenAIRE

    Golden-Marx, Jesse B.; Oey, M. S.; Lamb, Joel B.; Graus, Andrew S.

    2014-01-01

    No classical Oe/Be stars with spectral type earlier than O7.5e have been identified to date in the Milky Way (MW). This is consistent with the decretion disk model because strong stellar winds cause early-type O stars to lose angular momentum, thereby preventing them from rotating fast enough to spin out decretion disks. How- ever, metal-poor O stars have weaker stellar winds, allowing the stars to retain angular momentum. Therefore, low-metallicity environments should promote the formation o...

  17. Non-LTE iron abundances in cool stars: The role of hydrogen collisions

    CERN Document Server

    Ezzeddine, Rana; Plez, Bertrand

    2015-01-01

    In the aim of determining accurate iron abundances in stars, this work is meant to empirically calibrate H-collision cross-sections with iron, where no quantum mechanical calculations have been published yet. Thus, a new iron model atom has been developed, which includes hydrogen collisions for excitation, ionization and charge transfer processes. We show that collisions with hydrogen leading to charge transfer are important for an accurate non-LTE modeling. We apply our calculations on several benchmark stars including the Sun, the metal-rich star {\\alpha} Cen A and the metal-poor star HD140283.

  18. The mass of the galactic halo derived from the luminosity function high-velocity stars

    International Nuclear Information System (INIS)

    The local luminosity function of high-velocity stars is derived on the basis of a complete sample of stars of large proper motion with trigonometric parallaxes. The fraction of these stars belonging to a roughly spherical galactic halo is deduced by using a kinematical criterion based on space velocities of metal-poor RR Lyrae variables. The local mass density of halo stars is about 1.7times10-4 solar masses per cubic parsec, corresponding to a fractional mass within the Sun's distance from the center of 6 percent, i.e., an order of magnitude lower than that of the massive halo proposed by Ostriker and Peebles

  19. The Magellan PFS Planet Search Program: Radial Velocity and Stellar Abundance Analyses of the 360 AU, Metal-Poor Binary "Twins" HD 133131A & B

    CERN Document Server

    Teske, Johanna K; Vogt, Steve S; Díaz, Matías; Butler, R Paul; Crane, Jeffrey D; Thompson, Ian B; Arriagada, Pamela

    2016-01-01

    We present a new precision radial velocity (RV) dataset that reveals multiple planets orbiting the stars in the $\\sim$360 AU, G2$+$G2 "twin" binary HD 133131AB. Our 6 years of high-resolution echelle observations from MIKE and 5 years from PFS on the Magellan telescopes indicate the presence of two eccentric planets around HD 133131A with minimum masses of 1.43$\\pm$0.03 and 0.63$\\pm$0.15 $\\mathcal{M}_{\\rm J}$ at 1.44$\\pm$0.005 and 4.79$\\pm$0.92 AU, respectively. Additional PFS observations of HD 133131B spanning 5 years indicate the presence of one eccentric planet of minimum mass 2.50$\\pm$0.05 $\\mathcal{M}_{\\rm J}$ at 6.40$\\pm$0.59 AU, making it one of the longest period planets detected with RV to date. These planets are the first to be reported primarily based on data taken with PFS on Magellan, demonstrating the instrument's precision and the advantage of long-baseline RV observations. We perform a differential analysis between the Sun and each star, and between the stars themselves, to derive stellar par...

  20. Population III Stars Around the Milky Way

    Science.gov (United States)

    Komiya, Yutaka; Suda, Takuma; Fujimoto, Masayuki Y.

    2016-03-01

    We explore the possibility of observing Population III (Pop III) stars, born of primordial gas. Pop III stars with masses below 0.8 M⊙ should survive to date though are not yet observed, but the existence of stars with low metallicity as [{{Fe}}/{{H}}]\\lt -5 in the Milky Way halo suggests the surface pollution of Pop III stars with accreted metals from the interstellar gas after birth. In this paper, we investigate the runaway of Pop III stars from their host mini-halos, considering the ejection of secondary members from binary systems when their massive primaries explode as supernovae. These stars save them from surface pollution. By computing the star formation and chemical evolution along with the hierarchical structure formation based on the extended Press-Schechter merger trees, we demonstrate that several hundreds to tens of thousands of low-mass Pop III stars escape from the building blocks of the Milky Way. The second and later generations of extremely metal-poor stars also escaped from the mini-halos. We discuss the spatial distributions of these escaped stars by evaluating the distances between the mini-halos in the branches of merger trees under the spherical collapse model of dark matter halos. It is demonstrated that the escaped stars distribute beyond the stellar halo with a density profile close to the dark matter halo, while Pop III stars are slightly more centrally concentrated. 6%-30% of the escaped stars leave the Milky Way and go out into the intergalactic space. Based on the results, we discuss the feasibility of observing the Pop III stars with the pristine surface abundance.

  1. The mass spectrum of the first stars

    Energy Technology Data Exchange (ETDEWEB)

    Susa, Hajime; Tominaga, Nozomu [Department of Physics, Konan University, Okamoto, Kobe (Japan); Hasegawa, Kenji, E-mail: susa@konan-u.ac.jp [Center for Computational Science, University of Tsukuba (Japan)

    2014-09-01

    We perform cosmological hydrodynamics simulations with non-equilibrium primordial chemistry to obtain 59 minihalos that host first stars. The obtained minihalos are used as the initial conditions of local three-dimensional radiation hydrodynamics simulations to investigate the formation of the first stars. We find that two-thirds of the minihalos host multiple stars, while the other third has single stars. The mass of the stars found in our simulations are in the range of 1 M {sub ☉} ≲ M ≲ 300 M {sub ☉}, peaking at several× 10 M {sub ☉}. Most of the very massive stars of ≳ 140 M {sub ☉} are born as single stars, although not all of the single stars are very massive. We also find a few stars of ≲ 1 M {sub ☉} that are kicked by the gravitational three body interactions to the position distant from the center of mass. The frequency that a star forming minihalo contains a binary system is ∼50%. We also investigate the abundance pattern of the stellar remnants by summing up the contributions from the first stars in the simulations. Consequently, the pattern is compatible with that of the low metallicity damped Lyα systems or the extremely metal-poor (EMP) stars, if the mass spectrum obtained in our experiment is shifted to the low mass side by 0.2 dex. If we consider the case that an EMP star is born in the remnant of the individual minihalo without mixing with others, the chemical signature of the pair instability supernova is more prominent, because most of them are born as single stars.

  2. The mass spectrum of the first stars

    International Nuclear Information System (INIS)

    We perform cosmological hydrodynamics simulations with non-equilibrium primordial chemistry to obtain 59 minihalos that host first stars. The obtained minihalos are used as the initial conditions of local three-dimensional radiation hydrodynamics simulations to investigate the formation of the first stars. We find that two-thirds of the minihalos host multiple stars, while the other third has single stars. The mass of the stars found in our simulations are in the range of 1 M ☉ ≲ M ≲ 300 M ☉, peaking at several× 10 M ☉. Most of the very massive stars of ≳ 140 M ☉ are born as single stars, although not all of the single stars are very massive. We also find a few stars of ≲ 1 M ☉ that are kicked by the gravitational three body interactions to the position distant from the center of mass. The frequency that a star forming minihalo contains a binary system is ∼50%. We also investigate the abundance pattern of the stellar remnants by summing up the contributions from the first stars in the simulations. Consequently, the pattern is compatible with that of the low metallicity damped Lyα systems or the extremely metal-poor (EMP) stars, if the mass spectrum obtained in our experiment is shifted to the low mass side by 0.2 dex. If we consider the case that an EMP star is born in the remnant of the individual minihalo without mixing with others, the chemical signature of the pair instability supernova is more prominent, because most of them are born as single stars.

  3. Mining the Sloan Digital Sky Survey in Search of Extremely α-poor Stars in the Galaxy

    Science.gov (United States)

    Xing, Q. F.; Zhao, G.

    2014-07-01

    As we know, the majority of metal-poor Galactic halo stars appear to have chemical abundances that were enhanced by α-elements (e.g., O, Mg, Si, Ca, and Ti) during the early stage of the Galaxy. Observed metal-poor halo stars preserved this pattern by exhibiting abundance ratios [α/Fe] ~+0.4. A few striking exceptions that show severe departures from the general enhanced α-element chemical abundance trends of the halo have been discovered in recent years. They possess relatively low [α/Fe] compared to other comparable-metallicity stars, with abundance ratios over 0.5 dex lower. These stars may have a different chemical enrichment history from the majority of the halo. Similarly, low-α abundances are also displayed by satellite dwarf spheroidal (dSph) galaxies. We present a method to select extremely α-poor (EAP) stars from the SDSS/SEGUE survey. The method consists of a two-step approach. In the first step, we select suspected metal-poor ([Fe/H] 4.0, +0.5], 14 candidate stars were identified. Three of these stars are found to have already been confirmed by other research.

  4. Metal rich stars in omega Cen: preliminary FLAMES GTO results

    CERN Document Server

    Pancino, E

    2004-01-01

    I present preliminary results for a sample of ~700 red giants in omega Cen, observed during the Ital-FLAMES Consortium GTO time in May 2003, for the Bologna Project on omega Cen. Preliminary Fe and Ca abundances confirm previous results: while the metal-poor and intermediate populations show a normal halo alpha-enhancement of [alpha/Fe]=$+0.3, the most metal-rich stars show a significantly lower [alpha/Fe]=+0.1. If the metal-rich stars have evolved within the cluster in a process of self-enrichment, the only way to lower their alpha-enhancement would be SNe type Ia intervention.

  5. Chemical Abundances of the Milky Way Thick Disk and Stellar Halo I.: Implications of [alpha/Fe] for Star Formation Histories in Their Progenitors

    CERN Document Server

    Ishigaki, M N; Aoki, W

    2012-01-01

    We present the abundance analysis of 97 nearby metal-poor (-3.3-2$. These results favor the scenarios that the MW thick disk formed through rapid chemical enrichment primarily through Type II supernovae of massive stars, while the stellar halo has formed at least in part via accretion of progenitor stellar systems having been chemically enriched with different timescales.

  6. Radiative transfer modelling of dust in IRAS 18333-2357: the only planetary nebula in the metal-poor globular cluster M22

    Science.gov (United States)

    Muthumariappan, C.; Parthasarathy, M.; Ita, Y.

    2013-10-01

    We report results from our 1D radiative transfer modelling of dust in the hydrogen-deficient planetary nebula IRAS 18333-2357 located in the globular cluster M22. A spectral energy distribution was constructed from archival UV, optical and IR data including Akari photometry at its 18, 65, 90, 140 and 160 μm bands. An archival Spitzer spectrum shows several aromatic infrared bands indicating a carbon-rich dust shell. The spectral energy distribution is well fitted by a model which considers a modified Mathis-Rumpl-Nordsieck grain size distribution and a radial density function which includes compression of the nebula by its interaction with the Galactic halo gas. The model indicates that a significant amount of cold dust, down to a temperature of 50 K, is present at the outer edge of the nebula. At the inner edge, the dust temperature is 97 K. The dust shell has a size of 26 ± 6.3 arcsec. We find a large amount of excess emission, over the emission from thermal equilibrium dust, in the mid-IR region. This excess emission may have originated from the thermally fluctuating dust grains with size ˜12 Å in the UV field of the hot central star. These grains, however, come from the same population and conditions as the thermal equilibrium grains. The dust mass of this grain population is (1.2 ± 0.73) × 10-3 M⊙ and for the thermal equilibrium grains it is (1.4 ± 0.60) × 10-4 M⊙, leading to a total dust mass of (1.3 ± 0.91) × 10-3 M⊙. The derived dust-to-gas mass ratio is 0.3 ± 0.21. For a derived bolometric luminosity of (1700 ± 1230) L⊙ and an assumed central star mass of (0.55 ± 0.02) M⊙, the surface gravity is derived to be log g = 4.6 ± 0.24. We propose that the progenitor of IRAS 18333-2357 had possibly evolved from an early stellar merger case and the hydrogen-deficient nebula results from a late thermal pulse. The hydrogen-rich nebula, which was ejected by the progenitor during its normal asymptotic giant branch evolution, might have been

  7. Non-LTE neutral carbon spectral line formation in late-type stars

    OpenAIRE

    Fabbian, Damian; Asplund, Martin; Carlsson, Mats; Kiselman, Dan

    2005-01-01

    We present non-Local Thermodynamic Equilibrium (non-LTE) calculations for neutral carbon spectral line formation, carried out for a grid of model atmospheres covering the range of late-type stars. The results of our detailed calculations suggest that the carbon non-LTE corrections in these stars are higher than usually adopted, remaining substantial even at low metallicity. For the most metal-poor stars in the sample of Akerman et al. (2004), the non-LTE abundance corrections are of the order...

  8. The Initial Mass Function of Stars Evidence for Uniformity in Variable Systems

    CERN Document Server

    Kroupa, P

    2002-01-01

    The distribution of stellar masses that form in one star-formation event in a given volume of space is called the initial mass function (IMF). The IMF has been estimated from low-mass brown dwarfs to very massive stars. Combining IMF estimates for different populations in which the stars can be observed individually unveils an extraordinary uniformity of the IMF. This general insight appears to hold for populations including present-day star formation in small molecular clouds, rich and dense massive star-clusters forming in giant clouds, through to ancient and metal-poor exotic stellar populations that may be dominated by dark matter. This apparent universality of the IMF is a challenge for star formation theory because elementary considerations suggest that the IMF ought to systematically vary with star-forming conditions.

  9. OXYGEN ABUNDANCES IN LOW- AND HIGH-α FIELD HALO STARS AND THE DISCOVERY OF TWO FIELD STARS BORN IN GLOBULAR CLUSTERS

    International Nuclear Information System (INIS)

    Oxygen abundances of 67 dwarf stars in the metallicity range –1.6 < [Fe/H] < –0.4 are derived from a non-LTE analysis of the 777 nm O I triplet lines. These stars have precise atmospheric parameters measured by Nissen and Schuster, who find that they separate into three groups based on their kinematics and α-element (Mg, Si, Ca, Ti) abundances: thick disk, high-α halo, and low-α halo. We find the oxygen abundance trends of thick-disk and high-α halo stars very similar. The low-α stars show a larger star-to-star scatter in [O/Fe] at a given [Fe/H] and have systematically lower oxygen abundances compared to the other two groups. Thus, we find the behavior of oxygen abundances in these groups of stars similar to that of the α elements. We use previously published oxygen abundance data of disk and very metal-poor halo stars to present an overall view (–2.3 < [Fe/H] < +0.3) of oxygen abundance trends of stars in the solar neighborhood. Two field halo dwarf stars stand out in their O and Na abundances. Both G53-41 and G150-40 have very low oxygen and very high sodium abundances, which are key signatures of the abundance anomalies observed in globular cluster (GC) stars. Therefore, they are likely field halo stars born in GCs. If true, we estimate that at least 3% ± 2% of the local field metal-poor star population was born in GCs.

  10. OXYGEN ABUNDANCES IN LOW- AND HIGH-{alpha} FIELD HALO STARS AND THE DISCOVERY OF TWO FIELD STARS BORN IN GLOBULAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Ramirez, I. [McDonald Observatory and Department of Astronomy, University of Texas at Austin, 1 University Station, C1400 Austin, TX 78712-0259 (United States); Melendez, J. [Departamento de Astronomia do IAG/USP, Universidade de Sao Paulo, Rua do Matao 1226, Sao Paulo 05508-900, SP (Brazil); Chaname, J. [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Av. Vicuna Mackenna 4860, 782-0436 Macul, Santiago (Chile)

    2012-10-01

    Oxygen abundances of 67 dwarf stars in the metallicity range -1.6 < [Fe/H] < -0.4 are derived from a non-LTE analysis of the 777 nm O I triplet lines. These stars have precise atmospheric parameters measured by Nissen and Schuster, who find that they separate into three groups based on their kinematics and {alpha}-element (Mg, Si, Ca, Ti) abundances: thick disk, high-{alpha} halo, and low-{alpha} halo. We find the oxygen abundance trends of thick-disk and high-{alpha} halo stars very similar. The low-{alpha} stars show a larger star-to-star scatter in [O/Fe] at a given [Fe/H] and have systematically lower oxygen abundances compared to the other two groups. Thus, we find the behavior of oxygen abundances in these groups of stars similar to that of the {alpha} elements. We use previously published oxygen abundance data of disk and very metal-poor halo stars to present an overall view (-2.3 < [Fe/H] < +0.3) of oxygen abundance trends of stars in the solar neighborhood. Two field halo dwarf stars stand out in their O and Na abundances. Both G53-41 and G150-40 have very low oxygen and very high sodium abundances, which are key signatures of the abundance anomalies observed in globular cluster (GC) stars. Therefore, they are likely field halo stars born in GCs. If true, we estimate that at least 3% {+-} 2% of the local field metal-poor star population was born in GCs.

  11. Mining the Sloan digital sky survey in search of extremely α-poor stars in the galaxy

    International Nuclear Information System (INIS)

    As we know, the majority of metal-poor Galactic halo stars appear to have chemical abundances that were enhanced by α-elements (e.g., O, Mg, Si, Ca, and Ti) during the early stage of the Galaxy. Observed metal-poor halo stars preserved this pattern by exhibiting abundance ratios [α/Fe] ∼+0.4. A few striking exceptions that show severe departures from the general enhanced α-element chemical abundance trends of the halo have been discovered in recent years. They possess relatively low [α/Fe] compared to other comparable-metallicity stars, with abundance ratios over 0.5 dex lower. These stars may have a different chemical enrichment history from the majority of the halo. Similarly, low-α abundances are also displayed by satellite dwarf spheroidal (dSph) galaxies. We present a method to select extremely α-poor (EAP) stars from the SDSS/SEGUE survey. The method consists of a two-step approach. In the first step, we select suspected metal-poor ([Fe/H] <–0.5) and α-poor ([Mg/Fe] <0) stars as our targets. In the second step, we determine [Mg/Fe] from low-resolution (R = 2000) stellar spectra for our targets and select stars with [Mg/Fe] <–0.1 as candidate EAP stars. In a sample of 40,000 stars with atmospheric parameters in the range of Teff = [4500, 7000] K, log g = [1.0, 5.0], and [Fe/H] = [–4.0, +0.5], 14 candidate stars were identified. Three of these stars are found to have already been confirmed by other research.

  12. Neutron-capture elements in the s- and r-process-rich stars: Constraints on neutron-capture nucleosynthesis processes

    CERN Document Server

    Zhang, B; Zhou, G; Zhang, Bo; Ma, Kun; Zhou, Guide

    2006-01-01

    The chemical abundances of the very metal-poor double-enhanced stars are excellent information for setting new constraints on models of neutron-capture processes at low metallicity. These stars are known as s+r stars, since they show enhancements of both s-process and r-process elements. The observed abundance ratios for the double-enhanced stars can be explained by those of stars that were polluted by an AGB star and subsequently accreted very significant amounts of r-process material out of an AIC (accretion-induced collapse) or Type 1.5 supernova. In this paper we present for the first time an attempt to fit the elemental abundances observed in the s- and r-rich, very metal-poor stars using a parametric model and suggest a new concept of component coefficients to describe the contributions of the individual neutron-capture processes to double-enhanced stars. We find that the abundance ratios of these stars are best fitted by enrichments of s- and r-process material. The overlap factor in the AGB stars wher...

  13. Formation of the first stars

    International Nuclear Information System (INIS)

    Understanding the formation of the first stars is one of the frontier topics in modern astrophysics and cosmology. Their emergence signalled the end of the cosmic dark ages, a few hundred million years after the Big Bang, leading to a fundamental transformation of the early Universe through the production of ionizing photons and the initial enrichment with heavy chemical elements. We here review the state of our knowledge, separating the well understood elements of our emerging picture from those where more work is required. Primordial star formation is unique in that its initial conditions can be directly inferred from the Λ cold dark matter (ΛCDM) model of cosmological structure formation. Combined with gas cooling that is mediated via molecular hydrogen, one can robustly identify the regions of primordial star formation, the so-called minihalos, having total masses of ∼106 M⊙ and collapsing at redshifts z ≃ 20–30. Within this framework, a number of studies have defined a preliminary standard model, with the main result that the first stars were predominantly massive. This model has recently been modified to include a ubiquitous mode of fragmentation in the protostellar disks, such that the typical outcome of primordial star formation may be the formation of a binary or small multiple stellar system. We will also discuss extensions to this standard picture due to the presence of dynamically significant magnetic fields, of heating from self-annihalating WIMP dark matter, or cosmic rays. We conclude by discussing possible strategies to empirically test our theoretical models. Foremost among them are predictions for the upcoming James Webb space telescope (JWST), to be launched ∼2018, and for ‘stellar archaeology’, which probes the abundance pattern in the oldest, most-metal poor stars in our cosmic neighborhood, thereby constraining the nucleosynthesis inside the first supernovae. (review article)

  14. Ca II triplet spectroscopy of RGB stars in NGC 6822: kinematics and metallicities

    Science.gov (United States)

    Swan, J.; Cole, A. A.; Tolstoy, E.; Irwin, M. J.

    2016-03-01

    We present a detailed analysis of the chemistry and kinematics of red giants in the dwarf irregular galaxy NGC 6822. Spectroscopy at ≈8500 Å was acquired for 72 red giant stars across two fields using FORS2 at the VLT. Line-of-sight extinction was individually estimated for each target star to accommodate the variable reddening across NGC 6822. The mean radial velocity was found to be = -52.8 ± 2.2 km s-1 with dispersion σv = 24.1 km s-1, in agreement with other studies. Ca II triplet equivalent widths were converted into [Fe/H] metallicities using a V magnitude proxy for surface gravity. The average metallicity was = -0.84 ± 0.04 with dispersion σ = 0.31 dex and interquartile range 0.48. Our assignment of individual reddening values makes our analysis more sensitive to spatial variations in metallicity than previous studies. We divide our sample into metal-rich and metal-poor stars; the former were found to cluster towards small radii with the metal-poor stars more evenly distributed across the galaxy. The velocity dispersion of the metal-poor stars was found to be higher than that of the metal-rich stars (σ _{v_MP}=27.4 km s-1; σ _{v_MR}=21.1 km s-1); combined with the age-metallicity relation this indicates that the older populations have either been dynamically heated during their lifetimes or were born in a less disc-like distribution than the younger stars.. The low ratio vrot/σv suggests that within the inner 10 arcmin, NGC 6822's stars are dynamically decoupled from the H I gas, and possibly distributed in a thick disc or spheroid structure.

  15. Forming Stars From the Cosmic Web

    Science.gov (United States)

    Kohler, Susanna

    2015-09-01

    Scientists have recently identified a connection between metal-poor regions in a set of dwarf galaxies and bursts of star-formation activity within them. These observations provide long-awaited evidence supporting predictions of how stars formed in the early universe and in dwarf galaxies today. Metal-Poor Clues: The primary driver of star formation over cosmic history is thought to be the accretion onto galaxies of cold gas streaming from the cosmic web. The best way to confirm this model would be to observe a cloud of cosmic gas flowing into an otherwise-quiescent galaxy and launching a wave of star formation. But because cold gas doesnt emit much radiation, its difficult to detect directly.Now, a team of scientists have found a clever way around this problem: they searched galaxies for a correlation between areas of active star formation and metal-poor regions. Why? Because metal-poor regions could be a smoking gun indicating a recently accreted cloud of cold gas from the cosmic web. Impacting Clouds: Distribution of metallicity along the major axis of one of the target galaxies. The red bar in the top image shows the position of the spectrograph slit along the galaxy, with the arrow showing the direction of growing distance in the plot below. The plot shows the metallicity variation (red symbols) and star-formation rate (blue line) along the galaxys major axis. The metallicity drop coincides with the brightest knot of the galaxy. [Snchez Almeida et al. 2015]The authors of this study, led by Jorge Snchez Almeida (Instituto de Astrofisica de Canarias and University of La Laguna, Spain), used the Great Canary Telescope to obtain high-quality spectra of ten dwarf galaxies with especially low average metallicities. They aligned the spectrograph slit along the major axes of the galaxies in order to measure abundances as a function of position within each galaxy.The team found that, in nine out of the ten cases, the galaxies displayed sharp drops (by factors of 310

  16. Sulphur abundances in halo stars from Multiplet 3 at 1045 nm

    CERN Document Server

    Caffau, Elisabetta; Ludwig, Hans-Günter; Bonifacio, Piercarlo; Spite, Monique

    2010-01-01

    Sulphur is a volatile alpha-element which is not locked into dust grains in the interstellar medium (ISM). Hence, its abundance does not need to be corrected for dust depletion when comparing the ISM to the stellar atmospheres. The abundance of sulphur in the photosphere of metal-poor stars is a matter of debate: according to some authors, [S/Fe] versus [Fe/H] forms a plateau at low metallicity, while, according to other studies, there is a large scatter or perhaps a bimodal distribution. In metal-poor stars sulphur is detectable by its lines of Mult.1 at 920 nm, but this range is heavily contaminated by telluric absorptions, and one line of the multiplet is blended by the hydrogen Paschen zeta line. We study the possibility of using Mult. 3 (at 1045 nm) for deriving the sulphur abundance because this range, now observable at the VLT with the infra-red spectrograph CRIRES, is little contaminated by telluric absorption and not affected by blends at least in metal-poor stars. We compare the abundances derived f...

  17. Spectroscopic Study of Extended Star Clusters in Dwarf Galaxy NGC 6822

    CERN Document Server

    Hwang, Narae; Lee, Myung Gyoon; Lim, Sungsoon; Hodge, Paul W; Kim, Sang Chul; Miller, Bryan; Weisz, Daniel

    2014-01-01

    We present a spectroscopic study of the four extended star clusters (ESCs) in NGC 6822 based on the data obtained with Gemini Multi-Object Spectrograph (GMOS) on the Gemini-South 8.1m telescope. Their radial velocities derived from the spectra range from $-61.2 \\pm 20.4$ km s$^{-1}$ (for C1) to $-115.34 \\pm 57.9$ km s$^{-1}$ (for C4) and, unlike the intermediate age carbon stars, they do not display any sign of systematic rotation around NGC 6822. The ages and metallicities derived using the Lick indices show that the ESCs are old ($\\geq 8$ Gyr) and metal poor ([Fe/H]$\\lesssim -1.5$). NGC 6822 is found to have both metal poor ([Fe/H]$\\approx -2.0$) and metal rich ([Fe/H]$\\approx -0.9$) star clusters within 15 arcmin (2 kpc) from the center, while only metal poor clusters are observed in the outer halo with $r \\geq 20$ arcmin (2.6 kpc). The kinematics, old ages, and low metallicities of ESCs suggest that ESCs may have accreted into the halo of NGC 6822. Based on the velocity distribution of ESCs, we have deter...

  18. Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data

    OpenAIRE

    Lawler, J. E.; Sneden, C.; Cowan, J. J.; Ivans, I. I.; Hartog, E.A. den

    2009-01-01

    Recent radiative lifetime measurements accurate to +/- 5% using laser-induced fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 921 lines of Ce II. This improved laboratory data set has been used to determine a new solar photospheric Ce abundance, log epsilon = 1.61 +/- 0.01 (sigma = 0.06 from 45 lines), a value in excellent agree...

  19. Nucleosynthesis in Hot Bubbles of SNe-Origin of EMP Stars: HNe or SNe ?

    International Nuclear Information System (INIS)

    The observational trends of extremely metal-poor (EMP) stars reflect SN nucleosynthesis of Population III, or almost metal-free stars. The observation of EMP stars can be reproduced by HNe, not by normal SNe. However, if the innermost neutron-rich or proton-rich matter is ejected, the abundance patterns of ejected matter are changed, and there is a possibility that normal SNe can also reproduce the observations of EMP stars. In this paper, we calculate nucleosynthesis with various Ye and entropy taking into account neutrino processes. We investigate whether normal SNe with this innermost matter can reproduce the observations of EMP stars. We find that neutron-rich (Ye = 0.45-0.50) and proton-rich (Ye = 0.51-0.55) matters can improve Zn and Co, but tend to overproduce other Fe-peak elements. On the other hand, HNe can naturally reproduce the observations of EMP stars.

  20. OB stars at the lowest Local Group metallicity. GTC-OSIRIS observations of Sextans A

    Science.gov (United States)

    Camacho, I.; Garcia, M.; Herrero, A.; Simón-Díaz, S.

    2016-01-01

    Context. Massive stars play an important role in the chemical and dynamical evolution of the Universe. The first metal-poor stars may have started the reionization of the Universe. To understand these early epochs it is necessary to know the behavior and the physical properties of massive stars in very metal-poor environments. We focus on the massive stellar content of the metal-poor irregular galaxy Sextans A. Aims: Our aim is to find and classify OB stars in Sextans A, so as to later determine accurate stellar parameters of these blue massive stars in this low-metallicity region (Z ~ 0.1 Z⊙). Methods: Using UBV photometry, the reddening-free index Q and GALEX imaging, we built a list of blue massive star candidates in Sextans A. We obtained low-resolution (R ~ 1000) GTC-OSIRIS spectra for a fraction of them and carried out spectral classification. For the confirmed O-stars, we derived preliminary stellar parameters. Results: The target selection criteria and observations were successful and have produced the first spectroscopic atlas of OB-type stars in Sextans A. From the whole sample of 18 observed stars, 12 were classified as early OB-types, including 5 O-stars. The radial velocities of all target stars are in agreement with their Sextans A membership, although three of them show significant deviations. We determined the stellar parameters of the O-type stars using the stellar atmosphere code FASTWIND and revisited the sub-SMC temperature scale. Two of the O-stars are consistent with relatively strong winds and enhanced helium abundances, although results are not conclusive. We discuss the position of the OB stars in the HRD. Initial stellar masses run from slightly below 20 up to 40 solar masses. Conclusions: The target selection method worked well for Sextans A. The stellar temperatures are consistent with findings in other galaxies. Some of the targets deserve follow-up spectroscopy because of indications of a runaway nature, an enhanced helium abundance