WorldWideScience

Sample records for bulge metal-poor globular

  1. 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...

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

    Science.gov (United States)

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

    2016-09-01

    detected in our sample. The heavy elements Y, Zr, Ba, La, and Eu also exhibit oversolar abundances. Three out of the five stars analysed here show slightly enhanced [Y/Ba] ratios similar to those found in other metal-poor bulge globular clusters (NGC 6522 and M 62). Conclusions: This sample shows enhancement in the first-to-second peak abundance ratios of heavy elements, as well as dominantly s-process element excesses. This can be explained by different nucleosynthesis scenarios: (a) the main r-process plus extra mechanisms, such as the weak r-process; (b) mass transfer from asymptotic giant branch stars in binary systems; (c) an early generation of fast-rotating massive stars. Larger samples of moderately metal-poor bulge stars, with detailed chemical abundances, are needed to better constrain the source of dominantly s-process elements in the early Universe. Observations collected at the European Southern Observatory, Paranal, Chile (ESO), under programmes 089.B-0208(A).

  3. The Gaia-ESO Survey: the most metal-poor stars in the Galactic bulge

    CERN Document Server

    Howes, L; Casey, A R; Keller, S C; Yong, D; Gilmore, G; Lind, K; Worley, C; Bessell, M S; Casagrande, L; Marino, A F; Nataf, D M; Owen, C I; Da Costa, G S; Schmidt, B P; Tisserand, P; Randich, S; Feltzing, S; Vallenari, A; Prieto, C Allende; Bensby, T; Flaccomio, E; Korn, A J; Pancino, E; Recio-Blanco, A; Smiljanic, R; Bergemann, M; Costado, M T; Damiani, F; Heiter, U; Hill, V; Hourihane, A; Jofré, P; Lardo, C; de Laverny, P; Magrini, L; Maiorca, E; Masseron, T; Morbidelli, L; Sacco, G G; Minniti, D; Zoccali, M

    2014-01-01

    We present the first results of the EMBLA survey (Extremely Metal-poor BuLge stars with AAOmega), aimed at finding metal-poor stars in the Milky Way bulge, where the oldest stars should now preferentially reside. EMBLA utilises SkyMapper photometry to pre-select metal-poor candidates, which are subsequently confirmed using AAOmega spectroscopy. We describe the discovery and analysis of four bulge giants with -2.72<=[Fe/H]<=-2.48, the lowest metallicity bulge stars studied with high-resolution spectroscopy to date. Using FLAMES/UVES spectra through the Gaia-ESO Survey we have derived abundances of twelve elements. Given the uncertainties, we find a chemical similarity between these bulge stars and halo stars of the same metallicity, although the abundance scatter may be larger, with some of the stars showing unusual [{\\alpha}/Fe] ratios.

  4. 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 ...

  5. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Garcia Perez, Ana E.; Majewski, Steven R.; Hearty, Fred R. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Cunha, Katia [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Shetrone, Matthew [McDonald Observatory, University of Texas at Austin, Fort Davis, TX 79734 (United States); Johnson, Jennifer A.; Zasowski, Gail [Department of Astronomy, The Ohio State University, Columbus, OH 43210 (United States); Smith, Verne V.; Beers, Timothy C. [National Optical Astronomy Observatories, Tucson, AZ 85719 (United States); Schiavon, Ricardo P. [Gemini Observatory, 670 N. A' Ohoku Place, Hilo, HI 96720 (United States); Holtzman, Jon [Department of Astronomy, MSC 4500, New Mexico State University, P.O. Box 30001, Las Cruces, NM 88003 (United States); Nidever, David [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Allende Prieto, Carlos [Departamento de Astrofisica, Universidad de La Laguna, E-38206 La Laguna, Tenerife (Spain); Bizyaev, Dmitry; Ebelke, Garrett; Malanushenko, Elena; Malanushenko, Viktor [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); Eisenstein, Daniel J. [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Frinchaboy, Peter M. [Department of Physics and Astronomy, Texas Christian University, 2800 South University Drive, Fort Worth, TX 76129 (United States); Girardi, Leo [Laboratorio Interinstitucional de e-Astronomia - LIneA, Rua Gal. Jose Cristino 77, Rio de Janeiro, RJ - 20921-400 (Brazil); and others

    2013-04-10

    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] {approx} -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 {alpha}-elements O, Mg, and Si without significant {alpha}-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.

  7. 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...

  8. 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.

  9. Evidence for a metal-poor population in the inner Galactic Bulge

    CERN Document Server

    Schultheis, M; Zasowski, G; Pérez, A E García; Sellgren, K; Smith, V; García-Hernández, D A; Zamora, O; Fritz, T K; Anders, F; Prieto, C Allende; Bizyaev, D; Kinemuchi, K; Pan, K; Malanushenko, E; Malanushenko, V; Shetrone, M D

    2015-01-01

    The inner Galactic Bulge has, until recently, been avoided in chemical evolution studies due to extreme extinction and stellar crowding. Large, near-IR spectroscopic surveys, such as APOGEE, allow for the first time the measurement of metallicities in the inner region of our Galaxy. We study metallicities of 33 K/M giants situated in the Galactic Center region from observations obtained with the APOGEE survey. We selected K/M giants with reliable stellar parameters from the APOGEE/ASPCAP pipeline. Distances, interstellar extinction values, and radial velocities were checked to confirm that these stars are indeed situated in the inner Galactic Bulge. We find a metal-rich population centered at [M/H] = +0.4 dex, in agreement with earlier studies of other bulge regions, but also a peak at low metallicity around $\\rm [M/H] = -1.0\\,dex$, suggesting the presence of a metal-poor population which has not previously been detected in the central region. Our results indicate a dominant metal-rich population with a metal...

  10. 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...

  11. 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...

  12. 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 ...

  13. 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...

  14. 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...

  15. 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 ...

  16. 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...

  17. High resolution spectroscopic analysis of seven giants in the bulge globular cluster NGC 6723

    Science.gov (United States)

    Rojas-Arriagada, A.; Zoccali, M.; Vásquez, S.; Ripepi, V.; Musella, I.; Marconi, M.; Grado, A.; Limatola, L.

    2016-03-01

    Context. Globular clusters associated with the Galactic bulge are important tracers of stellar populations in the inner Galaxy. High resolution analysis of stars in these clusters allows us to characterize them in terms of kinematics, metallicity, and individual abundances, and to compare these fingerprints with those characterizing field populations. Aims: We present iron and element ratios for seven red giant stars in the globular cluster NGC 6723, based on high resolution spectroscopy. Methods: High resolution spectra (R ~ 48 000) of seven K giants belonging to NGC 6723 were obtained with the FEROS spectrograph at the MPG/ESO 2.2 m telescope. Photospheric parameters were derived from ~130 Fe i and Fe ii transitions. Abundance ratios were obtained from line-to-line spectrum synthesis calculations on clean selected features. Results: An intermediate metallicity of [Fe/H] = -0.98 ± 0.08 dex and a heliocentric radial velocity of vhel = -96.6 ± 1.3 km s-1 were found for NGC 6723. Alpha-element abundances present enhancements of [O/Fe] = 0.29 ± 0.18 dex, [Mg/Fe] = 0.23 ± 0.10 dex, [Si/Fe] = 0.36 ± 0.05 dex, and [Ca/Fe] = 0.30 ± 0.07 dex. Similar overabundance is found for the iron-peak Ti with [Ti/Fe] = 0.24 ± 0.09 dex. Odd-Z elements Na and Al present abundances of [Na/Fe] = 0.00 ± 0.21 dex and [Al/Fe] = 0.31 ± 0.21 dex, respectively. Finally, the s-element Ba is also enhanced by [Ba/Fe] = 0.22 ± 0.21 dex. Conclusions: The enhancement levels of NGC 6723 are comparable to those of other metal-intermediate bulge globular clusters. In turn, these enhancement levels are compatible with the abundance profiles displayed by bulge field stars at that metallicity. This hints at a possible similar chemical evolution with globular clusters and the metal-poor of the bulge going through an early prompt chemical enrichment.

  18. Insights into the chemical composition of the metal-poor Milky Way halo globular cluster NGC 6426

    Science.gov (United States)

    Hanke, M.; Koch, A.; Hansen, C. J.; McWilliam, A.

    2017-03-01

    We present our detailed spectroscopic analysis of the chemical composition of four red giant stars in the halo globular cluster NGC 6426. We obtained high-resolution spectra using the Magellan2/MIKE spectrograph, from which we derived equivalent widths and subsequently computed abundances of 24 species of 22 chemical elements. For the purpose of measuring equivalent widths, we developed a new semi-automated tool, called EWCODE. We report a mean Fe content of [Fe/H] =-2.34 ± 0.05 dex (stat.) in accordance with previous studies. At a mean α-abundance of [(Mg, Si, Ca)/3 Fe] = 0.39 ± 0.03 dex, NGC 6426 falls on the trend drawn by the Milky Way halo and other globular clusters at comparably low metallicities. The distribution of the lighter α-elements as well as the enhanced ratio [Zn/Fe] = 0.39 dex could originate from hypernova enrichment of the pre-cluster medium. We find tentative evidence for a spread in the elements Mg, Si, and Zn, indicating an enrichment scenario, where ejecta of evolved massive stars of a slightly older population have polluted a newly born younger one. The heavy element abundances in this cluster fit well into the picture of metal-poor globular clusters, which in that respect appear to be remarkably homogeneous. The pattern of the neutron-capture elements heavier than Zn points toward an enrichment history governed by the r-process with little, if any, sign of s-process contributions. This finding is supported by the striking similarity of our program stars to the metal-poor field star HD 108317. This paper includes data gathered with the 6.5-m Magellan Telescopes located at Las Campanas Observatory, Chile.Equivalent widths and full Table 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A97

  19. New Breakthroughs in the Battle of the Bulge Using Globular Clusters

    Science.gov (United States)

    Geisler, D.; Mauro, F.; Bidin, C. M.; Cohen, R.; Chené, A.; Villanova, S.; Cummings, J.; Gormaz, A.; Minniti, D.; Alonso-García, J.; Hempel, M.; VVV Team

    2015-05-01

    We present some recent work undertaken mostly at the Universidad de Concepción using bulge globular clusters to better understand this important but poorly studied Galactic component, especially based on data from the VVV Survey. This includes discovering new bulge globulars, investigating dual HBs, and obtaining Ca triplet metallicities and velocities.

  20. Discovery of a Metal-poor Field Giant with a Globular Cluster Second-generation Abundance Pattern

    Science.gov (United States)

    Fernández-Trincado, J. G.; Robin, A. C.; Moreno, E.; Schiavon, R. P.; García Pérez, A. E.; Vieira, K.; Cunha, K.; Zamora, O.; Sneden, C.; Souto, Diogo; Carrera, R.; Johnson, J. A.; Shetrone, M.; Zasowski, G.; García-Hernández, 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.

    2016-12-01

    We report on the detection, from observations obtained with the Apache Point Observatory Galactic Evolution Experiment spectroscopic survey, of a metal-poor ([Fe/H] = -1.3 dex) field giant star with an extreme Mg-Al abundance ratio ([Mg/Fe] = -0.31 dex; [Al/Fe] = 1.49 dex). Such low Mg/Al ratios are seen only among the second-generation population of globular clusters (GCs) and are not present among Galactic disk field stars. The light-element abundances of this star, 2M16011638-1201525, suggest that it could have been born in a GC. We explore several origin scenarios, studying the orbit of the star in particular to check the probability of its being kinematically related to known GCs. We performed simple orbital integrations assuming the estimated distance of 2M16011638-1201525 and the available six-dimensional phase-space coordinates of 63 GCs, looking for close encounters in the past with a minimum distance approach within the tidal radius of each cluster. We found a very low probability that 2M16011638-1201525 was ejected from most GCs; however, we note that the best progenitor candidate to host this star is GC ω Centauri (NGC 5139). Our dynamical investigation demonstrates that 2M16011638-1201525 reaches a distance | {Z}\\max | \\lt 3 {kpc} from the Galactic plane and minimum and maximum approaches to the Galactic center of R min < 0.62 kpc and R max < 7.26 kpc in an eccentric (e ˜ 0.53) and retrograde orbit. Since the extreme chemical anomaly of 2M16011638-1201525 has also been observed in halo field stars, this object could also be considered a halo contaminant, likely to have been ejected into the Milky Way disk from the halo. We conclude that 2M16011638-20152 is also kinematically consistent with the disk but chemically consistent with halo field stars.

  1. The Color-Magnitude Relation for Metal-Poor Globular Clusters in M87: Confirmation From Deep HST/ACS Imaging

    CERN Document Server

    Peng, Eric W; Blakeslee, John P; Mieske, Steffen; Cote, Patrick; Ferrarese, Laura; Harris, William E; Madrid, Juan P; Meurer, Gerhardt R

    2009-01-01

    Metal-poor globular clusters (GCs) are our local link to the earliest epochs of star formation and galaxy building. Studies of extragalactic GC systems using deep, high-quality imaging have revealed a small but significant slope to the color-magnitude relation for metal-poor GCs in a number of galaxies. We present a study of the M87 GC system using deep, archival HST/ACS imaging with the F606W and F814W filters, in which we find a significant color-magnitude relation for the metal-poor GCs. The slope of this relation in the I vs. V-I color-magnitude diagram ($\\gamma_I=-0.024\\pm0.006$) is perfectly consistent with expectations based on previously published results using data from the ACS Virgo Cluster Survey. The relation is driven by the most luminous GCs, those with $M_I<-10$, and its significance is largest when fitting metal-poor GCs brighter than $M_I=-7.8$, a luminosity which is ~1 mag fainter than our fitted Gaussian mean for the luminosity function (LF) of blue, metal-poor GCs (~0.8 mag fainter than...

  2. Evolutionary models for metal-poor low-mass stars lower main sequence of globular clusters and halo field stars

    CERN Document Server

    Baraffe, I; Allard, F; Hauschildt, P H; Baraffe, Isabelle; Chabrier, Gilles; Allard, France; Hauschildt, Peter

    1997-01-01

    We have performed evolutionary calculations of very-low-mass stars from 0.08 to 0.8 $\\msol$ for different metallicites from [M/H]= -2.0 to -1.0 and we have tabulated the mechanical, thermal and photometric characteristics of these models. The calculations include the most recent interior physics and improved non-grey atmosphere models. The models reproduce the entire main sequences of the globular clusters observed with the Hubble Space Telescope over the afore-mentioned range of metallicity. Comparisons are made in the WFPC2 Flight system including the F555, F606 and F814 filters, and in the standard Johnson-Cousins system. We examine the effects of different physical parameters, mixing-length, $\\alpha$-enriched elements, helium fraction, as well as the accuracy of the photometric transformations of the HST data into standard systems. We derive mass-effective temperature and mass-magnitude relationships and we compare the results with the ones obtained with different grey-like approximations. These latter ar...

  3. THE X-RAY LUMINOSITY FUNCTION OF LOW MASS X-RAY BINARIES IN EARLY-TYPE GALAXIES, THEIR METAL-RICH, AND METAL-POOR GLOBULAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Peacock, Mark B.; Zepf, Stephen E., E-mail: mpeacock@msu.edu [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 (United States)

    2016-02-10

    We present the X-ray luminosity function (XLF) of low-mass X-ray binaries (LMXBs) in the globular clusters (GCs) and fields of seven early-type galaxies. These galaxies are selected to have both deep Chandra observations, which allow their LMXB populations to be observed to X-ray luminosities of 10{sup 37}–10{sup 38} erg s{sup −1}, and Hubble Space Telescope optical mosaics that enable the X-ray sources to be separated into field LMXBs, GC LMXBs, and contaminating background and foreground sources. We find that at all luminosities the number of field LMXBs per stellar mass is similar in these galaxies. This suggests that the field LMXB populations in these galaxies are not effected by the GC specific frequency, and that properties such as binary fraction and the stellar initial mass function are either similar across the sample or change in a way that does not affect the number of LMXBs. We compare the XLF of the field LMXBs to that of the GC LMXBs and find that they are significantly different with a p-value of 3 × 10{sup −6} (equivalent to 4.7σ for a normal distribution). The difference is such that the XLF of the GC LMXBs is flatter than that of the field LMXBs, with the GCs hosting relatively more bright sources and fewer faint sources. A comparison of the XLF of the metal-rich and metal-poor GCs hints that the metal-poor clusters may have more bright LMXBs, but the difference is not statistically significant.

  4. 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...

  5. Signatures of intrinsic Li depletion and Li-Na anti-correlation in the metal-poor globular cluster NGC6397

    CERN Document Server

    Lind, K; Charbonnel, C; Grundahl, F; Asplund, M

    2009-01-01

    To alleviate the discrepancy between the prediction of the primordial lithium abundance in the universe and the abundances observed in Pop II dwarfs and subgiant stars, it has been suggested that the stars observable today have undergone photospheric depletion of Li. To constrain the nature of such depletion, we conduct a homogeneous analysis of a very large sample of stars in the metal-poor globular cluster NGC6397, covering well all evolutionary phases from below the main sequence turn-off to high up the red giant branch. Non-LTE Li abundances or abundance upper limits are obtained for all stars, and for a size-able sub-set of the targets also Na abundances are obtained. The sodium abundances are used to distinguish stars formed out of pristine material from stars formed out of material affected by pollution from a previous generation of more massive stars. The dwarfs, turn-off, and early subgiant stars form a thin abundance plateau, disrupted in the middle of the subgiant branch by the lithium dilution cau...

  6. Anisotropic Models for Globular Clusters, Galactic Bulges and Dark Halos

    CERN Document Server

    Nguyen, P H

    2013-01-01

    Spherical systems with a polytropic equation of state are of great interest in astrophysics. They are widely used to describe neutron stars, red giants, white dwarfs, brown dwarfs, main sequence stars, galactic halos and globular clusters of diverse sizes. In this paper we construct analytically a family of self-gravitating spherical models in the post-Newtonian approximation of general relativity. These models present interesting cusps in their density profiles which are appropriate for the modeling of galaxies and dark matter halos. The systems described here are anisotropic in the sense that their equiprobability surfaces in velocity space are non-spherical, leading to an overabundance of radial or circular orbits, depending on the parameters of the model in consideration. Among the family, we find the post-Newtonian generalization of the Plummer and Hernquist models. A close inspection of their equation of state reveals that these solutions interpolate smoothly between a polytropic sphere in the asymptoti...

  7. Variable stars in the bulge globular cluster NGC 6401

    CERN Document Server

    Tsapras, Y; Bramich, D M; Jaimes, R Figuera; Kains, N; Street, R; Hundertmark, M; Horne, K; Dominik, M; Snodgrass, C

    2016-01-01

    We present a study of variable stars in globular cluster NGC 6401. The cluster is only $5.3\\degr$ away from the Galactic centre and suffers from strong differential reddening. The photometric precision afforded us by difference image analysis resulted in improved sensitivity to variability in formerly inaccessible interior regions of the cluster. We find 23 RRab and 11 RRc stars within one cluster radius (2.4$\\arcmin$), for which we provide coordinates, finder-charts and time-series photometry. Through Fourier decomposition of the RR Lyrae star light curves we derive a mean metallicity of [Fe/H]$_{\\mathrm{UVES}} = -1.13 \\pm 0.06$ (${\\rm [Fe/H]}_{\\mathrm{ZW}} = -1.25 \\pm 0.06$), and a distance of $d\\approx 6.35 \\pm 0.81$ kpc. Using the RR Lyrae population, we also determine that NGC 6401 is an Oosterhoff type I cluster.

  8. Near-Infrared Photometry of Globular Clusters Towards the Galactic Bulge: Observations and Photometric Metallicity Indicators

    CERN Document Server

    Cohen, Roger E; Mauro, Francesco; Bonatto, Charles; Geisler, Douglas

    2016-01-01

    We present wide field JHKs photometry of 16 Galactic globular clusters located towards the Galactic bulge, calibrated on the 2MASS photometric system. Differential reddening corrections and statistical field star decontamination are employed for all of these clusters before fitting fiducial sequences to the cluster red giant branches (RGBs). Observed values and uncertainties are reported for several photometric features, including the magnitude of the RGB bump, tip, the horizontal branch (HB) and the slope of the upper RGB. The latest spectroscopically determined chemical abundances are used to build distance- and reddening-independent relations between observed photometric features and cluster metallicity, optimizing the sample size and metallicity baseline of these relations by supplementing our sample with results from the literature. We find that the magnitude different between the HB and the RGB bump can be used to predict metallicities, in terms of both iron abundance [Fe/H] and global metallicity [M/H]...

  9. High resolution spectroscopic analysis of seven giants in the bulge globular cluster NGC 6723

    CERN Document Server

    Rojas-Arriagada, A; Vásquez, S; Ripepi, V; Musella, I; Marconi, M; Grado, A; Limatola, L

    2016-01-01

    Globular clusters associated with the Galactic bulge are important tracers of stellar populations in the inner Galaxy. High resolution analysis of stars in these clusters allows us to characterize them in terms of kinematics, metallicity, and individual abundances, and to compare these fingerprints with those characterizing field populations. We present iron and element ratios for seven red giant stars in the globular cluster NGC~6723, based on high resolution spectroscopy. High resolution spectra ($R\\sim48~000$) of seven K giants belonging to NGC 6723 were obtained with the FEROS spectrograph at the MPG/ESO 2.2m telescope. Photospheric parameters were derived from $\\sim130$ FeI and FeII transitions. Abundance ratios were obtained from line-to-line spectrum synthesis calculations on clean selected features. An intermediate metallicity of [Fe/H]$=-0.98\\pm0.08$ dex and a heliocentric radial velocity of $v_{hel}=-96.6\\pm1.3~km s^{-1}$ were found for NGC 6723. Alpha-element abundances present enhancements of $[O/...

  10. The SLUGGS survey: Probing the supermassive black hole connection with bulges and haloes using red and blue globular cluster systems

    CERN Document Server

    Pota, Vincenzo; Forbes, Duncan A; Romanowsky, Aaron J; Brodie, Jean P; Strader, Jay

    2013-01-01

    Understanding whether the bulge or the halo provides the primary link to the growth of supermassive black holes has strong implications for galaxy evolution and supermassive black hole formation itself. In this paper, we approach this issue by investigating extragalactic globular cluster (GC) systems, which can be used to probe the physics of both the bulge and the halo of the host galaxy. We study the relation between the supermassive black hole masses M_BH and the globular cluster system velocity dispersions sigma_GC using an updated and improved sample of 21 galaxies. We exploit the dichotomy of globular cluster system colours, to test if the blue and red globular clusters correlate differently with black hole mass. This may be expected if they trace the potentially different formation history of the halo and of the bulge of the host galaxy respectively. We find that M_BH correlates with the total GC system velocity dispersion, although not as strongly as claimed by recent work of Sadoun & Colin. We al...

  11. Ultra-deep GEMINI near-infrared observations of the bulge globular cluster NGC 6624

    CERN Document Server

    Saracino, S; Ferraro, F R; Geisler, D; Mauro, F; Lanzoni, B; Origlia, L; Miocchi, P; Cohen, R E; Villanova, S; Bidin, C Moni

    2016-01-01

    We used ultra-deep $J$ and $K_s$ images secured with the near-infrared GSAOI camera assisted by the multi-conjugate adaptive optics system GeMS at the GEMINI South Telescope in Chile, to obtain a ($K_s$, $J-K_s$) color-magnitude diagram (CMD) for the bulge globular cluster NGC 6624. We obtained the deepest and most accurate near-infrared CMD from the ground for this cluster, by reaching $K_s$ $\\sim$ 21.5, approximately 8 magnitudes below the horizontal branch level. The entire extension of the Main Sequence (MS) is nicely sampled and at $K_s$ $\\sim$ 20 we detected the so-called MS "knee" in a purely near-infrared CMD. By taking advantage of the exquisite quality of the data, we estimated the absolute age of NGC 6624 ($t_{age}$ = 12.0 $\\pm$ 0.5 Gyr), which turns out to be in good agreement with previous studies in the literature. We also analyzed the luminosity and mass functions of MS stars down to M $\\sim$ 0.45 M$_{\\odot}$ finding evidence of a significant increase of low-mass stars at increasing distances f...

  12. Tidal radii and destruction rates of globular clusters in the Milky Way due to bulge-bar and disk shocking

    Energy Technology Data Exchange (ETDEWEB)

    Moreno, Edmundo; Pichardo, Bárbara [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70-264, 04510 México, D. F. (Mexico); Velázquez, Héctor [Observatorio Astronómico Nacional, Universidad Nacional Autónoma de México, Apdo. Postal 877, 22800 Ensenada (Mexico)

    2014-10-01

    We calculate orbits, tidal radii, and bulge-bar and disk shocking destruction rates for 63 globular clusters in our Galaxy. Orbits are integrated in both an axisymmetric and a nonaxisymmetric Galactic potential that includes a bar and a three-dimensional model for the spiral arms. With the use of a Monte Carlo scheme, we consider in our simulations observational uncertainties in the kinematical data of the clusters. In the analysis of destruction rates due to the bulge-bar, we consider the rigorous treatment of using the real Galactic cluster orbit instead of the usual linear trajectory employed in previous studies. We compare results in both treatments. We find that the theoretical tidal radius computed in the nonaxisymmetric Galactic potential compares better with the observed tidal radius than that obtained in the axisymmetric potential. In both Galactic potentials, bulge-shocking destruction rates computed with a linear trajectory of a cluster at its perigalacticons give a good approximation of the result obtained with the real trajectory of the cluster. Bulge-shocking destruction rates for clusters with perigalacticons in the inner Galactic region are smaller in the nonaxisymmetric potential than those in the axisymmetric potential. For the majority of clusters with high orbital eccentricities (e > 0.5), their total bulge+disk destruction rates are smaller in the nonaxisymmetric potential.

  13. Near-infrared photometry of globular clusters towards the Galactic bulge: observations and photometric metallicity indicators

    Science.gov (United States)

    Cohen, Roger E.; Moni Bidin, Christian; Mauro, Francesco; Bonatto, Charles; Geisler, Douglas

    2017-01-01

    We present wide-field JHKS photometry of 16 Galactic globular clusters located towards the Galactic bulge, calibrated on the Two Micron All-Sky Survey photometric system. Differential reddening corrections and statistical field star decontamination are employed for all of these clusters before fitting fiducial sequences to the cluster red giant branches (RGBs). Observed values and uncertainties are reported for several photometric features, including the magnitude of the RGB bump, tip, the horizontal branch (HB) and the slope of the upper RGB. The latest spectroscopically determined chemical abundances are used to build distance- and reddening-independent relations between observed photometric features and cluster metallicity, optimizing the sample size and metallicity baseline of these relations by supplementing our sample with results from the literature. We find that the magnitude difference between the HB and the RGB bump can be used to predict metallicities, in terms of both iron abundance [Fe/H] and global metallicity [M/H], with a precision of better than 0.1 dex in all three near-IR bandpasses for relatively metal-rich ([M/H] ≳ -1) clusters. Meanwhile, both the slope of the upper RGB and the magnitude difference between the RGB tip and bump are useful metallicity indicators over the entire sampled metallicity range (-2 ≲ [M/H] ≲ 0) with a precision of 0.2 dex or better, despite model predictions that the RGB slope may become unreliable at high (near-solar) metallicities. Our results agree with previous calibrations in light of the relevant uncertainties, and we discuss implications for clusters with controversial metallicities as well as directions for further investigation.

  14. Ultra-deep GEMINI Near-infrared Observations of the Bulge Globular Cluster NGC 6624.

    Science.gov (United States)

    Saracino, S.; Dalessandro, E.; Ferraro, F. R.; Geisler, D.; Mauro, F.; Lanzoni, B.; Origlia, L.; Miocchi, P.; Cohen, R. E.; Villanova, S.; Moni Bidin, C.

    2016-11-01

    We used ultra-deep J and K s images secured with the near-infrared (NIR) GSAOI camera assisted by the multi-conjugate adaptive optics system GeMS at the GEMINI South Telescope in Chile, to obtain a (K s , J - K s ) color-magnitude diagram (CMD) for the bulge globular cluster NGC 6624. We obtained the deepest and most accurate NIR CMD from the ground for this cluster, by reaching K s ˜ 21.5, approximately 8 mag below the horizontal branch level. The entire extension of the Main Sequence (MS) is nicely sampled and at K s ˜ 20 we detected the so-called MS “knee” in a purely NIR CMD. By taking advantage of the exquisite quality of the data, we estimated the absolute age of NGC 6624 (t age = 12.0 ± 0.5 Gyr), which turns out to be in good agreement with previous studies in the literature. We also analyzed the luminosity and mass functions of MS stars down to M ˜ 0.45 M⊙, finding evidence of a significant increase of low-mass stars at increasing distances from the cluster center. This is a clear signature of mass segregation, confirming that NGC 6624 is in an advanced stage of dynamical evolution. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). Based on observations gathered with ESO-VISTA telescope (program ID 179.B-2002).

  15. The X-ray luminosity function of low mass X-ray binaries in early-type galaxies, their metal-rich, and metal-poor globular clusters

    CERN Document Server

    Peacock, Mark B

    2015-01-01

    We present the X-ray luminosity function (XLF) of low mass X-ray binaries (LMXBs) in the globular clusters (GCs) and fields of seven early-types galaxies. These galaxies are selected to have both deep Chandra observations, which allow their LMXB populations to be observed to X-ray luminosities of $10^{37}-10^{38}$ erg/s, and HST optical mosaics which enable the X-ray sources to be separated into field LMXBs, GC LMXBs, and contaminating background and foreground sources. We find that at all luminosities the number of field LMXBs per stellar mass is similar in these galaxies. This suggests that the field LMXB populations in these galaxies are not effected by the GC specific frequency, and that properties such as binary fraction and the stellar initial mass function are either similar across the sample, or change in a way that does not effect the number of LMXBs. We compare the XLF of the field LMXBs to that of the GC LMXBs and find that they are significantly different with a p-value of $3\\times10^{-6}$ (equiva...

  16. 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

  17. Tidal radii and destruction rates of globular clusters in the Milky Way due to bulge-bar and disk shocking

    CERN Document Server

    Moreno, Edmundo; Velazquez, Hector

    2014-01-01

    We calculate orbits, tidal radii, and bulge-bar and disk shocking destruction rates for 63 globular clusters in our Galaxy. Orbits are integrated in both an axisymmetric and a non-axisymmetric Galactic potential that includes a bar and a 3D model for the spiral arms. With the use of a Monte Carlo scheme, we consider in our simulations observational uncertainties in the kinematical data of the clusters. In the analysis of destruction rates due to the bulge-bar, we consider the rigorous treatment of using the real Galactic cluster orbit, instead of the usual linear trajectory employed in previous studies. We compare results in both treatments. We ?nd that the theoretical tidal radius computed in the nonaxisymmetric Galactic potential compares better with the observed tidal radius than that obtained in the axisymmetric potential. In both Galactic potentials, bulge-shocking destruction rates computed with a linear trajectory of a cluster at its perigalacticons give a good approximation to the result obtained with...

  18. Using the Multi-Object Adaptive Optics demonstrator RAVEN to observe metal-poor stars in and towards the Galactic Centre

    CERN Document Server

    Lamb, Masen; Andersen, David; Oya, Shin; Shetrone, Matthew; Fattahi, Azadeh; Howes, Louise; Asplund, Martin; Lardiere, Olivier; Akiyama, Masayuki; Ono, Yoshito; Terada, Hiroshi; Hayano, Yutaka; Suzuki, Genki; Blain, Celia; Jackson, Kathryn; Correia, Carlos; Youakim, Kris; Bradley, Colin

    2016-01-01

    The chemical abundances for five metal-poor stars in and towards the Galactic bulge have been determined from H-band infrared spectroscopy taken with the RAVEN multi-object adaptive optics science demonstrator and the IRCS spectrograph at the Subaru 8.2-m telescope. Three of these stars are in the Galactic bulge and have metallicities between -2.1 < [Fe/H] < -1.5, and high [alpha/Fe] ~+0.3, typical of Galactic disk and bulge stars in this metallicity range; [Al/Fe] and [N/Fe] are also high, whereas [C/Fe] < +0.3. An examination of their orbits suggests that two of these stars may be confined to the Galactic bulge and one is a halo trespasser, though proper motion values used to calculate orbits are quite uncertain. An additional two stars in the globular cluster M22 show [Fe/H] values consistent to within 1 sigma, although one of these two stars has [Fe/H] = -2.01 +/- 0.09, which is on the low end for this cluster. The [alpha/Fe] and [Ni/Fe] values differ by 2 sigma, with the most metal-poor star sho...

  19. Two Groups of Red Giants with Distinct Chemical Abundances in the Bulge Globular Cluster NGC 6553 Through the Eyes of APOGEE

    CERN Document Server

    Tang, Baitian; Geisler, Doug; Schiavon, Ricardo; Majewski, Steven R; Villanova, Sandro; Carrera, Ricardo; Zamora, Olga; Garcia-Hernandez, D A; Shetrone, Matthew; Frinchaboy, Peter; Meza, Andres; Fernández-Trincado, J G; Muñoz, Ricardo R; Lin, Chien-Cheng; Lane, Richard R; Nitschelm, Christian; Pan, Kaike; Bizyaev, Dmitry; Oravetz, Daniel; Simmons, Audrey

    2016-01-01

    Multiple populations revealed in globular clusters (GCs) are important windows to the formation and evolution of these stellar systems. The metal-rich GCs in the Galactic bulge are an indispensable part of this picture, but the high optical extinction in this region has prevented extensive research. In this work, we use the high resolution near-infrared (NIR) spectroscopic data from APOGEE to study the chemical abundances of NGC 6553, which is one of the most metal-rich bulge GCs. We identify ten red giants as cluster members using their positions, radial velocities, iron abundances, and NIR photometry. Our sample stars show a mean radial velocity of $-0.14\\pm5.47$ km s$^{-1}$, and a mean [Fe/H] of $-0.15\\pm 0.05$. We clearly separate two populations of stars in C and N in this GC for the first time. NGC 6553 is the most metal-rich GC where the multiple stellar population phenomenon is found until now. Substantial chemical variations are also found in Na, O, and Al. However, the two populations show similar S...

  20. Two Groups of Red Giants with Distinct Chemical Abundances in the Bulge Globular Cluster NGC 6553 Through the Eyes of APOGEE

    Science.gov (United States)

    Tang, Baitian; Cohen, Roger; Geisler, Douglas; Schiavon, Ricardo P.; Majewski, Steven R.; Villanova, Sandro; Carrera, Ricardo; Zamora, Olga; Garcia-Hernandez, D.; Shetrone, Matthew D.; Frinchaboy, Peter M.; Fernandez Trincado, Jose Gregorio; APOGEE Team

    2017-01-01

    Multiple populations revealed in globular clusters (GCs) are important windows to the formation and evolution of these stellar systems. The metal-rich GCs in the Galactic bulge are an indispensable part of this picture, but the high optical extinction in this region has prevented extensive research. In this work, we use the high resolution near-infrared (NIR) spectroscopic data from APOGEE to study the chemical abundances of NGC 6553, which is one of the most metal-rich bulge GCs. We identify ten red giants as cluster members using their positions, radial velocities, iron abundances, and NIR photometry. Our sample stars show a mean radial velocity of -0.14 km/s, and a mean [Fe/H] of -0.15. We clearly separate two populations of stars in C and N in this GC for the first time. NGC 6553 is the most metal-rich GC where the multiple stellar population phenomenon is found until now. Substantial chemical variations are also found in Na, O, and Al. However, the two populations show similar Si, Ca, and iron-peak element abundances. Therefore, we infer that the CNO, NeNa, and MgAl cycles have been activated, but the MgAl cycle is too weak to show its effect on Mg. The Si leakage from the MgAl cycle is negligible. Type Ia and Type II supernovae do not seem to have significantly polluted the second generation stars. Comparing the APOGEE results with other GC studies, we find that NGC 6553 shows similar chemical variations as other relatively metal-rich GCs. We also confront current GC formation theories with our results, and suggest possible avenues for improvement in the models.

  1. Two groups of red giants with distinct chemical abundances in the bulge globular cluster NGC 6553 through the eyes of APOGEE

    Science.gov (United States)

    Tang, Baitian; Cohen, Roger E.; Geisler, Doug; Schiavon, Ricardo P.; Majewski, Steven R.; Villanova, Sandro; Carrera, Ricardo; Zamora, Olga; Garcia-Hernandez, D. A.; Shetrone, Matthew; Frinchaboy, Peter; Meza, Andres; Fernández-Trincado, J. G.; Muñoz, Ricardo R.; Lin, Chien-Cheng; Lane, Richard R.; Nitschelm, Christian; Pan, Kaike; Bizyaev, Dmitry; Oravetz, Daniel; Simmons, Audrey

    2017-02-01

    Multiple populations revealed in globular clusters (GCs) are important windows to the formation and evolution of these stellar systems. The metal-rich GCs in the Galactic bulge are an indispensable part of this picture, but the high optical extinction in this region has prevented extensive research. In this work, we use the high-resolution near-infrared (NIR) spectroscopic data from Apache Point Observatory Galactic Evolution Experiment (APOGEE) to study the chemical abundances of NGC 6553, which is one of the most metal-rich bulge GCs. We identify 10 red giants as cluster members using their positions, radial velocities, iron abundances, and NIR photometry. Our sample stars show a mean radial velocity of -0.14 ± 5.47 km s-1, and a mean [Fe/H] of -0.15 ± 0.05. We clearly separate two populations of stars in C and N in this GC for the first time. NGC 6553 is the most metal-rich GC where the multiple stellar population phenomenon is found until now. Substantial chemical variations are also found in Na, O, and Al. However, the two populations show similar Si, Ca, and iron-peak element abundances. Therefore, we infer that the CNO, NeNa, and MgAl cycles have been activated, but the MgAl cycle is too weak to show its effect on Mg. Type Ia and Type II supernovae do not seem to have significantly polluted the second generation stars. Comparing with other GC studies, NGC 6553 shows similar chemical variations as other relatively metal-rich GCs. We also confront current GC formation theories with our results, and suggest possible avenues for improvement in the models.

  2. Stroemgren - near-infrared photometry of the Baade's Window. I. The bulge globular cluster NGC6528 and the surrounding field

    CERN Document Server

    Calamida, Annalisa; Lagioia, Edoardo P; Milone, Antonino P; Fabrizio, Michele; Saviane, Ivo; Bidin, Christian Moni; Mauro, Francesco; Buonanno, Roberto; Ferraro, Ivan; Iannicola, Giacinto; Zoccali, Manuela

    2014-01-01

    We present Stroemgren-NIR photometry of NGC6528 and its surroundings in the Baade's Window. uvby images were collected with EFOSC2@NTT, while NIR catalogs are based on VIRCAM@VISTA and SOFI@NTT data. The matching with HST photometry allowed us to obtain proper-motion-cleaned samples of cluster and bulge stars. The huge color sensitivity of Stroemgren-NIR CMDs helped us in disentangling age and metallicity effects. The RGB of NGC6528 is reproduced by scaled-solar isochrones with solar abundance or alpha-enhanced isochrones with the same iron content, and an age of t = 11+/-1 Gyr. These findings support literature age estimates for NGC6528. We also performed a theoretical metallicity calibration based on the Stroemgren index m1 and on visual-NIR colors for RGs, by adopting scaled-solar and alpha-enhanced models. We applied the calibration to estimate the metallicity of NGC6528, finding [Fe/H] = -0.04+/-0.02, with an intrinsic dispersion of 0.27 dex (by averaging abundances based on the scaled-solar [m], y - J a...

  3. Discovery of RR Lyrae Stars in the Nuclear Bulge of the Milky Way

    CERN Document Server

    Minniti, D; Zoccali, M; Rejkuba, M; Gonzalez, O A; Valenti, E; Gran, F

    2016-01-01

    Galactic nuclei, like the one of the Milky Way, are extreme places with high stellar densities and, in most cases, hosting a supermassive black hole. One of the scenarios proposed for the formation of the Galactic nucleus is by merging of primordial globular clusters (Capuzzo-Dolcetta 1993). An implication of this model is that this region should host stars characteristically found in old Milky Way globular clusters. RR Lyrae stars are primary distance indicators, well known representatives of old and metal-poor stellar populations, and therefore regularly found in globular clusters. Here we report the discovery of a dozen RR Lyrae ab-type stars in the vicinity of the Galactic center, i.e. in the so-called nuclear stellar bulge of the Milky Way. This discovery provides the first direct observational evidence that the Galactic nuclear stellar bulge contains ancient stars (>10 Gyr old). Based on this we conclude that merging globular clusters likely contributed to building-up the high stellar density in the nuc...

  4. Serendipitous Discovery of a Thin Stellar Stream near the Galactic Bulge in the Pan-STARRS1 3Pi Survey

    CERN Document Server

    Bernard, Edouard J; Schlafly, Edward F; Abbas, Mohamad; Bell, Eric F; Deacon, Niall R; Martin, Nicolas F; Rix, Hans-Walter; Sesar, Branimir; Slater, Colin T; Peñarrubia, Jorge; Wyse, Rosemary F G; Burgett, William S; Chambers, Kenneth C; Draper, Peter W; Hodapp, Klaus W; Kaiser, Nicholas; Kudritzki, Rolf-Peter; Magnier, Eugene A; Metcalfe, Nigel; Morgan, Jeffrey S; Price, Paul A; Tonry, John L; Wainscoat, Richard J; Waters, Christopher

    2014-01-01

    We report the discovery of a thin stellar stream found in Pan-STARRS1 photometry near the Galactic bulge in the constellation of Ophiuchus. It appears as a coherent structure in the colour-selected stellar density maps produced to search for tidal debris around nearby globular clusters. The stream is exceptionally short and narrow; it is about 2.5{\\deg} long and 6' wide in projection. The colour-magnitude diagram of this object, which harbours a blue horizontal-branch, is consistent with an old and relatively metal-poor population ([Fe/H]~-1.3) located 9.5 +/- 0.9 kpc away at (l,b) ~ (5{\\deg},+32{\\deg}), and 5.0 +/- 1.0 kpc from the Galactic centre. These properties argue for a globular cluster as progenitor. The finding of such a prominent, nearby stream suggests that many streams could await discovery in the more densely populated regions of our Galaxy.

  5. EXTREMELY METAL-POOR GALAXIES: THE ENVIRONMENT

    Energy Technology Data Exchange (ETDEWEB)

    Filho, M. E. [Universidad de Las Palmas de Gran Canaria–Universidad de La Laguna, CIE Canarias: Tri-Continental Atlantic Campus, Canary Islands (Spain); Almeida, J. Sánchez; Muñoz-Tuñón, C. [Instituto Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain); Nuza, S. E.; Kitaura, F.; Heß, S., E-mail: mfilho@astro.up.pt [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany)

    2015-04-01

    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 H i 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 neighbors. 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 fraction of a certain galaxy type, it does not determine the overall observational properties. With the exception of five documented cases (four sources with companions and one recent merger), XMPs do not generally show signatures of major mergers and interactions; we find only one XMP with a companion galaxy within a distance of 100 kpc, and the H i gas in XMPs is typically well-behaved, demonstrating asymmetries mostly in the outskirts. We conclude that metal-poor accretion flows may be driving the XMP evolution. Such cosmological accretion could explain all the major XMP observational properties: isolation, lack of interaction/merger signatures, asymmetric optical morphology, large amounts of unsettled, metal-poor H i gas, metallicity inhomogeneities, and large specific star formation.

  6. 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).

  7. 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...

  8. 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...

  9. The Chemical Properties of Milky Way and M31 Globular Clusters: II. Stellar Population Model Predictions

    CERN Document Server

    Beasley, M A; Strader, J; Forbes, D A; Proctor, R N; Barmby, P; Huchra, J P; Beasley, Michael A.; Brodie, Jean P.; Strader, Jay; Forbes, Duncan A.; Proctor, Robert N.; Barmby, Pauline; Huchra, John P.

    2004-01-01

    We derive ages, metallicities and [alpha/Fe] ratios from the integrated spectra of 23 globular clusters in M31, by employing multivariate fits to two stellar population models. In parallel we analyze spectra of 21 Galactic globular clusters in order to facilitate a differential analysis. We find that the M31 globular clusters separate into three distinct components in age and metallicity. We identify an old, metal-poor group (7 clusters), an old, metal-rich group (10 clusters) and an intermediate age (3-6 Gyr), intermediate-metallicity ([Z/H]~-1) group (6 clusters). This third group is not identified in the Galactic globular cluster sample. The majority of globular clusters in both samples appear to be enhanced in alpha-elements, the degree of enhancement being model-dependent. The intermediate age GCs appear to be the most enhanced, with [alpha/Fe]~0.4. These clusters are clearly depressed in CN with respect to the models and the bulk of the M31 and Milky Way sample. Compared to the bulge of M31, M32 and NGC...

  10. The Terzan 5 puzzle: discovery of a third, metal-poor component

    CERN Document Server

    Origlia, L; Rich, R M; Mucciarelli, A; Ferraro, F R; Dalessandro, E; Lanzoni, B

    2013-01-01

    We report on the discovery of 3 metal-poor giant stars in Terzan 5, a complex stellar system in the the Galactic bulge, known to have two populations at [Fe/H]=-0.25 and +0.3. For these 3 stars we present new echelle spectra obtained with NIRSPEC at Keck II, which confirm their radial velocity membership and provide average [Fe/H]=-0.79 dex iron abundance and [alpha/Fe]=+0.36 dex enhancement. This new population extends the metallicity range of Terzan~5 0.5 dex more metal poor, and it has properties consistent with having formed from a gas polluted by core collapse supernovae.

  11. Origins of carbon enhanced metal poor stars

    CERN Document Server

    Sharma, Mahavir; Frenk, Carlos; Cooke, Ryan

    2016-01-01

    We investigate the nature of carbon-enhanced metal poor (CEMP) stars in Milky Way (MW) analogues selected from the EAGLE cosmological hydrodynamical simulation. The stellar evolution model in EAGLE includes the physics of enrichment by asymptotic giant branch (AGB) stars, winds from massive stars, and type I and type II supernovae (SNe). In the simulation, star formation in young MW progenitors is bursty due to efficient stellar feedback, which causes poor metal mixing leading to the formation of CEMP stars with extreme abundance patterns. In this scenario, two classes of CEMP stars emerge: those mostly enriched by low-metallicity type II SNe with low Fe yields that drive galactic outflows, and those mostly enriched by AGB stars when a gas-poor progenitor accretes pristine gas. The first class resembles CEMP-no stars with high [C/Fe] and low [C/O], the second class resembles CEMP-s stars overabundant in s-process elements and high values of [C/O]. This scenario explains several trends seen in data: (i) the in...

  12. Eyes - bulging

    Science.gov (United States)

    ... emotional support is important. When to Contact a Medical Professional Call your health care provider if: You have bulging eyes and the cause has not yet been diagnosed. Bulging eyes are accompanied by other symptoms. ... The provider will ask about your medical history and do a physical exam. Some questions ...

  13. Galactic bulges

    NARCIS (Netherlands)

    Wyse, RFG; Gilmore, G; Franx, M

    1997-01-01

    We discuss the present observational and theoretical understanding of the stellar populations of bulges and their implications for galaxy formation and evolution. The place of bulges as key to the Hubble Sequence remains secure, but some old paradigms are giving way to new ones as observations devel

  14. 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...

  15. Galactic bulges

    CERN Document Server

    Peletier, Reynier; Gadotti, Dimitri

    2016-01-01

    This book consists of invited reviews on Galactic Bulges written by experts in the field. A central point of the book is that, while in the standard picture of galaxy formation a significant amount of the baryonic mass is expected to reside in classical bulges, the question what is the fraction of galaxies with no classical bulges in the local Universe has remained open. The most spectacular example of a galaxy with no significant classical bulge is the Milky Way. The reviews of this book attempt to clarify the role of the various types of bulges during the mass build-up of galaxies, based on morphology, kinematics, and stellar populations, and connecting their properties at low and high redshifts. The observed properties are compared with the predictions of the theoretical models, accounting for the many physical processes leading to the central mass concentration and their destruction in galaxies. This book serves as an entry point for PhD students and non-specialists and as a reference work for researchers...

  16. Common Origin of Two RR Lyrae Populations and the Double Red Clump in the Milky Way Bulge

    CERN Document Server

    Lee, Young-Wook

    2016-01-01

    A recent survey toward the Milky Way bulge has discovered two sequences of RR Lyrae stars on the period-amplitude diagram with a maximum period-shift of {\\Delta}log P = 0.015 between the two populations. Here we show, from our synthetic horizontal-branch models, that this period-shift is most likely due to the small difference in helium abundance ({\\Delta}Y = 0.012) between the first and second-generation stars (G1 and G2), as is the case in our models for the inner halo globular clusters with similar metallicity ([Fe/H] = -1.1). We further show that the observed double red clump (RC) in the bulge is naturally reproduced when these models are extended to solar metallicity following {\\Delta}Y/{\\Delta}Z = 6 for G2, as would be expected from the chemical evolution models. Therefore, the two populations of RR Lyrae stars and the double RC observed in the bulge appear to be different manifestations of the same multiple population phenomenon in the metal-poor and metal-rich regimes respectively.

  17. EVIDENCE FOR ENRICHMENT BY SUPERNOVAE IN THE GLOBULAR CLUSTER NGC 6273

    Energy Technology Data Exchange (ETDEWEB)

    Han, Sang-Il; Lim, Dongwook; Seo, Hyunju; Lee, Young-Wook, E-mail: ywlee2@yonsei.ac.kr [Center for Galaxy Evolution Research and Department of Astronomy, Yonsei University, Seoul 03722 (Korea, Republic of)

    2015-11-10

    In our recent investigation, we showed that narrowband photometry can be combined with low-resolution spectroscopy to effectively search for globular clusters (GCs) with supernova (SN) enrichments. Here we apply this technique to the metal-poor bulge GC NGC 6273 and find that the red giant branch stars in this GC are clearly divided into two distinct subpopulations with different calcium abundances. The Ca rich subpopulation in this GC is also enhanced in CN and CH, showing a positive correlation between them. This trend is identical to the result we found in M22, suggesting that this might be a ubiquitous nature of GCs more strongly affected by SNe in their chemical evolution. Our results suggest that NGC 6273 was massive enough to retain SN ejecta, which would place this cluster in the growing group of GCs with Galactic building block characteristics, such as ω Centauri and Terzan 5.

  18. ESO 546-G34: The most metal poor LSB galaxy?

    CERN Document Server

    Mattsson, Lars; Bergvall, Nils

    2011-01-01

    We present a re-analysis of spectroscopic data for 23 HII-regions in 12 blue, metal-poor low surface brightness galaxies (LSBGs) taking advantage of recent developments in calibrating strong-line methods. In doing so we have identified a galaxy (ESO 546-G34) which may be the most metal-poor LSB galaxy found in the local Universe. Furthermore, we see evidence that blue metal-poor LSBGs, together with blue compact galaxies (BCGs) and many other HII galaxies, fall outside the regular luminosity-metallicity relation. This suggests there might be an evolutionary connection between LSBGs and BCGs. In such case, several very metal-poor LSBGs should exist in the local Universe.

  19. Mixing along the Red Giant Branch in Metal-poor Field Stars

    CERN Document Server

    Carretta, E; Sneden, C; Bragaglia, A; Carretta, Eugenio; Gratton, Raffaele; Sneden, Chris; Bragaglia, Angela

    1999-01-01

    We have determined Li, C, N, O, Na, and Fe abundances, and 12C/13C isotopic ratios for a sample of 62 field metal-poor stars (plus 43 taken from the literature). This large sample was used to show that small mass lower-RGB stars (i.e., fainter than the RGB bump) have abundances of light elements in agreement with theoretical predictions from classical evolutionary models. A second, distinct mixing episode occurs just after the RGB bump, reaching regions of incomplete CNO burning. No O-Na anticorrelation, as observed in globular cluster stars, is found in field stars. This means that the mixing episode is not deep enough to reach regions where ON-burning occurs.

  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 chemical compositions of two nitrogen-rich, metal-poor, halo dwarf stars

    Science.gov (United States)

    Beveridge, Renee C.; Sneden, Cristopher

    1994-07-01

    New high resolution, high signal-to-noise spectra have been obtained for HD 25329 and HD 74000, dwarf stars that are metal-poor but nitrogen-rich members of the galactic halo. An atmosphere parameter and chemical composition analysis confirms earlier assertions of both their metal poverty, (Fe/H) approximately equals -2, and their high gravity, log g greater than 4. The relative abundances of the alpha-capture and iron-peak elements are normal for metal-poor stars. Overabundances of sodium, and possibly aluminum as well, are derived, but there are no pronounced depletions of oxygen; thus these stars do not show the sodium/oxygen or nitrogen/oxygen anticorrelations seen in globular cluster giants. All very heavy elements synthesized through s-process neutron-capture nucleosynthesis are enhanced in these stars. It is likely that the enrichments of nitrogen, sodium, aluminum, and the very heavy elements in these stars originated in material dredged up from the helium-burning shells of former AGB stars, but there is no direct evidence for binary companions for these stars.

  2. The Oldest Stars of the Extremely Metal-Poor Local Group Dwarf Irregular Galaxy Leo A

    CERN Document Server

    Schulte-Ladbeck, R E; Drozdovsky, I O; Greggio, L; Crone, M M; Schulte-Ladbeck, Regina E.; Hopp, Ulrich; Drozdovsky, Igor O.; Greggio, Laura; Crone, Mary M.

    2002-01-01

    We present deep Hubble Space Telescope single-star photometry of Leo A in B, V, and I. Our new field of view is offset from the centrally located field observed by Tolstoy et al. (1998) in order to expose the halo population of this galaxy. We report the detection of metal-poor red horizontal branch stars, which demonstrate that Leo A is not a young galaxy. In fact, Leo A is as least as old as metal-poor Galactic Globular Clusters which exhibit red horizontal branches, and are considered to have a minimum age of about 9 Gyr. We discuss the distance to Leo A, and perform an extensive comparison of the data with stellar isochrones. For a distance modulus of 24.5, the data are better than 50% complete down to absolute magnitudes of 2 or more. We can easily identify stars with metallicities between 0.0001 and 0.0004, and ages between about 5 and 10 Gyr, in their post-main-sequence phases, but lack the detection of main-sequence turnoffs which would provide unambiguous proof of ancient (>10 Gyr) stellar generation...

  3. Correlations between Kinematics and Metallicity in the Galactic Bulge: A Review

    Science.gov (United States)

    Babusiaux, Carine

    2016-06-01

    Recent large-scale surveys of galactic bulge stars allowed to build a detailed map of the bulge kinematics. The bulge exhibits cylindrical rotation consistent with a disky origin which evolved through bar-driven secular evolution. However, correlations between metallicity and kinematics complicate this picture. In particular a metal-poor component with distinct kinematic signatures has been detected. Its origin, density profile and link with the other Milky Way stellar populations are currently still poorly constrained.

  4. Abundances in the metal poor dwarf Ross 451

    Science.gov (United States)

    Spiesman, William J.

    1990-01-01

    High dispersion echelle spectra of the high velocity subdwarf Ross 451 (= G236-080) were obtained using the 4-m telescope at Kitt Peak. Initial abundance determinations for six elements are presented, using absolute oscillator strengths and metal-poor stellar-atmosphere models.

  5. 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

  6. 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

  7. Supernova Nucleosynthesis and Extremely Metal-Poor Stars

    CERN Document Server

    Tominaga, Nozomu; Maeda, Keiichi; Iwamoto, Nobuyuki; Nomoto, Ken'ichi

    2008-01-01

    We investigate hydrodynamical and nucleosynthetic properties of the jet-induced explosion of a population III $40M_\\odot$ star and compare the abundance patterns of the yields with those of the metal-poor stars. We conclude that (1) the ejection of Fe-peak products and the fallback of unprocessed materials can account for the abundance patterns of the extremely metal-poor (EMP) stars and that (2) the jet-induced explosion with different energy deposition rates can explain the diversity of the abundance patterns of the metal-poor stars. Furthermore, the abundance distribution after the explosion and the angular dependence of the yield are shown for the models with high and low energy deposition rates $\\dot{E}_{\\rm dep}=120\\times10^{51} {\\rm ergs s^{-1}}$ and $1.5\\times10^{51} {\\rm ergs s^{-1}}$. We also find that the peculiar abundance pattern of a Si-deficient metal-poor star HE 1424--0241 can be reproduced by the angle-delimited yield for $\\theta=30^\\circ-35^\\circ$ of the model with $\\dot{E}_{\\rm dep}=120\\ti...

  8. Extremely metal-poor star candidates in the SDSS

    Institute of Scientific and Technical Information of China (English)

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

    2013-01-01

    For a sample of metal-poor stars (-3.3 ≤ [Fe/H] ≤-2.2) that have highresolution spectroscopic abundance determinations,we have measured equivalent widths of the Ca Ⅱ K,Mg Ⅰ b and near-infrared Ca Ⅱ triplet lines using low-resolution spectra from the Sloan Digital Sky Survey (SDSS),calculated effective temperatures from (g-z)o 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.

  9. The GIRAFFE Inner Bulge Survey (GIBS). III. Metallicity distributions and kinematics of 26 Galactic bulge fields

    Science.gov (United States)

    Zoccali, M.; Vasquez, S.; Gonzalez, O. A.; Valenti, E.; Rojas-Arriagada, A.; Minniti, J.; Rejkuba, M.; Minniti, D.; McWilliam, A.; Babusiaux, C.; Hill, V.; Renzini, A.

    2017-02-01

    Context. Several recent studies have demonstrated that the Galactic bulge hosts two components with different mean metallicities, and possibly different spatial distribution and kinematics. As a consequence, both the metallicity distribution and the radial velocity of bulge stars vary across different lines of sight. Aims: We present here the metallicity distribution function of red clump stars in 26 fields spread across a wide area of the bulge, with special emphasis on fields close to Galactic plane, at latitudes b = -2° and b = -1°, that have not been explored before. Methods: This paper includes new metallicities from a sample of approximately 5000 K giant stars, observed at spectral resolution R 6500, in the Calcium II Triplet region. These represent the main dataset from the GIRAFFE Inner Bulge Survey. As part of the same survey we have previously published results for a sample of approximately 600 K giant stars, at latitude b -4°, derived from higher resolution spectra (R = 22 500). Results: The combined sample allows us to trace and characterize the metal poor and metal rich bulge populations down to the inner bulge. We present a density map for each of the two components. Contrary to expectations from previous works, we found the metal poor population to be more centrally concentrated than the metal rich one, and with a more axisymmetric spatial distribution. The metal rich population, on the other hand, is arranged in a boxy distribution, consistent with an edge-on bar. By coupling metallicities and radial velocities we show that the metal poor population has a velocity dispersion that varies rather mildly with latitude. On the contrary, the metal rich population has a low velocity dispersion far from the plane (b = -8.5°), yet has a steeper gradient with latitude, becoming higher than the metal poor one in the innermost field (b = -1°). Conclusions: This work provides new observational constraints on the actual chemodynamical properties of the

  10. 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...

  11. 6Li/7Li estimates for metal-poor stars

    CERN Document Server

    Perez, A E Garcia; Inoue, S; Ryan, S G; Suzuki, T K; Chiba, M

    2009-01-01

    The presence of the lithium-6 isotope in some metal-poor stars is a matter of surprise because of the high values observed. Non-standard models of Big Bang nucleosynthesis and pre-Galactic cosmic ray fusion and spallation have been proposed to explain these values. However, the observations of this light isotope are challenging which may make some detections disputable. The goal was to determine 6Li/7Li for a sample of metal-poor stars; three of them have been previously studied and the remaining two are new for this type of study. The purpose was to increase, if possible, the number of lithium-6 detections and to confirm previously published results. Spectra of the resonance doublet line of neutral lithium Li I 670.78nm were taken with the High Dispersion Spectrograph at the Subaru 8.2m-telescope for a sample of five metal-poor stars (-3.12 < [Fe/H] < -2.19). The contribution of lithium-6 to the total observed line profile was estimated from the 1D-LTE analysis of the line asymmetry. Observed asymmetri...

  12. Stellar Archaeology -- Exploring the Universe with Metal-Poor Stars

    CERN Document Server

    Frebel, Anna

    2010-01-01

    The abundance patterns of the most metal-poor stars in the Galactic halo and small dwarf galaxies provide us with a wealth of information about the early Universe. In particular, these old survivors allow us to study the nature of the first stars and supernovae, the relevant nucleosynthesis processes responsible for the formation and evolution of the elements, early star- and galaxy formation processes, as well as the assembly process of the stellar halo from dwarf galaxies a long time ago. This review presents the current state of the field of "stellar archaeology" -- the diverse use of metal-poor stars to explore the high-redshift Universe and its constituents. In particular, the conditions for early star formation are discussed, how these ultimately led to a chemical evolution, and what the role of the most iron-poor stars is for learning about Population III supernovae yields. Rapid neutron-capture signatures found in metal-poor stars can be used to obtain stellar ages, but also to constrain this complex ...

  13. Planetary companions around the metal-poor star HIP 11952

    Science.gov (United States)

    Setiawan, J.; Roccatagliata, V.; Fedele, D.; Henning, Th.; Pasquali, A.; Rodríguez-Ledesma, M. V.; Caffau, E.; Seemann, U.; Klement, R. J.

    2012-04-01

    Aims: We carried out a radial-velocity survey to search for planets around metal-poor stars. In this paper we report the discovery of two planets around HIP 11952, a metal-poor star with [Fe/H] = -1.9 that belongs to our target sample. Methods: Radial velocity variations of HIP 11952 were monitored systematically with FEROS at the 2.2 m telescope located at the ESO La Silla observatory from August 2009 until January 2011. We used a cross-correlation technique to measure the stellar radial velocities (RV). Results: We detected a long-period RV variation of 290 d and a short-period one of 6.95 d. The spectroscopic analysis of the stellar activity reveals a stellar rotation period of 4.8 d. The Hipparcos photometry data shows intra-day variabilities, which give evidence for stellar pulsations. Based on our analysis, the observed RV variations are most likely caused by the presence of unseen planetary companions. Assuming a primary mass of 0.83 M⊙, we computed minimum planetary masses of 0.78 MJup for the inner and 2.93 MJup for the outer planet. The semi-major axes are a1 = 0.07 AU and a2 = 0.81 AU, respectively. Conclusions: HIP 11952 is one of very few stars with [Fe/H] < -1.0 which have planetary companions. This discovery is important to understand planet formation around metal-poor stars.

  14. 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....

  15. Space Velocities of Southern Globular Clusters VI. Nine Clusters in the Inner Milky Way

    CERN Document Server

    Casetti-Dinescu, Dana I; Korchagin, Vladimir I; van Altena, William F; Lopez, Carlos E

    2010-01-01

    (abridged) We have measured the absolute proper motions of nine low-latitude, inner Galaxy globular clusters, namely NGC 6273 (M 19), NGC 6284, NGC 6287, NGC 6293, NGC 6333 (M 9), NGC 6342, NGC 6356, NGC 6388 and NGC 6441. These are the first determinations ever made for these clusters. The proper motions are on the ICRS via Hipparcos. The proper-motion errors range between 0.4 and 0.9 mas/yr, and are dominated by the number of measurable cluster members in these regions which are very crowded by the bulge/bar and the thick disk. This samle contains five metal poor ([Fe/H < -1.0) and four metal rich clusters; seven clusters are located within 4 kpc from the Galactic center, while the remaining two, namely NGC 6356 and NGC 6284 are in the background of the bulge at 7.5 kpc from the Galactic center. By combining proper motions with radial velocities and distances from the literature we derive 3D velocities. In a number of cases, distance uncertainties make the kinematical classification ambiguous. The two me...

  16. Spatially resolved dust emission of extremely metal-poor galaxies

    OpenAIRE

    Zhou, Luwenjia; Shi, Yong; 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 ≲ 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 f_(70μm)/f_(160 μm) ratios at a given f_(160 μm)/f_(2...

  17. 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...

  18. 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.

  19. 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...

  20. Planetary companions around the metal-poor star HIP 11952

    CERN Document Server

    Setiawan, J; Fedele, D; Henning, Th; Pasquali, A; Rodríguez-Ledesma, M V; Caffau, E; Seemann, U; Klement, R J; 10.1051/0004-6361/201117826

    2012-01-01

    Aims. We carried out a radial-velocity survey to search for planets around metal-poor stars. In this paper we report the discovery of two planets around HIP 11952, a metal-poor star with [Fe/H]= -1.9 that belongs to our target sample. Methods. Radial velocity variations of HIP 11952 were monitored systematically with FEROS at the 2.2 m telescope located at the ESO La Silla observatory from August 2009 until January 2011. We used a cross-correlation technique to measure the stellar radial velocities (RV). Results. We detected a long-period RV variation of 290 d and a short-period one of 6.95 d. The spectroscopic analysis of the stellar activity reveals a stellar rotation period of 4.8 d. The Hipparcos photometry data shows intra-day variabilities, which give evidence for stellar pulsations. Based on our analysis, the observed RV variations are most likely caused by the presence of unseen planetary companions. Assuming a primary mass of 0.83 M\\odot, we computed minimum planetary masses of 0.78 MJup for the inne...

  1. Carbon and Strontium Abundances of Metal-Poor Stars

    CERN Document Server

    Lai, David K; Bolte, Michael; Lucatello, Sara

    2007-01-01

    We present carbon and strontium abundances for 100 metal-poor stars measured from R$\\sim $7000 spectra obtained with the Echellette Spectrograph and Imager at the Keck Observatory. Using spectral synthesis of the G-band region, we have derived carbon abundances for stars ranging from [Fe/H]$=-1.3$ to [Fe/H]$=-3.8$. The formal errors are $\\sim 0.2$ dex in [C/Fe]. The strontium abundance in these stars was measured using spectral synthesis of the resonance line at 4215 {\\AA}. Using these two abundance measurments along with the barium abundances from our previous study of these stars, we show it is possible to identify neutron-capture-rich stars with our spectra. We find, as in other studies, a large scatter in [C/Fe] below [Fe/H]$ = -2$. Of the stars with [Fe/H]$<-2$, 9$\\pm$4% can be classified as carbon-rich metal-poor stars. The Sr and Ba abundances show that three of the carbon-rich stars are neutron-capture-rich, while two have normal Ba and Sr. This fraction of carbon enhanced stars is consistent with ...

  2. THE ACS VIRGO CLUSTER SURVEY. XVII. THE SPATIAL ALIGNMENT OF GLOBULAR CLUSTER SYSTEMS WITH EARLY-TYPE HOST GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Wang Qiushi; Peng, Eric W. [Department of Astronomy, Peking University, Beijing 100871 (China); Blakeslee, John P.; Cote, Patrick; Ferrarese, Laura [Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Jordan, Andres [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Mei, Simona [University of Paris 7 Denis Diderot, F-75205 Paris Cedex 13 (France); West, Michael J., E-mail: peng@pku.edu.cn [Maria Mitchell Observatory, 4 Vestal Street, Nantucket, MA 02554 (United States)

    2013-06-01

    We study the azimuthal distribution of globular clusters (GCs) in early-type galaxies and compare them to their host galaxies using data from the ACS Virgo Cluster Survey. We find that in host galaxies with visible elongation ({epsilon} > 0.2) and intermediate to high luminosities (M{sub z} < -19), the GCs are preferentially aligned along the major axis of the stellar light. The red (metal-rich) GC subpopulations show strong alignment with the major axis of the host galaxy, which supports the notion that these GCs are associated with metal-rich field stars. The metal-rich GCs in lenticular galaxies show signs of being more strongly associated with disks rather than bulges. Surprisingly, we also find that the blue (metal-poor) GCs can also show the same correlation. If the metal-poor GCs are part of the early formation of the halo and built up through mergers, then our results support a picture where halo formation and merging occur anisotropically, and that the present-day major axis is an indicator of the preferred merging axis.

  3. Molecular bands in extremely metal-poor stars. Granulation effects

    CERN Document Server

    Bonifacio, Piercarlo; Ludwig, Hans-Günter; Spite, Monique; Plez, Bertrand; Steffen, Matthias; Spite, François

    2013-01-01

    The bands of diatomic molecules are important abundance indicators, especially in metal-poor stars, where they are still measurable in metallicity regimes where the atomic lines of their constituting metallic elements have become vanishingly small. In order to use them for abundance determinations it is imperative to understand the formation of these bands. In this contribution we report on our results obtained using CO5BOLD hydrodynamical simulations. Some effects that are qualitatively different from what found in 1D computations are highlighted. Due to the large number of lines that form the bands, their spectrum synthesis is computationally challenging. We discuss some of the computational strategies we employed to parallelise the computation and possible future developments.

  4. 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.

  5. A common colour-magnitude relation from giant elliptical galaxies to globular clusters?

    CERN Document Server

    Castelli, A V Smith; Richtler, T; Faifer, F; Forte, J C; Cellone, S A

    2009-01-01

    We discuss the existence of a common colour-magnitude relation (CMR) of metal-poor globular clusters and early-type galaxies, i.e. giant ellipticals, normal ellipticals and lenticulars, dwarf ellipticals and lenticulars, and dwarf spheroidals. Such CMR would cover a range of ~ 14 mag, extending from the brightest galaxies, down to the globular clusters on the fainter side.

  6. The formation of the Galactic bulge of the Milky Way

    Directory of Open Access Journals (Sweden)

    Freeman K.

    2012-02-01

    Full Text Available We aim to determine if the bulge formed via mergers as predicted by Cold Dark Matter (CDM theory, or from disk instabilities, as suggested by its boxy shape, or both processes. We are observing about 28,000 bulge stars in fields that span longitudes of − 31 to + 26° and latitudes of − 5° to − 10°, targeting mostly red clump giants and we are measuring stellar velocities and chemical abundances. We have almost concluded our observations and have analysed data of 23,000 stars. We find a cylindrical rotation profile for the bulge which blends smoothly out into the disk and from the [Fe/H] results we find the bulge to be comprised of separate components, with an underlying slowly rotating metal poor subsample which we believe to be the inner halo stars and metal weak thick disk. We find only a small [Fe/H] gradient with latitude in the bulge, of − 0.07dex/kpc. This weak gradient does not necessarily support a merger origin for our bulge and the composite nature of the bulge is consistent with formation out of the thin disk as per instability formation models.

  7. The Oldest Stars of the Extremely Metal-Poor Local Group Dwarf Irregular Galaxy Leo A

    Science.gov (United States)

    Schulte-Ladbeck, Regina E.; Hopp, Ulrich; Drozdovsky, Igor O.; Greggio, Laura; Crone, Mary M.

    2002-08-01

    We present deep Hubble Space Telescope (HST) single-star photometry of Leo A in B, V, and I. Our new field of view is offset from the centrally located field observed by Tolstoy et al. in order to expose the halo population of this galaxy. We report the detection of metal-poor red horizontal branch stars, which demonstrate that Leo A is not a young galaxy. In fact, Leo A is as least as old as metal-poor Galactic Globular Clusters that exhibit red horizontal branches and are considered to have a minimum age of about 9 Gyr. We discuss the distance to Leo A and perform an extensive comparison of the data with stellar isochrones. For a distance modulus of 24.5, the data are better than 50% complete down to absolute magnitudes of 2 or more. We can easily identify stars with metallicities between 0.0001 and 0.0004, and ages between about 5 and 10 Gyr, in their post-main-sequence phases, but we lack the detection of main-sequence turnoffs that would provide unambiguous proof of ancient (>10 Gyr) stellar generations. Blue horizontal branch stars are above the detection limits but difficult to distinguish from young stars with similar colors and magnitudes. Synthetic color-magnitude diagrams show it is possible to populate the blue horizontal branch in the halo of Leo A. The models also suggest ~50% of the total astrated mass in our pointing to be attributed to an ancient (>10 Gyr) stellar population. We conclude that Leo A started to form stars at least about 9 Gyr ago. Leo A exhibits an extremely low oxygen abundance, only 3% of solar, in its ionized interstellar medium. The existence of old stars in this very oxygen-deficient galaxy illustrates that a low oxygen abundance does not preclude a history of early star formation. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

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

    Science.gov (United States)

    Mortier, A.; Santos, N. C.; Sozzetti, A.; Mayor, M.; Latham, D.; Bonfils, X.; Udry, S.

    2012-07-01

    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 ≤ [Fe/H] ≤ 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 should have been found in these data. Hot Jupiters around metal-poor stars have a frequency lower than 1.0% at one sigma. Giant planets with periods up to 1800 days, however, have a higher frequency of fp = 2.63-0.8+2.5%. Taking into account the different metallicities of the stars, we show that giant planets appear to be very frequent (fp = 4.48-1.38+4.04%) around stars with [Fe/H] > - 0.7, while they are rare around stars with [Fe/H] ≤ - 0.7 ( ≤ 2.36% at one sigma). Conclusions: Giant planet frequency is indeed a strong function of metallicity, even in the low-metallicity tail. However, the frequencies are most likely higher than previously thought. The data presented herein are based on observations collected at the La Silla Parana Observatory, ESO (Chile) with the HARPS spectrograph at the 3.6-m telescope (ESO runs ID 72.C-0488, 082.C-0212, and 085.C-0063) and at the W. M. Keck Observatory that is operated as a scientific partnership among the

  9. 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 ...

  10. Star formation in metal-poor gas clouds

    CERN Document Server

    Glover, Simon C O

    2012-01-01

    Observations of molecular clouds in metal-poor environments typically find that they have much higher star formation rates than one would expect based on their observed CO luminosities and the molecular gas masses that are inferred from them. This finding can be understood if one assumes that the conversion factor between CO luminosity and H2 mass is much larger in these low metallicity systems than in nearby molecular clouds. However, it is unclear whether this is the only factor at work, or whether the star formation rate of the clouds is directly sensitive to the metallicity of the gas. To investigate this, we have performed numerical simulations of the coupled dynamical, chemical and thermal evolution of model clouds with metallicities ranging from 0.01 Z_solar to Z_solar. We find that the star formation rate in our model clouds has little sensitivity to the metallicity. Reducing the metallicity of the gas by two orders of magnitude delays the onset of star formation in the clouds by no more than a cloud ...

  11. 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 -...

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

    CERN Document Server

    Schuler, S C; 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 iron abundance is found to be [Fe/H] = -2.5, making HE 1305+0132 the most Fe-deficient star, by more than an order of magnitude, for which the abundance of fluorine has been measured. Using spectral synthesis, we derive a super-solar fluorine abundance of A(19F) = 4.96 +/- 0.21, corresponding to a relative abundance of [F/Fe] = 2.90. A single line of the Phillips C_2 system is identified in our Phoenix spectrum, and along with multiple lines of the first-overtone vibration-rotation CO (3-1) band head, C and O abundances of ...

  13. Lithium isotopic abundances in metal-poor halo stars

    CERN Document Server

    Asplund, M; Nissen, P E; Primas, F; Smith, V V; Asplund, Martin; Lambert, David L.; Nissen, Poul Erik; Primas, Francesca; Smith, Verne V.

    2005-01-01

    Very high-quality spectra of 24 metal-poor halo dwarfs and subgiants have been acquired with ESO's VLT/UVES for the purpose of determining Li isotopic abundances. The derived 1D, non-LTE 7Li abundances from the LiI 670.8nm line reveal a pronounced dependence on metallicity but with negligible scatter around this trend. Very good agreement is found between the abundances from the LiI 670.8nm line and the LiI 610.4nm line. The estimated primordial 7Li abundance is $7Li/H = 1.1-1.5 x 10^-10, which is a factor of three to four lower than predicted from standard Big Bang nucleosynthesis with the baryon density inferred from the cosmic microwave background. Interestingly, 6Li is detected in nine of our 24 stars at the >2sigma significance level. Our observations suggest the existence of a 6Li plateau at the level of log 6Li = 0.8; however, taking into account predictions for 6Li destruction during the pre-main sequence evolution tilts the plateau such that the 6Li abundances apparently increase with metallicity. Ou...

  14. 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...

  15. NLTE Strontium and Barium in metal poor red giant stars

    CERN Document Server

    Short, C I

    2006-01-01

    We present atmospheric models of red giant stars of various metallicities, including extremely metal poor (XMP, [Fe/H]<-3.5) models, with many chemical species, including, significantly, the first two ionization stages of Strontium (Sr) and Barium (Ba), treated in Non-Local Thermodynamic Equilibrium (NLTE) with various degrees of realism. We conclude that 1) for all lines that are useful Sr and Ba abundance diagnostics the magnitude and sense of the computed NLTE effect on the predicted line strength is metallicity dependent, 2) the indirect NLTE effect of overlap between Ba and Sr transitions and transitions of other species that are also treated in NLTE non-negligibly enhances NLTE abundance corrections for some lines, 3) the indirect NLTE effect of NLTE opacity of other species on the equilibrium structure of the atmospheric model is not significant, 4) the computed NLTE line strengths differ negligibly if collisional b-b and b-f rates are an order of magnitude smaller or larger than those calculated wi...

  16. 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...

  17. 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...

  18. 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 ...

  19. Abundance correlations in mildly metal-poor stars

    CERN Document Server

    Jehin, E; Neuforge, C; Noels, A; Parmentier, G; Thoul, A A

    1999-01-01

    Accurate relative abundances have been obtained for a sample of 21 mildly metal-poor stars from the analysis of high resolution and high signal-to-noise spectra. With these accurate results, correlations between relative abundances have been searched for, with a special emphasis on the neutron capture elements. This analysis shows that the r elements are closely correlated to the alpha elements, which is in agreement with the generally accepted idea that the r-process takes place during the explosion of massive stars. The situation is more complex as far as the s elements are concerned. Their relation with the alpha elements is not linear. In a first group of stars, the relative abundance of the s elements increases only slightly with the alpha elements overabundance until the latter reaches a maximum value. For the second group, the s elements show a rather large range of enhancement and a constant (and maximum) value of the alpha elements overabundance. This peculiar behaviour leads us to distinguish betwee...

  20. 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...

  1. Extremely Metal-Poor Star Candidates in the SDSS

    CERN Document Server

    Xu, Siyao; Liu, Xiaowei

    2012-01-01

    For a sample of metal-poor stars (-3.3< [Fe/H] <-2.2) that have high-resolution spectroscopic abundance determinations, we have measured equivalent widths (EW) of the Ca II K, Mg I b and near-infrared (NIR) Ca II triplet lines using low-resolution spectra of the Sloan 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 (DR7). 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 corrected for the NLTE effect for the Mg I b lines and Ca II tr...

  2. 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.

  3. Artificial Neural Network for search for metal poor galaxies

    CERN Document Server

    Shi, F; Kong, X; Chen, Y

    2013-01-01

    In order to find a fast and reliable method for selecting metal poor galaxies (MPGs), especially in large surveys and huge database, an Artificial Neural Network (ANN) method is applied to a sample of star-forming galaxies from the Sloan Digital Sky Survey (SDSS) data release 9 (DR9) provided by the Max Planck Institute and the Johns Hopkins University (MPA/JHU). A two-step approach is adopted:(i) The ANN network must be trained with a subset of objects that are known to be either MPGs or MRGs(Metal Rich galaxies), treating the strong emission line flux measurements as input feature vectors in an n-dimensional space, where n is the number of strong emission line flux ratios. (ii) After the network is trained on a sample of star-forming galaxies, remaining galaxies are classified in the automatic test analysis as either MPGs or MRGs. We consider several random divisions of the data into training and testing sets: for instance, for our sample, a total of 70 percent of the data are involved in training the algor...

  4. The GIRAFFE Inner Bulge Survey (GIBS) III. Metallicity distributions and kinematics of 26 Galactic bulge fields

    CERN Document Server

    Zoccali, M; Gonzalez, O A; Valenti, E; Rojas-Arriagada, A; Minniti, J; Rejkuba, M; Minniti, D; McWilliam, A; Babusiaux, C; Hill, V; Renzini, A

    2016-01-01

    Several recent studies have demonstrated that the Galactic bulge hosts two components with different mean metallicities, and possibly different spatial distribution and kinematics. As a consequence, both the metallicity distribution and the radial velocity of bulge stars vary across different line of sights. We present here the metallicity distribution function of red clump stars in 26 fields spread across a wide area of the bulge, with special emphasis on fields close to Galactic plane, at latitudes b=-2 and b=-1, that were not explored before. This paper includes new metallicities from a sample of about 5000 K giant stars, observed at spectral resolution R=6500, in the Calcium II Triplet region. They are the main dataset of the GIRAFFE Inner Bulge Survey. As part of the same survey we have previously published results for a sample of about 600 K giant stars, at latitude b=-4 , derived from higher resolution spectra (R=22,500). Results. The combined sample allows us to trace and characterize the metal poor a...

  5. 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.

  6. Artificial neural network to search for metal-poor galaxies

    Science.gov (United States)

    Shi, Fei; Liu, Yu-Yan; Kong, Xu; Chen, Yang

    2014-02-01

    Aims: To find a fast and reliable method for selecting metal-poor galaxies (MPGs), especially in large surveys and huge databases, an artificial neural network (ANN) method is applied to a sample of star-forming galaxies from the Sloan Digital Sky Survey (SDSS) data release 9 (DR9) provided by the Max Planck Institute and the Johns Hopkins University (MPA/JHU). Methods: A two-step approach is adopted: (i) The ANN network 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 the network is trained on a sample of star-forming galaxies, the remaining galaxies are classified in the automatic test analysis as either MPGs or MRGs. We consider several random divisions of the data into training and testing sets; for instance, for our sample, a total of 70 percent of the data are involved in training the algorithm, 15 percent are involved in validating the algorithm, and the remaining 15 percent are used for blind testing the resulting classifier. Results: For target selection, we have achieved an acquisition rate for MPGs of 96 percent and 92 percent for an MPGs 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 ANN method can easily be extended to any MPGs target selection task when the physical property of the target can be expressed as a quantitative variable. The code in the paper is available on the web (http://fshi5388.blog.163.com).

  7. Bright Metal-Poor Stars from the Hamburg/ESO Survey. II. A Chemodynamical Analysis

    Science.gov (United States)

    Beers, Timothy C.; Placco, Vinicius M.; Carollo, Daniela; Rossi, Silvia; Lee, Young Sun; Frebel, Anna; Norris, John E.; Dietz, Sarah; Masseron, Thomas

    2017-01-01

    We obtain estimates of stellar atmospheric parameters for a previously published sample of 1777 relatively bright (9Survey. The original Frebel et al. analysis of these stars was able to derive estimates of [Fe/H] and [C/Fe] only for a subset of the sample, due to limitations in the methodology then available. A new spectroscopic analysis pipeline has been used to obtain estimates of {T}{eff}, {log} g, [Fe/H], and [C/Fe] for almost the entire data set. This sample is very local—about 90% of the stars are located within 0.5 kpc of the Sun. We consider the chemodynamical properties of these stars in concert with a similarly local sample of stars from a recent analysis of the Bidelman and MacConnell “weak metal” candidates by Beers et al. We use this combined sample to identify possible members of the halo stream of stars suggested by Helmi et al. and Chiba & Beers, as well as stars that may be associated with stripped debris from the putative parent dwarf of the globular cluster Omega Centauri, suggested to exist by previous authors. We identify a clear increase in the cumulative frequency of carbon-enhanced metal-poor (CEMP) stars with declining metallicity, as well as an increase in the fraction of CEMP stars with distance from the Galactic plane, consistent with previous results. We also identify a relatively large number of CEMP stars with kinematics consistent with the metal-weak thick-disk population, with possible implications for its origin.

  8. Gravitational interactions between globular and open clusters: an introduction

    CERN Document Server

    Marcos, R de la Fuente; Reilly, D

    2014-01-01

    Historically, it has been assumed that globular and open clusters never interact. However, recent evidence suggests that: globular clusters passing through the disk may be able to perturb giant molecular clouds (GMCs) triggering formation of open clusters and some old open clusters may be linked to accreted globulars. Here, we further explore the existence of possible dynamical connections between globular and open clusters, and realize that the most obvious link must be in the form of gravitational interactions. If open clusters are born out of GMCs, they have to move in similar orbits. If we accept that globulars can interact with GMCs, triggering star formation, it follows that globular and open clusters must also interact. Consistently, theoretical arguments as well as observational evidence, show that globular and open clusters certainly are interacting populations and their interactions are far more common than usually thought, especially for objects part of the bulge/disk. Monte Carlo calculations conf...

  9. The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei and Stellar Halos

    OpenAIRE

    Lotz, Jennifer M.; Miller, Bryan W.; Ferguson, Henry C.

    2004-01-01

    We present the results of a Hubble Space Telescope WFPC2 F555W and F814W survey of 69 dwarf elliptical galaxies (dEs) in the Virgo and Fornax Clusters and Leo Group. The $V-I$ colors of the dE globular clusters, nuclei, and underlying field star populations are used to trace the dE star-formation histories. We find that the dE globular cluster candidates are as blue as the metal-poor globular clusters of the Milky Way. The observed correlation of the dE globular cluster systems' $V-I$ color w...

  10. Eyes, Bulging (Proptosis)

    Science.gov (United States)

    ... a disorder causing overactivity of the thyroid gland ( hyperthyroidism ). Bulging eyes are not the same as prominent ... or pain Whether the person has symptoms of hyperthyroidism, such as inability to tolerate heat, increased sweating, ...

  11. Rejuvenation of spiral bulges

    CERN Document Server

    Thomas, D; Thomas, Daniel; Davies, Roger L.

    2006-01-01

    We seek to understand whether the stellar populations of galactic bulges show fingerprints of secular evolution triggered by the presence of the disc. For this purpose we re-analyse the sample of Proctor and Sansom, deriving stellar population ages and element abundances from absorption line indices. We obtain very consistent constraints on ages from the three Balmer indices Hbeta, Hgamma, and Hdelta, in good agreement with those of Proctor and Sansom based on a completely different method. Like other studies in the literature, we find that bulges have relatively low luminosity weighted ages, the lowest age derived for the smallest bulges being 1.3 Gyr. Hence bulges are not generally old but actually rejuvenated systems. We discuss evidence that this might be true also for the bulge of the Milky Way. We show that the smallest bulges, being the youngest with the lowest alpha/Fe ratios, must have experienced star formation events involving 10-30 per cent of their total mass in the past 1-2 Gyr. No significant c...

  12. The Sagittarius Dwarf Galaxy Survey (SDGS); 1, CMDs, Reddening and Population Gradients First evidences of a very metal poor population

    CERN Document Server

    Bellazzini, M; Buonanno, R

    1998-01-01

    We present first results of a large photometric survey devoted to study the star formation history of the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Three wide strips (9 X 35 arcmin^2) located at l~5 and b=-16, -14, -12 have been observed. Each strip is roughly EW oriented, nearly along the major axis of the galaxy. A control field (~9 X 24 arcmin^2), located outside the body of Sgr dSph has also been observed for statistic decontamination purposes. Accurate and well calibrated V,I photometry down to V~22 have been obtained for is the largest photometric sample (covering the widest spatial extension) ever observed in the Sgr dSph up to now. The main new results presented in this paper are: (1) the possible discovery of a strong asymmetry in the distribution of stars along the major axis, since the north-western arm of the Sgr galaxy (i.e. the region nearer to the Galactic Bulge) apparently shows a significant deficiency of Sgr stars and (2) the first direct detection of a very metal poor (and presumably ...

  13. The oldest and most metal poor stars in the APOSTLE Local Group simulations

    CERN Document Server

    Starkenburg, Else; Navarro, Julio F; Crain, Robert A; Fattahi, Azadeh; Frenk, Carlos S; Sawala, Till; Schaye, Joop

    2016-01-01

    We examine the spatial distribution of the oldest and most metal poor stellar populations of Milky Way-sized galaxies using the APOSTLE cosmological hydrodynamical simulations of the Local Group. In agreement with earlier work, we find strong radial gradients in the fraction of the oldest (tform < 0.8 Gyr) and most metal poor ([Fe/H]< -2.5) stars, both of which increase outwards. The most metal poor stars form over an extended period of time; half of them form after z = 5.3, and the last 10% after z = 2.8. The age of the metal poor stellar population also shows significant variation with environment; a high fraction of them are old in the galaxy's central regions and an even higher fraction in some individual dwarf galaxies, with substantial scatter from dwarf to dwarf. Overall, over half of the stars that belong to both the oldest and most metal-poor population are found outside the solar circle. Somewhat counter-intuitively, we find that dwarf galaxies with a large fraction of metal poor stars that ar...

  14. Detailed Abundances of Two Very Metal-Poor Stars in Dwarf Galaxies

    CERN Document Server

    Kirby, Evan N

    2012-01-01

    The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae. These supernovae 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 halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two Milky Way 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-[alpha/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 supernova yields is the cause. The earlies...

  15. The oldest and most metal-poor stars in the APOSTLE Local Group simulations

    Science.gov (United States)

    Starkenburg, Else; Oman, Kyle A.; Navarro, Julio F.; Crain, Robert A.; Fattahi, Azadeh; Frenk, Carlos S.; Sawala, Till; Schaye, Joop

    2017-02-01

    We examine the spatial distribution of the oldest and most metal-poor stellar populations of Milky Way-sized galaxies using the A Project Of Simulating The Local Environment (APOSTLE) cosmological hydrodynamical simulations of the Local Group. In agreement with earlier work, we find strong radial gradients in the fraction of the oldest (tform stars, both of which increase outwards. The most metal-poor stars form over an extended period of time; half of them form after z = 5.3, and the last 10 per cent after z = 2.8. The age of the metal-poor stellar population also shows significant variation with environment; a high fraction of them are old in the galaxy's central regions and an even higher fraction in some individual dwarf galaxies, with substantial scatter from dwarf to dwarf. We investigate the dependence of these results on the assumptions made for metal mixing. Overall, over half of the stars that belong to both the oldest and most metal-poor population are found outside the solar circle. Somewhat counter-intuitively, we find that dwarf galaxies with a large fraction of metal-poor stars that are very old are systems where metal-poor stars are relatively rare, but where a substantial old population is present. Our results provide guidance for interpreting the results of surveys designed to hunt for the earliest and most pristine stellar component of our Milky Way.

  16. ACS photometry of the globular cluster B514

    CERN Document Server

    Galleti, S; Bellazzini, M; Buzzoni, A; Pecci, F F

    2006-01-01

    We present deep F606W, F814W ACS photometry of the recently discovered globular cluster B514, the outermost known globular in the M31 galaxy. The cluster appears quite extended and member stars are unequivocally identified out to ~200 pc from the center. The Color Magnitude Diagram reveals a steep Red Giant Branch (RGB), and a Horizontal Branch (HB) extending blue ward of the instability strip, indicating that B514 is a classical old metal-poor globular cluster. The RGB locus and the position of the RGB Bump are both consistent with a metallicity [Fe/H] ~ -1.8, in excellent agreement with spectroscopic estimates. A preliminary estimate of the integrated absolute V magnitude (M_V< -9.1) suggests that B514 is among the brightest globulars of M31.

  17. Integrated spectral study of reddened globular clusters and candidates

    Science.gov (United States)

    Bica, E.; Claria, J. J.; Piatti, A. E.; Bonatto, C.

    1998-09-01

    This paper presents integrated spectra in the range 6700 - 9500 Angstroms for 20 Galactic globular clusters (and candidates) in the bulge and 5 others projected on the Galactic disk (|l|>30mbox {^{\\circ}}\\ and |b|Complejo Astronómico El Leoncito (CASLEO), Argentina, and European Southern Observatory (ESO), Chile.

  18. Study of Neutron-Capture Element Abundances in Metal-Poor Stars

    CERN Document Server

    Li, Hongjie; Liang, Shuai; Cui, Wenyuan; Zhang, Bo

    2013-01-01

    This work describes a study of elemental abundances for 30 metal-poor stars whose chemical abundances provide excellent information for setting constraints on models of neutron-capture processes. Based on the abundances of main r- and weak r-process stars, the abundance patterns of main r-process and weak r-process are obtained. The two r-process component coefficients are defined to determine the relative contributions from individual neutron-capture process to abundances of metal-poor stars. Based on the component coefficients, we find that metal-poor stars BD+4 2621 and HD 4306 are also weak r-process stars, which means that the abundance pattern produced by weak r-process is stable. All metal-poor star abundances contain the contributions of both main r-process and weak r-process. The elements produced by weak r-process have increased along with Fe over the polluted history. Most of the metal-poor star abundances do not follow the pattern observed in solar system, but there is a small fraction that do. Fo...

  19. 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...

  20. The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime

    Science.gov (United States)

    Cooke, Ryan; Pettini, Max; Steidel, Charles C.; Rudie, Gwen C.; Nissen, Poul E.

    2011-10-01

    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 are reported here for the first time. Together with recent measures of the abundances of C and O in Galactic metal-poor stars, we reinvestigate the trend of C/O in the very metal-poor (VMP) regime and we compare, for the first time, the O/Fe ratios in the most metal-poor DLAs and in halo stars. We 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 []=+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 pattern for a typical VMP DLA and compare it to model calculations of Population II and Population III nucleosynthesis to determine the origin of the metals in VMP DLAs. Our results suggest that the most metal-poor DLAs may have been enriched by a generation of metal-free stars; however, given that abundance measurements are currently available for only a few elements, we cannot yet rule out an additional contribution from Population II stars. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile [VLT programme IDs 67.A-0078(A), 69.A-0613(A), 083.A-0042(A), 085.A-0109(A)], and at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of

  1. Heavy elements Ba, La, Ce, Nd, and Eu in 56 Galactic bulge red giants

    CERN Document Server

    Van der Swaelmen, M; Hill, V; Zoccali, M; Minniti, D; Ortolani, S; Gomez, A

    2016-01-01

    Aims. The aim of this work is the study of abundances of the heavy elements Ba, La, Ce, Nd, and Eu in 56 bulge giants (red giant branch and red clump) with metallicities ranging from -1.3 dex to 0.5 dex. Methods. We obtained high-resolution spectra of our giant stars using the FLAMES-UVES spectrograph on the Very Large Telescope. We inspected four bulge fields along the minor axis. Results. We measure the chemical evolution of heavy elements, as a function of metallicity, in the Galactic bulge. Conclusions. The [Ba, La, Ce, Nd/Fe] vs. [Fe/H] ratios decrease with increasing metallicity, in which aspect they differ from disc stars. In our metal-poor bulge stars, La and Ba are enhanced relative to their thick disc counterpart, while in our metal-rich bulge stars La and Ba are underabundant relative to their disc counterpart. Therefore, this contrast between bulge and discs trends indicates that bulge and (solar neighbourhood) thick disc stars could behave differently. An increase in [La, Nd/Eu] with increasing m...

  2. s- and r-process elements in two very metal-poor stars

    CERN Document Server

    Ryan, S G; Blake, L A J; Norris, J E; Beers, T C; Gallino, R; Busso, M; Ando, H; Ryan, Sean G.; Aoki, Wako; Blake, Lisa A. J.; Norris, John E.; Beers, Timothy C.; Gallino, Roberto; Busso, Maurizio; Ando, Hiroyasu

    2000-01-01

    New measurements of neutron-capture elements are presented for two very metal-poor stars ([Fe/H] ~ -3). One (LP 625-44) has an s-process signature believed to be due to mass transfer from a now-extinct metal-poor AGB companion, and the second (CS 22897-008) is one of a number of very metal-poor stars having high [Sr/Ba] ratios which is not expected from the r-process. In the s-process star, many elements including lead have been detected, providing strong constraints on the 13C pocket in the now-extinct AGB star. In the Sr-rich star, Zn, Y, and Zr are also seen to be overabundant, and several possible nucleosynthesis mechanisms are discussed.

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

    Energy Technology Data Exchange (ETDEWEB)

    Kirby, Evan N.; Cohen, Judith G. [Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249-17, Pasadena, CA 91125 (United States)

    2012-12-01

    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-[{alpha}/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] {approx} -3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo.

  4. Detailed Abundances of Two Very Metal-poor Stars in Dwarf Galaxies

    Science.gov (United States)

    Kirby, Evan N.; Cohen, Judith G.

    2012-12-01

    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] Lt -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. Data herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

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

    Science.gov (United States)

    Giridhar, S.; Goswami, A.; Kunder, A.; Muneer, S.; Selvakumar, G.

    2013-08-01

    Context. Identification of metal-poor stars among field stars is extremely useful for studying the structure and evolution of the Galaxy and of external galaxies. Aims: We search for metal-poor stars using the artificial neural network (ANN) and extend its usage to determine absolute magnitudes. Methods: 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 Teff and log g by nearly a factor of two. Results: We calculated Teff, 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 with well-estimated parallaxes. A better calibration accuracy for MV could be obtained by training separate ANNs for cool, warm, and metal-poor stars. The current accuracy of MV calibration is ±0.3 mag. Conclusions: A list of newly identified metal-poor stars is presented. The MV calibration procedure developed here is reddening-independent and hence may serve as a powerful tool in studying galactic structure.

  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. 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.

  8. Chemical Analysis of the Ninth Magnitude Carbon-Enhanced Metal-Poor Star BD+44 493

    CERN Document Server

    Ito, H; Beers, T C; Tominaga, N; Honda, S

    2013-01-01

    We present detailed chemical abundances for the bright carbon-enhanced metal-poor (CEMP) star BD+44 493, previously reported on by Ito et al. Our measurements confirm that BD+44 493 is an extremely metal-poor ([Fe/H]=-3.8) subgiant star with excesses of carbon and oxygen. No significant excesses are found for nitrogen and neutron-capture elements (the latter of which place it in the CEMP-no class of stars). Other elements that we measure exhibit abundance patterns that are typical for non-CEMP extremely metal-poor stars. No evidence for variations of radial velocity have been found for this star. These results strongly suggest that the carbon enhancement in BD+44 493 is unlikely to have been produced by a companion asymptotic giant-branch star and transferred to the presently observed star, nor by pollution of its natal molecular cloud by rapidly-rotating, massive, mega metal-poor ([Fe/H] < -6.0) stars. A more likely possibility is that this star formed from gas polluted by the elements produced in a "fain...

  9. Extremely metal-poor stars in classical dwarf spheroidal galaxies : Fornax, Sculptor, and Sextans

    NARCIS (Netherlands)

    Tafelmeyer, M.; Jablonka, P.; Hill, V.; Shetrone, M.; Tolstoy, E.; Irwin, M. J.; Battaglia, G.; Helmi, A.; Starkenburg, E.; Venn, K. A.; Abel, T.; Francois, P.; Kaufer, A.; North, P.; Primas, F.; Szeifert, T.

    2010-01-01

    We present the results of a dedicated search for extremely metal-poor stars in the Fornax, Sculptor, and Sextans dSphs. Five stars were selected from two earlier VLT/Giraffe and HET/HRS surveys and subsequently followed up at high spectroscopic resolution with VLT/UVES. All of them turned out to hav

  10. Extremely metal-poor stars in classical dwarf spheroidal galaxies: Fornax, Sculptor and Sextans

    CERN Document Server

    Tafelmeyer, M; Hill, V; Shetrone, M; Tolstoy, E; Irwin, M J; Battaglia, G; Helmi, A; Starkenburg, E; Venn, K A; Abel, T; Francois, P; Kaufer, A; North, P; Primas, F; Szeifert, T

    2010-01-01

    We present the results of a dedicated search for extremely metal-poor stars in the Fornax, Sculptor and Sextans dSphs. Five stars were selected from two earlier VLT/Giraffe and HET/HRS surveys and subsequently followed up at high spectroscopic resolution with VLT/UVES. All of them turned out to have [Fe/H] <= -3 and three stars are below [Fe/H]~-3.5. This constitutes the first evidence that the classical dSphs Fornax and Sextans join Sculptor in containing extremely metal-poor stars and suggests that all of the classical dSphs contain extremely metal-poor stars. One giant in Sculptor at [Fe/H]=-3.96 +- 0.10 is the most metal-poor star ever observed in an external galaxy. We carried out a detailed analysis of the chemical abundances of the alpha, iron peak, and the heavy elements, and we performed a comparison with the Milky Way halo and the ultra faint dwarf stellar populations. Carbon, barium and strontium show distinct features characterized by the early stages of galaxy formation and can constrain the o...

  11. Population Synthesis of Binary Carbon-enhanced Metal-poor Stars

    CERN Document Server

    Izzard, Robert G; Stancliffe, Richard J; Pols, Onno

    2009-01-01

    The carbon-enhanced metal-poor (CEMP) stars constitute approximately one fifth of the metal-poor ([Fe/H] ~< -2) population but their origin is not well understood. The most widely accepted formation scenario, invokes mass-transfer of carbon-rich material from a thermally-pulsing asymptotic giant branch (TPAGB) primary star to a less massive main-sequence companion which is seen today. Recent studies explore the possibility that an initial mass function biased toward intermediate-mass stars is required to reproduce the observed CEMP fraction in stars with metallicity [Fe/H] < -2.5. These models also implicitly predict a large number of nitrogen-enhanced metal-poor (NEMP) stars which is not seen. We investigate whether the observed CEMP and NEMP to extremely metal-poor (EMP) ratios can be explained without invoking a change in the initial mass function. We confirm earlier findings that with current detailed TPAGB models the large observed CEMP fraction cannot be accounted for. We find that efficient third...

  12. 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 ...

  13. 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)

  14. The Gaia-ESO Survey: Metal-rich Bananas in the Bulge

    Science.gov (United States)

    Williams, Angus A.; Evans, N. W.; Molloy, Matthew; Kordopatis, Georges; Smith, M. C.; Shen, J.; Gilmore, G.; Randich, S.; Bensby, T.; Francois, P.; Koposov, S. E.; Recio-Blanco, A.; Bayo, A.; Carraro, G.; Casey, A.; Costado, T.; Franciosini, E.; Hourihane, A.; de Laverny, P.; Lewis, J.; Lind, K.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C.; Zaggia, S.; Mikolaitis, Š.

    2016-06-01

    We analyze the kinematics of ˜2000 giant stars in the direction of the Galactic bulge, extracted from the Gaia-ESO survey in the region -10^\\circ ≲ {\\ell }≲ 10^\\circ and -11^\\circ ≲ b≲ -3^\\circ . We find distinct kinematic trends in the metal-rich ([{{M}}/{{H}}]\\gt 0) and metal-poor ([{{M}}/{{H}}]\\lt 0) stars in the data. The velocity dispersion of the metal-rich stars drops steeply with latitude, compared to a flat profile in the metal-poor stars, as has been seen previously. We argue that the metal-rich stars in this region are mostly on orbits that support the boxy-peanut shape of the bulge, which naturally explains the drop in their velocity dispersion profile with latitude. The metal-rich stars also exhibit peaky features in their line of sight velocity histograms, particularly along the minor axis of the bulge. We propose that these features are due to stars on resonant orbits supporting the boxy-peanut bulge. This conjecture is strengthened through the comparison of the minor axis data with the velocity histograms of resonant orbits generated in simulations of buckled bars. The “banana” or 2:1:2 orbits provide strongly bimodal histograms with narrow velocity peaks that resemble the Gaia-ESO metal-rich data.

  15. The Gaia-ESO survey: Metal-rich bananas in the bulge

    CERN Document Server

    Williams, Angus A; Molloy, Matthew; Kordopatis, Georges; Smith, M C; Shen, J; Gilmore, G; Randich, S; Bensby, T; Francois, P; Koposov, S E; Recio-Blanco, A; Bayo, A; Carraro, G; Casey, A; Costado, T; Franciosini, E; Hourihane, A; de Laverny, P; Lewis, J; Lind, K; Magrini, L; Monaco, L; Morbidelli, L; Sacco, G G; Worley, C; Zaggia, S; Mikolaitis, S

    2016-01-01

    We analyse the kinematics of $\\sim 2000$ giant stars in the direction of the Galactic bulge, extracted from the Gaia-ESO survey in the region $-10^\\circ \\lesssim \\ell \\lesssim 10^\\circ$ and $-11^\\circ \\lesssim b \\lesssim -3^\\circ$. We find distinct kinematic trends in the metal rich ($\\mathrm{[M/H]}>0$) and metal poor ($\\mathrm{[M/H]}<0$) stars in the data. The velocity dispersion of the metal-rich stars drops steeply with latitude, compared to a flat profile in the metal-poor stars, as has been seen previously. We argue that the metal-rich stars in this region are mostly on orbits that support the boxy-peanut shape of the bulge, which naturally explains the drop in their velocity dispersion profile with latitude. The metal rich stars also exhibit peaky features in their line-of-sight velocity histograms, particularly along the minor axis of the bulge. We propose that these features are due to stars on resonant orbits supporting the boxy-peanut bulge. This conjecture is strengthened through the comparison ...

  16. 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...

  17. A High-velocity Bulge RR Lyrae Variable on a Halo-like Orbit

    Science.gov (United States)

    Kunder, Andrea; Rich, R. M.; Hawkins, K.; Poleski, R.; Storm, J.; Johnson, C. I.; Shen, J.; Li, Z.-Y.; Cordero, M. J.; Nataf, D. M.; Bono, G.; Walker, A. R.; Koch, A.; De Propris, R.; Udalski, A.; Szymański, M. K.; Soszyński, I.; Pietrzyński, G.; Ulaczyk, K.; Wyrzykowski, Ł.; Pietrukowicz, P.; Skowron, J.; Kozłowski, S.; Mróz, P.

    2015-07-01

    We report on the RR Lyrae variable star, MACHO 176.18833.411, located toward the Galactic bulge and observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay, which has the unusual radial velocity of -372 ± 8 km s-1 and true space velocity of -482 ± 22 km s-1 relative to the Galactic rest frame. Located less than 1 kpc from the Galactic center and toward a field at (l, b) = (3, -2.5), this pulsating star has properties suggesting it belongs to the bulge RR Lyrae star population, yet a velocity indicating it is abnormal, at least with respect to bulge giants and red clump stars. We show that this star is most likely a halo interloper and therefore suggest that halo contamination is not insignificant when studying metal-poor stars found within the bulge area, even for stars within 1 kpc of the Galactic center. We discuss the possibility that MACHO 176.18833.411 is on the extreme edge of the bulge RR Lyrae radial velocity distribution, and also consider a more exotic scenario in which it is a runaway star moving through the Galaxy.

  18. A HIGH-VELOCITY BULGE RR LYRAE VARIABLE ON A HALO-LIKE ORBIT

    Energy Technology Data Exchange (ETDEWEB)

    Kunder, Andrea; Storm, J. [Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam (Germany); Rich, R. M. [Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, CA 90095-1562 (United States); Hawkins, K. [Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom); Poleski, R. [Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States); Johnson, C. I. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Shen, J.; Li, Z.-Y. [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China); Cordero, M. J. [Astronomisches Rechen-Institut: Zentrum für Astronomie, Mönchhofstr. 12-14, D-69120 Heidelberg (Germany); Nataf, D. M. [Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611 (Australia); Bono, G. [Dipartimento di Fisica, Universita di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma (Italy); Walker, A. R. [Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena (Chile); Koch, A. [Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, D-69117 Heidelberg (Germany); De Propris, R. [Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Turku (Finland); Udalski, A.; Szymanski, M. K.; Soszynski, I.; Pietrzynski, G.; Ulaczyk, K.; Wyrzykowski, Ł. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); and others

    2015-07-20

    We report on the RR Lyrae variable star, MACHO 176.18833.411, located toward the Galactic bulge and observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay, which has the unusual radial velocity of −372 ± 8 km s{sup −1} and true space velocity of −482 ± 22 km s{sup −1} relative to the Galactic rest frame. Located less than 1 kpc from the Galactic center and toward a field at (l, b) = (3, −2.5), this pulsating star has properties suggesting it belongs to the bulge RR Lyrae star population, yet a velocity indicating it is abnormal, at least with respect to bulge giants and red clump stars. We show that this star is most likely a halo interloper and therefore suggest that halo contamination is not insignificant when studying metal-poor stars found within the bulge area, even for stars within 1 kpc of the Galactic center. We discuss the possibility that MACHO 176.18833.411 is on the extreme edge of the bulge RR Lyrae radial velocity distribution, and also consider a more exotic scenario in which it is a runaway star moving through the Galaxy.

  19. Shedding Light on Lithium Evolution: The Globular Cluster Perspective

    CERN Document Server

    Korn, A J

    2012-01-01

    I shall review what has been learnt during 20 years of lithium observations in stars belonging to metal-poor globular clusters. The focus will be on little evolved main-sequence, turnoff-point (TOP) and subgiant-branch (SGB) stars expected to display Spite-plateau lithium abundances like those found in the majority of field stars of similar metallicities. But is the Spite plateau of globular clusters the same as those of field stars? What effect does, e.g., cluster-internal pollution have on lithium abundances in the now dominant second generation of stars? It will be shown that it is primarily our incomplete knowledge of the temperature scale of Population II stars which currently limits the diagnostic power of globular clusters as regards the stellar-surface evolution of lithium.

  20. Variable stars in the VVV globular clusters. I. 2MASS-GC 02 and Terzan 10

    Energy Technology Data Exchange (ETDEWEB)

    Alonso-García, Javier; Dékány, István; Catelan, Márcio; Ramos, Rodrigo Contreras; Gran, Felipe; Leyton, Paul; Minniti, Dante [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile); Amigo, Pía, E-mail: jalonso@astro.puc.cl, E-mail: idekany@astro.puc.cl, E-mail: mcatelan@astro.puc.cl, E-mail: rcontrer@astro.puc.cl, E-mail: fgran@astro.puc.cl, E-mail: pia.amigo@uv.cl, E-mail: pleyton@astro.puc.cl, E-mail: dante@astrofisica.cl [Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile)

    2015-03-01

    The VISTA Variables in the Vía Láctea (VVV) ESO Public Survey is opening a new window to study inner Galactic globular clusters (GCs) using their variable stars. These GCs have been neglected in the past due to the difficulties caused by the presence of elevated extinction and high field stellar densities in their lines of sight. However, the discovery and study of any present variables in these clusters, especially RR Lyrae stars, can help to greatly improve the accuracy of their physical parameters. It can also help to shed some light on the questions raised by the intriguing Oosterhoff dichotomy in the Galactic GC system. In a series of papers we plan to explore variable stars in the GCs falling inside the field of the VVV survey. In this first paper, we search for and study the variables present in two highly reddened, moderately metal-poor, faint, inner Galactic GCs: 2MASS-GC 02 and Terzan 10. We report the discovery of sizable populations of RR Lyrae stars in both GCs. We use near-infrared period–luminosity relations to determine the color excess of each RR Lyrae star, from which we obtain both accurate distances to the GCs and the ratios of the selective-to-total extinction in their directions. We find the extinction toward both clusters to be elevated, non-standard, and highly differential. We also find both clusters to be closer to the Galactic center than previously thought, with Terzan 10 being on the far side of the Galactic bulge. Finally, we discuss their Oosterhoff properties, and conclude that both clusters stand out from the dichotomy followed by most Galactic GCs.

  1. 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.

  2. Sistema de cúmulos globulares de la galaxia lenticular NGC 6861: en busca de indicios sobre la formación de las S0s.

    Science.gov (United States)

    Escudero, C. G.; Faifer, F. R.; Bassino, L. P.; Calderón, J. P.; Caso, J. P.

    We present a preliminar photometric study of the globular cluster system (GCS), associated to the lenticular galaxy (S0) NGC 6861, which is located in a low density environment (d˜31.8 Mpc). It is based on GEMINI/GMOS images (GS-2010B-Q-2: PI Lilia P. Bassino) in the filters g', r', i' of three fields, one of them centered in the galaxy. We find a large number of GCs candidates and detect the presence of at least two sub-populations of GCs (``blue''/metal-poor and ``red''/metal-rich). The spatial distribution of ``red'' candidates presents a higher concentration toward the galaxy (associated to the bulge?), while the distribution of ``blue'' candidates is more homogeneus over the three fields (associated to the halo?). In the color-magnitud diagram, the ``blue'' GC candidates show a possible mass-luminosity relation, known as ``blue-tilt'', probably detected for the first time in a lenticular galaxy. FULL TEXT IN SPANISH

  3. The s-Process Nucleosynthesis in Extremely Metal-Poor Stars as the Generating Mechanism of Carbon Enhanced Metal-Poor Stars

    CERN Document Server

    Suda, Takuma; Fujimoto, Masayuki Y

    2016-01-01

    The origin of carbon-enhanced metal-poor (CEMP) stars plays a key role in characterising the formation and evolution of the first stars and the Galaxy since the extremely-poor (EMP) stars with [Fe/H] \\leq -2.5 share the common features of carbon enhancement in their surface chemical compositions. The origin of these stars is not yet established due to the controversy of the origin of CEMP stars without the enhancement of s-process element abundances, i.e., so called CEMP-no stars. In this paper, we elaborate the s-process nucleosynthesis in the EMP AGB stars and explore the origin of CEMP stars. We find that the efficiency of the s-process is controlled by O rather than Fe at [Fe/H] \\lesssim -2. We demonstrate that the relative abundances of Sr, Ba, Pb to C are explained in terms of the wind accretion from AGB stars in binary systems.

  4. 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...

  5. 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.

  6. 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.

  7. How important are metal-poor AGB stars as cosmic dust producers?

    CERN Document Server

    Mattsson, Lars; Andersen, Anja C

    2015-01-01

    The efficiency of dust formation in oxygen-rich AGB stars should (in theory) be metallicity dependent since they are not producing their own raw material for dust production. Metal-poor carbon stars may not be very efficient dust producers either, because of more radiative heating of the grains forming in their atmospheres. We have just confirmed that inefficient dust and wind formation in simulations of metal-poor carbon stars is a real physical effect, albeit within the limitations of our simulations. Taken at face value, this implies that the amount of dust supplied by low-metallicity AGB stars to the build up of the cosmic dust component is clearly limited. Consequently, one may also ask how large a contribution AGB stars can make in general, when compared to recent observations of cosmic dust, which are suggesting major contributions from other sources?

  8. The elusive origin of Carbon-Enhanced Metal-Poor stars

    CERN Document Server

    Abate, C; Izzard, R G; Mohamed, S S; de Mink, S E

    2013-01-01

    Carbon-enhanced metal-poor (CEMP) stars count for 9-25% of all the very metal-poor stars of the halo. In at least some CEMP stars the chemical enrichment is believed to be due to wind mass transfer in the past from an AGB donor star on to a low-mass companion. However, binary population synthesis models predict much lower CEMP fractions. As an alternative to the canonical Bondi-Hoyle-Lyttleton (BHL) wind accretion model, recent hydrodynamical simulations suggest an efficient mode of wind mass transfer, called wind Roche-lobe overflow (WRLOF), can reproduce observations of AGB winds in binary systems. We use our population synthesis model to test the consequences of WRLOF on a population of CEMP stars. Compared to previous predictions based on the BHL model we find a modest increase of the fraction of CEMP stars and substantial differences in the distributions of carbon and periods in the population of CEMP stars.

  9. 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.

  10. Carbon-enhanced metal-poor stars: the most pristine objects?

    Science.gov (United States)

    Spite, M.; Caffau, E.; Bonifacio, P.; Spite, F.; Ludwig, H.-G.; Plez, B.; Christlieb, N.

    2013-04-01

    Context. Carbon-enhanced metal-poor stars (CEMP) form a significant proportion of the metal-poor stars, their origin is not well understood, and this carbon-enhancement appears in stars that exhibit different abundance patterns. Aims: Three very metal-poor C-rich turnoff stars were selected from the SDSS survey, observed with the ESO VLT (UVES) to precisely determine the element abundances. In turnoff stars (unlike giants) the carbon abundance has not been affected by mixing with deep layers and is therefore easier to interpret. Methods: The analysis was performed with one dimensional (1D) local thermodynamical equilibrium (LTE) static model atmospheres. When available, non-LTE corrections were applied to the classical LTE abundances. The 3D effects on the CH and CN molecular bands were computed using hydrodynamical simulations of the stellar atmosphere (CO5BOLD) and are found to be very important. Results: To facilitate a comparison with previous results, only 1D abundances are used in the discussion. The abundances (or upper limits) of the elements enable us to place these stars in different CEMP classes. The carbon abundances confirm the existence of a plateau at A(C)= 8.25 for [Fe/H] ≥ -3.4. The most metal-poor stars ([Fe/H] < -3.4) have significantly lower carbon abundances, suggesting a lower plateau at A(C) ≈ 6.5. Detailed analyses of a larger sample of very low metallicity carbon-rich stars are required to confirm (or refute) this possible second plateau and specify the behavior of the CEMP stars at very low metallicity. Based on observations obtained with the ESO Very Large Telescope at Paranal Observatory, Chile (ID 087.D-0123(A).Table 5 is available in electronic form at http://www.aanda.org

  11. Origins of the Thick Disk as Traced by the Alpha Elements of Metal-poor Giant Stars Selected from Rave

    NARCIS (Netherlands)

    Ruchti, G. R.; Fulbright, J. P.; Wyse, R. F. G.; Gilmore, G. F.; Bienaymé, O.; Binney, J.; Bland-Hawthorn, J.; Campbell, R.; Freeman, K. C.; Gibson, B. K.; Grebel, E. 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

    Theories of thick-disk formation can be differentiated by measurements of stellar elemental abundances. We have undertaken a study of metal-poor stars selected from the RAVE spectroscopic survey of bright stars to establish whether or not there is a significant population of metal-poor thick-disk st

  12. The Stellar Populations of Nuclei, Globular Clusters, and Stars in dE Galaxies in Virgo and Fornax

    Science.gov (United States)

    Whitfield Miller, Bryan; Hyazinth Puzia, Thomas; Hilker, Michael; Sanchez-Janssen, Ruben; Kissler-Patig, Markus

    2015-08-01

    We present ages and metallicities for globular clusters, nuclei, and underlying stars in nucleated dwarf elliptical galaxies (dE,N) in the Virgo and Fornax Cluster based on Lick/IDS index measurements and SSP models. Gemini/GMOS spectroscopy shows that the globular clusters are mostly old and metal-poor, very similar to the globular clusters in the Milky Way halo. The nuclei and underlying stars tend to be more metal-rich than the globular clusters and have a wide range of ages. The [α/Fe] ratios for both the globular clusters and nuclei range between 0.0 and 0.3. Formation scenarios for globular clusters and nuclei will be discussed.

  13. Destruction of the galactic globular cluster system

    CERN Document Server

    Gnedin, O Y; Gnedin, Oleg Y; Ostriker, Jeremiah P

    1996-01-01

    We investigate the dynamical evolution of the Galactic Globular Cluster System in considerably greater detail than has been done hitherto, finding that destruction rates are significantly larger than given by previous estimates. More than half of the present clusters (52%-58% for the OC galactic model, and 75%-86% for the BSS model) will be destroyed in the next Hubble time. For the evolution of individual clusters we use a Fokker-Planck code including two-body relaxation, tidal truncation of clusters, compressive gravitational shocks while clusters pass through the Galactic disk, and tidal shocks due to passage close to the bulge. Gravitational shocks are treated comprehensively, using a recent result by Kundic & Ostriker (1995) that the shock-induced relaxation term, driving an additional dispersion of energies, is generally more important than the usual energy shift term. We discuss some implications for a past history of the Globular Cluster System, and the initial distribution of the destruction time...

  14. CS 30322-023: an ultra metal-poor TP-AGB star?

    CERN Document Server

    Masseron, T; Famaey, B; Goriely, S; Plez, B; Siess, L; Beers, T C; Primas, F; Jorissen, A

    2006-01-01

    With [Fe/H] = -3.5, CS 30322-023 is the most metal-poor star to exhibit a clear s-process signature and the most metal-poor ``lead star'' known. CS 30322-023 is also remarkable in having the lowest surface gravity (log g <= -0.3) among the metal-poor stars studied to date. The available evidence indicates that this star is presently a thermally-pulsing asymptotic giant branch (TP-AGB) star, with no strong indication of binarity thus far (although a signal of period 192 d is clearly present in the radial-velocity data, this is likely due to pulsation of the stellar envelope). We show that low-mass TP-AGB stars are not expected to be exceedingly rare in a magnitude-limited sample such as the HK survey, because their high luminosities make it possible to sample them over a very large volume. The strong N overabundance and the low 12C/13C ratio (4) in this star is typical of the operation of the CN cycle. Coupled with a Na overabundance and the absence of a strong C overabundance, this pattern seems to imply t...

  15. The Chandra Galactic Bulge Survey

    NARCIS (Netherlands)

    Hynes, Robert I.; Jonker, P.G.; Bassa, C. G.; Dieball, A.; Greiss, S.; Maccarone, T. J.; Nelemans, G.; Steeghs, D.; Torres, M. A. P.; Britt, C. T.; Clem, J. L.; Gossen, L.; Grindlay, J. E.; Groot, P.J.; Kuiper, L.; Kuulkers, E.; Mendez, M.; Mikles, V. J.; Ratti, E. M.; Rea, N.; van Haaften, L.; Wijnands, R.; in't Zand, J. J. M.

    2011-01-01

    The Chandra Galactic Bulge Survey (CGBS) is a shallow but wide survey of two approximately 6x1 degree strips of the Galactic Bulge about a degree above and below the plane. The survey by design targets regions where extinction and crowding are manageable and optical counterparts are accessible to de

  16. The Chandra Galactic Bulge Survey

    NARCIS (Netherlands)

    Hynes, Robert I.; Jonker, P. G.; Bassa, C. G.; Nelemans, G.; Steeghs, D.; Torres, M. A. P.; Maccarone, T. J.; Greiss, S.; Clem, J.; Dieball, A.; Mikles, V. J.; Britt, C. T.; Gossen, L.; Collazzi, A. C.; Wijnands, R.; In't Zand, J. J. M.; Mendez, M.; Rea, N.; Kuulkers, E.; Ratti, E. M.; van Haaften, L. M.; Heinke, C.; Ozel, F.; Groot, P. J.; Verbunt, F.

    2012-01-01

    The Chandra Galactic Bulge Survey (GBS) is a shallow but wide survey of two approximately 6x1 degree strips of the Galactic Bulge about a degree above and below the plane. The survey by design targets regions where extinction and crowding are manageable and optical counterparts are accessible to det

  17. PROPER MOTIONS IN THE GALACTIC BULGE: PLAUT'S WINDOW

    Directory of Open Access Journals (Sweden)

    K. Vieira

    2009-01-01

    Full Text Available A proper motion study of a eld of 20' x20' inside Plaut's low extinction window (l,b=(0 ;-8 , has been completed. Relative proper motions and photographic BV photometry have been derived for -21; 000 stars reaching to V - 20:5 mag, based on the astrometric reduction of 43 photographic plates, spanning over 21 years of epoch di erence. Proper motion errors are typically 1 mas yr-1. Cross-referencing with the 2MASS catalog yielded a sample of - 8700 stars, from which predominantly disk and bulge subsamples were selected photometrically from the JH color-magnitude diagram. The two samples exhibited di erent proper-motion distributions, with the disk displaying the expected re ex solar motion. Galactic rotation was also detected for stars between -2 and -3 kpc from us. The bulge sample, represented by red giants, has an intrinsic proper motion dispersion of (l; b = (3:39; 2:91 = (0:11; 0:09 mas yr-1, which is in good agreement with previous results. A mean distance of 6:37+0:87 -0:77 kpc has been estimated for the bulge sample, based on the observed K magnitude of the horizontal branch red clump. The metallicity [M=H] distribution was also obtained for a subsample of 60 bulge giants stars, based on calibrated photometric indices. The observed [M=H] shows a peak value at [M=H]-0:1 with an extended metal poor tail and around 30% of the stars with supersolar metallicity. No change in proper motion dispersion was observed as a function of [M=H]. We are currently in the process of obtaining CCD UBV RI photometry for the entire proper-motion sample of - 21; 000 stars.

  18. VIMOS mosaic integral-field spectroscopy of the bulge and disc of the early-type galaxy NGC 4697

    Science.gov (United States)

    Spiniello, C.; Napolitano, N. R.; Coccato, L.; Pota, V.; Romanowsky, A. J.; Tortora, C.; Covone, G.; Capaccioli, M.

    2015-09-01

    We present an integral-field study of the internal structure, kinematics and stellar population of the almost edge-on, intermediate-luminosity (L★) elliptical galaxy NGC 4697. We build extended two-dimensional (2D) maps of the stellar kinematics and line strengths of the galaxy up to ˜0.7 effective radii (Reff) using a mosaic of eight VIMOS (VIsible Multi-Objects Spectrograph, on the Very Large Telescope) integral-field unit pointings. We find clear evidence for a rotation-supported structure along the major axis from the 2D kinematical maps, confirming the previous classification of this system as a `fast rotator'. We study the correlations between the third and fourth Gauss-Hermite moments of the line-of-sight velocity distribution (LOSVD) h3 and h4 with the rotation parameter (V/σ), and compare our findings to hydrodynamical simulations. We find remarkable similarities to predictions from gas-rich mergers. Based on photometry, we perform a bulge/disc decomposition and study the stellar population properties of the two components. The bulge and the disc show different stellar populations, with the stars in the bulge being older (age_bulge=13.5^{+1.4}_{-1.4} Gyr, age_disc=10.5^{+1.6}_{-2.0} Gyr) and more metal poor ({[M/H]_{bulge}} = -0.17^{+0.12}_{-0.1}, {[M/H]_{disc}} = -0.03^{+0.02}_{-0.1}). The evidence of a later-formed, more metal-rich disc embedded in an older, more metal poor bulge, together with the LOSVD structure, supports a mass assembly scenario dominated by gas-rich minor mergers and possibly with a late gas-rich major merger that left a previously rapidly rotating system unchanged. The bulge and the disc do not show signs of different stellar initial mass function (IMF) slopes, and both match well with a Milky Way-like IMF.

  19. Forming Globular Cluster Systems in a Semi-analytic Scheme

    CERN Document Server

    Beasley, M A; Forbes, D A; Sharples, R M; Frenk, C S; Beasley, Michael A.; Baugh, Carlton M.; Forbes, Duncan A.; Sharples, Ray M.; Frenk, Carlos S.

    2002-01-01

    We apply the semi-analytical galaxy formation code of Cole et al. to investigate the formation of globular cluster (GC) systems in hierarchical clustering scenarios. The nature of the model allows us to investigate the properties of GC systems and their parent galaxies within a cosmological framework, over a wide dynamic range of mass and time resolution. Assuming GCs form during mergers of gaseous systems, the metal-rich peak of the classical 'bimodal' metallicity distribution of GCs naturally falls out of our model, where such merging occurs over a wide range of redshifts. The physical origin of old, metal-poor GCs (the metal-poor peak) is harder to understand, since their formation must be decoupled from the ongoing star formation in these systems at high redshift (z~5). Within the context of semi-analytic models in general, a possible solution lies in a cut-off in the GC formation efficiency at a characteristic local star formation rate.

  20. Constraints on mass loss of globular clusters in dwarf galaxies

    CERN Document Server

    Larsen, S S; Brodie, J P

    2013-01-01

    The Fornax dwarf spheroidal galaxy is well known for its very high globular cluster specific frequency, SN=26. Furthermore, while the field star metallicity distribution peaks at [Fe/H]=-1, four of the five GCs have [Fe/H]<-2. Only about 5 percent of the field stars have such low metallicities. Hence, a very large fraction of about 1/5-1/4 of the most metal-poor stars belong to the four most metal-poor GCs. This implies that these clusters could, at most, have been a factor of 4-5 more massive initially. A second, even more extreme case may be the IKN dwarf galaxy where SN=124. Although metallicities are not accurately known, the GCs account for about 13 percent of the total V-band luminosity of IKN.

  1. Formation History of Metal-Poor Halo Stars with Hierarchical Model and the Effect of ISM accretion on the Most Metal-Poor Stars

    CERN Document Server

    Komiya, Yutaka; 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. (2) A high mass IMF of peak mass ~10Msun with the contribution of binaries, derived from the statistics of carbon enhanced EMP stars (Komiya et al. 2007), predicts the frequency of low-mass survivors consistent with the number of EMP stars observed for -4~<[Fe/H]~<-2.5. (3) The stars formed from primordial gas before the first supernova explosions in their host mini-halos are assigned to the HMP stars with [Fe/H]~-5. (4) There is no indication of significant changes in the IMF and the binary contribution at metallic...

  2. Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

    Science.gov (United States)

    Hopkins, Philip F.; Conroy, Charlie

    2017-02-01

    Large dust grains can fluctuate dramatically in their local density, relative to the 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 (>100 Å) under these conditions. This can have important consequences for star formation and stellar metal abundances in extremely metal-poor stars. Low-mass stars can form in dust-enhanced regions almost immediately after some dust forms even if the galaxy-average metallicity is too low for fragmentation to occur. We argue that the metal 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 and/or fluctuate almost independently. Remarkably, the otherwise puzzling abundance patterns of some metal-poor stars can be well fit by standard IMF-averaged core-collapse SNe yields if we allow for fluctuating local dust-to-gas ratios. We also show that the observed log-normal distribution of enhancements in these species agrees with our simulations. Moreover, we confirm that Mg and Si are correlated in these stars the abundance ratios are similar to those in local silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure SNe yields, shows very large enhancements and variations up to factors of ≳100 as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. Together, this suggests that (1) dust exists in second-generation star formation, (2) local dust-to-gas ratio fluctuations occur in protogalaxies and can be important for star formation, and (3) the light element abundances of these stars may be affected by the local chemistry of dust where they formed, rather than directly tracing nucleosynthesis from earlier

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

    Science.gov (United States)

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

    2016-08-01

    Context. 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. Aims: Only two dozen stars with ([Fe/H] cases, at high resolution on 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. Results: We find consistency between the metallicities estimated from SDSS and those from new data at the level of 0.3 dex. The analysis of medium resolution data obtained with ISIS on the WHT allows us to refine the metallicities and in some cases measure other elemental abundances. Our sample contains 11 new metal-poor stars with [Fe/H] < -3.0, one of them with an estimated metallicity of [Fe/H] ~ -4.0. We also discuss metallicity discrepancies of some stars in common with previous works in the literature. Only one of these stars is found to be C-enhanced at about [C/Fe] ~ + 1, whereas the other metal-poor stars show C abundances at the level of [C/Fe] ~ + 0.45. 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.The reduced spectra as FITS files are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/593/A10

  4. Hot, Massive Stars in the Extremely Metal-Poor Galaxy, I Zw 18

    Science.gov (United States)

    Heap, Sara R.; Malumuth, Eliot M.

    2010-01-01

    The carbon-enhanced metal-poor galaxy, I Zw 18, is the Rosetta Stone for understanding galaxies in the early universe by providing constraints on the IMF of massive stars, the role of galaxies in reionization of the universe, mixing of newly synthesized material in the ISM, and gamma-ray bursts at low metallicity, and on the earliest generations of stars producing the observed abundance pattern. We describe these constraints as derived from analyses of HST/COS spectra of I Zw 18 including stellar atmosphere analysis and photo-ionization modeling of both the emission and absorption spectra of the nebular material and interstellar medium.

  5. Kinematics of Extremely Metal-poor Galaxies: Evidence for Stellar Feedback

    CERN Document Server

    Olmo-Garcia, A; Munoz-Tunon, C; Filho, M E; Elmegreen, B G; Elmegreen, D M; Perez-Montero, E; Mendez-Abreu, J

    2016-01-01

    The extremely metal-poor (XMP) galaxies analyzed in a previous paper have large star-forming regions with a metallicity lower than the rest of the galaxy. Such a chemical inhomogeneity reveals the external origin of the metal-poor gas fueling star formation, possibly indicating accretion from the cosmic web. This paper studies the kinematic properties of the ionized gas in these galaxies. Most XMPs have rotation velocity around a few tens of km/s. The star-forming regions appear to move coherently. The velocity is constant within each region, and the velocity dispersion sometimes increases within the star-forming clump towards the galaxy midpoint, suggesting inspiral motion toward the galaxy center. Other regions present a local maximum in velocity dispersion at their center, suggesting a moderate global expansion. The Halpha line wings show a number of faint emission features with amplitudes around a few percent of the main Halpha component, and wavelength shifts between 100 and 400 km/s. The components are ...

  6. Mass-loss predictions for evolved very metal-poor massive stars

    CERN Document Server

    Muijres, Lianne; de Koter, A; Hirschi, R; Langer, N; Yoon, S -C

    2012-01-01

    (shortened) The first couple of stellar generations may have been massive, of order 100 Msun, and to have played a dominant role in galaxy formation and the chemical enrichment of the early Universe. Some fraction of these objects may have died as pair-instability supernovae or gamma-ray bursts. The winds if these stars may have played an important role in determining these outcomes. As the winds are driven by radiation pressure on spectral lines, their strengths are expected to vary with metallicity. Until now, most mass-loss predictions for metal-poor O-type stars have assumed a scaled-down solar-abundance pattern. However, Population III evolutionary tracks show significant surface enrichment through rotational mixing of CNO-processed material, because even metal-poor stars switch to CNO-burning early on. We address the question of whether the CNO surface enhanced self-enrichment in the first few generations of stars could impact their mass-loss properties. For this, we employ Monte Carlo simulations to es...

  7. 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...

  8. 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...

  9. The Impact of Carbon Enhancement on Extra Mixing in Metal-Poor Stars

    CERN Document Server

    Denissenkov, Pavel A

    2007-01-01

    We critically examine the constraints imposed by carbon-enhanced metal-poor (CEMP) stars on the mixing mechanisms that operate in red giants. CEMP stars are created when the surface layers of a metal-poor dwarf are enriched with He-burning products via mass transfer from an evolved donor. The difference between main sequence (MS) and red giant CEMP abundances can be used as a diagnostic of the timescale for the mixing of the processed material into stellar interiors on the MS. Abundance trends with luminosity among red giant CEMP stars test theories of canonical extra mixing for low mass giants with a high bulk metallicity. We find a significant dilution in CN enrichment in giant CEMP stars relative to their MS precursors, and take this as evidence that thermohaline mixing induced by mean molecular weight inversions is ineffective in CEMP stars. This contradicts models that rely on efficient thermohaline mixing induced by small mu gradients in red giants, because such models would predict that MS CEMP stars w...

  10. Ongoing Large Surveys for Metal-Poor Stars in the Galactic Halo

    CERN Document Server

    Christlieb, N; Christlieb, Norbert; Beers, Timothy C.

    2000-01-01

    We report on two major surveys for metal-poor stars in the galactic halo, the HK survey, and the Hamburg/ESO survey, which have been undertaken in order to provide targets for high-resolution spectroscopy with the Subaru HDS and other large telescopes. We compare basic properties of these two surveys and their current status, and add some historical remarks. The candidate selection procedures of both surveys are described in detail. We evaluate the candidate selection by comparing effective yields (EYs) of the survey techniques for the identification of metal-poor stars. It is found that EY for stars below [Fe/H]=-2.0 in the HES can be up to 80% for stars selected by automatic classification from machine-scanned unwidened plates, whereas in the HK survey, where stars are selected by visual inspection of widened survey plates, the EY is between 11% and 32%, depending on whether a pre-selection based on BV photometry has been applied. Finally, we describe techniques used for determining stellar parameters of th...

  11. Diversity of abundance patterns of neutron-capture elements in very metal-poor stars

    Science.gov (United States)

    Aoki, Misa; Aoki, Wako; Ishimaru, Yuhri; Wanajo, Shinya

    2014-05-01

    Observations of Very Metal-Poor stars indicate that there are at least two sites to r-process; "weak r-process" and "main r-process". A question is whether these two are well separated or there exists a variation in the r-process. We present the results of abundance analysis of neutron-capture elements in the two Very Metal-Poor stars HD107752 and HD110184 in the Milky Way halo observed with the Subaru Telescope HDS. The abundance patterns show overabundace at light n-capture elements (e.g. Sr, Y), inferring the element yielding of weak r-process, while heavy neutron-capture elements (e.g. Ba, Eu) are deficient; however, the overabundance of light ones is not as significant as that previously found in stars representing the weak r-process (e.g. HD122563; Honda et al. 2006). Our study show diversity in the abundance patterns from light to heavy neutron-capture elements in VMP stars, suggesting a variation in r-process, which may depend on electron fraction of environment.

  12. Spectroscopic Studies of Extremely Metal-Poor Stars with Subaru/HDS:I. Observational Data

    CERN Document Server

    Honda, S; Ando, H; Izumiura, H; Kajino, T; Kambe, E; Kawanomoto, S; Noguchi, K; Okita, K; Sadakane, K; Sato, B; Takada-Hidai, M; Takeda, Y; Watanabe, E; Beers, T C; Norris, J E; Ryan, S G

    2004-01-01

    We have obtained high-resolution (R $\\simeq$ 50,000 or 90,000), high-quality (S/N $\\ga$ 100) spectra of 22 very metal-poor stars ([Fe/H] $\\la$ -2.5) with the High Dispersion Spectrograph fabricated for the 8.2m Subaru Telescope. The spectra cover the wavelength range from 3500 to 5100 {\\AA}; equivalent widths are measured for isolated lines of numerous elemental species, including the $\\alpha$ elements, the iron-peak elements, and the light and heavy neutron-capture elements. Errors in the measurements and comparisons with previous studies are discussed. These data will be used to perform detailed abundance analyses in the following papers of this series. Radial velocities are also reported, and are compared with previous studies. At least one moderately r-process-enhanced metal-poor star, HD 186478, exhibits evidence of a small-amplitude radial velocity variation, confirming the binary status noted previously. During the course of this initial program, we have discovered a new moderately r-process-enhanced, ...

  13. Lithium Abundances of Extremely Metal-Poor Turn-off Stars

    CERN Document Server

    Aoki, Wako; Beers, Timothy C; Christlieb, Norbert; Inoue, Susumu; Perez, Ana E Garcia; Norris, John E; Carollo, Daniela

    2009-01-01

    We have determined Li abundances for eleven metal-poor turn-off stars, among which eight have [Fe/H]<-3, based on LTE analyses of high-resolution spectra obtained with the HDS on the Subaru telescope. The Li abundances for four of these eight stars are determined for the first time by this study. Effective temperatures are determined by a profile analysis of H-alpha and H-beta. While seven stars have Li abundances as high as the Spite Plateau value, the remaining four objects with [Fe/H] <-3 have A(Li)=log(Li/H)+12 ~< 2.0, confirming the existence of extremely metal-poor turn-off stars having low Li abundances, as reported by previous work. The average of the Li abundances for stars with [Fe/H]<-3 is lower by 0.2 dex than that of the stars with higher metallicity. No clear constraint on the metallicity dependence or scatter of the Li abundances is derived from our measurements for the stars with [Fe/H]<-3. Correlations of the Li abundance with effective temperatures, with abundances of Na, Mg a...

  14. Chemical Abundance Analysis of the Extremely Metal-Poor Star HE 1300+0157

    CERN Document Server

    Frebel, A; Aoki, W; Honda, S; Bessell, M S; Takada-Hidai, M; Beers, T C; Christlieb, N; Frebel, Anna; Norris, John E.; Aoki, Wako; Honda, Satoshi; Bessell, Michael S.; Takada-Hidai, Masahide; Beers, Timothy C.; Christlieb, Norbert

    2006-01-01

    We present a detailed chemical abundance analysis of HE 1300+0157, a subgiant with [Fe/H]=-3.9. From a high-resolution, high-S/N Subaru/HDS spectrum we find the star to be enriched in C ([C/Fe]_1D ~ +1.4) and O ([O/Fe]_1D ~ +1.8). With the exception of these species, HE 1300+0157 exhibits an elemental abundance pattern similar to that found in many other very and extremely metal-poor stars. The Li abundance is lower than the Spite-plateau value, in agreement with expectation for its evolutionary status. Of particular interest, no neutron-capture elements are detected in HE 1300+0157. This type of abundance pattern has been found by recent studies in several other metal-poor giants. We suggest that HE 1300+0157 is an unevolved example of this group of stars, which exhibit high C abundances together with low (or absent) abundances of neutron-capture elements. Several potential enrichment scenarios are presented. The low neutron-capture elements, including Sr, Ba, and Pb, suggests that the carbon excess observed...

  15. Diversity of abundance patterns of neutron-capture elements in very metal-poor stars

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, Misa; Ishimaru, Yuhri [International Christian University 10-2, Osawa, Mitaka, Tokyo 181-0015 (Japan); Aoki, Wako; Wanajo, Shinya [National Astronomical Observatory of Japan (NAOJ) 2-21-1, Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2014-05-02

    Observations of Very Metal-Poor stars indicate that there are at least two sites to r-process; “weak r-process” and “main r-process”. A question is whether these two are well separated or there exists a variation in the r-process. We present the results of abundance analysis of neutron-capture elements in the two Very Metal-Poor stars HD107752 and HD110184 in the Milky Way halo observed with the Subaru Telescope HDS. The abundance patterns show overabundace at light n-capture elements (e.g. Sr, Y), inferring the element yielding of weak r-process, while heavy neutron-capture elements (e.g. Ba, Eu) are deficient; however, the overabundance of light ones is not as significant as that previously found in stars representing the weak r-process (e.g. HD122563; Honda et al. 2006). Our study show diversity in the abundance patterns from light to heavy neutron-capture elements in VMP stars, suggesting a variation in r-process, which may depend on electron fraction of environment.

  16. Detailed Iron-Group Abundances in a Very Metal-Poor Main Sequence Turnoff Star

    Science.gov (United States)

    Sneden, Chris; Roederer, Ian U.; Boesgaard, Ann M.; Lawler, James E.; Den Hartog, Elizabeth; Cowan, John J.; Sobeck, Jennifer

    2017-01-01

    We have obtained Keck HIRES and HST STIS high resolution, high signal-to-noise spectra of the very metal-poor ([Fe/H] ~ -2.9) main-sequence turnoff star BD+03 740. A detailed chemical composition analysis based on synthetic spectrum computations has been conducted. Our initial focus has been on the iron-group elements in the Z = 21-28 range. This study takes advantage of recent improvements in neutral and ionzied species transition data for all of these elements except Sc (Z = 21) by the Wisconsin atomic physics group (see a companion presentation on Cr II at this meeting). Several metal-poor abundance surveys have concluded that there are large overabundances of Co and underabundances of Cr with respect to Fe for stars with [Fe/H] synthesis in the Galaxy.This work has been supported by HST STScI Program GO-14232; and NSF grants AST-1211585 and AST-1616040 to CS; AST-1516182 to JEL and EDH; NASA grant NNX16AE96G to JEL

  17. 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...

  18. 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 ...

  19. Ultra-Luminous X-Ray Sources in the Most Metal Poor Galaxies

    CERN Document Server

    Prestwich, A H; Zezas, A; Jackson, F E; Roberts, T P; Foltz, R; Linden, T; Kalogera, V

    2013-01-01

    Ultra-Luminous X-ray sources (ULX) are X-ray binaries with Lx>1E^39 ergs/s. The most spectacular examples of ULX occur in starburst galaxies and are now understood to be young, luminous High Mass X-ray Binaries. The conditions under which ULX form are poorly understood, but recent evidence suggests they may be more common in low metallicity systems. Here we investigate the hypothesis that ULX form preferentially in low metallicity galaxies by searching for ULX in a sample of Extremely Metal Poor Galaxies (XMPG) observed with the Chandra X-ray Observatory. XMPG are defined as galaxies with log(O/H)+12<7.65, or less than 5% solar. These are the most metal-deficient galaxies known, and a logical place to find ULX if they favor metal poor systems. We compare the number of ULX (corrected for background contamination) per unit of star formation (Nulx) in the XMPG sample with Nulx in a comparison sample of galaxies with higher metallicities taken from the Spitzer Infrared Galaxy Sample (SINGS). We find that ULX o...

  20. Wind Roche-lobe overflow: Application to carbon-enhanced metal-poor stars

    CERN Document Server

    Abate, C; Izzard, R G; Mohamed, S S; de Mink, S E

    2013-01-01

    Carbon-enhanced metal-poor stars (CEMP) are observed as a substantial fraction of the very metal-poor stars in the Galactic halo. Most CEMP stars are also enriched in s-process elements and these are often found in binary systems. This suggests that the carbon enrichment is due to mass transfer in the past from an asymptotic giant branch (AGB) star on to a low-mass companion. Models of binary population synthesis are not able to reproduce the observed fraction of CEMP stars without invoking non-standard nucleosynthesis or a substantial change in the initial mass function. This is interpreted as evidence of missing physical ingredients in the models. Recent hydrodynamical simulations show that efficient wind mass transfer is possible in the case of the slow and dense winds typical of AGB stars through a mechanism called wind Roche-lobe overflow (WRLOF), which lies in between the canonical Bondi-Hoyle-Lyttleton (BHL) accretion and Roche-lobe overflow. WRLOF has an effect on the accretion efficiency of mass tran...

  1. 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.

  2. HE 0557-4840 - Ultra-Metal-Poor and Carbon-Rich

    CERN Document Server

    Norris, John E; Korn, A J; Eriksson, K; Bessell, M S; Beers, Timothy C; Wisotzki, L; Reimers, D

    2007-01-01

    We report the discovery and high-resolution, high S/N, spectroscopic analysis of the ultra-metal-poor red giant HE 0557-4840, which is the third most heavy-element deficient star currently known. Its atmospheric parameters are T_eff = 4900 K, log g = 2.2, and [Fe/H]= -4.75. This brings the number of stars with [Fe/H] < -4.0 to three, and the discovery of HE 0557-4840 suggests that the metallicity distribution function of the Galactic halo does not have a "gap" between [Fe/H] = -4.0, where several stars are known, and the two most metal-poor stars, at [Fe/H] ~ -5.3. HE 0557-4840 is carbon rich - [C/Fe] = +1.6 - a property shared by all three objects with [Fe/H] < -4.0, suggesting that the well-known increase of carbon relative to iron with decreasing [Fe/H] reaches its logical conclusion - ubiquitous carbon richness - at lowest abundance. We also present abundances (nine) and limits (nine) for a further 18 elements. For species having well-measured abundances or strong upper limits, HE 0557-4840 is "norm...

  3. 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,...

  4. 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...

  5. 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 ...

  6. 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.

  7. Formation of carbon-enhanced metal-poor stars in the presence of far ultraviolet radiation

    CERN Document Server

    Bovino, S; Schleicher, D R G; Latif, M A

    2014-01-01

    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$^+$, O, O$^+$, Si, Si$^+$, and Si$^{2+}$ 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 CMB temperature for a metallicity of Z/Z$_\\odot$=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$_\\odot$=10$...

  8. 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 ...

  9. 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...

  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. 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...

  12. 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 ...

  13. 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...

  14. 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...

  15. Metal-Poor Stars and the Chemical Enrichment of the Universe

    CERN Document Server

    Frebel, Anna

    2011-01-01

    Metal-poor stars hold the key to our understanding of the origin of the elements and the chemical evolution of the Universe. This chapter describes the process of discovery of these rare stars, the manner in which their surface abundances (produced in supernovae and other evolved stars) are determined from the analysis of their spectra, and the interpretation of their abundance patterns to elucidate questions of origin and evolution. More generally, studies of these stars contribute to other fundamental areas that include nuclear astrophysics, conditions at the earliest times, the nature of the first stars, and the formation and evolution of galaxies -- including our own Milky Way. We illustrate this with results from studies of lithium formed during the Big Bang; of stars dated to within ~1 Gyr of that event; of the most metal-poor stars, with abundance signatures very different from all other stars; and of the build-up of the elements over the first several Gyr. The combination of abundance and kinematic si...

  16. 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...

  17. Carbon-rich dust production in metal-poor galaxies in the Local Group

    CERN Document Server

    Sloan, G C; Lagadec, E; van Loon, J Th; Kraemer, K E; McDonald, I; Groenewegen, M A T; Wood, P R; Bernard-Salas, J; Zijlstra, A A

    2012-01-01

    We have observed a sample of 19 carbon stars in the Sculptor, Carina, Fornax, and Leo I dwarf spheroidal galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. The spectra show significant quantities of dust around the carbon stars in Sculptor, Fornax, and Leo I, but little in Carina. Previous comparisons of carbon stars with similar pulsation properties in the Galaxy and the Magellanic Clouds revealed no evidence that metallicity affected the production of dust by carbon stars. However, the more metal-poor stars in the current sample appear to be generating less dust. These data extend two known trends to lower metallicities. In more metal-poor samples, the SiC dust emission weakens, while the acetylene absorption strengthens. The bolometric magnitudes and infrared spectral properties of the carbon stars in Fornax are consistent with metallicities more similar to carbon stars in the Magellanic Clouds than in the other dwarf spheroidals in our sample. A study of the carbon budget in these sta...

  18. Modelling the nucleosynthetic properties of carbon-enhanced metal-poor RR Lyrae stars

    CERN Document Server

    Stancliffe, Richard J; Lau, Herbert H B; Beers, Timothy C

    2013-01-01

    Certain carbon-enhanced metal-poor stars likely obtained their composition via pollution from some of the earliest generations of asymptotic giant branch stars and as such provide important clues to early Universe nucleosynthesis. Recently, Kinman et al. discovered that the highly carbon- and barium-enriched metal-poor star SDSS J1707+58 is in fact an RR Lyrae pulsator. This gives us an object in a definite evolutionary state where the effects of dilution of material during the Main Sequence are minimised owing to the object having passed through first dredge-up. We perform detailed stellar modelling of putative progenitor systems in which we accreted material from asymptotic giant branch stars in the mass range 1-2 solar masses. We investigate how the surface abundances are affected by the inclusion of mechanisms like thermohaline mixing and gravitational settling. While we are able to find a reasonable fit to the carbon and sodium abundances of SDSS J1707+58, suggesting accretion of around 0.1 solar masses ...

  19. The INT Search for Metal-Poor Stars. Spectroscopic Observations and Classification via Artificial Neural Networks

    CERN Document Server

    Allende-Prieto, C; García-López, R J; Serra-Ricart, M; Beers, T C; Rossi, S; Bonifacio, P; Molaro, P

    2000-01-01

    With the dual aims of enlarging the list of extremely metal-poor stars identified in the Galaxy, and boosting the numbers of moderately metal-deficient stars in directions that sample the rotational properties of the thick disk, we have used the 2.5m Isaac Newton Telescope and the Intermediate Dispersion Spectrograph to carry out a survey of brighter (primarily northern hemisphere) metal-poor candidates selected from the HK objective-prism/interference-filter survey of Beers and collaborators. Over the course of only three observing runs (15 nights) we have obtained medium-resolution (resolving power ~ 2000) spectra for 1203 objects (V ~ 11-15). Spectral absorption-line indices and radial velocities have been measured for all of the candidates. Metallicities, quantified by [Fe/H], and intrinsic (B-V)o colors have been estimated for 731 stars with effective temperatures cooler than roughly 6500 K, making use of artificial neural networks (ANNs), trained with spectral indices. We show that this method performs ...

  20. Variable Stars in the Globular Cluster NGC 4590 (M68

    CERN Document Server

    Sariya, Devesh Path; Yadav, R K S

    2013-01-01

    We present results of time series photometry to search for variable stars in the field of metal-poor globular cluster NGC 4590 (M68). Periods have been revised for 40 known variables and no significant changes were found. A considerable change in Blazhko effect for V25 has been detected. Among nine newly discovered variable candidates, 5 stars are of RRc Bailey type variables while 4 stars are unclassified. The variable stars V10, V21, V50 and V51 are found to be cluster members based on the radial velocity data taken from literature.

  1. Variable stars in the globular cluster NGC 4590 (M68)

    Science.gov (United States)

    Sariya, Devesh P.; Lata, Sneh; Yadav, R. K. S.

    2014-02-01

    We present results of time series photometry to search for variable stars in the field of metal-poor globular cluster NGC 4590 (M68). Periods have been revised for 40 known variables and no significant changes were found. A considerable change in Blazhko effect for V25 has been detected. Among nine newly discovered variable candidates, 5 stars are of RRc Bailey type variables while 4 stars are unclassified. The variable stars V10, V21, V50 and V51 are found to be cluster members based on the radial velocity data taken from literature.

  2. VizieR Online Data Catalog: Abundances of bright metal-poor stars (Schlaufman+, 2014)

    Science.gov (United States)

    Schlaufman, K. C.; Casey, A. R.

    2016-11-01

    As input to our sample selection, we use the APASS DR6 Catalog, the 2MASS All-Sky Point Source Catalog, and the AllWISE Source Catalog (Henden+ 2012JAVSO..40..430H; Skrutskie+ 2006AJ....131.1163S; Wright+ 2010AJ....140.1868W; Mainzer+ 2011ApJ...731...53M). We followed up our metal-poor star candidates with the Mayall 4m/Echelle, Gemini South/GMOS-S, and Magellan/MIKE telescopes and spectrographs. We observed 98 stars with the Mayall 4m/Echelle on 2013 June 25-27. We observed 90 stars with Gemini South/GMOS-S in service mode from 2014 March to July (R~3700). We observed 416 stars with Magellan/MIKE on 2014 June 21-23 and July 8-10 (R~41000 in the blue and R~35000 in the red). (3 data files).

  3. Modeling Mid-Ultraviolet Spectra. I. Temperatures of Metal-Poor Stars

    CERN Document Server

    Peterson, R C; Rood, R T; Peterson, Ruth C.; Dorman, Ben; Rood, Robert T.

    2001-01-01

    Determining the properties of old stellar systems using evolutionary population synthesis requires a library of model stellar fluxes. The reliability of the interpretation of the observations depends to a great extent on the reliability of the flux library. The mid-ultraviolet waveband of these systems is dominated by the contribution from the main sequence turnoff stars. Here we present detailed spectral synthesis calculations which match accurately the mid-ultraviolet spectrum of a set of nearby stars with a range of metallicities. We have redetermined temperatures of our sample of eight nearby, mildly to extremely metal-poor turnoff stars, by simultaneously analyzing mid-ultraviolet and optical echelle spectra. An attempt is made to fit all mid-UV lines individually, by modifying line parameters for lines whose energy levels have been measured in the laboratory and adding approximate identifications for the strongest missing lines. Without recourse to additional missing opacity, this suffices to reproduce ...

  4. VizieR Online Data Catalog: Carbon-enhanced metal-poor stars (Placco+, 2014)

    Science.gov (United States)

    Placco, V. M.; Frebel, A.; Beers, T. C.; Stancliffe, R. J.

    2017-01-01

    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 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. (2 data files).

  5. 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.

  6. Discovery of the benchmark metal poor T8 dwarf BD+01 2920B

    CERN Document Server

    Pinfield, D J; Lodieu, N; Leggett, S K; Tinney, C G; van Spaandonk, L; Marocco, F; Smart, R; Gomes, J; Smith, L; Lucas, P W; Day-Jones, A C; Murray, D N; Katsiyannis, A C; Catalan, S; Cardoso, C; Clarke, J R A; Folkes, S; Galvez-Ortiz, M C; Homeier, D; Jenkins, J S; Jones, H R A; Zhang, Z H

    2012-01-01

    We have searched the WISE first data release for widely separated (<10,000AU) late T dwarf companions to Hipparcos and Gliese stars. We have discovered a new binary system containing a K-band suppressed T8p dwarf WISEP J1423+0116 and the mildly metal poor ([Fe/H]=-0.38+-0.06) primary BD+01 2920 (Hip 70319), a G1 dwarf at a distance of 17.2pc. This new benchmark has Teff=680+-55K and a mass of 20-50 Mjup. Its spectral properties are well modelled except for known discrepancies in the Y and K bands. Based on the well determined metallicity of its companion, the properties of BD+01 2920B imply that the currently known T dwarfs are dominated by young low-mass objects. We also present an accurate proper motion for the T8.5 dwarf WISEP J075003.84+272544.8.

  7. 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.

  8. Testing the Asteroseismic Mass Scale Using Metal-Poor Stars Characterized with APOGEE and Kepler

    CERN Document Server

    Epstein, Courtney R; Johnson, Jennifer A; Shetrone, Matthew; Mosser, Benoît; Hekker, Saskia; Tayar, Jamie; Harding, Paul; Pinsonneault, Marc; Aguirre, Víctor Silva; Basu, Sarbani; Beers, Timothy C; Bizyaev, Dmitry; Bedding, Timothy R; Chaplin, William J; Frinchaboy, Peter M; García, Rafael A; Pérez, Ana E García; Hearty, Fred R; Huber, Daniel; Ivans, Inese I; Majewski, Steven R; Mathur, Savita; Nidever, David; Serenelli, Aldo; Schiavon, Ricardo P; Schneider, Donald P; Schönrich, Ralph; Sobeck, Jennifer S; Stassun, Keivan G; Stello, Dennis; Zasowski, Gail

    2014-01-01

    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 scal...

  9. Structural and Nucleosynthetic Evolution of Metal-poor & Metal-free Low and Intermediate Mass Stars

    Science.gov (United States)

    Campbell, Simon W.; Lattanzio, John C.

    2008-03-01

    We report on an investigation into stellar evolution and nucleosynthesis in the low and extremely low metallicity regime, including models of stars with a pure Big Bang composition (i.e. Z = 0). The metallicity range of the extremely metal- poor (EMP) models we have calculated is -6.5format. Although subject to many uncertainties these are, as far as we are aware, the only yields available in this mass and metallicity range. In this paper we briefly describe some of the results in the context of abundance observations of EMP halo stars. This work formed part of SWC's PhD thesis (completed in March 2007) and a series of subsequent papers will describe the results of the study in more detail.

  10. 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.

  11. THE KENNICUTT–SCHMIDT RELATION IN EXTREMELY METAL-POOR DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Filho, M. E.; Almeida, J. Sánchez; Muñoz-Tuñón, C. [Instituto Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain); Amorín, R. [National Institute for Astrophysics, Astronomical Observatory of Rome, Via Frascati 33, I-00040 Monteporzio Catone (Rome) (Italy); Elmegreen, B. G. [IBM, T. J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States); Elmegreen, D. M., E-mail: mfilho@astro.up.pt [Department of Physics and Astronomy, Vassar College, Poughkeepsie, NY 12604 (United States)

    2016-04-01

    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 H i data occupy the same region as dwarfs and extend the relation for low surface brightness galaxies. Considering the H i gas alone, a considerable fraction of the XMPs already fall off the KS law. Significant quantities of “dark” H{sub 2} mass (i.e., not traced by CO) would imply that XMPs possess low star formation efficiencies (SFE{sub gas}). Low SFE{sub gas} in XMPs may be the result of the metal-poor nature of the H i gas. Alternatively, the H i reservoir may be largely inert, the star formation being dominated by cosmological accretion. Time lags between gas accretion and star formation may also reduce the apparent SFE{sub gas}, as may galaxy winds, which can expel most of the gas into the intergalactic medium. Hence, on global scales, XMPs could be H i-dominated, high-specific-SFR (≳10{sup −10} yr{sup −1}), low-SFE{sub gas} (≲10{sup −9} yr{sup −1}) systems, in which the total H i mass is likely not a good predictor of the total H{sub 2} mass, nor of the SFR.

  12. Wide Binaries among High-Velocity and Metal-Poor Stars

    Science.gov (United States)

    Allen, C.; Herrera, M. A.; Poveda, A.

    The properties of old disk and halo binaries are of interest for the understanding of the processes of formation and early dynamical evolution of the Galaxy. The luminosity function of the components of wide binaries and multiples, their mass function, the fraction of halo or old disk stars that are members of wide binaries, and the distribution of its separations are some of the basic properties that are poorly understood, mainly because of the paucity of known wide binaries among halo and old disk stars. The present work is an attempt to ameliorate this situation. We have elaborated a list of 130 halo and old disk wide binaries by searching for common proper motion companions to the high-velocity and metal-poor stars studied by Schuster and Nissen (1988, 1993). Based on Stromgren photometry, these authors have derived distances, metallicities and ages for their stars. Since each star has a large and well determined proper motion it was possible to compare this value with that of NLTT stars of its vicinity. In this way we were able to identify 130 high-velocity and metal-poor common proper motion binary systems. Each system was carefully checked to avoid misidentifications, and when possible, distances were updated using the Hipparcos trigonometric parallaxes. We have determined the distribution of angular separations for our wide binaries. Reliable distances are available for all of our systems, so this distribution can be converted into a separation distribution in AU. We find that 12 systems have separations in excess of 10000 AU, and their existence poses interesting dynamical problems. Since many systems also have known radial velocities, space velocities for them can be determined, and galactic orbits have been computed and characterized. The secondaries of these wide binaries are interesting in themselves, since they represent a sampling of the faint end of the main sequence of old disk and halo stars.

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

    Energy Technology Data Exchange (ETDEWEB)

    Epstein, Courtney R.; Johnson, Jennifer A.; Tayar, Jamie; Pinsonneault, Marc [Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States); Elsworth, Yvonne P.; Chaplin, William J. [School of Physics and Astronomy, University of Birmingham, Edgbaston Park Road, West Midlands, Birmingham B15 2TT (United Kingdom); Shetrone, Matthew [McDonald Observatory, The University of Texas at Austin, 1 University Station, C1400, Austin, TX 78712-0259 (United States); Mosser, Benoît [LESIA, CNRS, Université Pierre et Marie Curie, Université Denis Diderot, Observatoire de Paris, F-92195 Meudon Cedex (France); Hekker, Saskia [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Harding, Paul [Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106-7215 (United States); Silva Aguirre, Víctor [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Basu, Sarbani [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719, USA and JINA: Joint Institute for Nuclear Astrophysics (United States); Bizyaev, Dmitry [Apache Point Observatory, Sunspot, NM 88349 (United States); Bedding, Timothy R. [Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia); Frinchaboy, Peter M. [Department of Physics and Astronomy, Texas Christian University, TCU Box 298840, Fort Worth, TX 76129 (United States); García, Rafael A. [Laboratoire AIM, CEA/DSM-CNRS, Universit Paris 7 Diderot, IRFU/SAp, Centre de Saclay, F-91191, Gif-sur-Yvette (France); Pérez, Ana E. García; Hearty, Fred R., E-mail: epstein@astronomy.ohio-state.edu [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); and others

    2014-04-20

    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 {sub ☉}) 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 {sub ☉} 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.

  14. Discovery of the most metal-poor damped Lyman-α system

    Science.gov (United States)

    Cooke, Ryan J.; Pettini, Max; Steidel, Charles C.

    2017-01-01

    We report the discovery and analysis of the most metal-poor damped Lyman-α (DLA) system currently known, based on observations made with the Keck HIRES spectrograph. The metal paucity of this system has only permitted the determination of three element abundances: [C/H] =-3.43 ± 0.06, [O/H] =-3.05 ± 0.05, and [Si/H] =-3.21 ± 0.05, as well as an upper limit on the abundance of iron: [Fe/H] ≤-2.81. This DLA is among the most carbon-poor environment currently known with detectable metals. By comparing the abundance pattern of this DLA to detailed models of metal-free nucleosynthesis, we find that the chemistry of the gas is consistent with the yields of a 20.5 M⊙ metal-free star that ended its life as a core-collapse supernova; the abundances we measure are inconsistent with the yields of pair-instability supernovae. Such a tight constraint on the mass of the progenitor Population III star is afforded by the well-determined C/O ratio, which we show depends almost monotonically on the progenitor mass when the kinetic energy of the supernova explosion is Eexp ≳ 1.5 × 1051 erg. We find that the DLA presented here has just crossed the critical `transition discriminant' threshold, rendering the DLA gas now suitable for low mass star formation. We also discuss the chemistry of this system in the context of recent models that suggest some of the most metal-poor DLAs are the precursors of the `first galaxies', and are the antecedents of the ultra-faint dwarf galaxies.

  15. Kinematics of Extremely Metal-poor Galaxies: Evidence for Stellar Feedback

    Science.gov (United States)

    Olmo-García, A.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Filho, M. E.; Elmegreen, B. G.; Elmegreen, D. M.; Pérez-Montero, E.; Méndez-Abreu, J.

    2017-01-01

    The extremely metal-poor (XMP) galaxies analyzed in a previous paper have large star-forming regions with a metallicity lower than the rest of the galaxy. Such a chemical inhomogeneity reveals the external origin of the metal-poor gas fueling star formation, possibly indicating accretion from the cosmic web. This paper studies the kinematic properties of the ionized gas in these galaxies. Most XMPs have a rotation velocity around a few tens of km s‑1. The star-forming regions appear to move coherently. The velocity is constant within each region, and the velocity dispersion sometimes increases within the star-forming clump toward the galaxy midpoint, suggesting inspiral motion toward the galaxy center. Other regions present a local maximum in velocity dispersion at their center, suggesting a moderate global expansion. The Hα line wings show a number of faint emission features with amplitudes around a few per cent of the main Hα component, and wavelength shifts between 100 and 400 km s‑1. The components are often paired, so that red and blue emission features with similar amplitudes and shifts appear simultaneously. Assuming the faint emission to be produced by expanding shell-like structures, the inferred mass loading factor (mass loss rate divided by star formation rate) exceeds 10. Since the expansion velocity far exceeds the rotational and turbulent velocities, the gas may eventually escape from the galaxy disk. The observed motions involve energies consistent with the kinetic energy released by individual core-collapse supernovae. Alternative explanations for the faint emission have been considered and discarded.

  16. Stellar Populations and Star Formation History of the Metal-poor Dwarf Galaxy DDO 68

    Science.gov (United States)

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

    2016-10-01

    We present the star formation history (SFH) of the extremely metal-poor dwarf galaxy DDO 68, based on our photometry with the Advanced Camera for Surveys. With a metallicity of only 12+{log}({{O}}/{{H}})=7.15 and a very isolated location, DDO 68 is one of the most metal-poor galaxies known. It has been argued that DDO 68 is a young system that started forming stars only ∼0.15 Gyr ago. Our data provide a deep and uncontaminated optical color–magnitude diagram (CMD) that allows us to disprove this hypothesis since we find a population of at least ∼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 ≃0.01 M ⊙ yr‑1, corresponding to a total astrated mass of ≃1.3 × 108 M ⊙. Our photometry allows us to infer the distance from the tip of the red giant branch, D = 12.08 ± 0.67 Mpc; however, to let our synthetic CMD reproduce the observed ones, we need a slightly higher distance, D = 12.65 Mpc, or (m ‑ M)0 = 30.51, still inside the errors of the previous determination, and we adopt the latter. DDO 68 shows a very interesting and complex history, with its quite disturbed shape and a long tail, probably due to tidal interactions. The SFH of the tail differs from that of the main body mainly for enhanced activity at recent epochs likely triggered by the interaction. Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA Contract NAS5-26555.

  17. Spectroscopy of Globular Clusters in M81

    CERN Document Server

    Schroder, L L; Kissler-Patig, M; Phillips, A C; Huchra, J P; Schroder, Linda L.; Brodie, Jean P.; Kissler-Patig, Markus; Phillips, John P. Huchra & Andrew C.

    2002-01-01

    We present moderate-resolution spectroscopy of globular clusters (GCs) around the Sa/Sb spiral galaxy M81 (NGC 3031). Sixteen candidate clusters were observed with the Low Resolution Imaging Spectrograph on the Keck I telescope. All are confirmed as bona fide GCs, although one of the clusters appears to have been undergoing a transient event during our observations. In general, the M81 globular cluster system (GCS) is found to be very similar to the Milky Way (MW) and M31 systems, both chemically and kinematically. A kinematic analysis of the velocities of 44 M81 GCS, (the 16 presented here and 28 from previous work) strongly suggests that the red, metal-rich clusters are rotating in the same sense as the gas in the disk of M81. The blue, metal-poor clusters have halo-like kinematics, showing no evidence for rotation. The kinematics of clusters whose projected galactocentric radii lie between 4 and 8 kpc suggest that they are rotating much more than those which lie outside these bounds. We suggest that these ...

  18. Hot Populations in M87 Globular Clusters

    CERN Document Server

    Sohn, S T; Kundu, A; Landsman, W B; Burstein, D; Bohlin, R C; Frogel, J A; Rose, J A

    2005-01-01

    We have obtained HST/STIS far- and near-UV photometry of globular clusters in four fields in the gE galaxy M87. To a limit of m(FUV) = 25 we detect a total of 66 globular clusters (GCs) in common with the deep HST optical-band study of Kundu et al. (1999). Despite strong overlap in V- and I-band properties, the M87 GCs have UV/optical properties that are distinct from clusters in the Milky Way and in M31. M87 clusters, especially metal-poor ones, produce larger hot HB populations than do Milky Way analogues. Cluster mass is probably not a factor in these distinctions. The most metal-rich M87 GCs in our sample are near Z_sun and overlap the local E galaxy sample in estimated Mg_2 line indices. Nonetheless, the clusters produce much more UV light at a given Mg_2, being up to 1 mag bluer than any gE galaxy in (FUV-V) color. The M87 GCs do not appear to represent a transition between Milky Way-type clusters and E galaxies. The differences are in the correct sense if the clusters are significantly older than the E...

  19. Chemical composition and constraints on mass loss for globular clusters in dwarf galaxies: WLM and IKN

    CERN Document Server

    Larsen, S S; Forbes, D A; Strader, J

    2014-01-01

    We determine the metallicities for globular clusters (GCs) in the WLM and IKN dwarf galaxies, using VLT/UVES and Keck/ESI spectroscopy. For the WLM GC we also measure detailed abundance ratios for a number of light, alpha, Fe-peak and n-capture elements. We find low metallicities of [Fe/H]=-2.0 and -2.1 for the WLM GC and the GC IKN-5, respectively. We estimate that 17%-31% of the metal-poor stars in WLM belong to the GC, and IKN-5 may even contain a similar number of metal-poor stars as the whole of the IKN dwarf itself. These high ratios of metal-poor GCs to field stars are in tension with GC formation scenarios that require GCs to have lost a very large fraction of their initial mass. The GCs in the WLM and IKN dwarf galaxies resemble those in the Fornax dSph by being significantly more metal-poor than a typical halo GC in the Milky Way and other large galaxies. They are also substantially more metal-poor than the bulk of the field stars in their parent galaxies. The overall abundance patterns in the WLM G...

  20. Finding the Most Metal-poor Stars of the Galactic Halo with the Hamburg/ESO Objective-Prism Survey

    CERN Document Server

    Christlieb, N

    2003-01-01

    I review the status of the search for extremely metal-poor halo stars with the Hamburg/ESO objective-prism survey (HES). 2194 candidate metal-poor turn-off stars and 6133 giants in the magnitude range 14 < B < 17.5 have been selected from 329 (out of 380) HES fields, covering an effective area of 6400 square degrees in the southern extragalactic sky. Moderate-resolution follow-up observations for 3200 candidates have been obtained so far, and ~200 new stars with [Fe/H] <- 3.0 have been found, which trebles the total number of such extremely low-metallicity stars identified by all previous surveys. We use VLT-UT2/UVES, Keck/HIRES, Subaru/HDS, TNG/SARG, and Magellan/MIKE for high-resolution spectroscopy of HES metal-poor stars. I provide an overview of the scientific aims of these programs, and highlight several recent results.

  1. The Formation of Galactic Bulges

    NARCIS (Netherlands)

    Peletier, R.; Balcells, M.; Falcon-Barroso, J.; Graham, A.

    2005-01-01

    We summarise some recent results about nearby galactic bulges that are relevant to their formation. We highlight a number of significant advances in our understanding of the surface brightness profiles, stellar populations, and especially the very centers of spiral galaxies. We also view our own Mil

  2. 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

  3. Wide-Field Survey of Globular Clusters in M31. II. Kinematics of the Globular Cluster System

    CERN Document Server

    Lee, Myung Gyoon; Kim, Sang Chul; Park, Hong Soo; Geisler, Doug; Sarajedini, Ata; Harris, William E

    2007-01-01

    We present a kinematic analysis of the globular cluster(GC) system in M31. Using the photometric and spectroscopic database of 504 GCs, we have investigated the kinematics of the M31 GC system. We find that the all GC system shows strong rotation, with rotation amplitude of v_rot~190km/s, and that a weak rotation persists even for the outermost samples at |Y|>5kpc. The rotation-corrected velocity dispersion for the GC system is estimated to be sigma_{p,r}~130km/s, and it increases from sigma_{p,r}~120km/s at |Y|5kpc. These results are very similar to those for the metal-poor GCs. This shows that there is a dynamically hot halo in M31 that is rotating but primarily pressure-supported. We have identified 50 "friendless" GCs, and they appear to rotate around the major axis of M31. For the subsamples of metal-poor and metal-rich GCs, we have found that the metal-rich GCs are more centrally concentrated than the metal-poor GCs, and both subsamples show strong rotation. For the subsamples of bright and faint GCs, i...

  4. The Gaia-ESO Survey: metallicity and kinematic trends in the Milky Way bulge

    CERN Document Server

    Rojas-Arriagada, A; Hill, V; de Laverny, P; Schultheis, M; Babusiaux, C; Zoccali, M; Minniti, D; Gonzalez, O A; Feltzing, S; Gilmore, G; Randich, S; Vallenari, A; Alfaro, E J; Bensby, T; Bragaglia, A; Flaccomio, E; Lanzafame, A C; Pancino, E; Smiljanic, R; Bergemann, M; Costado, M T; Damiani, F; Hourihane, A; Jofré, P; Lardo, C; Magrini, L; Maiorca, E; Morbidelli, L; Sbordone, L; Worley, C C; Zaggia, S; Wyse, R

    2014-01-01

    (Abridged) We analyzed the stellar parameters and radial velocities of ~1200 stars in five bulge fields as determined from the Gaia-ESO survey data (iDR1). We use VISTA Variables in The Via Lactea (VVV) photometry to obtain reddening values by using a semi-empirical T_eff-color calibration. From a Gaussian decomposition of the metallicity distribution functions, we unveil a clear bimodality in all fields, with the relative size of components depending of the specific position on the sky. In agreement with some previous studies, we find a mild gradient along the minor axis (-0.05 dex/deg between b=-6 and b=-10) that arises from the varying proportion of metal-rich and metal-poor components. The number of metal-rich stars fades in favor of the metal-poor stars with increasing b. The K-magnitude distribution of the metal-rich population splits into two peaks for two of the analyzed fields that intersects the near and far branches of the X-shaped bulge structure. In addition, two lateral fields at (l,b)=(7,-9) an...

  5. The stellar population and luminosity function in M31 bulge and Inner Disk Fields

    Science.gov (United States)

    Rich, R. Michael; Mould, J. R.; Graham, James R.

    1993-01-01

    /mag. We advance the possibility that the bulge of M31 may be younger than the oldest Galactic globular clusters. We note that M33 has recently been found to have an r(exp 1/4)-law spheroid consisting of intermediate-age stars; bulges can form later than the old halo population.

  6. Neutron Capture Elements in s-Process-Rich, Very Metal-Poor Stars

    CERN Document Server

    Aoki, W; Norris, J E; Beers, T C; Ando, H; Iwamoto, N; Kajino, T; Mathews, G J; Fujimoto, M; Aoki, Wako; Ryan, Sean G.; Norris, John E.; Beers, Timothy C.; Ando, Hiroyasu; Iwamoto, Nobuyuki; Kajino, Toshitaka; Mathews, Grant J.; Fujimoto, Masayuki

    2001-01-01

    We report abundance estimates for neutron-capture elements, including lead (Pb), and nucleosynthesis models for their origin, in two carbon-rich, very metal-poor stars, LP625-44 and LP706-7. These stars are subgiants whose surface abundances are likely to have been strongly affected by mass transfer from companion AGB stars that have since evolved to white dwarfs. The detections of Pb, which forms the final abundance peak of the s-process, enable a comparison of the abundance patterns from Sr (Z=38) to Pb (Z=82) with predictions of AGB models. The derived chemical compositions provide strong constraints on the AGB stellar models, as well as on s-process nucleosynthesis at low metallicity. The present paper reports details of the abundance analysis for 16 neutron-capture elements in LP 625-44, including the effects of hyperfine splitting and isotope shifts of spectral lines for some elements. A Pb abundance is also derived for LP706-7 by a re-analysis of a previously observed spectrum. We investigate the chara...

  7. Bright Metal-Poor Stars from the Hamburg/ESO Survey. II. A Chemodynamical Analysis

    CERN Document Server

    Beers, Timothy C; Carollo, Daniela; Rossi, Silvia; Frebel, Anna; Norris, John E; Dietz, Sarah; Masseron, Thomas

    2016-01-01

    We obtain estimates of stellar atmospheric parameters for a previously published sample of 1777 relatively bright (9 < B < 14) metal-poor candidates from the Hamburg/ESO Survey. The original Frebel et al. analysis of these stars was only able to derive estimates of [Fe/H] and [C/Fe] for a subset of the sample, due to limitations in the methodology then available. A new spectroscopic analysis pipeline has been used to obtain estimates of Teff, log g, [Fe/H], and [C/Fe] for almost the entire dataset. This sample is very local - about 90% of the stars are located within 0.5 kpc of the Sun. We consider the chemodynamical properties of these stars in concert with a similarly local sample of stars from a recent analysis of the Bidelman & MacConnell 'weak-metal' candidates by Beers et al. We use this combined sample to identify possible members of the suggested halo stream of stars by Helmi et al. and Chiba & Beers, as well as stars that may be associated with stripped debris from the putative parent d...

  8. Discovery of An Extremely Metal--Poor Galaxy Optical Spectroscopy of UGCA 292

    CERN Document Server

    Van Zee, L

    2000-01-01

    The results of optical spectroscopy of two HII regions in UGCA 292 (CVn I dwA) are presented. UGCA 292 is a nearby (D=3.1 Mpc) gas-rich dwarf irregular galaxy (M_H/L_B ~ 6.9) which was first discovered in a blind HI survey. The derived oxygen abundance is the third lowest of known star-forming galaxies [12 + log(O/H) = 7.30 +/- 0.05], making UGCA 292 one of the nearest metal-poor galaxies known. The derived N/O ratio is similar to that found in other low metallicity galaxies [log(N/O) = -1.47 +/- 0.10], and is indicative of a primary origin for nitrogen. The derived oxygen abundance is consistent with closed-box chemical evolution for this low mass galaxy. The observed blue colors, high gas mass fraction, and low metallicity suggest that UGCA 292 is relatively unevolved. The possibility that future blind HI surveys may yield similar low metallicity galaxies is discussed.

  9. 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.

  10. Early-Age Evolution of the Milky Way Related by Extremely Metal-Poor Stars

    CERN Document Server

    Komiya, Yutaka; Fujimoto, Masayuki Y

    2009-01-01

    We exploit the recent observations of extremely metal-poor (EMP) stars in the Galactic halo and investigate the constraints on the IMF of the stellar population that left these low-mass survivors of [Fe/H]<-2.5 and the chemical evolution that they took part in. A high-mass IMF with the typical mass~10Msun and the overwhelming contribution of low-mass members of binaries to the EMP survivors are derived from the statistics of carbon-enriched EMP stars with and without the enhancement of s-process elements (Komiya et al. 2007). We first examine the analysis to confirm their results for various assumptions on the mass-ratio distribution function. As compared with the uniform distribution, the increase or decrease function of the mass ratio gives a higher- or lower-mass IMF, and a lower-mass IMF results for the independent distribution with the both members in the same IMF, but the derived ranges of typical mass differ less than by a factor of two and overlap for the extreme cases. Furthermore, we prove that t...

  11. Simulating extremely metal-poor gas and DLA metal content at redshift z=7

    CERN Document Server

    Maio, Umberto; Mueller, Volker

    2013-01-01

    We present the first theoretical study of metals in damped Ly-alpha (DLA) systems at redshift z=7. The features of cold, primordial gas are studied by means of N-body, hydro, chemistry simulations, including atomic and molecular non-equilibrium chemistry, cooling, star formation for population III and population II-I regimes, stellar evolution, cosmic metal spreading according to proper yields (for He, C, O, Si, Fe, Mg, S, etc.) and lifetimes, and feedback effects. Theoretical expectations are then compared to recently available constraints from DLA observations. We find that DLA galaxies at z=7 account for 10 per cent of the whole galaxy population and for most of the metal-poor galaxies at these epochs. About 7 per cent of these DLA galaxies contain purely pristine material and 34 per cent of them consist of very weakly polluted gas, being, therefore, suitable candidate s as population III sites. The remaining 59 per cent are enriched above ~10^{-4} Zsun. Additionally, DLA candidates appear to have: gas mas...

  12. Seven New Carbon-Enhanced Metal-Poor RR Lyrae Stars

    CERN Document Server

    Kennedy, Catherine R; Kuehn, Charles; Beers, Timothy C; Kinman, T D; Placco, Vinicius M; Reggiani, Henrique; Rossi, Silvia; Lee, Young Sun

    2014-01-01

    We report estimated carbon-abundance ratios, [C/Fe], for seven newly-discovered carbon-enhanced metal-poor (CEMP) RR Lyrae stars. These are well-studied RRab stars that had previously been selected as CEMP candidates based on low-resolution spectra. For this pilot study, we observed eight of these CEMP RR Lyrae candidates with the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope. Prior to this study, only two CEMP RR Lyrae stars had been discovered: TY Gru and SDSS J1707+58. We compare our abundances to new theoretical models of the evolution of low-mass stars in binary systems. These simulations evolve the secondary stars, post accretion from an AGB donor, all the way to the RR Lyrae stage. The abundances of CEMP RR Lyrae stars can be used as direct probes of the nature of the donor star, such as its mass, and the amount of material accreted onto the secondary. We find that the majority of the sample of CEMP RR Lyrae stars is consistent with AGB donor masses of around 1.5 - 2.0 solar masses and accr...

  13. On the dearth of ultra-faint extremely metal poor galaxies

    CERN Document Server

    Almeida, J Sanchez; Vecchia, C Dalla; Skillman, E D

    2016-01-01

    Local extremely metal-poor (XMP) galaxies are of particular astrophysical interest since they allow us to look into physical processes characteristic of the early Universe, from the assembly of galaxy disks to the formation of stars in conditions of low metallicity. Given the luminosity-metallicity relationship, all galaxies fainter than Mr < -13 are expected to be XMPs. Therefore, XMPs should be common in galaxy surveys. However, they are not, because several observational biases hamper their detection. This work compares the number of faint XMPs in the SDSS-DR7 spectroscopic survey with the expected number, given the known biases and the observed galaxy luminosity function. The faint end of the luminosity function is poorly constrained observationally, but it determines the expected number of XMPs. Surprisingly, the number of observed faint XMPs (around 10) is over-predicted by our calculation, unless the upturn in the faint end of the luminosity function is not present in the model. The lack of an uptur...

  14. 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...

  15. 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...

  16. Dust-to-Gas Ratio in the Extremely Metal Poor Galaxy I ZW 18

    CERN Document Server

    Herrera-Camus, Rodrigo; Bolatto, Alberto D; Leroy, Adam K; Walter, Fabian; Gordon, Karl D; Roman-Duval, Julia; Donaldson, Jessica; Meléndez, Marcio; Cannon, John M

    2012-01-01

    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 {\\it Spitzer}, {\\it 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 $J=1\\rightarrow0$ transition. We use dust emission models to derive a dust mass upper limit of only M$_{dust}\\leq1.1\\times10^4$ M$_{\\odot}$ ($3\\sigma$ limit). This upper limit is driven by the non-detection at 160 $\\mu$m, and it is a factor of 4-10 times smaller than previous estimates (depending upon the model used). We also estimate an upper limit to the total dust-to-gas mass ratio of M$_{Dust}$/M$_{gas}\\leq5.0\\times10^{-5}$. If a linear correlation between the dust-to-gas mass ratio and metallicity (measure as O/H) were to hold, we would expect a ratio of 3.9$\\times10^{-4}$. We also show that the infrared SED is similar to that of starbursting s...

  17. DUST-TO-GAS RATIO IN THE EXTREMELY METAL-POOR GALAXY I Zw 18

    Energy Technology Data Exchange (ETDEWEB)

    Herrera-Camus, Rodrigo; Fisher, David B.; Bolatto, Alberto D. [Department of Astronomy and Laboratory of Millimeter Astronomy, University of Maryland, College Park, MD 20742 (United States); Leroy, Adam K. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States); Walter, Fabian [Max-Planck-Institut fuer Astronomie, Konigstuehl 17, D-69117 Heidelberg (Germany); Gordon, Karl D.; Roman-Duval, Julia [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Donaldson, Jessica; Melendez, Marcio [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Cannon, John M. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States)

    2012-06-20

    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 {yields} 0 transition. We use dust emission models to derive a dust mass upper limit of only M{sub dust} {<=} 1.1 Multiplication-Sign 10{sup 4} M{sub Sun} (3{sigma} limit). This upper limit is driven by the non-detection at 160 {mu}m, 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 M{sub Dust}/M{sub gas} {<=} 5.0 Multiplication-Sign 10{sup -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 Multiplication-Sign 10{sup -4}. We also show that the infrared spectral energy distribution is similar to that of starbursting systems.

  18. 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 +/- ...

  19. Carbon-Enhanced Metal-Poor Stars in the Early Galaxy

    CERN Document Server

    Marsteller, B; Rossi, S; Christlieb, N; Bessell, M; Rhee, J

    2004-01-01

    Very metal-deficient stars that exhibit enhancements of their carbon abundances are of crucial importance for understanding a number of issues -- the nature of stellar evolution among the first generations of stars, the shape of the Initial Mass Function, and the relationship between carbon enhancement and neutron-capture processes, in particular the astrophysical s-process. One recent discovery from objective-prism surveys dedicated to the discovery of metal-deficient stars is that the frequency of Carbon-Enhanced Metal-Poor (CEMP) stars increases with declining metallicity, reaching roughly 25% for [Fe/H] < -2.5. In order to explore this phenomenon in greater detail we have obtained medium-resolution (2 A) spectroscopy for about 350 of the 413 objects in the Christlieb et al. catalog of carbon-rich stars, selected from the Hamburg/ESO objective prism survey on the basis of their carbon-enhancement, rather than metal deficiency. Based on these spectra, and near-IR JHK photometry from the 2MASS Point Sourc...

  20. Chromium: NLTE abundances in metal-poor stars and nucleosynthesis in the Galaxy

    CERN Document Server

    Bergemann, Maria

    2010-01-01

    Aims. We investigate statistical equilibrium of Cr in the atmospheres of late-type stars to show whether the systematic abundance discrepancy between Cr I and Cr II lines, as often encountered in the literature, is due to deviations from LTE. Furthermore, we attempt to interpret the NLTE trend of [Cr/Fe] with [Fe/H] using chemical evolution models for the solar neighborhood. Methods. NLTE calculations are performed for the model of Cr atom, comprising 340 levels and 6806 transitions in total. We make use of the quantum-mechanical photoionization cross-sections of Nahar (2009) and investigate sensitivity of the model to uncertain cross-sections for H I collisions. NLTE line formation is performed for the MAFAGS-ODF model atmospheres of the Sun and 10 metal-poor stars with -3.2 < [Fe/H] < -0.5, and abundances of Cr are derived by comparison of the synthetic and observed flux spectra. Results. We achieve good ionization equilibrium of Cr for the models with different stellar parameters, if inelastic collis...

  1. 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...

  2. Molecular opacities for low-mass metal-poor AGB stars undergoing the Third Dredge Up

    CERN Document Server

    Cristallo, S; Lederer, M T; Aringer, B

    2007-01-01

    The concomitant overabundances of C, N and s-process elements are commonly ascribed to the complex interplay of nucleosynthesis, mixing and mass loss taking place in Asymptotic Giant Branch stars. At low metallicity, the enhancement of C and/or N may be up to 1000 times larger than the original iron content and significantly affects the stellar structure and its evolution. For this reason, the interpretation of the already available and still growing amount of data concerning C-rich metal-poor stars belonging to our Galaxy as well as to dwarf spheroidal galaxies would require reliable AGB stellar models for low and very low metallicities. In this paper we address the question of calculation and use of appropriate opacity coefficients, which take into account the C enhancement caused by the third dredge up. A possible N enhancement, caused by the cool bottom process or by the engulfment of protons into the convective zone generated by a thermal pulse and the subsequent huge third dredge up, is also considered....

  3. 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...

  4. Chemical analysis of a carbon-enhanced very metal-poor star: CD-27 14351

    CERN Document Server

    Karinkuzhi, Drisya; Masseron, Thomas

    2016-01-01

    We present the first time abundance analysis of a very metal-poor carbon-enhanced star CD-27 14351 based on a high resolution (R ~ 48000) FEROS spectrum. Our abundance analysis performed using Local Thermodynamic Equilibrium (LTE) model atmospheres shows that the object is a cool star with stellar atmospheric parameters, effective temperature Teff = 4335 K, surface gravity log g = 0.5, microturbulence = 2.42 km/s, and, metallicity [Fe/H] = -2.6. The star exhibits high carbon and nitrogen abundances with [C/Fe] = 2.89 and [N/Fe] = 1.89. Overabundances of neutron-capture elements are evident in Ba, La, Ce, and Nd with estimated [X/Fe] > 1, the largest enhancement being seen in Ce with [Ce/Fe] = 2.63. While the first peak s-process elements Sr and Y are found to be enhanced with respect to Fe, ([Sr/Fe] = 1.73 and [Y/Fe] = 1.91) the third peak s-process element Pb could not be detected in our spectrum at the given resolution. Europium, primarily a r-process element also shows an enhancement with [Eu/Fe] = 1.65. W...

  5. 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...

  6. 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$_{\\...

  7. 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.

  8. Leo P: A very low-mass, extremely metal-poor, star-forming galaxy

    Science.gov (United States)

    McQuinn, Kristen B.; Leo P Team

    2017-01-01

    Leo P is a low-luminosity dwarf galaxy just outside the Local Group with properties that make it an ideal probe of galaxy evolution at the faint-end of the luminosity function. Using combined data from 2 Hubble Space Telescope (HST) observing campaigns, the Very Large Array, the Spitzer Space telescope, as well as ground based data, we have constructed a robust evolutionary picture of Leo P. Leo P is one the most metal-poor, gas-rich galaxies ever discovered, has a stellar mass of a 5x105 Msun, comparable gas mass, and a single HII region. The star formation history reconstructed from the resolved stellar populations in Leo P shows it is unquenched, despite its very low mass. Based on the star formation history and metallicity measurements, the galaxy has lost 95% of its oxygen produced via nucleosynthesis, presumably to outflows. The neutral gas in the galaxy shows signs of rotation, although the velocity dispersion is comparable to the rotation velocity. Thus, Leo P bridges the gap between more massive dwarf irregular and less massive dwarf spheroidals on the baryonic Tully-Fisher relation. Furthermore, the galaxy hosts several, extremely dusty AGB candidates which will be probed with new HST and Spitzer observations. If confirmed as AGB stars, these may be our best local proxies for studying chemically unevolved star formation and subsequent dust production in metallicity environments comparable to the early universe.

  9. Tracing the Metal-Poor M31 Stellar Halo with Blue Horizontal Branch Stars

    CERN Document Server

    Williams, Benjamin F; Gilbert, Eric F BellKaroline M; Guhathakurta, Puragra; Dorman, Claire; Lauer, Tod R; Seth, Anil C; Kalirai, Jason S; Rosenfield, Philip; Girardi, Leo

    2015-01-01

    We have analyzed new HST/ACS and HST/WFC3 imaging in F475W and F814W of two previously-unobserved fields along the M31 minor axis to confirm our previous constraints on the shape of M31's inner stellar halo. Both of these new datasets reach a depth of at least F814W$<$27 and clearly detect the blue horizontal branch (BHB) of the field as a distinct feature of the color-magnitude diagram. We measure the density of BHB stars and the ratio of BHB to red giant branch stars in each field using identical techniques to our previous work. We find excellent agreement with our previous measurement of a power-law for the 2-D projected surface density with an index of 2.6$^{+0.3}_{-0.2}$ outside of 3 kpc, which flattens to $\\alpha <$1.2 inside of 3 kpc. Our findings confirm our previous suggestion that the field BHB stars in M31 are part of the halo population. However, the total halo profile is now known to differ from this BHB profile, which suggests that we have isolated the metal-poor component. This component ...

  10. On the Dearth of Ultra-faint Extremely Metal-poor Galaxies

    Science.gov (United States)

    Sánchez Almeida, J.; Filho, M. E.; Dalla Vecchia, C.; Skillman, E. D.

    2017-02-01

    Local extremely metal-poor galaxies (XMPs) are of particular astrophysical interest since they allow us to look into physical processes characteristic of the early universe, from the assembly of galaxy disks to the formation of stars in conditions of low metallicity. Given the luminosity–metallicity relationship, all galaxies fainter than Mr ≃ ‑13 are expected to be XMPs. Therefore, XMPs should be common in galaxy surveys. However, they are not common, because several observational biases hamper their detection. This work compares the number of faint XMPs in the SDSS-DR7 spectroscopic survey with the expected number, given the known biases and the observed galaxy luminosity function (LF). The faint end of the LF is poorly constrained observationally, but it determines the expected number of XMPs. Surprisingly, the number of observed faint XMPs (∼10) is overpredicted by our calculation, unless the upturn in the faint end of the LF is not present in the model. The lack of an upturn can be naturally understood if most XMPs are central galaxies in their low-mass dark matter halos, which are highly depleted in baryons due to interaction with the cosmic ultraviolet background and to other physical processes. Our result also suggests that the upturn toward low luminosity of the observed galaxy LF is due to satellite galaxies.

  11. 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...

  12. Granulation signatures in the spectrum of the very metal-poor red giant HD122563

    CERN Document Server

    Ramirez, I; Lambert, D L; Prieto, C Allende; Asplund, M

    2010-01-01

    A very high resolution (R=200,000), high signal-to-noise ratio (S/N=340) blue-green spectrum of the very metal-poor ([Fe/H]=-2.6) red giant star HD122563 has been obtained by us at McDonald Observatory. We measure the asymmetries and core wavelengths of a set of unblended FeI lines covering a wide range of line strength. Line bisectors exhibit the characteristic C-shape signature of surface convection (granulation) and they span from about 100 m/s in the strongest FeI features to 800 m/s in the weakest ones. Core wavelength shifts range from about -100 to -900 m/s, depending on line strength. In general, larger blueshifts are observed in weaker lines, but there is increasing scatter with increasing residual flux. Assuming local thermodynamic equilibrium (LTE), we synthesize the same set of spectral lines using a state-of-the-art three-dimensional hydrodynamic simulation for a stellar atmosphere of fundamental parameters similar to those of HD122563. We find good agreement between model predictions and observa...

  13. 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...

  14. The Most Metal-Poor Stars. III. The Metallicity Distribution Function and CEMP Fraction

    CERN Document Server

    Yong, David; Bessell, M S; Christlieb, N; Asplund, M; Beers, Timothy C; Barklem, P S; Frebel, Anna; Ryan, S G

    2012-01-01

    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-S/N 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 the fraction of CEMP objects below [Fe/H] = -3.0 is 23 +/- 6% and 32 +/- 8% when adopting the Beers et al. and Aoki et al. CEMP definitions, respectively. The former value is in fair agreement with some previous measurements, which adopt the Beers et al. criterion.

  15. High-resolution abundance analysis of very metal-poor r-I stars

    CERN Document Server

    Siqueira-Mello, C; Barbuy, B; Spite, M; Spite, F; Beers, T C; Caffau, E; Bonifacio, P; Cayrel, R; François, P; Schatz, H; Wanajo, S

    2014-01-01

    Moderately r-process-enriched stars (r-I) are at least four times as common as those that are greatly enriched in r-process elements (r-II), and the abundances in their atmospheres are important tools for obtaining a better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak. The main aim of this work is to derive abundances for a sample of seven metal-poor stars with classified as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is(are) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars. We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph. The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code Turbospectrum. We have derived abundances of light elements Li, C, and N, alpha-elements, odd-Z elements, iron-...

  16. Fluorine in carbon-enhanced metal-poor stars: a binary scenario

    CERN Document Server

    Lugaro, M; Izzard, R G; Campbell, S W; Karakas, A I; Cristallo, S; Pols, O R; Lattanzio, J C; Straniero, O; Gallino, R; Beers, T C

    2008-01-01

    A super-solar fluorine abundance was observed in the carbon-enhanced metal-poor (CEMP) star HE 1305+0132 ([F/Fe] = +2.90, [Fe/H] = -2.5). We propose that this observation can be explained using a binary model that involve mass transfer from an asymptotic giant branch (AGB) star companion and, based on this model, we predict F abundances in CEMP stars in general. We discuss wether F can be used to discriminate between the formation histories of most CEMP stars: via binary mass transfer or from the ejecta of fast-rotating massive stars. We compute AGB yields using different stellar evolution and nucleosynthesis codes to evaluate stellar model uncertainties. We use a simple dilution model to determine the factor by which the AGB yields should be diluted to match the abundances observed in HE 1305+0132. We further employ a binary population synthesis tool to estimate the probability of F-rich CEMP stars. The abundances observed in HE 1305+0132 can be explained if this star accreted 3-11% of the mass lost by its f...

  17. C, N, O Abundances in the Most Metal-Poor Damped Lyman alpha Systems

    CERN Document Server

    Pettini, Max; Steidel, Charles C; Chaffee, Fred H

    2007-01-01

    This study focuses on some of the most metal-poor damped Lyman alpha absorbers known in the spectra of high redshift QSOs, using new and archival observations obtained with UV-sensitive echelle spectrographs on the Keck and VLT telescopes. The weakness and simple velocity structure of the absorption lines in these systems allows us to measure the abundances of several elements, and in particular those of C, N, and O, a group that is difficult to study in DLAs of more typical metallicities. We find that when the oxygen abundance is less than about 1/100 of solar, the C/O ratio in high redshift DLAs and sub-DLAs matches that of halo stars of similar metallicity and shows higher values than expected from galactic chemical evolution models based on conventional stellar yields. Furthermore, there are indications that at these low metallicities the N/O ratio may also be above simple expectations and may exhibit a minimum value, as proposed by Centurion and her collaborators in 2003. Both results can be interpreted ...

  18. 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...

  19. Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor

    CERN Document Server

    Frebel, Anna; Simon, Joshua D

    2009-01-01

    Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. Based on the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. However, verification of the iron-deficiency and measurements of additional elements, such as the alpha-element Mg, are mandatory for demonstrating that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming the iron abundance of less than 1/4000th that of the Sun, and showing that the overall abundance pattern mirrors th...

  20. 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...

  1. CHEMICAL ABUNDANCE ANALYSIS OF A NEUTRON-CAPTURE ENHANCED RED GIANT IN THE BULGE PLAUT FIELD

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Christian I.; Rich, R. Michael [Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States); McWilliam, Andrew, E-mail: cijohnson@astro.ucla.edu, E-mail: rmr@astro.ucla.edu, E-mail: cjohnson@cfa.harvard.edu, E-mail: andy@obs.carnegiescience.edu [Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States)

    2013-09-20

    We present chemical abundances for 27 elements ranging from oxygen to erbium in the metal-poor ([Fe/H] = –1.67) bulge red giant branch star 2MASS 18174532-3353235. The results are based on equivalent width and spectrum synthesis analyses of a high-resolution (R ∼ 30, 000) spectrum obtained with the Magellan-MIKE spectrograph. While the light (Z ∼< 30) element abundance patterns match those of similar metallicity bulge and halo stars, the strongly enhanced heavy element abundances are more similar to 'r-II' halo stars (e.g., CS 22892-052) typically found at [Fe/H] ∼< – 2.5. We find that the heaviest elements (Z ≥ 56) closely follow the scaled-solar r-process abundance pattern. We do not find evidence supporting significant s-process contributions; however, the intermediate mass elements (e.g., Y and Zr) appear to have been produced through a different process than the heaviest elements. The light and heavy element abundance patterns of 2MASS 18174532-3353235 are in good agreement with the more metal-poor r-process enhanced stars CS 22892-052 and BD +17{sup o}3248. 2MASS 18174532-3353235 also shares many chemical characteristics with the similar metallicity but comparatively α-poor Ursa Minor dwarf galaxy giant COS 82. Interestingly, the Mo and Ru abundances of 2MASS 18174532-3353235 are also strongly enhanced and follow a similar trend recently found to be common in moderately metal-poor main-sequence turn-off halo stars.

  2. Discovery in the Galactic Bulge

    Science.gov (United States)

    Kohler, Susanna

    2015-11-01

    In our efforts to map our galaxys structure, one region has remained very difficult to probe: the galactic center. A new survey, however, uses infrared light to peer through the gas and dust in the galactic plane, searching for variable stars in the bulge of the galaxy. This study has discovered a population of very young stars in a thin disk in the galactic center, providing clues to the star formation history of the Milky Way over the last 100 million years.Obscured CenterThe center of the Milky Way is dominated by a region known as the galactic bulge. Efforts to better understand this region in particular, its star formation history have been hindered by the stars, gas, and dust of the galactic disk, which prevent us from viewing the galactic bulge at low latitudes in visible light.The positions of the 35 classical Cepheids discovered in VVV data, projected onto an image of the galactic plane. Click for a better look! The survey area is bounded by the blue lines, and the galactic bar is marked with a red curve. The bottom panel shows the position of the Cepheids overlaid on the VVV bulge extinction map. [Dkny et al. 2015]Infrared light, however, can be used to probe deeper through the dust than visible-light searches. A new survey called VISTA Variables in the Via Lactea (VVV) uses the VISTA telescope in Chile to search, in infrared, for variable stars in the inner part of the galaxy. The VVV survey area spans the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high.Led by Istvn Dkny, a researcher at the Millennium Institute of Astrophysics and the Pontifical Catholic University of Chile, a team has now used VVV data to specifically identify classical Cepheid variable stars in the bulge. Why? Cepheids are pulsating stars with a very useful relation between their periods and luminosities that allows them to be used as distance indicators. Moreover, classical Cepheids are indicators of young stellar populations which can

  3. 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'.

  4. 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 ...

  5. The Effect of Scattering on the Temperature Stratification of 3D Model Atmospheres of Metal-Poor Red Giants

    Science.gov (United States)

    Collet, Remo; Hayek, Wolfgang; Asplund, Martin

    2011-08-01

    We study the effects of different approximations of scattering in 3D radiation-hydrodynamics simulations on the photospheric temperature stratification of metal-poor red giant stars. We find that assuming a Planckian source function and neglecting the contribution of scattering to extinction in optically thin layers provides a good approximation of the effects of coherent scattering on the photospheric temperature balance.

  6. 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...

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

    Science.gov (United States)

    Salaris, M.; Groenewegen, M. A. T.; Weiss, A.

    2000-03-01

    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. When properly calibrated, our models with diffusion reproduce well within the errors the Hertzsprung-Russell diagram of Hipparcos subdwarfs with empirically determined T_eff values and high resolution spectroscopical [Fe/H] determinations. 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. This is at odds with the basic assumption of the MS-fitting technique for distance determinations. However, the use of the rather large sample of Hipparcos lower MS subdwarfs with accurate parallaxes keeps at minimum the effect of these differences, for two reasons. First, it is possible to use subdwarfs with observed [Fe/H] values close to the cluster one; this minimizes the colour corrections (which are derived from the isochrones) needed to reduce all the subdwarfs to a mono-metallicity sequence having the same [Fe/H] than the cluster. Second, one can employ objects sufficiently faint so that the differences between the subdwarfs and cluster MS with the same observed value of [Fe/H] are small (they increase for increasing luminosity). We find therefore that the distances based on standard isochrones are basically unaltered when diffusion is taken properly into account. On the other hand, the absolute ages

  8. A Color-Magnitude Diagram for a Globular Cluster In the Giant Elliptical Galaxy NGC 5128

    CERN Document Server

    Harris, G L H; Harris, W E

    1998-01-01

    The Hubble Space Telescope has been used to obtain WFPC2 (V,I) photometry for a large sample of stars in the outer halo of the giant elliptical NGC 5128 (d = 4 Mpc). The globular cluster N5128-C44, at the center of the Planetary Camera field, is well enough resolved to permit the construction of a color-magnitude diagram (CMD) for it which covers the brightest two magnitudes of the giant branch. The CMD is consistent with that of a normal old, moderately low-metallicity ([Fe/H] = -1.30 globular cluster, distinctly more metal-poor than most of the field halo stars at the same projected location (which average [Fe/H] ~ -0.5). This is the most distant globular cluster in which direct color-magnitude photometry has been achieved to date, and the first one belonging to a giant E galaxy.

  9. 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.

  10. 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.

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

    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)

    2014-04-01

    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 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.

  12. Fluorine in carbon-enhanced metal-poor stars: a binary scenario

    Science.gov (United States)

    Lugaro, M.; de Mink, S. E.; Izzard, R. G.; Campbell, S. W.; Karakas, A. I.; Cristallo, S.; Pols, O. R.; Lattanzio, J. C.; Straniero, O.; Gallino, R.; Beers, T. C.

    2008-06-01

    Aims: A super-solar fluorine abundance was observed in the carbon-enhanced metal-poor (CEMP) star HE 1305+0132 ([F/Fe] = +2.90, [Fe/H] = -2.5). We propose that this observation can be explained using a binary model that involve mass transfer from an asymptotic giant branch (AGB) star companion and, based on this model, we predict F abundances in CEMP stars in general. We discuss wether F can be used to discriminate between the formation histories of most CEMP stars: via binary mass transfer or from the ejecta of fast-rotating massive stars. Methods: We compute AGB yields using different stellar evolution and nucleosynthesis codes to evaluate stellar model uncertainties. We use a simple dilution model to determine the factor by which the AGB yields should be diluted to match the abundances observed in HE 1305+0132. We further employ a binary population synthesis tool to estimate the probability of F-rich CEMP stars. Results: The abundances observed in HE 1305+0132 can be explained if this star accreted 3-11% of the mass lost by its former AGB companion. The primary AGB star should have dredged-up at least 0.2 {M}⊙ of material from its He-rich region into the convective envelope via third dredge-up, which corresponds to AGB models of Z ≃ 0.0001 and mass ≃2 {M}⊙. Many AGB model uncertainties, such as the treatment of convective borders and mass loss, require further investigation. We find that in the binary scenario most CEMP stars should also be FEMP stars, that is, have [F/Fe] > +1, while fast-rotating massive stars do not appear to produce fluorine. We conclude that fluorine is a signature of low-mass AGB pollution in CEMP stars, together with elements associated with the slow neutron-capture process.

  13. Chemical Analysis of a Carbon-enhanced Very Metal-poor Star: CD-27 14351

    Science.gov (United States)

    Karinkuzhi, Drisya; Goswami, Aruna; Masseron, Thomas

    2017-01-01

    We present, for the first time, an abundance analysis of a very metal-poor carbon-enhanced star CD-27 14351 based on a high-resolution (R ∼ 48,000) FEROS spectrum. Our abundance analysis performed using local thermodynamic equilibrium model atmospheres shows that the object is a cool star with stellar atmospheric parameters, effective temperature Teff = 4335 K, surface gravity log g = 0.5, microturbulence ξ = 2.42 km s‑1, and metallicity [Fe/H] = ‑2.6. The star exhibits high carbon and nitrogen abundances with [C/Fe] = 2.89 and [N/Fe] = 1.89. Overabundances of neutron-capture elements are evident in Ba, La, Ce, and Nd, with estimated [X/Fe] > 1, the largest enhancement being seen in Ce with [Ce/Fe] = 2.63. While the first peak s-process elements Sr and Y are found to be enhanced with respect to Fe, ([Sr/Fe] = 1.73 and [Y/Fe] = 1.91), the third peak s-process element Pb could not be detected in our spectrum at the given resolution. Europium, primarily an r-process element also shows an enhancement with [Eu/Fe] = 1.65. With [Ba/Eu] = 0.12, the object CD-27 14351 satisfies the classification criterion for a CEMP-r/s star. The elemental abundance distributions observed in this star are discussed in light of the chemical abundances observed in other CEMP stars in the literature.

  14. 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.

  15. Clumpy Disc and Bulge Formation

    CERN Document Server

    Perez, J; Tissera, P; Michel-Dansac, L

    2013-01-01

    We present a set of hydrodynamical/Nbody controlled simulations of isolated gas rich galaxies that self-consistently include SN feedback and a detailed chemical evolution model, both tested in cosmological simulations. The initial conditions are motivated by the observed star forming galaxies at z ~ 2-3. We find that the presence of a multiphase interstellar media in our models promotes the growth of disc instability favouring the formation of clumps which in general, are not easily disrupted on timescales compared to the migration time. We show that stellar clumps migrate towards the central region and contribute to form a classical-like bulge with a Sersic index, n > 2. Our physically-motivated Supernova feedback has a mild influence on clump survival and evolution, partially limiting the mass growth of clumps as the energy released per Supernova event is increased, with the consequent flattening of the bulge profile. This regulation does not prevent the building of a classical-like bulge even for the most ...

  16. The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge

    CERN Document Server

    Ferraro, F R; Mucciarelli, A; Beccari, G; Rich, R M; Origlia, L; Lanzoni, B; Rood, R T; Valenti, E; Bellazzini, M; Ransom, S M; Cocozza, G; 10.1038/nature08581

    2009-01-01

    Globular star clusters are compact and massive stellar systems old enough to have witnessed the entire history of our Galaxy, the Milky Way. Although recent results suggest that their formation may have been more complex than previously thought, they still are the best approximation to a stellar population formed over a relatively short time scale (less than 1 Gyr) and with virtually no dispersion in the iron content. Indeed, only one cluster-like system (omega Centauri) in the Galactic halo is known to have multiple stellar populations with a significant spread in iron abundance and age4,5. Similar findings in the Galactic bulge have been hampered by the obscuration arising from thick and varying layers of interstellar dust. Here we report that Terzan 5, a globular-cluster-like system in the Galactic bulge, has two stellar populations with different iron content and ages. Terzan 5 could be the surviving remnant of one of the primordial building blocks that are thought to merge and form galaxy bulges.

  17. Nonlinear Color-Metallicity Relations of Globular Clusters. III. On the Discrepancy in Metallicity between Globular Cluster Systems and their Parent Elliptical Galaxies

    CERN Document Server

    Yoon, Suk-Jin; Blakeslee, John P; Peng, Eric W; Sohn, Sangmo T; Cho, Jaeil; Kim, Hak-Sub; Chung, Chul; Kim, Sooyoung; Lee, Young-Wook

    2011-01-01

    One of the conundrums in extragalactic astronomy is the discrepancy in observed metallicity distribution functions (MDFs) between the two prime stellar components of early-type galaxies-globular clusters (GCs) and halo field stars. This is generally taken as evidence of highly decoupled evolutionary histories between GC systems and their parent galaxies. Here we show, however, that new developments in linking the observed GC colors to their intrinsic metallicities suggest nonlinear color-to-metallicity conversions, which translate observed color distributions into strongly-peaked, unimodal MDFs with broad metal-poor tails. Remarkably, the inferred GC MDFs are similar to the MDFs of resolved field stars in nearby elliptical galaxies and those produced by chemical evolution models of galaxies. The GC MDF shape, characterized by a sharp peak with a metal-poor tail, indicates a virtually continuous chemical enrichment with a relatively short timescale. The characteristic shape emerges across three orders of magni...

  18. Hu1-2: a metal-poor bipolar planetary nebula with fast collimated outflows

    CERN Document Server

    Fang, Xuan; Miranda, Luis F; Riera, Angels; Velazquez, Pablo F; Raga, Alejandro C

    2015-01-01

    We present narrow-band optical and near-IR imaging and optical long-slit spectroscopic observations of Hu1-2, a Galactic planetary nebula (PN) with a pair of [N II]-bright, fast-moving (> 340 km/s) bipolar knots. Intermediate-dispersion spectra are used to derive physical conditions and abundances across the nebula, and high-dispersion spectra to study the spatio-kinematical structure. Generally Hu1-2 has high He/H (~0.14) and N/O ratios (~0.9), typical of Type I PNe. On the other hand, its abundances of O, Ne, S, and Ar are low as compared with the average abundances of Galactic bulge and disc PNe. The position-velocity maps can be generally described as an hour-glass shaped nebula with bipolar expansion, although the morphology and kinematics of the innermost regions cannot be satisfactorily explained with a simple, tilted equatorial torus. The spatio-kinematical study confines the inclination angle of its major axis to be within 10 degrees of the plane of sky. As in the irradiated bow-shocks of IC4634 and ...

  19. Dynamics of the Globular Cluster NGC 665 with WFPC2

    Institute of Scientific and Technical Information of China (English)

    CHEN Ding; CHEN Li; WANG Jia-Ji

    2004-01-01

    @@ We have used the Hubble Space Telescope observations to measure proper motion of the globular cluster NGC6656 (M22) with respect to the background bulge stars and its internal velocity dispersion profile. Based on the proper motion of the cluster, its space velocity (II, (-) , W) = (184 ± 3, 209 ±14, 132 ± 15) km s- 1 and galactic orbit are also obtained. The central velocity dispersion in radial and tangential components of the internal motion of cluster stars is 16.99 km s-1. We derive the mass-to-light ratio M/ LV ~ 3.3 ± 0.2, which is relatively higher than the previous results.

  20. The Primordial Deuterium Abundance of the Most Metal-poor Damped Lyman-α System

    Science.gov (United States)

    Cooke, Ryan J.; Pettini, Max; Nollett, Kenneth M.; Jorgenson, Regina

    2016-10-01

    We report the discovery and analysis of the most metal-poor damped Lyα (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, 105 (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 (BBN) that incorporate the latest determinations of several key nuclear reaction cross-sections, and propagate their associated uncertainty. Combining our measurement of (D/H)P with these BBN calculations yields an estimate of the cosmic baryon density, 100 ΩB,0 h 2(BBN) = 2.156 ± 0.020, if we adopt the most recent theoretical determination of the d{(p,γ )}3{He} reaction rate. This measure of ΩB,0 h 2 differs by ˜2.3σ from the Standard Model value estimated from the Planck observations of the cosmic microwave background. Using instead a d{(p,γ )}3{He} reaction rate that is based on the best available experimental cross-section data, we estimate 100 ΩB,0 h 2(BBN) = 2.260 ± 0.034, which is in somewhat better agreement with the Planck value. Forthcoming measurements of the crucial d{(p,γ )}3{He} cross-section may shed further light on this discrepancy. Based on observations collected at the European Organisation for Astronomical Research in the Southern

  1. Optical Gravitational Lensing Experiment. The Distance Scale Galactic Bulge - LMC - SMC

    CERN Document Server

    Udalski, A

    1998-01-01

    We analyze the mean luminosity of three samples of field RRab Lyr stars observed in the course of the OGLE microlensing experiment: 73 stars from the Galactic bulge and 110 and 128 stars from selected fields in the LMC and SMC, respectively. The fields are the same as in the recent distance determination to the Magellanic Clouds with the red clump stars method by Udalski et al (1998). We determine the relative distance scale d_{GB}:d_{LMC}:d_{SMC} equal to: (0.194+/-0.010):1.00:(1.30+/-0.08). We calibrate our RR Lyr distance scale with the recent calibration of Gould and Popowski (1998) based on statistical parallaxes. We obtain the following distance moduli to the Galactic bulge, LMC and SMC: m-M=14.53+/-0.15, m-M=18.09+/-0.16 and m-M=18.66+/-0.16 mag. We use the RR Lyr mean V-band luminosity at the Galactic bulge metallicity as the reference brightness and analyze the mean, I-band luminosity of the red clump stars in objects with different ages and metallicities. We add to our analysis the metal poor Carina...

  2. Multivariate analysis of the globular clusters in M87

    CERN Document Server

    Das, Sukanta; Davoust, Emmanuel

    2015-01-01

    An objective classification of 147 globular clusters in the inner region of the giant elliptical galaxy M87 is carried out with the help of two methods of multivariate analysis. First independent component analysis is used to determine a set of independent variables that are linear combinations of various observed parameters (mostly Lick indices) of the globular clusters. Next K-means cluster analysis is applied on the independent components, to find the optimum number of homogeneous groups having an underlying structure. The properties of the four groups of globular clusters thus uncovered are used to explain the formation mechanism of the host galaxy. It is suggested that M87 formed in two successive phases. First a monolithic collapse, which gave rise to an inner group of metal-rich clusters with little systematic rotation and an outer group of metal-poor clusters in eccentric orbits. In a second phase, the galaxy accreted low-mass satellites in a dissipationless fashion, from the gas of which the two othe...

  3. Globular cluster ages and the formation of the galactic halo

    CERN Document Server

    Chaboyer, B; Sarajedini, A; Chaboyer, Brian; Sarajedini, Ata

    1995-01-01

    Main sequence turnoff magnitudes from the recent set of Yale isochrones (Chaboyer \\ea 1995) have been combined with a variety of relations for the absolute magnitude of RR Lyr stars (\\mvrr) to calibrate age as a function of the difference in magnitude between the main sequence turn-off and the horizontal branch (\\dv). A best estimate for the calibration of \\mvrr is derived from a survey of the current literature: \\mvrr = 0.20 \\feh + 0.98. This estimate, together with other calibrations (with slopes ranging from 0.15 to 0.30) has been used to derive \\dv ages for 43 Galactic globular clusters. Independent of the choice of \\mvrr, there is no strong evidence for an age-Galacto\\-centric distance relationship among the 43 globular clusters. However, an age-metallicity relation exists, with the metal-poor clusters being the oldest. A study of the age distribution reveals that an age range of 5 Gyr exists among the bulk of the globular clusters. In addition, about 10\\% of the sample are substantially younger, and inc...

  4. A Genuine Intermediate-Age Globular Cluster in M33

    CERN Document Server

    Chandar, R; Sarajedini, A; Goudfrooij, P; Chandar, Rupali; Puzia, Thomas H.; Sarajedini, Ata

    2006-01-01

    We present deep integrated-light spectroscopy of nine M33 globular clusters taken with the Hectospec instrument at the MMT Observatory. Based on our spectroscopy and previous deep color-magnitude diagrams obtained with HST/WFPC2, we present evidence for the presence of a genuine intermediate-age globular cluster in M33. The analysis of Lick line indices indicates that all globular clusters are metal-poor ([Z/H] <~ -1.0) and that cluster M33-C38 is about 5-8 Gyr younger than the rest of the sample M33 star clusters. We find no evidence for a population of blue horizontal branch stars in the CMD of M33-C38, which rules out the possibility of an artificially young spectroscopic age due to the presence of hot stars. We infer a total mass of 5-9 x 10^4 M_sol for M33-C38, which implies that M33-C38 has survived ~2-3 times longer than some dynamical evolution model predictions for star clusters in M33, although it is not yet clear to which dynamical component of M33 - thin disk, thick disk, halo - the cluster is ...

  5. Spectroscopic characterization of a sample of metal-poor solar-type stars from the HARPS planet search program

    CERN Document Server

    Sousa, Sérgio G; Israelian, Garik; Lovis, C; Mayor, Michel; Silva, Pedro B; Udry, Stephane

    2010-01-01

    Stellar metallicity strongly correlates with the presence of planets and their properties. To check for new correlations between stars and the existence of an orbiting planet, we determine precise stellar parameters for a sample of metal-poor solar-type stars. This sample was observed with the HARPS spectrograph and is part of a program to search for new extrasolar planets. The stellar parameters were determined using an LTE analysis based on equivalent widths (EW) of iron lines and by imposing excitation and ionization equilibrium. The ARES code was used to allow automatic and systematic derivation of the stellar parameters. Precise stellar parameters and metallicities were obtained for 97 low metal-content stars. We also present the derived masses, luminosities, and new parallaxes estimations based on the derived parameters, and compare our spectroscopic parameters with an infra-red flux method calibration to check the consistency of our method in metal poor stars. Both methods seems to give the same effect...

  6. PopIII-star siblings in IZw18 and metal-poor WR galaxies unveiled from integral field spectroscopy

    Science.gov (United States)

    Kehrig, C.; Vílchez, J. M.; Pérez-Montero, E.; Iglesias-Páramo, J.; Brinchmann, J.; Crowther, P. A.; Durret, F.; Kunth, D.

    Here, we highlight our recent results from the IFS study of Mrk178, the closest metal-poor WR galaxy, and of IZw18, the most metal-poor star-forming galaxy known in the local Universe. The IFS data of Mrk178 show the importance of aperture effects on the search for WR features, and the extent to which physical variations in the ISM properties can be detected. Our IFS data of IZw18 reveal its entire nebular HeIIλ4686-emitting region, and indicate for the very first time that peculiar, hot (nearly) metal-free ionizing stars (called here PopIII-star siblings) might hold the key to the HeII-ionization in IZw18.

  7. PopIII-star siblings in IZw18 and WRs in metal-poor galaxies unveiled from integral field spectroscopy

    CERN Document Server

    Kehrig, Carolina; Perez-Montero, Enrique; Iglesias-Paramo, Jorge; Brinchmann, Jarle; Crowther, Paul A; Durret, Florence; Kunth, Daniel

    2015-01-01

    Here we highlight our recent results from the IFS study of Mrk178, the closest metal-poor WR galaxy, and of IZw18, the most metal-poor star-forming galaxy known in the local Universe. The IFS data of Mrk178 show the importance of aperture effects on the search for WR features, and the extent to which physical variations in the ISM properties can be detected. Our IFS data of IZw18 reveal its entire nebular HeII4686-emitting region, and indicate for the first time that peculiar, very hot (nearly) metal-free ionizing stars (called here PopIII-star siblings) might hold the key to the HeII-ionization in IZw18.

  8. A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-Poor Stars

    CERN Document Server

    Roederer, Ian U; Thompson, Ian B; Shectman, Stephen A; Sneden, Christopher; Burley, Gregory S; Kelson, Daniel D

    2014-01-01

    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-year observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coude 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 ab...

  9. 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.

  10. 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.

  11. 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.

  12. Globular clusters in the outer Galactic halo: new HST/ACS imaging of 6 globular clusters and the Galactic globular cluster age-metallicity relation

    CERN Document Server

    Dotter, Aaron; Anderson, Jay

    2011-01-01

    Color-magnitude diagrams (CMDs) derived from Hubble Space Telescope (HST) Advanced Camera for Surveys F606W,F814W photometry of 6 globular clusters (GCs) are presented. The six GCs form two loose groupings in Galactocentric distance (Rgc): IC 4499, NGC 6426, and Ruprecht 106 at ~15-20 kpc and NGC 7006, Palomar 15, and Pyxis at ~40 kpc. The CMDs allow the ages to be estimated from the main sequence turnoff in every case. In addition, the age of Palomar 5 (Rgc ~ 18 kpc) is estimated using archival HST Wide Field Planetary Camera 2 V,I photometry. The age analysis reveals the following: IC 4499, Ruprecht 106, and Pyxis are 1-2 Gyr younger than inner halo GCs with similar metallicities; NGC 7006 and Palomar 5 are marginally younger than their inner halo counterparts; NGC 6426 and Palomar 15, the two most metal-poor GCs in the sample, are coeval with all the other metal-poor GCs within the uncertainties. Combined with our previous efforts, the current sample provides strong evidence that the Galactic GC age-metall...

  13. The most metal-poor damped Lyman alpha systems: An insight into dwarf galaxies at high redshift

    CERN Document Server

    Cooke, Ryan; Jorgenson, Regina A

    2014-01-01

    In this paper, we analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Lyman alpha 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 alpha-capture and Fe-peak elements when the metallicity is [Fe/H] ~ -2.0. 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 m...

  14. 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...

  15. 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...

  16. Three-dimensional surface convection simulations of metal-poor stars -- The effect of scattering on the photospheric temperature stratification

    CERN Document Server

    Collet, R; Asplund, M; Nordlund, Å; Trampedach, R; Gudiksen, B

    2011-01-01

    Three-dimensional (3D) radiative hydrodynamic model atmospheres of metal-poor late-type stars are characterized by cooler upper photospheric layers than their 1D counterparts. This property of 3D models can dramatically affect elemental abundances derived from temperature-sensitive spectral lines. We investigate whether the cool surface temperatures predicted by metal-poor 3D models can be ascribed to the approximated treatment of scattering in the radiative transfer. We use the Bifrost code to test three different ways to handle scattering in 3D model atmospheres of metal-poor stars. First, we solve self-consistently the radiative transfer equation for a source function with a coherent scattering term. Second, we solve the radiative transfer equation for a Planckian source function, neglecting the contribution of continuum scattering to extinction in the optically thin layers; this has been the default mode in previous models of ours. Third, we treat scattering as pure absorption everywhere, which is the sta...

  17. The GAPS Programme with HARPS-N@TNG II: No giant planets around the metal-poor star HIP 11952

    CERN Document Server

    Desidera, S; Bonomo, A S; Gratton, R; Poretti, E; Claudi, R; Latham, D W; Affer, L; Cosentino, R; Damasso, M; Esposito, M; Giacobbe, P; Malavolta, L; Nascimbeni, V; Piotto, G; Rainer, M; Scardia, M; Schmid, V S; Lanza, A F; Micela, G; Pagano, I; Bedin, L; Biazzo, K; Borsa, F; Carolo, E; Covino, E; Faedi, F; Hebrard, G; Lovis, C; Maggio, A; Mancini, L; Marzari, F; Messina, S; Molinari, E; Munari, U; Pepe, F; Santos, N; Scandariato, G; Shkolnik, E; Southworth, J

    2013-01-01

    In the context of the program Global Architecture of Planetary Systems (GAPS), we have performed radial velocity monitoring of the metal-poor star HIP 11952 on 35 nights over about 150 days using the newly installed high resolution spectrograph HARPS-N at the TNG and HARPS at ESO 3.6m telescope. The radial velocities show a scatter of 7 m/s, compatible with the measurement errors for such a moderately warm metal-poor star (Teff = 6040+-120K; [Fe/H] =-1.9+-0.1). We then exclude the presence of the two giant planets with periods of 6.95+-0.01 d and 290.0+-16.2 d and radial velocity semi-amplitudes of 100.3+-19.4 m/s and 105.2+-14.7 m/s, respectively, which had recently been announced. This result is important considering that HIP 11952 was thought to be the most metal-poor star hosting a planetary system with giant planets, thus challenging some models of planet formation.

  18. SEARCHES FOR METAL-POOR STARS FROM THE HAMBURG/ESO SURVEY USING THE CH G BAND

    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 05508-090 (Brazil); Kennedy, Catherine R.; Beers, Timothy C.; Lee, Young Sun [Department of Physics and Astronomy and JINA (Joint Institute for Nuclear Astrophysics), Michigan State University, East Lansing, MI 48824 (United States); Christlieb, Norbert [Zentrum fuer Astronomie der Universitaet Heidelberg, Landessternwarte, Koenigstuhl 12, 69117 Heidelberg (Germany); Sivarani, Thirupathi [Indian Institute of Astrophysics, 2nd Block, Koramangala, Bangalore 560034 (India); Reimers, Dieter [Hamburger Sternwarte, Universitaet Hamburg, Gojenbergsweg 112, 21029 Hamburg (Germany); Wisotzki, Lutz, E-mail: vmplacco@astro.iag.usp.br [Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam (Germany)

    2011-12-15

    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 overabundances of carbon are common among metal-poor stars, as has been found by numerous studies over the past two decades. The selection was made by considering two line indices in the 4300 A 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. A simple numerical procedure, based on available photometry, was developed to correct the line indices and overcome this limitation. Visual inspection and classification of the spectra from the HES plates yielded a list of 5288 new metal-poor (and by selection, carbon-rich) 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, based on follow-up medium-resolution spectra obtained with the SOAR 4.1 m and Gemini 8 m telescopes. We demonstrate that our new method improves the metal-poor star fractions found by our pilot study by up to a factor of three in the same magnitude range, as compared with our pilot study based on only one CH G-band index. Our selection scheme obtained roughly a 40% success rate for identification of stars with [Fe/H] <-1.0; the primary contaminant is late-type stars with near-solar abundances and, often, emission line cores that filled in the Ca II K line on the prism spectrum. Because the selection is based on carbon, we greatly increase the numbers of known carbon-enhanced metal-poor stars from the HES with intermediate metallicities -2

  19. Three-dimensional surface convection simulations of metal-poor stars. The effect of scattering on the photospheric temperature stratification

    Science.gov (United States)

    Collet, R.; Hayek, W.; Asplund, M.; Nordlund, Å.; Trampedach, R.; Gudiksen, B.

    2011-04-01

    Context. Three-dimensional (3D) radiative hydrodynamic model atmospheres of metal-poor late-type stars are characterized by cooler upper photospheric layers than their one-dimensional counterparts. This property of 3D model atmospheres can dramatically affect the determination of elemental abundances from temperature-sensitive spectral features, with profound consequences on galactic chemical evolution studies. Aims: We investigate whether the cool surface temperatures predicted by 3D model atmospheres of metal-poor stars can be ascribed to approximations in the treatment of scattering during the modelling phase. Methods: We use the Bifrost code to construct 3D model atmospheres of metal-poor stars and test three different ways to handle scattering in the radiative transfer equation. As a first approach, we solve iteratively the radiative transfer equation for the general case of a source function with a coherent scattering term, treating scattering in a correct and consistent way. As a second approach, we solve the radiative transfer equation in local thermodynamic equilibrium approximation, neglecting altogether the contribution of continuum scattering to extinction in the optically thin layers; this has been the default mode in our previous 3D modelling as well as in present Stagger-Code models. As our third and final approach, we treat continuum scattering as pure absorption everywhere, which is the standard case in the 3D modelling by the CO5BOLD collaboration. Results: For all simulations, we find that the second approach produces temperature structures with cool upper photospheric layers very similar to the case in which scattering is treated correctly. In contrast, treating scattering as pure absorption leads instead to significantly hotter and shallower temperature stratifications. The main differences in temperature structure between our published models computed with the Stagger- and Bifrost codes and those generated with the CO5BOLD code can be traced

  20. Ultrasonographic findings in patients with peristomal bulging

    DEFF Research Database (Denmark)

    Sjödahl, Rune I; Thorelius, Lars; Hallböök, Olof J

    2011-01-01

    The aim of this study was to obtain a classification of peristomal bulging based on findings at ultrasonography in patients with a sigmoid colostomy.......The aim of this study was to obtain a classification of peristomal bulging based on findings at ultrasonography in patients with a sigmoid colostomy....

  1. Dust properties in the Galactic bulge

    NARCIS (Netherlands)

    Pottasch, S. R.; Bernard-Salas, J.

    2013-01-01

    Context. It has been suggested that the ratio of total-to-selective extinction RV in dust in the interstellar medium differs in the Galactic bulge from its value in the local neighborhood. Aims: We attempt to test this suggestion. Methods: The mid-infrared hydrogen lines in 16 Galactic bulge PNe mea

  2. 3-Dimensional dynamics of the galactic bulge

    NARCIS (Netherlands)

    Soto Vicencio, Mario Humberto

    2010-01-01

    This thesis is part of a project which attempts to unveil the structure of the galactic bulge of our galaxy through the study of the kinematics of stars in low foreground extinction windows.Thus, in order to effectively constraint the phase-space distribution function of the galactic bulge, we have

  3. Dissolution of Globular Clusters

    OpenAIRE

    Baumgardt, Holger

    2006-01-01

    Globular clusters are among the oldest objects in galaxies, and understanding the details of their formation and evolution can bring valuable insight into the early history of galaxies. This review summarises the current knowledge about the dissolution of star clusters and discusses the implications of star cluster dissolution for the evolution of the mass function of star cluster systems in galaxies.

  4. Variable stars in the VVV globular clusters. I. 2MASS-GC02 and Terzan10

    CERN Document Server

    Alonso-García, Javier; Catelan, Márcio; Ramos, Rodrigo Contreras; Gran, Felipe; Amigo, Pía; Leyton, Paul; Minniti, Dante

    2014-01-01

    The VISTA Variables in the Via Lactea (VVV) ESO Public Survey is opening a new window to study the inner Galactic globular clusters using their variable stars. These globular clusters have been neglected in the past due to the difficulties caused by the presence of an elevated extinction and high field stellar densities in their lines of sight. However, the discovery and study of any present variables in these clusters, especially RRLyrae stars, can help to greatly improve the accuracy of their physical parameters. It can also help to shed some light on the interrogations brought by the intriguing Oosterhoff dichotomy in the Galactic globular cluster system. In a series of papers we plan to explore the variable stars in the globular clusters falling inside the field of the VVV survey. In this first paper we search and study the variables present in two highly-reddened, moderately metal-poor, faint, inner Galactic globular clusters: 2MASS-GC02 and Terzan10. We report the discovery of sizable populations of RR ...

  5. Intra Cluster Globular Clusters around NGC 1399 in Fornax?

    CERN Document Server

    Schuberth, Y; Bassino, L; Hilker, M

    2007-01-01

    We investigate whether the globular clusters (GCs) in the recently published sample of GCs in the Fornax cluster by Bergond and coworkers are indeed intra-cluster objects. We combine the catalogue of radial velocity measurements by Bergond et al. with our CTIO MOSAIC photometry in the Washington system and analyse the relation of metal-poor and metal-rich GCs with their host galaxies. The metal-rich GCs appear to be kinematically associated with their respective host galaxies. The vast majority of the metal-poor GCs found in between the galaxies of the Fornax cluster have velocities which are consistent with them being members of the very extended NGC 1399 GC system. We find that when the sample is restricted to the most accurate velocity measurements, the GC velocity dispersion profile can be described with a mass model derived for the NGC 1399 GC system within 80 kpc. We identify one ``vagrant'' GC whose radial velocity suggests that it is not bound to any galaxy unless its orbit has a very large apogalacti...

  6. FAILURE ANALYSIS: WASTEWATER DRUM BULGING

    Energy Technology Data Exchange (ETDEWEB)

    Vormelker, P

    2008-09-15

    A 55 gallon wastewater drum lid was found to be bulged during storage in a remote area. Drum samples were obtained for analysis. The interior surface of these samples revealed blistering and holes in the epoxy phenolic drum liner and corrosion of the carbon steel drum. It is suspected that osmotic pressure drove permeation of the water through the epoxy phenolic coating which was weakened from exposure to low pH water. The coating failed at locations throughout the drum interior. Subsequent corrosion of the carbon steel released hydrogen which pressurized the drum causing deformation of the drum lid. Additional samples from other wastewater drums on the same pallet were also evaluated and limited corrosion was visible on the interior surfaces. It is suspected that, with time, the corrosion would have advanced to cause pressurization of these sealed drums.

  7. Observational Constraints on First-Star Nucleosynthesis. II. Spectroscopy of an Ultra metal-poor CEMP-no Star

    Science.gov (United States)

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

    2016-12-01

    We report on the first high-resolution spectroscopic analysis of HE 0020-1741, 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, HE 0020-1741 is subclassified as a carbon-enhanced metal-poor star without enhancements in neutron-capture elements (CEMP-no). We show that the light-element abundance pattern of HE 0020-1741 is consistent with predicted yields from a massive (M = 21.5 {M}⊙ ), 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{--}100 {M}⊙ ), 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}}] \\lt -4.0, as the abundance patterns for more than half of the sample studied in this work (7 out of 12 stars) cannot be easily reproduced by the predicted yields. Based on observations gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile, and the New Technology Telescope (NTT) of the European Southern Observatory (088.D-0344A), La Silla, Chile.

  8. 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.

  9. The Most Metal-poor Damped Lyα Systems: An Insight into Dwarf Galaxies at High-redshift

    Science.gov (United States)

    Cooke, Ryan J.; Pettini, Max; Jorgenson, Regina A.

    2015-02-01

    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] sime -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 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. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (VLT program IDs: 60.A-9022(A), 65.O-0063(B), 65.O-0296(A), 67.A-0022(A), 67.A-0078(A), 68.A-0600(A), 68.B-0115(A), 70.A-0425(C), 078.A-0185(A), 080.A-0014(A), 082.A-0544(A), 083.A-0042(A), 083.A-0454(A), 085.A-0109(A), 086.A-0204(A)), and at the

  10. CU Comae a new field double-mode RR Lyrae, the most metal poor discovered to date

    CERN Document Server

    Clementini, G; Fabrizio, L D; Bragaglia, A; Merighi, R; Tosi, M P; Carretta, E; Gratton, R G; Ivans, I I; Kinard, A; Marconi, M; Smith, H A; Wilhelm, R; Woodruff, T; Sneden, C

    2000-01-01

    We report the discovery of a new double-mode RR Lyrae variable (RRd) in the field of our Galaxy: CU Comae. CU Comae is the sixth such RRd identified to date and is the most metal-poor RRd ever detected. Based on BVI CCD photometry spanning eleven years of observations, we find that CU Comae has periods P0=0.5441641 +/-0.0000049d and P1=0.4057605 +/-0.0000018d. The amplitude of the primary (first-overtone) period of CU Comae is about twice the amplitude of the secondary (fundamental) period. The combination of the fundamental period of pulsation P0 and the period ratio of P1/P0=0.7457 places the variable on the metal-poor side of the Petersen diagram, in the region occupied by M68 and M15 RRd's. A mass of 0.83 solar masses is estimated for CU Comae using an updated theoretical calibration of the Petersen diagram. High resolution spectroscopy (R=30,000) covering the full pulsation cycle of CU Comae was obtained with the 2.7 m telescope of the Mc Donald Observatory, and has been used to build up the radial veloc...

  11. On the use of the index N2 to derive the metallicity in metal-poor galaxie

    CERN Document Server

    Morales-Luis, A B; Almeida, J Sanchez; Tunon, C Munoz

    2014-01-01

    The N2 index ([N II]6584/Ha) 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 the work was to improve the calibrations used to infer oxygen abundance from N2 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. (2011). 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 overstimate the oxygen abundance for most low metallicity galaxies, and then they can be used only 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 HII regions producing the e...

  12. 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.

  13. 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,...

  14. Spectroscopic Studies of Extremly Metal-Poor Stars with Subaru/HDS:II.The r-process Elements, Including Thorium

    CERN Document Server

    Honda, S; Kajino, T; Ando, H; Beers, T C; Izumiura, H; Sadakane, K; Takada-Hidai, M

    2004-01-01

    We present the abundance analyses for the neutron-capture elements, and discuss the observed abundance distributions in very metal-poor stars with excesses of r-process elements. As has been found by previous abundance studies, the star-to-star scatter in the abundances of neutron-capture elements are very large. The abundance patterns of the heavy neutron-capture elements (56 $\\leq$ Z $\\leq$ 70) in seven objects with moderate to large excesses of the neutron-capture elements are similar to that of the solar system r-process component. These results strongly suggest that the heavy neutron-capture elements in these objects are primarily synthesized by the r-process. On the other hand, the abundance ratios of the light neutron-capture elements (38 $\\leq$ Z $\\leq$ 46) exhibit a rather large dispersion. Our inspection of the correlation between Sr and Ba abundances in very metal-poor stars reveals that the dispersion of the Sr abundances clearly decreases with increasing Ba abundance. This results support previou...

  15. 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...

  16. THE CHEMICAL COMPOSITIONS OF VERY METAL-POOR STARS HD 122563 AND HD 140283: A VIEW FROM THE INFRARED

    Energy Technology Data Exchange (ETDEWEB)

    Afşar, Melike [Department of Astronomy and Space Sciences, Ege University, 35100 Bornova, İzmir (Turkey); Sneden, Christopher; Kim, Hwihyun, E-mail: melike.afsar@ege.edu.tr, E-mail: chris@astro.as.utexas.edu, E-mail: dtj@astro.as.utexas.edu, E-mail: hwihyun@astro.as.utexas.edu, E-mail: mace@astro.as.utexas.edu, E-mail: afrebel@mit.edu [Department of Astronomy and McDonald Observatory, The University of Texas, Austin, TX 78712 (United States); and others

    2016-03-10

    From high resolution (R ≃ 45,000), high signal-to-noise ratio (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 determine more reliable abundances for additional metal-poor stars whose optical features are either not detectable, or too weak, or are based on lines with analytical difficulties.

  17. 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...

  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. 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...

  20. 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.

  1. Formation of Carbon-enhanced Metal-poor Stars in the Presence of Far-ultraviolet Radiation

    Science.gov (United States)

    Bovino, S.; Grassi, T.; Schleicher, D. R. G.; Latif, M. A.

    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+, 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.

  2. 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.

  3. 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...

  4. 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...

  5. TERZAN 5: the remnant of a pristine fragment of the Galactic Bulge?

    CERN Document Server

    Lanzoni, Barbara

    2013-01-01

    Terzan 5 is a stellar system in the Galactic bulge commonly catalogued as a globular cluster. Through dedicated NIR photometry and spectroscopy we have discovered that it harbors two main stellar populations defining two distinct red clumps (RCs) in the colour-magnitude diagram, and displaying different iron content: [Fe/H] = -0.2 and [Fe/H]=+0.3 for the faint and the bright red clumps, respectively. In addition, a third minor population with significantly lower metallicity ([Fe/H]=-0.79) has been recently detected, thus enlarging the metallicity range covered by Terzan 5 to Delta[Fe/H] ~ 1 dex. This evidence demonstrates that, similarly to omega Centauri in the Galactic halo, Terzan 5 is not a genuine globular cluster, but a stellar system that experienced a much more complex star formation and chemical enrichment history. Moreover the striking chemical similarity with the bulge stars suggests that Terzan 5 could be the relic of one of the massive clumps that contributed through strong dynamical interactions...

  6. Globular Clusters: DNA of Early-Type galaxies?

    CERN Document Server

    Forte, J C; Faifer, F R; Castelli, A V Smith; Escudero, Carlos; González, N M; Sesto, L A

    2014-01-01

    This paper explores if the mean properties of Early-Type Galaxies (ETG) can be reconstructed from "genetic" information stored in their GCs (i.e., in their chemical abundances, spatial distributions and ages). This approach implies that the formation of each globular occurs in very massive stellar environments, as suggested by some models that aim at explaining the presence of multi-populations in these systems. The assumption that the relative number of globular clusters to diffuse stellar mass depends exponentially on chemical abundance, [Z/H], and the presence of two dominant GC sub-populations blue and red, allows the mapping of low metallicity halos and of higher metallicity (and more heterogeneous) bulges. In particular, the masses of the low-metallicity halos seem to scale up with dark matter mass through a constant. We also find a dependence of the globular cluster formation efficiency with the mean projected stellar mass density of the galaxies within their effective radii. The analysis is based on a...

  7. Manganese Abundances In Three Metal-poor Stars Using Improved log(gf) Data For Mn I And Mn II Lines

    Science.gov (United States)

    Lawler, James E.; Sobeck, J. S.; Den Hartog, E. A.; Sneden, C.; Cowan, J. J.; Truran, J. W.

    2012-01-01

    We present accurate Mn abundances for three very metal-poor stars using new log(gf) measurements [Den Hartog et al. 2011] for transitions of Mn I and Mn II spanning a wavelength range from 2300 to 6050 Å. The three metal-poor ([Fe/H] Hartog, E A, Lawler J E, Sobeck J S, Sneden C, and Cowan J J 2011, ApJS 194, 35

  8. A spectroscopic study of the Globular Cluster NGC 4147

    CERN Document Server

    Villanova, Sandro; Bidin, Cristian Moni; Assmann, Paulina

    2016-01-01

    We present the abundance analysis for a sample of 18 red giant branch stars in the metal-poor globular cluster NGC 4147 based on medium and high resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Y, Ba, and Eu. We find a metallicity of [Fe/H]=-1.84+-0.02 and an alpha-enhancement of +0.38+-0.05 (errors on the mean), typical of halo globular clusters in this metallicity regime. A significant spread is observed in the abundances of light elements C, N, O, Na, and Al. In particular we found a Na-O anti-correlation and Na-Al correlation. The cluster contains only 15% of stars that belong to the first generation (Na-poor and O-rich). This implies that it suffered a severe mass loss during its lifetime. Its [Ca/Fe] and [Ti/Fe] mean values agree better with the Galactic Halo trend than with the trend of extragalactic environments at the cluster metallicity. This possibly suggests that NGC 4147 is a genuine Galactic ...

  9. Theoretical Models of the Galactic Bulge

    CERN Document Server

    Shen, Juntai

    2015-01-01

    Near infrared images from the COBE satellite presented the first clear evidence that our Milky Way galaxy contains a boxy shaped bulge. Recent years have witnessed a gradual paradigm shift in the formation and evolution of the Galactic bulge. Bulges were commonly believed to form in the dynamical violence of galaxy mergers. However, it has become increasingly clear that the main body of the Milky Way bulge is not a classical bulge made by previous major mergers, instead it appears to be a bar seen somewhat end-on. The Milky Way bar can form naturally from a precursor disk and thicken vertically by the internal firehose/buckling instability, giving rise to the boxy appearance. This picture is supported by many lines of evidence, including the asymmetric parallelogram shape, the strong cylindrical rotation (i.e., nearly constant rotation regardless of the height above the disk plane), the existence of an intriguing X-shaped structure in the bulge, and perhaps the metallicity gradients. We review the major theor...

  10. Is the Galactic Bulge Devoid of Planets?

    Science.gov (United States)

    Penny, Matthew T.; Henderson, Calen B.; Clanton, Christian

    2016-10-01

    We consider a sample of 31 exoplanetary systems detected by gravitational microlensing and investigate whether or not the estimated distances to these systems conform to the Galactic distribution of planets expected from models. We derive the expected distribution of distances and relative proper motions from a simulated microlensing survey, correcting for the dominant selection effects that affect the sensitivity of planet detection as a function of distance, and compare it to the observed distribution using Anderson-Darling (AD) hypothesis testing. Taking the relative abundance of planets in the bulge to that in the disk, {f}{bulge}, as a model parameter, we find that our model is consistent with the observed distribution only for {f}{bulge}\\lt 0.54 (for a p-value threshold of 0.01) implying that the bulge may be devoid of planets relative to the disk. Allowing for a dependence of planet abundance on metallicity and host mass, or an additional dependence of planet sensitivity on event timescale, does not restore consistency for {f}{bulge}=1. We examine the distance estimates of some events in detail, and conclude that some parallax-based estimates could be significantly in error. Only by combining the removal of one problematic event from our sample and the inclusion of strong dependences of planet abundance or detection sensitivity on host mass, metallicity, and event timescale are we able to find consistency with the hypothesis that the bulge and disk have equal planet abundance.

  11. Radio detection prospects for a bulge population of millisecond pulsars as suggested by Fermi LAT observations of the inner Galaxy

    CERN Document Server

    Calore, Francesca; Donato, Fiorenza; Hessels, Jason W T; Weniger, Christoph

    2015-01-01

    Analogously to globular clusters, the dense stellar environment of the Galactic center has been proposed to host a large population of as-yet undetected millisecond pulsars (MSPs). Recently, this hypothesis found support in the analysis of gamma rays from the inner Galaxy seen by the Large Area Telescope (LAT) aboard the Fermi satellite, which revealed a possible excess of diffuse GeV photons in the inner 15 deg about the Galactic center (Fermi GeV excess). The excess can be interpreted as the collective emission of thousands of MSPs in the Galactic bulge, with a spherical distribution that strongly peaks towards the Galactic center. In order to fully establish the MSP interpretation, it is essential to find corroborating evidence in multi-wavelength searches, most notably through the detection of radio pulsation from individual bulge MSPs. Based on globular cluster observations and the gamma-ray emission from the inner Galaxy, we investigate the prospects for detecting MSPs in the Galactic bulge. While previ...

  12. The Chandra Galactic Bulge Survey

    Science.gov (United States)

    Britt, C. T.; Hynes, R. I.; Jonker, P. G.; Maccarone, T.; Torres, M. A. P.; Steeghs, D.; Nelemans, G.; Johnson, C.; Greiss, S.

    2015-05-01

    The Chandra Galactic Bulge Survey (GBS) is a multi-wavelength survey of two 6×1 degree strips above and below the Galactic plane, including deep r' and i' imaging and time domain photometry from CTIO and shallow, wide-field X-ray imaging with Chandra. Targeting fields above |b|=1 avoids most of the copious extinction along the Galactic plane while maintaining high source density. This results in targets that are accessible to follow up in optical and NIR wavelengths. The X-ray observations are shallow to maximize the number of quiescent Low Mass X-ray Binaries (LMXBs) relative to Cataclysmic Variables (CVs). The goals of the GBS are to conduct a census of Low Mass X-ray Binaries in the Milky Way in order to constrain models of binary evolution, the common envelope phase in particular, and to expand the number of known LMXBs for optical follow up. Mass measurements in particular will help constrain the black hole (BH) mass distribution and the equation of state for neutron stars (NS). Constraining the BH mass distribution will constrain models of their formation in supernovae. The current population of Galactic BHs suffers from selection effects, which the GBS avoids by finding new objects while still in quiescence. We expect to find qLMXBs, magnetic CVs, RS CVn stars, and smaller numbers of other types of sources. After removing duplicates, there are 1640 unique X-ray sources in the 12 square degree survey area, which closely matches the predicted number of 1648. We are currently matching X-ray sources to counterparts in other wavelengths using new photometric and spectroscopic observations as well as in archival data where it exists, and searching for variability and periodicity in the counterparts in photometric data. So far, we have spectroscopically identified 27 interacting binaries including promising candidates for quiescent black holes.

  13. The Stellar Abundances for Galactic Archeology (SAGA) Database - Compilation of the Characteristics of Known Extremely Metal-Poor Stars

    CERN Document Server

    Suda, Takuma; Yamada, Shimako; Suwa, Tamon; Ishizuka, Chikako; Komiya, Yutaka; Sorai, Kazuo; Aikawa, Masayuki; Fujimoto, Masayuki Y

    2008-01-01

    We describe the construction of a database of extremely metal-poor (EMP) stars in the Galactic halo whose elemental abundances have been determined. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the recent literature that report studies of EMP halo stars with [Fe/H] < -2.5. The compilation procedures for this database have been designed to assemble the data effectively from electronic tables available from online journals. We have also developed a data retrieval system that enables data searches by various criteria, and permits the user to explore relationships between the stored variables graphically. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering all of the relevant papers published by December 2007. We discuss the global characteristics of the present database, as re...

  14. Detection of low Eu abundances in extremely metal-poor stars and the origin of r-process elements

    CERN Document Server

    Ishimaru, Y; Aoki, W; Ryan, S G; Aoki, Wako; Ishimaru, Yuhri; Ryan, Sean G.; Wanajo, Shinya

    2003-01-01

    We report detailed abundance analyses for three extremely metal-poor stars with [Fe/H] lesssim -3 in the Galactic halo, using the Subaru High Dispersion Spectrograph (HDS). All these stars are found to have sub-solar relative abundances of [Eu/Fe], and exhibit the lowest [Eu/H] values at their metallicities. Comparison of these low Eu abundances with our chemical evolution model of the Galactic halo implies the dominant source of Eu to be the low-mass end of the Type II supernova mass range. This suggests that collapsing O-Ne-Mg cores resulting from 8-10 Msun stars are the major r-process site.

  15. ACS Photometry of the Remote M31 Globular Cluster B514

    Science.gov (United States)

    Galleti, S.; Federici, L.; Bellazzini, M.; Buzzoni, A.; Pecci, F. Fusi

    2006-10-01

    We present deep F606W, F814W ACS photometry of the recently discovered globular cluster B514, the outermost known globular in the M31 galaxy. The cluster appears quite extended, and member stars are unequivocally identified out to ~200 pc from the center. The color-magnitude diagram reveals a steep red giant branch (RGB), and a horizontal branch extending blueward of the instability strip, indicating that B514 is a classical old metal-poor globular cluster. The RGB locus and the position of the RGB bump are both consistent with a metallicity [Fe/H]~-1.8, in excellent agreement with spectroscopic estimates. A preliminary estimate of the integrated absolute V magnitude (MV<~-9.1) suggests that B514 is among the brightest globulars of M31. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  16. 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.

  17. MOLYBDENUM, RUTHENIUM, AND THE HEAVY r-PROCESS ELEMENTS IN MODERATELY METAL-POOR MAIN-SEQUENCE TURNOFF STARS

    Energy Technology Data Exchange (ETDEWEB)

    Peterson, Ruth C. [Astrophysical Advances, 607 Marion Place, Palo Alto, CA 94301 (United States)

    2013-05-01

    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 times overabundant. In contrast, the maximum overabundance is reduced to factors of three and two for the neighboring elements zirconium and palladium. Since the overproduction peaks sharply at Mo and Ru, a low-entropy HEW is confirmed as its origin. The overabundance level of the heavy r-process elements varies significantly, from none to a factor of four, but is uncorrelated with Mo and Ru overabundances. Despite their moderate metallicity, stars in this group trace the products of different nucleosynthetic events: possibly very few events, possibly events whose output depended on environment, metallicity, or time.

  18. 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.

  19. 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.

  20. Peanut-shaped metallicity distributions in bulges of edge-on galaxies: the case of NGC 4710

    CERN Document Server

    Gonzalez, Oscar A; Ness, Melissa; Erwin, Peter; Gadotti, Dimitri A

    2016-01-01

    Bulges of edge-on galaxies are often boxy/peanut-shaped (B/PS), and unsharp masks reveal the presence of an X shape. Simulations show that these shapes can be produced by dynamical processes driven by a bar which vertically thickens the centre. In the Milky Way, which contains such a B/PS bulge, the X-shaped structure is traced by the metal-rich stars but not by the metal-poor ones. Recently Debattista et al. (2016) interpreted this property as a result of the varying effect of the bar on stellar populations with different starting kinematics. This kinematic fractionation model predicts that cooler populations at the time of bar formation go on to trace the X shape, whereas hotter populations are more uniformly distributed. As this prediction is not specific to the Milky Way, we test it with MUSE observations of the B/PS bulge in the nearby galaxy NGC 4710. We show that the metallicity map is more peanut-shaped than the density distribution itself, in good agreement with the prediction. This result indicates ...

  1. Over 38000 RR Lyrae Stars in the OGLE Galactic Bulge Fields

    CERN Document Server

    Soszynski, I; Szymanski, M K; Pietrukowicz, P; Mroz, P; Skowron, J; Kozlowski, S; Poleski, R; Skowron, D; Pietrzynski, G; Wyrzykowski, L; Ulaczyk, K; Kubiak, M

    2014-01-01

    We present the most comprehensive picture ever obtained of the central parts of the Milky Way probed with RR Lyrae variable stars. This is a collection of 38257 RR Lyr stars detected over 182 square degrees monitored photometrically by the Optical Gravitational Lensing Experiment (OGLE) in the most central regions of the Galactic bulge. The sample consists of 16804 variables found and published by the OGLE collaboration in 2011 and 21453 RR Lyr stars newly detected in the photometric databases of the fourth phase of the OGLE survey (OGLE-IV). 93% of the OGLE-IV variables were previously unknown. The total sample consists of 27258 RRab, 10825 RRc, and 174 RRd stars. We provide OGLE-IV I- and V-band light curves of the variables along with their basic parameters. About 300 RR Lyr stars in our collection are plausible members of 15 globular clusters. Among others, we found the first pulsating variables that may belong to the globular cluster Terzan 1 and the first RRd star in the globular cluster M54. Our survey...

  2. The Variable Star Population of the Globular Cluster B514 in the Andromeda Galaxy

    CERN Document Server

    Clementini, Gisella; Federici, Luciana; Cacciari, Carla; Merighi, Roberto; Smith, Horace A; Catelan, Marcio; Pecci, Flavio Fusi; Marconi, Marcella; Kinemuchi, Karen; Pritzl, Barton J

    2009-01-01

    A rich harvest of RR Lyrae stars has been identified for the first time in B514, a metal-poor ([Fe/H] = 1.95 +/- 0.10 dex) globular cluster of the Andromeda galaxy (M31), based on Hubble Space Telescope Wide Field Planetary Camera 2 and Advanced Camera for Surveys time-series observations. We have detected and derived periods for 89 RR Lyrae stars (82 fundamental-mode -RRab- and 7 first-overtone -RRc- pulsators, respectively) among 161 candidate variables identified in the cluster. The average period of the RR Lyrae variables ( = 0.58 days and = 0.35 days, for RRab and RRc pulsators, respectively) and the position in the period-amplitude diagram both suggest that B514 is likely an Oosterhoff type I cluster. This appears to be in disagreement with the general behaviour of the metal-poor globular clusters in the Milky Way, which show instead Oosterhoff type II pulsation properties. The average apparent magnitude of the RR Lyrae stars sets the mean level of the cluster horizontal branch at = 25.18 +/- 0.02 (si...

  3. Relativistic Binaries in Globular Clusters

    Directory of Open Access Journals (Sweden)

    Benacquista Matthew J.

    2006-02-01

    Full Text Available The galactic population of globular clusters are old, dense star systems, with a typical cluster containing 10^4 - 10^7 stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss the theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution which lead to relativistic binaries, and current and possible future observational evidence for this population. Globular cluster evolution will focus on the properties that boost the production of hard binary systems and on the tidal interactions of the galaxy with the cluster, which tend to alter the structure of the globular cluster with time. The interaction of the components of hard binary systems alters the evolution of both bodies and can lead to exotic objects. Direct N-body integrations and Fokker-Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

  4. Relativistic Binaries in Globular Clusters

    Directory of Open Access Journals (Sweden)

    Benacquista Matthew

    2002-01-01

    Full Text Available The galactic population of globular clusters are old, dense star systems, with a typical cluster containing $10^4 - 10^6$ stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss the theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution which lead to relativistic binaries, and current and possible future observational evidence for this population. Globular cluster evolution will focus on the properties that boost the production of hard binary systems and on the tidal interactions of the galaxy with the cluster, which tend to alter the structure of the globular cluster with time. The interaction of the components of hard binary systems alters the evolution of both bodies and can lead to exotic objects. Direct $N$-body integrations and Fokker--Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

  5. The Interstellar Extinction Toward the Milky Way Bulge with Planetary Nebulae, Red Clump, and RR Lyrae stars

    CERN Document Server

    Nataf, David M

    2016-01-01

    I review the literature covering the issue of interstellar extinction toward the Milky Way bulge, with emphasis placed on findings from planetary nebulae, RR Lyrae, and red clump stars. I also report on observations from HI gas and globular clusters. I show that there has been substantial progress in this field in recent decades, most particularly from red clump stars. The spatial coverage of extinction maps has increased by a factor $\\sim 100 \\times$ in the past twenty years, and the total-to-selective extinction ratios reported have shifted by $\\sim$20-25\\%, indicative of the improved accuracy and separately, of a steeper-than-standard extinction curve. Problems remain in modelling differential extinction, explaining anomalies involving the planetary nebulae, and understanding the difference between bulge extinction coefficients and "standard" literature values.

  6. Does the Galactic Bulge Have Fewer Planets?

    Science.gov (United States)

    Kohler, Susanna

    2016-12-01

    The Milky Ways dense central bulge is a very different environment than the surrounding galactic disk in which we live. Do the differences affect the ability of planets to form in the bulge?Exploring Galactic PlanetsSchematic illustrating how gravitational microlensing by an extrasolar planet works. [NASA]Planet formation is a complex process with many aspects that we dont yet understand. Do environmental properties like host star metallicity, the density of nearby stars, or the intensity of the ambient radiation field affect the ability of planets to form? To answer these questions, we will ultimately need to search for planets around stars in a large variety of different environments in our galaxy.One way to detect recently formed, distant planets is by gravitational microlensing. In this process, light from a distant source star is bent by a lens star that is briefly located between us and the source. As the Earth moves, this momentary alignment causes a blip in the sources light curve that we can detect and planets hosted by the lens star can cause an additional observable bump.Artists impression of the Milky Way galaxy. The central bulge is much denserthan the surroundingdisk. [ESO/NASA/JPL-Caltech/M. Kornmesser/R. Hurt]Relative AbundancesMost source stars reside in the galactic bulge, so microlensing events can probe planetary systems at any distance between the Earth and the galactic bulge. This means that planet detections from microlensing could potentially be used to measure the relative abundances of exoplanets in different parts of our galaxy.A team of scientists led by Matthew Penny, a Sagan postdoctoral fellow at Ohio State University, set out to do just that. The group considered a sample of 31 exoplanetary systems detected by microlensing and asked the following question: are the planet abundances in the galactic bulge and the galactic disk the same?A Paucity of PlanetsTo answer this question, Penny and collaborators derived the expected

  7. The Demographics of galactic bulges in the SDSS database

    CERN Document Server

    Kim, Keunho; Jeong, Hyunjin; Aragon-Salamanca, Alfonso; Smith, Rory; Yi, Sukyoung K

    2016-01-01

    We present a new database of our two-dimensional bulge-disk decompositions for 14,233 galaxies drawn from SDSS DR12 in order to examine the properties of bulges residing in the local universe ($0.005 < z < 0.05$). We performed decompositions in $g$ and $r$ bands by utilizing the {\\sc{galfit}} software. The bulge colors and bulge-to-total ratios are found to be sensitive to the details in the decomposition technique, and hence we hereby provide full details of our method. The $g-r$ colors of bulges derived are almost constantly red regardless of bulge size except for the bulges in the low bulge-to-total ratio galaxies ($B/T_{\\rm r} \\lesssim 0.3$). Bulges exhibit similar scaling relations to those followed by elliptical galaxies, but the bulges in galaxies with lower bulge-to-total ratios clearly show a gradually larger departure in slope from the elliptical galaxy sequence. The scatters around the scaling relations are also larger for the bulges in galaxies with lower bulge-to-total ratios. Both the depa...

  8. Globular clusters with Gaia

    Science.gov (United States)

    Pancino, E.; Bellazzini, M.; Giuffrida, G.; Marinoni, S.

    2017-01-01

    The treatment of crowded fields in Gaia data will only be a reality in a few years from now. In particular, for globular clusters, only the end-of-mission data (public in 2022-2023) will have the necessary full crowding treatment and will reach sufficient quality for the faintest stars. As a consequence, the work on the deblending and decontamination pipelines is still ongoing. We describe the present status of the pipelines for different Gaia instruments, and we model the end-of-mission crowding errors on the basis of available information. We then apply the nominal post-launch Gaia performances, appropriately worsened by the estimated crowding errors, to a set of 18 simulated globular clusters with different concentration, distance, and field contamination. We conclude that there will be 103-104 stars with astrometric performances virtually untouched by crowding (contaminated by <1 mmag) in the majoritiy of clusters. The most limiting factor will be field crowding, not cluster crowding: the most contaminated clusters will only contain 10-100 clean stars. We also conclude that: (i) the systemic proper motions and parallaxes will be determined to 1% or better up to ≃15 kpc, and the nearby clusters will have radial velocities to a few km s-1 ; (ii) internal kinematics will be of unprecendented quality, cluster masses will be determined to ≃10% up to 15 kpc and beyond, and it will be possible to identify differences of a few km s-1 or less in the kinematics (if any) of cluster sub-populations up to 10 kpc and beyond; (iii) the brightest stars (V≃17 mag) will have space-quality, wide-field photometry (mmag errors), and all Gaia photometry will have 1-3% errors on the absolute photometric calibration.

  9. Deep SDSS optical spectroscopy of distant halo stars. III. Chemical analysis of extremely metal-poor stars

    Science.gov (United States)

    Fernández-Alvar, E.; Allende Prieto, C.; Beers, T. C.; Lee, Y. S.; Masseron, T.; Schneider, D. P.

    2016-09-01

    Aims: We present the results of an analysis of 107 extremely metal-poor (EMP) stars with metallicities lower than [Fe/H] =- 3.0, identified in medium-resolution spectra in the Sloan Digital Sky Survey (SDSS). Our analysis provides estimates of the stellar effective temperatures and surface gravities, as well as iron, calcium, and magnesium abundances. Methods: We followed the same method as in previous papers of this series. The method is based on comparisons of the observed spectra with synthetic spectra. The abundances of Fe, Ca, and Mg were determined by fitting spectral regions that are 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 analyzed our sample with the SEGUE stellar parameter pipeline to obtain additional determinations of the atmospheric parameters and iron and alpha-element abundances, which we thend compare with ours. In addition, we used these parameters to infer [C/Fe] ratios. Results: Ca is typically the only element in these spectra with a moderate to low signal-to-noise ratio and medium resolution in this metallicity regime with lines that are sufficiently strong to reliably measure its abundance. Fe and Mg exhibit weaker features that in most cases only provide upper limits. We measured [Ca/Fe] and [Mg/Fe] for EMP stars in the SDSS spectra and conclude that most of the stars exhibit the typical enhancement level for α-elements, ~+0.4, although some stars for which only [Fe/H] upper limits could be estimated indicate higher [α/Fe] ratios. We also find that 26% of the stars in our sample can be classified as carbon-enhanced metal-poor (CEMP) stars and that the frequency of CEMP stars also increases with decreasing metallicity, as has been reported for previous samples. We identify a rare, bright (g = 11.90) EMP star, SDSS J134144.61+474128.6, with [Fe/H] =- 3.27, [C/Fe] = + 0.95, and elevated magnesium ([Mg/Fe] =+ 0

  10. Observations of planetary nebulae in the Galactic Bulge

    CERN Document Server

    Cuisinier, F; Köppen, J; Acker, A; Stenholm, B

    2000-01-01

    High quality spectrophotometric observations of 30 Planetary Nebulae in the Galactic Bulge have been made. Accurate reddenings, plasma parameters, and abundances of He,O,N,S,Ar,Cl are derived. We find the abundances of O,S,Ar in the Planetary Nebulae in the Galactic Bulge to be comparable with the abundances of the Planetary Nebulae in the Disk, high abundances being maybe slightly more frequent in the Bulge. The distribution of the N/O ratio does not present in the Galactic Bulge Planetary Nebulae the extension to high values that it presents in the Disk Planetary Nebulae. We interpret this as a signature of the greater age of Bulge Planetary Nebulae. We thus find the Bulge Planetary Nebulae to be an old population, slightly more metal-rich than the Disk Planetary Nebulae. The population of the Bulge Planetary Nebulae shows hence the same characteristics than the Bulge stellar population.

  11. Bright Metal-Poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields

    CERN Document Server

    Frebel, A; Norris, J E; Beers, T C; Bessell, M S; Rhee, J; Fechner, C; Marsteller, B; Rossi, S; Thom, C; Wisotzki, L; Reimers, D

    2006-01-01

    We present a sample of 1777 bright (91.0) metal-poor ([Fe/H]20%) and higher values with increasing distance from the Galactic plane. Although the numbers of stars at low metallicity are falling rapidly at the lowest metallicities, there is evidence that the fraction of carbon-enhanced metal-poor stars is increasing rapidly as a function of declining metallicity. For ~60 objects, high-resolution data have already been obtained; one of these, HE 1327-2326, is the new record holder for the most iron-deficient star known.

  12. The inner Galactic globular clusters

    Directory of Open Access Journals (Sweden)

    Mateo M.

    2013-03-01

    Full Text Available Galactic globular clusters located towards the inner regions of the Milky Way have been historically neglected, mainly due to the difficulties caused by the presence of an elevated extinction by foreground dust, and high field star densities along the lines of sight where most of them lie. To overcome these difficulties we have developed a new method to map the differential extinction suffered by these clusters, which was successfully applied to a sample of moderately-extincted, luminous, extended, inner Galactic globular clusters observed in the optical, for which we have been able to determine more accurate physical parameters. For the most extincted inner Galactic globular clusters, near-infrared wavelengths provide a more suitable window for their study. The VVV survey, which is currently observing the central regions of the Milky Way at these wavelengths, will provide a comprehensive view, from the inner regions out to their tidal radii and beyond, of most of these globular clusters.

  13. Globular Cluster Systems in Brightest Cluster Galaxies. III: Beyond Bimodality

    Science.gov (United States)

    Harris, William E.; Ciccone, Stephanie M.; Eadie, Gwendolyn M.; Gnedin, Oleg Y.; Geisler, Douglas; Rothberg, Barry; Bailin, Jeremy

    2017-01-01

    We present new deep photometry of the rich globular cluster (GC) systems around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143 (Abell 2147), obtained with the Hubble Space Telescope (HST) ACS and WFC3 cameras. For comparison, we also present new reductions of similar HST/ACS data for the Coma supergiants NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to the radial limits of our data, comprising from 12,000 to 23,000 clusters per galaxy). The metallicity distribution functions (MDFs) of the GCs can still be matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes are separated by ≃ 0.8 dex, but the internal dispersions of each mode are so large that the total MDF becomes very broad and nearly continuous from [Fe/H] ≃ ‑2.4 to solar. There are, however, significant differences between galaxies in the relative numbers of metal-rich clusters, suggesting that they underwent significantly different histories of mergers with massive gas-rich halos. Last, the proportion of metal-poor GCs rises especially rapidly outside projected radii R≳ 4 {R}{eff}, suggesting the importance of accreted dwarf satellites in the outer halo. Comprehensive models for the formation of GCs as part of the hierarchical formation of their parent galaxies will be needed to trace the systematic change in structure of the MDF with galaxy mass, from the distinctly bimodal form in smaller galaxies up to the broad continuum that we see in the very largest systems.

  14. 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...

  15. A Subaru/HDS study of Lead (Pb) abundances in eight s-process-element-rich, metal-poor stars

    CERN Document Server

    Aoki, W; Norris, J E; Beers, T C; Ando, H

    2002-01-01

    We report the abundances of neutron-capture elements in eight carbon-rich, metal-poor (-2.7=<[Fe/H]=<-1.9) stars observed with the Subaru Telescope High Dispersion Spectrograph. The derived abundance patterns indicate that the neutron-capture elements in these objects primarily originated from s-process nucleosynthesis, although the [Ba/Eu] abundance ratios in some objects are lower than that of the solar-system s-process component. The present analysis has yielded the Pb abundances for seven objects, as well as an upper limit for one object, from use of the Pb I 4057A and 3683A lines. The values of [Pb/Ba] in these objects cover a wide range, between -0.3 and +1.2. Theoretical studies of s-process nucleosynthesis at low metallicity are required to explain this large dispersion of the [Pb/Ba] values. Variations in radial velocity have been found for two of the eight objects, suggesting that, at least in these instances, the observed excess of s-process elements is due to the transfer of material across ...

  16. 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...

  17. 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...

  18. Near-Infrared Spectroscopy of Carbon-Enhanced Metal-Poor Stars. I. A SOAR/OSIRIS Pilot Study

    CERN Document Server

    Beers, T C; Marstellar, B; Lee, Y S; Rossi, S; Plez, B; Beers, Timothy C.; Sivarani, Thirupathi; Marstellar, Brian; Lee, YoungSun; Rossi, Silvia; Plez, Bertrand

    2006-01-01

    We report on an abundance analysis for a pilot study of seven Carbon-Enhanced Metal-Poor (CEMP) stars, based on medium-resolution optical and near-infrared spectroscopy. The optical spectra are used to estimate [Fe/H], [C/Fe], [N/Fe], and [Ba/Fe] for our program stars. The near-infrared spectra, obtained during a limited early science run with the new SOAR 4.1m telescope and the Ohio State Infrared Imager and Spectrograph (OSIRIS), are used to obtain estimates of [O/Fe] and 12C/13C. The chemical abundances of CEMP stars are of importance for understanding the origin of CNO in the early Galaxy, as well as for placing constraints on the operation of the astrophysical s-process in very low-metallicity Asymptotic Giant Branch (AGB) stars. This pilot study includes a few stars with previously measured [Fe/H], [C/Fe], [N/Fe],[O/Fe], 12C/13C, and [Ba/Fe], based on high-resolution optical spectra obtained with large-aperture telescopes. Our analysis demonstrates that we are able to achieve reasonably accurate determi...

  19. 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...

  20. Metallicity inhomogeneities in local star-forming galaxies as sign of recent metal-poor gas accretion

    CERN Document Server

    Almeida, J Sanchez; Munoz-Tunon, C; Elmegreen, D M; Elmegreen, B G; Mendez-Abreu, J

    2014-01-01

    We measure the oxygen metallicity of the ionized gas along the major axis of seven dwarf star-forming galaxies. Two of them, SDSSJ1647+21 and SDSSJ2238+14, show 0.5 dex metallicity decrements in inner regions with enhanced star-formation activity. This behavior is similar to the metallicity drop observed in a number of local tadpole galaxies by Sanchez Almeida et al. (2013) and interpreted as showing early stages of assembling in disk galaxies, with the star formation sustained by external metal-poor gas accretion. The agreement with tadpoles has several implications: (1) it proves that galaxies other than the local tadpoles present the same unusual metallicity pattern. (2) Our metallicity inhomogeneities were inferred using the direct method, thus discarding systematic errors usually attributed to other methods. (3) Taken together with the tadpole data, our findings suggest a threshold around one tenth the solar value for the metallicity drops to show up. Although galaxies with clear metallicity drops are ra...

  1. HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: BOÖTES II

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Alexander P.; Frebel, Anna [Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Simon, Joshua D. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA 91101 (United States); Geha, Marla, E-mail: alexji@mit.edu [Astronomy Department, Yale University, New Haven, CT 06520 (United States)

    2016-01-20

    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.

  2. 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...

  3. 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.

  4. 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...

  5. 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...

  6. Rest-frame ultraviolet-to-optical spectral characteristics of extremely metal-poor and metal-free galaxies

    CERN Document Server

    Inoue, Akio K

    2011-01-01

    Finding the first generation of galaxies in the early Universe is the greatest step forward for understanding galaxy formation and evolution. For strategic survey of such galaxies and interpretation of the obtained data, this paper presents an ultraviolet-to-optical spectral model of galaxies with a great care of the nebular emission. In particular, we present a machine-readable table of intensities of 119 nebular emission lines from Ly$\\alpha$ to the rest-frame 1 $\\mu$m as a function of metallicity from zero to the Solar one. Based on the spectral model, we present criteria of broad-band colours and equivalent widths of Ly$\\alpha$, He {\\sc ii} $\\lambda1640$, H$\\alpha$, H$\\beta$, [O {\\sc iii}] $\\lambda5007$ to select extremely metal-poor and metal-free galaxies although these criteria have uncertainty caused by the Lyman continuum escape fraction and the star formation duration. The criteria of broad-band colours will be useful to select candidates for spectroscopic follow-up from drop-out galaxies. We propos...

  7. 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.

  8. Non-LTE Analysis of the Sodium Abundance of Metal-Poor Stars in the Galactic Disk and Halo

    Institute of Scientific and Technical Information of China (English)

    Yoichi Takeda; Gang Zhao; Masahide Takada-Hidai; Yu-Qin Chen; Yu-ji Saito; Hua-Wei Zhang

    2003-01-01

    We performed an extensive non-LTE analysis of the neutral sodiumlines of Na I 5683/5688, 5890/5896, 6154/6161, and 8183/8195 in disk/halo starsof types F-K covering a wide metallicity range (-4 [Fe/H] +0.4), using ourown data as well as data collected from the literature. For comparatively metal-rich disk stars (-1 [Fe/H] +0.4) where the weaker 6154/6161 lines are thebest abundance indicators, we confirmed [Na/Fe] ~ 0 with an "upturn" (i.e., ashallow/broad dip around -0.5 [Fe/H] 0) as already reported in previousstudies. For the metal-deficient halo stars, where the much stronger 5890/5896 or8183/8195 lines subject to considerable (negative) non-LTE corrections amountingto 0.5 dex have to be used, our analysis suggests mildly "subsolar" [Na/Fe] valuesdown to ~ -0.4 (with a somewhat large scatter of ~±0.2 dex) on the average at thetypical halo metallicity of [Fe/H] ~ -2, followed by a rise again to a near-solar ratioof [Na/Fe] ~ 0 at the very metal-poor regime [Fe/H] ~ -3 to -4. These resultsare discussed in comparison with the previous observational studies along with thetheoretical predictions from the available chemical evolution models.

  9. Probing the Site for r-Process Nucleosyntheis with Abundances of Barium and Magnesium in Extremely Metal-Poor Stars

    CERN Document Server

    Tsujimoto, T; Yoshii, Y; Tsujimoto, Takuji; Shigeyama, Toshikazu; Yoshii, Yuzuru

    2000-01-01

    We suggest that if the astrophysical site for r-process nucleosynthesis in the early Galaxy is confined to a narrow mass range of Type II supernova (SN II) progenitors, with a lower mass limit of Mms = 20 Msun, a unique feature in the observed distribution of [Ba/Mg] vs.[Mg/H] for extremely metal-poor stars can be adequately reproduced. We associate this feature, a bifurcation of the observed elemental ratios into two branches in the Mg abundance interval -2.7 20 Msun. The second branch, which we call the ``i''-branch, is associated with the elemental abundance ratios of stars which were formed in the dense shells of the interstellar medium swept up by SNe II with Mms < 20 Msun that do not synthesize r-process elements, and applies to stars with observed Mg abundances in the range [Mg/H] < -2.7. The Ba abundances in these stars reflect those of the interstellar gas at the (later) time of their formation. The existence of a [Ba/Mg] i-branch strongly suggests that SNe II which are associated with stars o...

  10. 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...

  11. 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 ...

  12. Predictions of the extent of self-enrichment in oxygen of giant metal-poor HII regions

    CERN Document Server

    Wofford, Aida

    2009-01-01

    In general, HII regions do not show clear signs of self-enrichment in products from massive stars (M > 8 M_sun). In order to explore why, I modeled the contamination with Wolf-Rayet star ejecta of metal-poor (Z=0.001) HII regions, ionised either by a 10^6 M_sun cluster of coeval stars (cluster 1), or a cluster resulting from continuous star formation at a rate of 1 M_sun yr^-1 (cluster 2). The clusters have Z=0.001 and a Salpeter initial mass function (IMF) from 0.1 to 120 M_sun. Independent one dimensional constant density simulations of the emission-line spectra of unenriched HII regions were computed at the discrete ages 1, 2, 3, 4, and 5 Myr, with the photoionisation code CLOUDY, using as input, radiative and mechanical stellar feedbacks predicted by the evolutionary synthesis code STARBURST99. Each HII region was placed at the outer radius of the adiabatically expanding superbubble of Mac Low and McCray (1988). For models with thermal and ionisation balance time-scales of less than 1 Myr, and with oxygen...

  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. First Stars XI. Chemical composition of the extremely metal-poor dwarfs in the binary CS 22876--032

    CERN Document Server

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

    2007-01-01

    We have used high-resolution, high-S/N ratio spectra from the UVES spectrograph at the ESO VLT telescope. Long-term radial-velocity measurements and broad-band photometry allow us to determine improved orbital elements and stellar parameters for both components. We use OSMARCS 1D models and the {{\\scshape turbospectrum}} spectral synthesis code to determine the abundances of Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co and Ni. We also use the CO$^5$BOLD model atmosphere code to compute the 3D abundance corrections, especially for Li and O. We find a metallicity of [Fe/H]$\\sim -3.6$ for both stars, using 1D models with 3D corrections of $\\sim -0.1$ dex from averaged 3D models. We determine the oxygen abundance from the near-UV OH bands; the 3D corrections are large, -1 and -1.5 dex for the secondary and primary respectively, and yield [O/Fe] $\\sim 0.8$, close to the high-quality results obtained from the [OI] 630 nm line in metal-poor giants. Other [$\\alpha$/Fe] ratios are consistent with those measured i...

  15. Something borrowed, something blue: The nature of blue metal-poor stars inferred from their colours and chemical abundances

    CERN Document Server

    Hansen, C J; Koch, A; McWilliam, A; Sneden, C S

    2016-01-01

    Blue metal-poor stars (BMPs) are main sequence stars that appear bluer and more luminous than normal turnoff stars. They were originally singled out by using B-V and U-B colour cuts. Early studies found that a larger fraction of field BMP stars were binaries compared to normal halo stars. Thus, BMP stars are ideal field blue straggler candidates for investigating internal stellar evolution processes and binary interaction. In particular, the presence or depletion in lithium in their spectra is a powerful indicator as to their origin. They are either old, halo blue stragglers experiencing internal mixing processes or mass transfer (Li-depletion), or intermediate-age, single stars of possibly extragalactic origin (2.2dex halo plateau Li). However, we note that internal mixing processes can lead to an increased level of Li. Hence, this study combines photometry and spectroscopy to unveil the origin of various BMP stars. We first show how to separate binaries from young blue stars using photometry, metallicity, a...

  16. An interferometric-spectroscopic orbit for the binary HD 195987 Testing models of stellar evolution for metal-poor stars

    CERN Document Server

    Torres, G; Latham, D W; Pan, M; Stefanik, R P; Torres, Guillermo; Boden, Andrew F.; Latham, David W.; Pan, Margaret; Stefanik, Robert P.

    2002-01-01

    We report spectroscopic and interferometric observations of the moderately metal-poor double-lined binary system HD 195987, with an orbital period of 57.3 days. By combining our radial-velocity and visibility measurements we determine the orbital elements and derive absolute masses for the components of M(A) = 0.844 +/- 0.018 Msun and M(B) = 0.6650 +/- 0.0079 Msun, with relative errors of 2% and 1%, respectively. We also determine the orbital parallax, pi(orb) = 46.08 +/- 0.27 mas, corresponding to a distance of 21.70 +/- 0.13 pc. The parallax and the measured brightness difference between the stars in V, H, and K yield the component absolute magnitudes in those bands. We also estimate the effective temperatures of the stars as Teff(A) = 5200 +/- 100 K and Teff(B) = 4200 +/- 200 K. Together with detailed chemical abundance analyses from the literature giving [Fe/H] approximately -0.5 (corrected for binarity) and [alpha/Fe] = +0.36, we use these physical properties to test current models of stellar evolution f...

  17. 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, ...

  18. The Hamburg/ESO R-process Enhanced Star survey (HERES)VII. Thorium abundances in metal-poor stars

    CERN Document Server

    Ren, Jin; Zhao, Gang

    2011-01-01

    We report thorium abundances for 77 metal-poor stars in the metallicity range of -3.5<[Fe/H]}<-1.0, based on "snapshot" spectra obtained with VLT-UT2/UVES during the HERES Survey. We were able to determine the thorium abundances with better than 1-sigma confidence for 17 stars, while for 60 stars we derived upper limits. For five stars common with previous studies, our results were in good agreement with the literature results. The thorium abundances span a wide range of about 4.0 dex, and scatter exists in the distribution of log(Th/Eu) ratios for lower metallicity stars, supporting previous studies suggesting the r-process is not universal. We derived ages from the log(Th/Eu) ratios for 12 stars, resulting in large scattered ages, and two stars with significant enhancement of Th relative to Eu are found, indicating the "actinide boost" does not seem to be a rare phenomenon and thus highlighting the risk in using log(Th/Eu) to derive stellar ages.

  19. Relativistic Binaries in Globular Clusters

    Directory of Open Access Journals (Sweden)

    Matthew J. Benacquista

    2013-03-01

    Full Text Available Galactic globular clusters are old, dense star systems typically containing 10^4 – 10^6 stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution that leads to relativistic binaries, and current and possible future observational evidence for this population. Our discussion of globular cluster evolution will focus on the processes that boost the production of tight binary systems and the subsequent interaction of these binaries that can alter the properties of both bodies and can lead to exotic objects. Direct N-body integrations and Fokker–Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

  20. Manganese abundances in Galactic bulge red giants

    Science.gov (United States)

    Barbuy, B.; Hill, V.; Zoccali, M.; Minniti, D.; Renzini, A.; Ortolani, S.; Gómez, A.; Trevisan, M.; Dutra, N.

    2013-11-01

    Context. Manganese is mainly produced in type II SNe during explosive silicon burning, in incomplete Si-burning regions, and depends on several nucleosynthesis environment conditions, such as mass cut between the matter ejected and falling back onto the remnant, electron and neutron excesses, mixing fallback, and explosion energy. Manganese is also produced in type Ia SNe. Aims: The aim of this work is the study of abundances of the iron-peak element Mn in 56 bulge giants, among which 13 are red clump stars. Four bulge fields along the minor axis are inspected. The study of abundances of Mn-over-Fe as a function of metallicity in the Galactic bulge may shed light on its production mechanisms. Methods: High-resolution spectra were obtained using the FLAMES+UVES spectrograph on the Very Large Telescope. The spectra were obtained within a program to observe 800 stars using the GIRAFFE spectrograph, together with the present UVES spectra. Results: We aim at identifying the chemical evolution of manganese, as a function of metallicity, in the Galactic bulge. We find [Mn/Fe] ~ -0.7 at [Fe/H] ~ -1.3, increasing to a solar value at metallicities close to solar, and showing a spread around - 0.7 ≲ [Fe/H] ≲ -0.2, in good agreement with other work on Mn in bulge stars. There is also good agreement with chemical evolution models. We find no clear difference in the behaviour of the four bulge fields. Whereas [Mn/Fe] vs. [Fe/H] could be identified with the behaviour of the thick disc stars, [Mn/O] vs. [O/H] has a behaviour running parallel, at higher metallicities, compared to thick disc stars, indicating that the bulge enrichment might have proceeded differently from that of the thick disc. Observations collected at the European Southern Observatory, Paranal, Chile (ESO programmes 71.B-0617A, 73.B0074A, and GTO 71.B-0196).Tables 1-6 and Figs. 1-6 are available in electronic form at http://www.aanda.org

  1. Functional myelographic differentiation of lumbar bulging annulus

    Energy Technology Data Exchange (ETDEWEB)

    Park, Choong Ki; Kim, Hong Kil; Park, Sang Gyu; Lee, Young Jung; Yoon, Jong Sup [Hallym University College of Medicine, Seoul (Korea, Republic of)

    1988-08-15

    Herniated disk and bulging annulus are the major causes of lower back pain. It is necessary to differentiate bulging annulus from herniated disk because of their different methods of treatment. Myelography is one of the useful diagnostic methods for disk diseases even though advanced diagnostic modalities such as CT and MRI are more accurate. Functional myelography is not a new technology expect for two additional views, flexion and extension, are obtained with conventional myelography. Differentiation between bulging annulus and herniated disk by conventional myelography is based on the extent and multiplicity of extradural deformity of the contrast filled dural sac and neural sleeve as well as the changes of nerve root. There is no previous report about differential points between bulging annulus and herniated disk according to functional myelography. It is the purpose of this study to find any additional differential points on functional myelography between bulging annulus and herniated disk over convectional myelography. Authors analysed functional myelographic findings of 152 cases from July 1986 to July 1987. Among them, 22 cases who had been suffered from cervical abnormality or vague lower back pain were diagnosed as normal by myelography, and 30 cases of L4-5 herniated disk and 21 cases of L4-5 bulging annulus which had been finally diagnosed by operation were studied. The results were as follows. 1. In normal group, anterior epidural space was gradually widened from the upper lumbar vertebra downward. And anterior epidural space was more sidened at the disk level in extension view than in flexion except for L5-S1 lever. 2. In bulging annulus group, the shape of anterior epidural space in flexion state was as similar as normal. Anoterior epidural space in extension state was more sidened at the buldging annulus than normal, but lesser than herniated disk. 3. In herniated disk group, widening of anterior epidural space at the herniated disk level was

  2. Ultraviolet Spectroscopy of Metal-Poor Stars: New Detections of Phosphorus, Germanium, Arsenic, Selenium, Cadmium, Tellurium, Lutetium, Osmium, Iridium, Platinum, Gold, and More!

    Science.gov (United States)

    Roederer, Ian U.

    2015-01-01

    Ultraviolet spectroscopy with HST/STIS provides a 30% increase in the number of elements that can be detected in metal-poor stars. Although nearly every element from hydrogen through bismuth is probably present in most metal-poor stars, not all elements can be detected. The resonance lines of the dominant species of some elements are only found in the UV in late-type stars. The chemical compositions of these stars reflect the history of stellar nucleosynthesis from the first stars to today. Here, I present a summary of recent work that has expanded the chemical inventory in metal-poor stars using UV spectroscopy conducted using HST/STIS. The highlights include new detections of phosphorus, germanium, arsenic, selenium, cadmium, tellurium, lutetium, osmium, iridium, platinum, and gold in metal-poor stars. These detections reveal new insights into stellar nucleosynthesis in the earliest generations of massive stars, provide new constraints on the r-process, and open new channels for chemically-tagging stars that have assembled to form the Milky Way stellar halo.

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

    Science.gov (United States)

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

    2013-10-01

    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 (N_{{H}^0}=10^{19.50+/- 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. .

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

    DEFF Research Database (Denmark)

    Amarsi, A. M.; Lind, K.; Asplund, M.;

    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...

  5. The Youngest Globular Clusters

    CERN Document Server

    Beck, Sara

    2014-01-01

    It is likely that all stars are born in clusters, but most clusters are not bound and disperse. None of the many protoclusters in our Galaxy are likely to develop into long-lived bound clusters. The Super Star Clusters (SSCs) seen in starburst galaxies are more massive and compact and have better chances of survival. The birth and early development of SSCs takes place deep in molecular clouds, and during this crucial stage the embedded clusters are invisible to optical or UV observations but are studied via the radio-infared supernebulae (RISN) they excite. We review observations of embedded clusters and identify RISN within 10 Mpc whose exciting clusters have a million solar masses or more in volumes of a few cubic parsecs and which are likely to not only survive as bound clusters, but to evolve into objects as massive and compact as Galactic globulars. These clusters are distinguished by very high star formation efficiency eta, at least a factor of 10 higher than the few percent seen in the Galaxy, probably...

  6. Something borrowed, something blue: The nature of blue metal-poor stars inferred from their colours and chemical abundances

    Science.gov (United States)

    Hansen, C. J.; Jofré, P.; Koch, A.; McWilliam, A.; Sneden, C. S.

    2017-01-01

    Blue metal-poor (BMP) stars are main sequence stars that appear bluer and more luminous than normal turnoff stars. They were originally singled out by using B-V and U-B colour cuts.Early studies found that a larger fraction of field BMP stars were binaries compared to normal halo stars. Thus, BMP stars are ideal field blue straggler candidates for investigating internal stellar evolution processes and binary interaction. In particular, the presence or depletion in lithium in their spectra is a powerful indicator of their origin. They are either old, halo blue stragglers experiencing internal mixing processes or mass transfer (Li-depletion), or intermediate-age, single stars of possibly extragalactic origin (2.2 dex halo plateau Li). However, we note that internal mixing processes can lead to an increased level of Li. Hence, this study combines photometry and spectroscopy to unveil the origin of various BMP stars. We first show how to separate binaries from young blue stars using photometry, metallicity and lithium. Using a sample of 80 BMP stars (T > 6300 K), we find that 97% of the BMP binaries have V-Ks0 < 1.08 ± 0.03, while BMP stars that are not binaries lie above this cut in two thirds of the cases. This cut can help classify stars that lack radial velocities from follow-up observations. We then trace the origin of two BMP stars from the photometric sample by conducting a full chemical analysis using new high-resolution and high signal-to-noise spectra. Based on their radial velocities, Li, α and s- and r-process abundances we show that BPS CS22874-042 is a single star (A(Li) = 2.38 ± 0.10 dex) while with A(Li)= 2.23 ± 0.07 dex CD-48 2445 is a binary, contrary to earlier findings. Our analysis emphasises that field blue stragglers can be segregated from single metal-poor stars, using (V-Ks) colours with a fraction of single stars polluting the binary sample, but not vice versa. These two groups can only be properly separated by using information from

  7. G64-12 and G64-37 Are Carbon-enhanced Metal-poor Stars

    Science.gov (United States)

    Placco, Vinicius M.; Beers, Timothy C.; Reggiani, Henrique; Meléndez, Jorge

    2016-10-01

    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 ratio 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 carboni cities, 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) versus [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 ({T}{eff}˜ 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, metal-free supernova models reduces the inferred progenitor masses by factors of ˜2-3, and explosion energies by factors of ˜10-15, compared to those derived using previously claimed carbon-abundance estimates. There are certainly many more warm CEMP-no stars near the halo main-sequence turnoff that have been overlooked in past studies, directly impacting the derived frequencies of CEMP-no stars as a function of metallicity, a probe that provides important constraints on Galactic chemical evolution models, the initial mass function in the early universe, and first-star nucleosynthesis.

  8. The extremely metal-poor galaxy DDO 68: the luminous blue variable, Hα shells and the most luminous stars

    Science.gov (United States)

    Pustilnik, S. A.; Makarova, L. N.; Perepelitsyna, Y. A.; Moiseev, A. V.; Makarov, D. I.

    2017-03-01

    This paper presents new results from the ongoing study of the unusual Lynx-Cancer void galaxy DDO 68, which has star-forming regions of record low metallicity [12+log (O/H) ∼7.14]. The results include the following. (i) A new spectrum and photometry have been obtained with the 6-m SAO RAS telescope (BTA) for the luminous blue variable (LBV = DDO68-V1). Photometric data sets were complemented with others based on the Sloan Digital Sky Survey (SDSS) and the Hubble Space Telescope (HST) archive images. (ii) We performed an analysis of the DDO 68 supergiant shell (SGS) and the prominent smaller Hα arcs/shells visible in the HST image coupled with kinematic maps in Hα obtained with the Fabry-Perot interferometer (FPI) at the BTA. (iii) We compiled a list of about 50 of the most luminous stars (-9.1 mag science to be investigated with the next generation of giant telescopes. We have confirmed earlier hints of significant variation of the LBV optical light, deriving its amplitude as ΔV ≳ 3.7 mag for the first time. New data suggest that in 2008-2010 the LBV reached MV = -10.5 mag and probably underwent a giant eruption. We argue that the structure of star-forming complexes along the SGS ('Northern Ring') perimeter provides evidence for sequential induced star-formation episodes caused by the shell gas instabilities and gravitational collapse. The variability of some luminous extremely metal-poor stars in DDO 68 can currently be monitored with medium-size telescopes at sites with superb seeing.

  9. The Demographics of Galactic Bulges in the SDSS Database

    Science.gov (United States)

    Kim, Keunho; Oh, Sree; Jeong, Hyunjin; Aragón-Salamanca, Alfonso; Smith, Rory; Yi, Sukyoung K.

    2016-07-01

    We present a new database of our two-dimensional bulge-disk decompositions for 14,233 galaxies drawn from Sloan Digital Sky Survey DR12 in order to examine the properties of bulges residing in the local universe (0.005 originate from the presence of young stars. The bulges in galaxies with low bulge-to-total ratios show signs of a frosting of young stars so substantial that their luminosity-weighted Balmer-line ages are as small as 1 Gyr in some cases. While bulges seem largely similar in optical properties to elliptical galaxies, they do show clear and systematic departures as a function of bulge-to-total ratio. The stellar properties and perhaps associated formation processes of bulges seem much more diverse than those of elliptical galaxies.

  10. Composite Bulges: The Coexistence of Classical Bulges and Disky Pseudobulges in S0 and Spiral Galaxies

    CERN Document Server

    Erwin, Peter; Fabricius, Maximilian; Thomas, Jens; Nowak, Nina; Rusli, Stephanie; Bender, Ralf; Beltran, Juan Carlos Vega; Beckman, John E

    2014-01-01

    We study nine S0-Sb galaxies with (photometric) bulges consisting of two distinct components. The outer component is a flattened, kinematically cool, disklike structure: a "disky pseudobulge". Embedded inside is a rounder, kinematically hot spheroid: a "classical bulge". This indicates that pseudobulges and classical bulges are not mutually exclusive: some galaxies have both. The disky pseudobulges almost always have an exponential disk (scale lengths = 125-870 pc, mean $\\sim 440$ pc) with disk-related subcomponents: nuclear rings, bars, and/or spiral arms. They constitute 11-59% of the galaxy stellar mass (mean PB/T = 0.33), with stellar masses $\\sim 7 \\times 10^{9}$-$9 \\times 10^{10} M_{\\odot}$. Classical-bulge components have Sersic indices of 0.9-2.2, effective radii of 25-430 pc and stellar masses of $5 \\times 10^{8}$-$3 \\times 10^{10} M_{\\odot}$ (usually < 10% of the galaxy's stellar mass; mean B/T = 0.06). The classical bulges show rotation, but are kinematically hotter than the disky pseudobulges. ...

  11. Are there carbon stars in the Bulge?

    CERN Document Server

    Ng, Y K

    1998-01-01

    The bulge carbon stars have been a mystery since their discovery, because they are about 2.5mag too faint to be regarded as genuine AGB stars, if located inside the metal-rich bulge (m-M=14.5mag). Part of the mystery can be solved if these carbon stars are related to the Sagittarius dwarf galaxy (SDG; m-M=17.0mag). They are in that case not old and metal-rich, but young, ~0.1 Gyr, with SMC-like metallicity. The sigma_RV=113+/-14 km/s radial velocity dispersion of the stars appears to be consistent with bulge membership. On the other hand, a similar velocity dispersion could be the result from an induced star formation event when the SDG crosses the galactic midplane. It is suggested that the carbon stars are tracers of such an event and that they therefore are located at distances related to the SDG. However, the majority of the carbon stars are not member of the SDG, nor are they similar to the C-stars which are member of the SDG. The radial velocities can be used to determine a possible membership to the SD...

  12. Manganese abundances in Galactic bulge red giants

    CERN Document Server

    Barbuy, B; Zoccali, M; Minniti, D; Renzini, A; Ortolani, S; Gomez, A; Trevisan, M; Dutra, N

    2013-01-01

    Manganese is mainly produced in type II SNe during explosive silicon burning, in incomplete Si-burning regions, and depends on several nucleosynthesis environment conditions, such as mass cut beween the matter ejected and falling back onto the remnant, electron and neutron excesses, mixing fallback, and explosion energy. Manganese is also produced in type Ia SNe. The aim of this work is the study of abundances of the iron-peak element Mn in 56 bulge giants, among which 13 are red clump stars. Four bulge fields along the minor axis are inspected. The study of abundances of Mn-over-Fe as a function of metallicity in the Galactic bulge may shed light on its production mechanisms. High-resolution spectra were obtained using the FLAMES+UVES spectrograph on the Very Large Telescope. The spectra were obtained within a program to observe 800 stars using the GIRAFFE spectrograph, together with the present UVES spectra. We aim at identifying the chemical evolution of manganese, as a function of metallicity, in the Gala...

  13. Dynamical Processes in Globular Clusters

    CERN Document Server

    McMillan, Stephen L W

    2014-01-01

    Globular clusters are among the most congested stellar systems in the Universe. Internal dynamical evolution drives them toward states of high central density, while simultaneously concentrating the most massive stars and binary systems in their cores. As a result, these clusters are expected to be sites of frequent close encounters and physical collisions between stars and binaries, making them efficient factories for the production of interesting and observable astrophysical exotica. I describe some elements of the competition among stellar dynamics, stellar evolution, and other processes that control globular cluster dynamics, with particular emphasis on pathways that may lead to the formation of blue stragglers.

  14. 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.

  15. Secular- and merger-built bulges in barred galaxies

    CERN Document Server

    Mendez-Abreu, J; Corsini, E M; Aguerri, J A L

    2014-01-01

    (Abridged) We study the incidence, as well as the nature, of composite bulges in a sample of 10 face-on barred galaxies to constrain the formation and evolutionary processes of the central regions of disk galaxies. We analyze the morphological, photometric, and kinematic properties of each bulge. Then, by using a case-by-case analysis we identify composite bulges and classify every component into a classical or pseudobulge. In addition, bar-related boxy/peanut (B/P) structures were also identified and characterised. We find only three galaxies hosting a single-component bulge (two pseudobulges and one classical bulge). We find evidence of composite bulges coming in two main types based on their formation: secular-built and merger- and secular-built. We call secular-built to composite bulges made of entirely by structures associated with secular processes such as pseudo bulges, central disks, or B/P bulges. We find four composite bulges of this kind in our sample. On the other hand, merger- and secular-built b...

  16. Central Star Formation in Pseudobulges and Classical Bulges

    CERN Document Server

    Fisher, D B

    2006-01-01

    I use Spitzer 3.6-8.0 \\mu m color profiles to compare the radial structure of star formation in pseudobulges and classical bulges. Pseudobulges are ``bulges'' which form through secular evolution, rather than mergers. In this study, pseudobulges are identified using the presence of disk-like structure in the center of the galaxy (nuclear spiral, nuclear bar, and/or high ellipticity in bulge); classical bulges are those galaxy bulges with smooth isophotes which are round compared to the outer disk, and show no disky structure in their bulge. I show that galaxies structurally identified as having pseudobulges have higher central star formation rates than those of classical bulges. Further, I also show that galaxies identified as having classical bulges have remarkably regular star formation profiles. The color profiles of galaxies with classical bulges show a star forming outer disk with a sharp change, consistent with a decline in star formation rates, toward the center of the galaxy. Classical bulges have a n...

  17. The origin of the Milky Way globular clusters

    CERN Document Server

    Renaud, Florent; Gieles, Mark

    2016-01-01

    We present a cosmological zoom-in simulation of a Milky Way-like galaxy used to explore the formation and evolution of star clusters. We investigate in particular the origin of the bimodality observed in the colour and metallicity of globular clusters, and the environmental evolution through cosmic times in the form of tidal tensors. Our results self-consistently confirm previous findings that the blue, metal-poor clusters form in satellite galaxies which are accreted onto the Milky Way, while the red, metal-rich clusters form mostly in situ or, to a lower extent in massive, self-enriched galaxies merging with the Milky Way. By monitoring the tidal fields these populations experience, we find that clusters formed in situ (generally centrally concentrated) feel significantly stronger tides than the accreted ones, both in the present-day, and when averaged over their entire life. Furthermore, we note that the tidal field experienced by Milky Way clusters is significantly weaker in the past than at present-day, ...

  18. New SX Phe variables in the globular cluster NGC288

    CERN Document Server

    Martinazzi, E; Costa, J E S; Pieres, A; Bonatto, C; Bica, E; Fraga, L

    2014-01-01

    We report the discovery of two new variable stars in the metal-poor globular cluster NGC 288, found by means of time-series CCD photometry. We classified the new variables as SX Phoenicis due to their characteristic fundamental mode periods (1.02 +- 0.01 and 0.69 +- 0.01 hours), and refine the period estimates for other six known variables. SX Phe stars are known to follow a well-defined Period-Luminosity (P-L) relation and, thus, can be used for determining distances; they are more numerous than RR Lyraes in NGC~288. We obtain the P-L relation for the fundamental mode M_V = (-2.59 +- 0.18) log P_0(d) + (-0.34 +- 0.24) and for the first-overtone mode M_V = (-2.59 +- 0.18) log P_1(d) + (0.50 +- 0.25). Multi-chromatic isochrone fits to our UBV color-magnitude diagrams, based on the Dartmouth Stellar Evolution Database, provide = -1.3 +- 0.1, E(B-V) = 0.02 +- 0.01 and absolute distance modulus (m-M)0 = 14.72 +- 0.01 for NGC 288.

  19. New SX Phe variables in the globular cluster NGC 288

    Science.gov (United States)

    Martinazzi, E.; Kepler, S. O.; Costa, J. E. S.; Pieres, A.; Bonatto, C.; Bica, E.; Fraga, L.

    2015-03-01

    We report the discovery of two new variable stars in the metal-poor globular cluster NGC 288, found by means of time series CCD photometry. We classified the new variables as SX Phoenicis (SX Phe) due to their characteristic fundamental mode periods (1.02 ± 0.01 and 0.69 ± 0.01 h), and refine the period estimates for other six known variables. SX Phe stars are known to follow a well-defined period-luminosity (P-L) relation and, thus, can be used for determining distances; they are more numerous than RR Lyraes in NGC 288. We obtain the P-L relation for the fundamental mode MV = (-2.59 ± 0.18) log P0(d) + (-0.34 ± 0.24) and for the first-overtone mode MV = (-2.59 ± 0.18) log P1(d) + (0.50 ± 0.25). Multichromatic isochrone fits to our UBV colour-magnitude diagrams, based on the Dartmouth Stellar Evolution Database, provide = -1.3 ± 0.1, E(B - V) = 0.02 ± 0.01 and absolute distance modulus (m - M)0 = 14.72 ± 0.01 for NGC 288.

  20. The Globular Cluster Systems around NGC 3311 and NGC 3309

    CERN Document Server

    Wehner, Elizabeth; Whitmore, Brad; Rothberg, Barry; Woodley, Kristin

    2008-01-01

    We present extensive new photometry in (g',i') of the large globular cluster (GC) system around NGC 3311, the central cD galaxy in the Hydra cluster. Our GMOS data cover a 5.5' field of view and reach a limiting magnitude i' = 26, about 0.5 magnitude fainter than the turnover point of the GC luminosity function. We find that NGC 3311 has a huge population of ~16, 000 GCs, closely similar to the prototypical high specific frequency Virgo giant M87. The color-magnitude distribution shows that the metal-poor blue GC sequence and the metal-richer red sequence are both present, with nearly equal numbers of clusters. Bimodal fits to the color distributions confirm that the blue sequence shows the same trend of progressively increasing metallicity with GC mass that has previously been found in many other large galaxies; the correlation we find corresponds to a scaling of GC metallicity with mass of Z ~ M^0.6 . By contrast, the red sequence shows no change of mean metallicity with mass, but it shows an upward extensi...

  1. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Crighton, Neil H. M.; Hennawi, Joseph F. [Max-Planck-Institut für Astronomie, Königstuhl 17, Heidelberg D-69117 (Germany); Prochaska, J. Xavier, E-mail: neilcrighton@gmail.com [Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)

    2013-10-20

    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 (N{sub H{sup 0}}=10{sup 19.50±0.16} cm{sup -2}) we detect neutral deuterium and oxygen, allowing a precise measurement of the metallicity: log{sub 10}(Z/Z {sub ☉}) = –2.0 ± 0.17, or (7-15) × 10{sup –3} solar. Furthermore, the narrow deuterium linewidth requires a cool temperature <20,000 K. Given the striking similarities between this system and the predictions of simulations, we argue that it represents the direct detection of a high-redshift cold-accretion stream. The low-metallicity gas cloud is a single component of an absorption system exhibiting a complex velocity, ionization, and enrichment structure. Two other components have metallicities >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.

  3. Cold gelation of globular proteins

    NARCIS (Netherlands)

    Alting, A.C.

    2003-01-01

    Keywords : globular proteins, whey protein, ovalbumin, cold gelation, disulfide bonds, texture, gel hardnessProtein gelation in food products is important to obtain desirable sensory and textural properties. Cold gelation is a novel method to produce protein-based gels. It is a two step process in w

  4. Separation of Stellar Populations by an Evolving Bar: Implications for the Bulge of the Milky Way

    CERN Document Server

    Debattista, Victor P; Gonzalez, Oscar A; Freeman, K; Zoccali, Manuela; Minniti, Dante

    2016-01-01

    We present a novel interpretation of the previously puzzling different behaviours of stellar populations of the Milky Way's bulge. We first show, by means of pure N-body simulations, that initially co-spatial stellar populations with different in-plane random motions separate when a bar forms. The radially cooler populations form a strong bar, and are vertically thin and peanut-shaped, while the hotter populations form a weaker bar and become a vertically thicker box. We demonstrate that it is the radial, not the vertical, velocity dispersion that drives this evolution. Assuming that early stellar discs heat rapidly as they form, then both the in-plane and vertical random motions correlate with stellar age and chemistry, leading to different density distributions for metal-rich and metal-poor stars. We then use a high resolution simulation, in which all stars form out of gas, to demonstrate that this is what happens. When we apply these results to the Milky Way we show that a very broad range of observed tren...

  5. 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,...

  6. The Explosive Yields Produced by the First Generation of Core Collapse Supernovae and the Chemical Composition of Extremely Metal Poor Stars

    CERN Document Server

    Chieffi, A; Chieffi, Alessandro; Limongi, Marco

    2002-01-01

    We present a detailed comparison between an extended set of elemental abundances observed in some of the most metal poor stars presently known and the ejecta produced by a generation of primordial core collapse supernovae. We used five stars which form our initial database and define a "template" ultra metal poor star which is then compared to the theoretical predictions. Our main findings are as follows: a) the fit to [Si/Mg] and [Ca/Mg] of these very metal poor stars seems to favor the presence of a rather large C abundance at the end of the central He burning; in a classical scenario in which the border of the convective core is strictly determined by the Schwarzschild criterion, such a large C abundance would imply a rather low C12(alpha,gamma)O16 reaction rate; b) a low C abundance left by the central He burning would imply a low [Al/Mg] (<-1.2 dex) independently on the initial mass of the exploding star while a rather large C abundance would produce such a low [Al/Mg] only for the most massive stella...

  7. Stars and Planetary Nebulae in the Galactic Bulge

    CERN Document Server

    Cuisinier, F; Acker, A; Maciel, W J

    2000-01-01

    We compare the populations of Red Giant stars and Planetary Nebulae in the Galactic Bulge, in the light of recent determinations of their abundances patterns. We find both populations to be compatible. From the planetary nebulae, we find evidences that the Bulge did not form stars recently. The whole abundances pattern remains however puzzling, some elements favoring a quick evolution of the Galactic Bulge (Mg and Ti), and others a much slower one (He, O, Si, S, Ar and Ca).

  8. Extragalactic Globular Clusters: Old Spectroscopic Ages and New Views on Their Formation

    CERN Document Server

    Strader, J; Cenarro, A J; Beasley, M A; Forbes, D A; Strader, Jay; Brodie, Jean P.; Beasley, Michael A.; Forbes, Duncan A.

    2005-01-01

    We present the results of a meta-analysis of Keck spectra of extragalactic globular clusters (GCs) in a sample of eight galaxies, ranging from dwarfs to massive ellipticals. We infer ages for the metal-poor and metal-rich GCs in these galaxies through comparisons to Galactic GCs. Both subpopulations appear to be no younger than their Galactic counterparts, with ages ~> 10 Gyr. This is the largest sample of galaxies for which ages have been constrained spectroscopically. Our results support the formation of most GCs in massive galaxies at high redshift. We propose a scenario for the formation of GC subpopulations that synthesizes aspects of both accretion and in situ approaches in the context of galaxy formation through hierarchical merging.

  9. WHERE ARE MOST OF THE GLOBULAR CLUSTERS IN TODAY’S UNIVERSE?

    Energy Technology Data Exchange (ETDEWEB)

    Harris, William E., E-mail: harris@physics.mcmaster.ca [Department of Physics and Astronomy, McMaster University, Hamilton, ON (Canada)

    2016-04-15

    The total number of globular clusters (GCs) in a galaxy rises continuously with the galaxy luminosity L, while the relative number of galaxies decreases with L following the Schechter function. The product of these two very nonlinear functions gives the relative number of GCs contained by all galaxies at a given L. It is shown that GCs, in this universal sense, are most commonly found in galaxies within a narrow range around L{sub ⋆}. In addition, blue (metal-poor) GCs outnumber the red (metal-richer) ones globally by 4 to 1 when all galaxies are added, pointing to the conclusion that the earliest stages of galaxy formation were especially favorable to forming massive, dense star clusters.

  10. 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

  11. Which bulges are favoured by barred S0 galaxies?

    CERN Document Server

    Barway, Sudhanshu; Vaghmare, Kaustubh; Kembhavi, Ajit K

    2016-01-01

    S0 galaxies are known to host classical bulges with a broad range of size and mass, while some such S0s are barred and some not. The origin of the bars has remained as a long-standing problem -- what made bar formation possible in certain S0s? By analysing a large sample of S0s with classical bulges observed by the Spitzer space telescope, we find that most of our barred S0s host comparatively low-mass classical bulges, typically with bulge-to-total ratio ($B/T$) less than $0.5$; whereas S0s with more massive classical bulges than these do not host any bar. Furthermore, we find that amongst the barred S0s, there is a trend for the longer and massive bars to be associated with comparatively bigger and massive classical bulges -- possibly suggesting bar growth being facilitated by these classical bulges. In addition, we find that the bulge effective radius is always less than the bar effective radius --indicating an interesting synergy between the host classical bulge and bars being maintained while bar growth ...

  12. Trajectories of Cepheid variable stars in the Galactic nuclear bulge

    Science.gov (United States)

    Matsunaga, Noriyuki

    2012-06-01

    The central region of our Galaxy provides us with a good opportunity to study the evolution of galactic nuclei and bulges because we can observe various phenomena in detail at the proximity of 8 kpc. There is a hierarchical alignment of stellar systems with different sizes; from the extended bulge, the nuclear bulge, down to the compact cluster around the central supermassive blackhole. The nuclear bulge contains stars as young as a few Myr, and even hosts the ongoing star formation. These are in contrast to the more extended bulge which are dominated by old stars, ~10Gyr. It is considered that the star formation in the nuclear bulge is caused by fresh gas provided from the inner disk. In this picture, the nuclear bulge plays an important role as the interface between the gas supplier, the inner disk, and the galactic nucleus. Kinematics of young stars in the nuclear bulge is important to discuss the star forming process and the gas circulation in the Galactic Center. We here propose spectroscopic observations of Cepheid variable stars, ~25 Myr, which we recently discovered in the nuclear bulge. The spectra taken in this proposal will allow timely estimates of the systemic velocities of the variable stars.

  13. Space Velocities of Southern Globular Clusters. V. A Low Galactic Latitude Sample

    CERN Document Server

    Casetti-Dinescu, D I; Herrera, D; Van Altena, W F; López, C E; Castillo, D J

    2007-01-01

    We have measured the absolute proper motions of globular clusters NGC 2808, 3201, 4372, 4833, 5927 and 5986. The proper motions are on the Hipparcos system and they are the first determinations ever made for these low Galactic latitude clusters. The proper motion uncertainties range from 0.3 to 0.5 mas/yr. The inferred orbits indicate that 1) the single metal rich cluster in our sample, NGC 5927, dynamically belongs to the thick disk, 2) the remaining metal poor clusters have rather low-energy orbits of high eccentricity; among these, there appear to be two "pairs" of dynamically associated clusters, 3) the most energetic cluster in our sample, NGC 3201 is on a highly retrograde orbit -- which had already been surmised from its radial velocity alone -- with an apocentric distance of 22 kpc, and 4) none of the metal poor clusters appear to be associated with the recently detected SDSS streams, or with the Monoceros structure. These are the first results of the Southern Proper-Motion Program (SPM) where the sec...

  14. The chemical composition of a regular halo globular cluster: NGC 5897

    CERN Document Server

    Koch, Andreas

    2014-01-01

    We report for the first time on the chemical composition of the halo cluster NGC 5897 (R=12.5 kpc), based on chemical abundance ratios for 27 alpha-, iron-peak, and neutron-capture elements in seven red giants. From our high-resolution, high signal-to-noise spectra obtained with the Magellan/MIKE spectrograph, we find a mean iron abundance from the neutral species of [Fe/H] = -2.04 +/- 0.01 (stat.) +/- 0.15 (sys.), which is more metal-poor than implied by previous photometric and low-resolution spectroscopic studies. NGC 5897 is alpha-enhanced (to 0.34 +/- 0.01 dex) and shows Fe-peak element ratios typical of other (metal-poor) halo globular clusters (GCs) with no overall, significant abundance spreads in iron nor in any other heavy element. Like other GCs, NGC 5897 shows a clear Na-O anti-correlation, where we find a prominent primordial population of stars with enhanced O abundances and ~Solar Na/Fe ratios, while two stars are Na-rich, providing chemical proof of the presence of multiple populations in this...

  15. Form of the galactic globular cluster system and the distance to the Galactic Centre

    Energy Technology Data Exchange (ETDEWEB)

    Frenk, C.S. (Cambridge Univ. (UK). Inst. of Astronomy); White, S.D.M. (California Univ., Berkeley (USA). Dept. of Astronomy)

    1982-01-01

    New quantitative methods are developed for analysing the structure of the galactic globular cluster system. Samples limited in galactic latitude which can be assumed complete are chosen, and the distance independent information contained in the positions of clusters on the sky, and the information contained in the apparent three-dimensional distribution, are considered separately. The cluster system is slightly flattened and there is no significant evidence for any variation in flattening as a function of metallicity. Its density is well described over the range 0.2 < r/Rsub(Sun) < 5 by a Hubble law, rho varies as r/sup -3/, or by a de Vaucouleurs law with rsub(e)/Rsub(Sun) = 0.50. Distance modulus errors of order one magnitude are required to explain the deviation of the apparent distribution of metal-rich clusters from axial symmetry. In addition a systematic difference in distance scale of about 0.5 magnitudes is necessary to reconcile the centroid of this distribution with that of the metal-poor clusters. This shift is in the same sense and of about the size predicted by theoretical pulsation models of RR Lyrae stars. If the standard distance scale is adopted for metal-poor clusters, the estimated distance from the Sun to the Galactic Centre is Rsub(Sun) = 6.8 +- 0.8 kpc.

  16. Globular Clusters and Spur Clusters in NGC 4921, the Brightest Spiral Galaxy in the Coma Cluster

    CERN Document Server

    Lee, Myung Gyoon

    2016-01-01

    We resolve a significant fraction of globular clusters (GCs) in NGC 4921, the brightest spiral galaxy in Coma. Also we find a number of extended bright star clusters (star complexes) in the spur region of the arms. The latter are much brighter and bluer than those in the normal star-forming region, being as massive as 3x10^5 M_odot. The color distribution of the GCs in this galaxy is found to be bimodal. The turnover magnitudes of the luminosity functions (LF) of the blue (metal-poor) GCs (0.70<(V-I)<1.05) in the halo are estimated to be V(max) =27.11+-0.09 mag and I(max)=26.21+-0.11 mag. We obtain similar values for NGC 4923, a companion S0 galaxy, and two Coma cD galaxies (NGC 4874 and NGC 4889). The mean value for the turnover magnitudes of these four galaxies is I(max)=26.25+-0.03 mag. Adopting M_I (max) = -8.56+-0.09 mag for the metal-poor GCs, we determine the mean distance to the four Coma galaxies, 91+-4 Mpc. Combining this and the Coma radial velocity, we derive a value of the Hubble constant, ...

  17. T-bulge-shaped quantum router

    Science.gov (United States)

    Liu, Lin; Lu, Jing

    2017-01-01

    The transport properties of a single photon scattered by a two-level system (TLS) in a T-bulge-shaped waveguide have been studied, which is made of two coupled-resonator waveguides (CRWs), an infinite CRW and a semi-infinite CRW with N-1 FP cavities below the node. The spontaneous emission of the TLS directs single photons from one CRW to the other. The N-1 FP cavities effect the extreme point's value and location of the propagation coefficient and incident energy curve.

  18. Radio Emission from Globular Clusters

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Radio emission of globular clusters is studied by analyzing the VLA radio survey data of the NVSS and FIRST. We find that 13 clusters have radio sources within their half-mass radii of clusters. Sources detected previously in NGC 7078and NGC 6440 are identified. Pulsars in NGC 6121, NGC 6440 and NGC 7078cannot be detected because of the insufficient survey sensitivity and resolution.There may be a pulsar in the core of Terzan 1. The nature of the extended radio source near the core of NGC 6440 remains unclear. In the core of a globular cluster,there may be many neutron stars or an intermediate mass black hole, but this cannot be clarified with the current radio observations.

  19. Bulge-driven Fueling of Seed Black Holes

    CERN Document Server

    Park, KwangHo; Natarajan, Priyamvada; Bogdanović, Tamara; Wise, John H

    2015-01-01

    We examine radiation-regulated accretion onto intermediate-mass and massive black holes (BHs) embedded in a bulge component. Using spherically symmetric one-dimensional radiation-hydrodynamics simulations, we track the growth of BHs accreting from a cold, neutral gas reservoir with temperature T=10^4 K. We find that the accretion rate of BHs embedded in bulges is proportional to r_{B,eff}/r_B, where r_{B,eff} is the increased effective Bondi radius that includes the gravitational potential of the bulge, and r_B is the Bondi radius of the BH. The radiative feedback from the BH suppresses the cold accretion rate to ~1 percent of the Bondi rate when a bulge is not considered. However, we find that the BH fueling rate increases rapidly when the bulge mass M_bulge is greater than the critical value of 10^6 M_sun and is proportional to M_bulge. Since the critical bulge mass is independent of the central BH mass M_{BH}, the growth rate of BHs with masses of 10^2, 10^4, and 10^6 M_sun exhibits distinct dependencies o...

  20. Surface photometry of bulge dominated low surface brightness galaxies

    NARCIS (Netherlands)

    Beijersbergen, M; de Blok, WJG; van der Hulst, JM

    1999-01-01

    We present results of broad band BVRI observations of a sample of galaxies with a low surface brightness (LSB) disk and a bulge. These galaxies are well described as exponential disks and exponential bulges with no preferred value for either scale length or central surface brightness. The median B b

  1. The Galactic Bulge The Stellar and Planetary Nebulae Populations

    CERN Document Server

    Cuisinier, F; Acker, A; Maciel, W J

    2001-01-01

    We compare abundances patterns in the Bulge for elements observed in stars and in planetary nebulae. Some alpha elements, like Mg and Ti, are overabundant respect to Fe, and others are not, like He, O, Si, S, Ar, Ca. The first ones favor a quick evolution of the Galactic Bulge, and the seconds a much slower one.

  2. Rotation and flattening of globular clusters

    Science.gov (United States)

    Fall, S. M.; Frenk, C. S.

    1985-01-01

    Methods for measuring globular cluster ellipticities and the results of such measurements are reviewed, and the processes that determine the shapes of globular clusters and the ways in which they change with time are discussed. The use of the virial tensor theorem to study the connection between the global rotation, velocity anisotropy, and the shape of a self-gravitating system is addressed, and the employment of N-body models to simulate the evolution of globular clusters with initially anisotropic velocity distributions is examined. The application of a simple evaporation model and Fokker-Planck integrations to study the two-body diffusion in globular clusters is reviewed.

  3. Natures of a clump-origin bulge: a pseudobulge-like but old metal-rich bulge

    CERN Document Server

    Inoue, Shigeki

    2011-01-01

    Bulges in spiral galaxies have been supposed to be classified into two types: classical bulges or pseudobulges. Classical bulges are thought to form by galactic merger with bursty star formation, whereas pseudobulges are suggested to form by secular evolution due to spiral arms and a barred structure funneling gas into the galactic centre. Noguchi (1998, 1999) suggested another bulge formation scenario, `clump-origin bulge'. He demonstrated using a numerical simulation that a galactic disc suffers dynamical instability to form clumpy structures in the early stage of disc formation since the premature disc is expected to be highly gas-rich, then the clumps are sucked into the galactic centre by dynamical friction and merge into a single bulge at the centre. This bulge formation scenario expected happen only at the high-redshift is different from the galactic merger and the secular evolution. Therefore, clump-origin bulges may have their own unique properties. We perform a high-resolution N-body/smoothed partic...

  4. Non-local thermodynamic equilibrium stellar spectroscopy with 1D and 3D models - II. Chemical properties of the Galactic metal-poor disk and the halo

    DEFF Research Database (Denmark)

    Bergemann, Maria; Collet, Remo; Schönrich, Ralph

    2016-01-01

    We have analysed high-resolution spectra of 328 stars and derived Mg abundances using non-local thermodynamic equilibrium (NLTE) spectral line formation calculations and plane-parallel model stellar atmospheres derived from the mean stratification of 3D hydrodynamical surface convection simulations....../Fe] ratios close to solar even at [Fe/H] ~ -2. This is at variance with results of classical abundance analyses based on local thermodynamic equilibrium (LTE) and 1D model stellar atmospheres, which argue for a constant elevated [Mg/Fe] in metal-poor stars of the Galactic thick disk and halo....

  5. Globular Cluster Abundances and What They Can Tell Us About Galaxy Formation

    CERN Document Server

    Cohen, Judith G

    2009-01-01

    We review the properties of globular clusters which make them useful for studying the Galactic halo, Galactic chemical evolution, and the early stages of the formation of the Milky Way. We review the evidence that GCs have a chemical inventory similar to those of halo field stars. We discuss the abundance ratios for dSph galaxies and show that it is possible to have formed at least part the Galactic halo field stellar population by dissolving globular clusters and/or accreting dSph galaxies but only if this occurred at an early stage in the formation of the Galaxy. We review the constraints on halo formation timescales deduced from the low Mg isotopic ratios in metal-poor halo field dwarfs which indicate that AGB stars did not have time to contribute significantly, while M71 contains two populations, one without and also one with a substantial AGB contribution. We review the limited evidence for GCs with a second population showing additional contributions from SNII, currently confined to Omega Cen, M54, and ...

  6. A spectroscopic study of the globular cluster M28 (NGC 6626)

    Science.gov (United States)

    Villanova, S.; Moni Bidin, C.; Mauro, F.; Munoz, C.; Monaco, L.

    2017-01-01

    We present the abundance analysis for a sample of 17 red giant branch stars in the metal-poor globular cluster M28 based on high-resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Ce, and Eu. We find a metallicity of [Fe/H] = -1.29 ± 0.01 and an α-enhancement of +0.34 ± 0.01 (errors on the mean), typical of halo globular clusters in this metallicity regime. A large spread is observed in the abundances of light elements O, Na, and Al. Mg also shows an anti-correlation with Al with a significance of 3σ. The cluster shows a Na-O anti-correlation and a Na-Al correlation. This correlation is not linear but `segmented' and that the stars are not distributed continuously, but form at least three well-separated sub-populations. In this aspect, M28 resembles NGC 2808 that was found to host at least five sub-populations. The presence of a Mg-Al anti-correlation favour massive AGB stars as the main polluters responsible for the multiple-population phenomenon.

  7. A spectroscopic study of the Globular Cluster M28 (NGC~6626)

    CERN Document Server

    Villanova, S; Mauro, F; Munoz, C; Monaco, L

    2016-01-01

    We present the abundance analysis for a sample of 17 red giant branch stars in the metal-poor globular cluster M28 based on high resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Ce, and Eu. We find a metallicity of [Fe/H]=-1.29+-0.01 and an alpha-enhancement of +0.34+-0.01 (errors on the mean), typical of Halo Globular Clusters in this metallicity regime. A large spread is observed in the abundances of light elements O, Na, and Al. Mg also shows an anticorrelation with Al with a significance of 3 sigma. The cluster shows a Na-O anticorrelation and a Na-Al correlation. This correlation is not linear but "segmented" and that the stars are not distributed continuously, but form at least 3 well separated sub-populations. In this aspect M28 resembles NGC~2808 that was found to host at least 5 sub-populations. The presence of a Mg-Al anticorrelation favor massive AGB stars as the main...

  8. High-resolution CCD spectra of stars in globular clusters. I - Oxygen in M13

    Science.gov (United States)

    Leep, E. M.; Wallerstein, G.; Oke, J. B.

    1986-01-01

    High-resolution (0.3 A) CCD spectra obtained at the 200 in. coude spectrograph have been analyzed for the abundances of O, Sc, Fe, and La in four stars in the globular cluster M13. Fe/H abundance is found to be = -1.6, as found by many other observers of this cluster. For three stars O/Fe abundance is found to be = +0.3 + or - 0.1, which is similar to O/Fe ratios in other globular clusters and metal-poor field stars. For star II-67, no oxygen line is visible at 6300 A and O/Fe abundance is found to be not greater than -0.4 (for a high carbon content) and not greater than -0.7 (for a low carbon content). The latter is more likely to be correct. Two possible explanations of the oxygen deficiency in II-67 are discussed: primordial deficiency, and CNO cycling at or above a temperature of 25,000,000 K.

  9. Integrated Light Chemical Tagging Analyses of Seven M31 Outer Halo Globular Clusters from the Pan-Andromeda Archaeological Survey

    CERN Document Server

    Sakari, Charli M; Mackey, Dougal; Shetrone, Matthew D; Dotter, Aaron; Ferguson, Annette M N; Huxor, Avon

    2015-01-01

    Detailed chemical abundances are presented for seven M31 outer halo globular clusters (with projected distances from M31 greater than 30 kpc), as derived from high resolution integrated light spectra taken with the Hobby Eberly Telescope. Five of these clusters were recently discovered in the Pan-Andromeda Archaeological Survey (PAndAS)---this paper presents the first determinations of integrated Fe, Na, Mg, Ca, Ti, Ni, Ba, and Eu abundances for these clusters. Four of the target clusters (PA06, PA53, PA54, and PA56) are metal-poor ([Fe/H] < -1.5), alpha-enhanced (though they are possibly less alpha-enhanced than Milky Way stars at the 1 sigma level), and show signs of star-to-star Na and Mg variations. The other three globular clusters (H10, H23, and PA17) are more metal rich, with metallicities ranging from [Fe/H] = -1.4 to -0.9. While H23 is chemically similar to Milky Way field stars, Milky Way globular clusters, and other M31 clusters, H10 and PA17 have moderately low [Ca/Fe], compared to Milky Way fi...

  10. Another Faint UV Object Associated with a Globular Cluster X-Ray Source The Case of M92

    CERN Document Server

    Ferraro, F R; Rood, R T; Pecci, F F; Buonanno, R; Ferraro, Francesco R.; Paltrinieri, Barbara; Rood, Robert T.; Pecci, Flavio Fusi; Buonanno, Roberto

    2000-01-01

    The core of the metal poor Galactic Globular Cluster M92 (NGC 6341) has been observed with WFPC2 on the Hubble Space Telescope through visual, blue and mid-UV filters in a program devoted to study the evolved stellar population in a selected sample of Galactic Globular Clusters. In the UV $(m_{255}, m_{255}-U)$ color magnitude diagram we have discovered a faint `UV-dominant' object. This star lies within the error box of a Low Luminosity Globular Cluster X-ray source (LLGCX) recently found in the core of M92. The properties of the UV star discovered in M92 are very similar to those of other UV stars found in the core of some clusters (M13, 47 Tuc, M80, etc)---all of them are brighter in the UV than in the visible and are located in the vicinity of a LLGCX. We suggest that these stars are a new sub-class of cataclysmic variables.

  11. A Connection Between Bulge Properties and the Bimodality of Galaxies

    CERN Document Server

    Drory, Niv

    2007-01-01

    The global colors of galaxies have recently been shown to follow bimodal distributions. Galaxies separate into a ``red sequence'', populated prototypically by early-type galaxies, and a ``blue cloud'', whose typical objects are late-type disk galaxies. Intermediate-type (Sa-Sbc) galaxies populate both regions. It has been suggested that this bimodality reflects the two-component nature of disk-bulge galaxies. However, it has now been established that there are two types of bulges: ``classical bulges'' that are dynamically hot systems resembling (little) ellipticals, and ``pseudobulges'', dynamically cold, flattened, disk-like structures that could not have formed via violent relaxation. Therefore thee question is whether at types Sa-Sbc, where both bulge types are found, the red-blue dichotomy separates galaxies at some value of disk-to-bulge ratio, $B/T$, or, whether it separates galaxies of different bulge type, irrespective of their $B/T$. We identify classical bulges and pseudobulges morphologically with ...

  12. Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. V. Oxygen abundance in the metal-poor giant HD 122563 from OH UV lines

    CERN Document Server

    Prakapavičius, D; Dobrovolskas, V; Klevas, J; Steffen, M; Bonifacio, P; Ludwig, H -G; Spite, M

    2016-01-01

    Although oxygen is an important tracer of the early Galactic evolution, its abundance trends with metallicity are still relatively poorly known at [Fe/H] < -2.5. This is in part due to a lack of reliable oxygen abundance indicators in the metal-poor stars, in part due to shortcomings in 1D LTE abundance analyses. In this study we determined the oxygen abundance in the metal-poor halo giant HD 122563 using a 3D hydrodynamical CO5BOLD model atmosphere. Our main goal was to understand whether a 3D LTE analysis may help to improve the reliability of oxygen abundances determined from OH UV lines in comparison to those obtained using standard 1D LTE methodology. The oxygen abundance in HD 122563 was determined using 71 OH UV lines located in the wavelength range between 308-330 nm. The analysis was done using a high-resolution VLT UVES spectrum with a 1D LTE spectral line synthesis performed using the SYNTHE package and classical ATLAS9 model atmosphere. Subsequently, a 3D hydrodynamical CO5BOLD, and 1D hydrosta...

  13. Metal-poor stars observed with the Magellan telescope. II. Discovery of four stars with [Fe/H] ≤ –3.5

    Energy Technology Data Exchange (ETDEWEB)

    Placco, Vinicius M.; Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Frebel, Anna [Massachussetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Christlieb, Norbert [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Lee, Young Sun [Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States); Kennedy, Catherine R. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia); Rossi, Silvia; Santucci, Rafael M. [Departamento de Astronomia-Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, SP 05508-900 (Brazil)

    2014-01-20

    We report on the discovery of seven low-metallicity stars selected from the Hamburg/ESO Survey, six of which are extremely metal-poor (EMP, [Fe/H] ≤ –3.0), with four having [Fe/H] ≤ –3.5. Chemical abundances or upper limits are derived for these stars based on high-resolution (R ∼ 35,000) Magellan/MIKE spectroscopy, and are in general agreement with those of other very and extremely metal-poor stars reported in the literature. Accurate metallicities and abundance patterns for stars in this metallicity range are of particular importance for studies of the shape of the metallicity distribution function of the Milky Way's halo system, in particular for probing the nature of its low-metallicity tail. In addition, taking into account suggested evolutionary mixing effects, we find that six of the program stars (with [Fe/H] ≤ –3.35) possess atmospheres that were likely originally enriched in carbon, relative to iron, during their main-sequence phases. These stars do not exhibit overabundances of their s-process elements, and hence may be, within the error bars, additional examples of the so-called CEMP-no class of objects.

  14. 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...

  15. OBSERVATIONS OF BINARY STARS WITH THE DIFFERENTIAL SPECKLE SURVEY INSTRUMENT. V. TOWARD AN EMPIRICAL METAL-POOR MASS–LUMINOSITY RELATION

    Energy Technology Data Exchange (ETDEWEB)

    Horch, Elliott P. [Department of Physics, Southern Connecticut State University, 501 Crescent Street, New Haven, CT 06515 (United States); Van Altena, William F.; Demarque, Pierre [Department of Astronomy, Yale University P.O. Box 208101, New Haven, CT 06520-8101 (United States); Howell, Steve B. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Everett, Mark E. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Ciardi, David R. [NASA Exoplanet Science Institute, California Institute of Technology, 770 South Wilson Avenue, Mail Code 100-22, Pasadena, CA 91125 (United States); Teske, Johanna K. [Department of Terrestrial Magnetism and Carnegie Observatories, Carnegie Institute of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Henry, Todd J.; Winters, Jennifer G., E-mail: horche2@southernct.edu, E-mail: william.vanaltena@yale.edu, E-mail: pierre.demarque@yale.edu, E-mail: steve.b.howell@nasa.gov, E-mail: everett@noao.edu, E-mail: ciardi@ipac.caltech.edu, E-mail: jteske@carnegiescience.edu, E-mail: thenry@astro.gsu.edu, E-mail: winters@astro.gsu.edu [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302 (United States)

    2015-05-15

    In an effort to better understand the details of the stellar structure and evolution of metal-poor stars, the Gemini North telescope was used on two occasions to take speckle imaging data of a sample of known spectroscopic binary stars and other nearby stars in order to search for and resolve close companions. The observations were obtained using the Differential Speckle Survey Instrument, which takes data in two filters simultaneously. The results presented here are of 90 observations of 23 systems in which one or more companions was detected, and six stars where no companion was detected to the limit of the camera capabilities at Gemini. In the case of the binary and multiple stars, these results are then further analyzed to make first orbit determinations in five cases, and orbit refinements in four other cases. The mass information is derived, and since the systems span a range in metallicity, a study is presented that compares our results with the expected trend in total mass as derived from the most recent Yale isochrones as a function of metal abundance. These data suggest that metal-poor main-sequence stars are less massive at a given color than their solar-metallicity analogues in a manner consistent with that predicted from the theory.

  16. Observations of Binary Stars with the Differential Speckle Survey Instrument. V. Toward an Empirical Metal-Poor Mass-Luminosity Relation

    Science.gov (United States)

    Horch, Elliott P.; van Altena, William F.; Demarque, Pierre; Howell, Steve B.; Everett, Mark E.; Ciardi, David R.; Teske, Johanna K.; Henry, Todd J.; Winters, Jennifer G.

    2015-05-01

    In an effort to better understand the details of the stellar structure and evolution of metal-poor stars, the Gemini North telescope was used on two occasions to take speckle imaging data of a sample of known spectroscopic binary stars and other nearby stars in order to search for and resolve close companions. The observations were obtained using the Differential Speckle Survey Instrument, which takes data in two filters simultaneously. The results presented here are of 90 observations of 23 systems in which one or more companions was detected, and six stars where no companion was detected to the limit of the camera capabilities at Gemini. In the case of the binary and multiple stars, these results are then further analyzed to make first orbit determinations in five cases, and orbit refinements in four other cases. The mass information is derived, and since the systems span a range in metallicity, a study is presented that compares our results with the expected trend in total mass as derived from the most recent Yale isochrones as a function of metal abundance. These data suggest that metal-poor main-sequence stars are less massive at a given color than their solar-metallicity analogues in a manner consistent with that predicted from the theory.

  17. Chemical composition of carbon-rich, very metal-poor subgiant LP625-44 observed with the Subaru/HDS

    CERN Document Server

    Aoki, W; Honda, S; Iye, M; Izumiura, H; Kajino, T; Kambe, E; Kawanomoto, S; Noguchi, K; Okita, K; Sadakane, K; Sato, B; Shelton, I; Takada-Hidai, M; Takeda, Y; Watanabe, E; Yoshida, M

    2002-01-01

    We have obtained a high resolution (R~90,000) spectrum of the carbon- and s-process-element-rich, very metal-poor ([Fe/H]=-2.7) subgiant LP625-44, as well as that of HD140283 (a metal-poor subgiant with normal abundance ratio) for comparison, with the High Dispersion Spectrograph (HDS) for the Subaru Telescope for detailed abundance study. The oxygen abundance derived from the O I triplet around 7770A is uncertain, but the excess of oxygen in LP625-44 seems remarkable (perhaps by nearly a factor 10), in comparison with that of HD140283 derived from the same lines. The Na enhancement in LP625-44 is by about a factor 50, suggesting hydrogen burning in the 22Ne-rich layer in an asymptotic giant branch star which produces the abundance pattern of this object. In our new spectrum of LP625-44, the Pb I lambda 3683A line has been detected, as well as the Pb I lambda 4057A line which has already been studied, confirming the Pb abundance (log epsilon(Pb)~1.9) derived by the previous work. The abundance ratio of s-proc...

  18. IMPROVED Co 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. [Department of Physics, University of Wisconsin-Madison, 1150 University Ave., 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: chris@verdi.as.utexas.edu, E-mail: jjcowan1@ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)

    2015-09-15

    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 ϵ(Co) = 4.955 ± 0.007 (σ = 0.059) based on 82 Co i lines and log ϵ(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. 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...

  1. 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...

  2. Dynamical Evolution of Globular Clusters in the Galaxy

    Institute of Scientific and Technical Information of China (English)

    武振宇; 束成钢; 陈文屏

    2003-01-01

    Given the initial conditions of spatial density distribution, velocity distribution and mass function, the dynamical evolution of globular clusters in the Milky Way is investigated in details by means of Monte Carlo simulations.Four dynamic mechanisms are considered: stellar evaporation, stellar evolution, tidal shocks due to both the disc and bulge, and dynamical friction. It is found that stellar evaporation dominates the evolution of low-mass clusters and all four are important for massive ones. For both the power-law and lognormal initial clusters mass functions, we can find the best-fitting models which can match the present-day observations with their main features of the mass function almost unchanged after evolution of several Gyr. This implies that it is not possible to determine the initial mass function only based on the observed mass function today. The dispersion of the modelled mass functions mainly depends on the potential wells of host galaxies with the almost constant peaks,which is consistent with current observations

  3. Planetary nebulae and the chemical evolution of the galactic bulge

    CERN Document Server

    Costa, R D D; Maciel, W J; Costa, Roberto D.D.; Escudero, Andre V.; Maciel, Walter J.

    2005-01-01

    Electron temperatures, densities, ionic and elemental abundances of helium, nitrogen, oxygen, argon, sulfur and neon were derived for a sample of bulge planetary nebulae, representative of its intermediate mass population. Using these results as constraints, a model for the chemical evolution of the galactic bulge was developed. The results indicate that the best fit is achieved using a double-infall model, where the first one is a fast collapse of primordial gas and the second is slower and enriched by material ejected by the bulge itself during the first episode.

  4. Kinematics in the Galactic Bulge with APOGEE. II. High-Order Kinematic Moments and Comparison to Extragalactic Bar Diagnostics

    Science.gov (United States)

    Zasowski, G.; Ness, M. K.; García Pérez, A. E.; Martinez-Valpuesta, I.; Johnson, J. A.; Majewski, S. R.

    2016-12-01

    Much of the inner Milky Way’s (MW) global rotation and velocity dispersion patterns can be reproduced by models of secularly evolved, bar-dominated bulges. More sophisticated constraints, including the higher moments of the line-of-sight velocity distributions (LOSVDs) and limits on the chemodynamical substructure, are critical for interpreting observations of the unresolved inner regions of extragalactic systems and for placing the MW in context with other galaxies. Here, we use SDSS-APOGEE data to develop these constraints, by presenting the first maps of the skewness and kurtosis of the LOSVDs of metal-rich and metal-poor inner MW stars (divided at [Fe/H] = -0.4), and comparing the observed patterns to those that are seen both in N-body models and in extragalactic bars. Despite closely matching the mean velocity and dispersion, the models do not reproduce the observed skewness patterns of the LOSVDs in different ways, which demonstrates that our understanding of the detailed orbital structure of the inner MW remains an important regime for improvement. We find evidence in the MW of the skewness-velocity correlation that is used as a diagnostic of extragalactic bars/bulges. This correlation appears in metal-rich stars only, providing further evidence for different evolutionary histories of chemically differentiated populations. We connect these skewness measurements to previous work on high-velocity “peaks” in the inner Galaxy, confirming the presence of that phenomenon, and we quantify the cylindrical rotation of the inner Galaxy, finding that the latitude-independent rotation vanishes outside l ˜ 7°. Finally, we evaluate the MW data in the light of selected extragalactic bar diagnostics and discuss the progress and challenges in using the MW as a resolved analog of unresolved stellar populations.

  5. Polarization in microlensing towards the Galactic bulge

    CERN Document Server

    Ingrosso, G; De Paolis, F; Jetzer, Ph; Nucita, A A; Strafella, F; Zakharov, A F

    2012-01-01

    Gravitational microlensing, when finite size source effects are relevant, provides an unique tool for the study of source star stellar atmospheres through an enhancement of a characteristic polarization signal. This is due to the differential magnification induced during the crossing of the source star. In this paper we consider a specific set of reported highly magnified, both single and binary exoplanetary systems, microlensing events towards the Galactic bulge and evaluate the expected polarization signal. To this purpose, we consider several polarization models which apply to different types of source stars: hot, late type main sequence and cool giants. As a result we compute the polarization signal P,which goes up to P=0.04% for late type stars and up to a few percent for cool giants, depending on the underlying physical polarization processes and atmosphere model parameters. Given a I band magnitude at maximum magnification of about 12, and a typical duration of the polarization signal up to 1 day, we c...

  6. Hiding its age: the case for a younger bulge

    CERN Document Server

    Haywood, M; Snaith, O; Calamida, A

    2016-01-01

    The determination of the age of the bulge has led to two contradictory results. On the one side, the color-magnitude diagrams in different bulge fields seem to indicate a uniformly old ($>$10 Gyr) population. On the other side, individual ages derived from dwarfs observed through microlensing events seem to indicate a large spread, from $\\sim$ 2 to $\\sim$ 13 Gyr. Because the bulge is now recognised as being mainly a boxy peanut-shaped bar, it is suggested that disk stars are one of its main constituents, and therefore also stars with ages significantly younger than 10 Gyr. Other arguments as well point to the fact that the bulge cannot be exclusively old, and in particular cannot be a burst population, as it is usually expected if the bulge was the fossil remnant of a merger phase in the early Galaxy. In the present study, we show that given the range of metallicities observed in the bulge, a uniformly old population would be reflected into a significant spread in color at the turn-off which is not observed. ...

  7. Stellar populations of the bulges of four spiral galaxies

    CERN Document Server

    Morelli, L; Corsini, E M; Bontà, E Dalla; Coccato, L; Méndez-Abreu, J; Parmiggiani, M

    2015-01-01

    Key information to understand the formation and evolution of disk galaxies are imprinted in the stellar populations of their bulges. This paper has the purpose to make available new measurements of the stellar population properties of the bulges of four spiral galaxies. Both the central values and radial profiles of the line strength of some of the most common Lick indices are measured along the major- and minor- axis of the bulge-dominated region of the sample galaxies. The corresponding age, metallicity, and {\\alpha}/Fe ratio are derived by using the simple stellar population synthesis model predictions. The central values and the gradients of the stellar population properties of ESO-LV1890070, ESO-LV4460170, and ESO-LV 5140100 are consistent with previous findings for bulges of spiral galaxies. On the contrary, the bulge of ESO-LV 4500200 shows peculiar chemical properties possibly due to the presence of a central kinematically-decoupled component. The negative metallicity gradient found in our bulges samp...

  8. Chemodynamical analysis of bulge stars for simulated disc galaxies

    Science.gov (United States)

    Rahimi, A.; Kawata, D.; Brook, Chris B.; Gibson, Brad K.

    2010-01-01

    We analyse the kinematics and chemistry of the bulge stars of two simulated disc galaxies using our chemodynamical galaxy evolution code GCD+. First, we compare stars that are born inside the galaxy with those that are born outside the galaxy and are accreted into the centre of the galaxy. Stars that originate outside the bulge are accreted into it early in its formation within 3 Gyr so that these stars have high [α/Fe] as well as a high total energy reflecting their accretion to the centre of the galaxy. Therefore, higher total energy is a good indicator for finding accreted stars. The bulges of the simulated galaxies formed through multiple mergers separated by about a Gyr. Since [α/Fe] is sensitive to the first few Gyr of star formation history, stars that formed during mergers at different epochs show different [α/Fe]. We show that the [Mg/Fe] against star formation time relation can be very useful to identify a multiple merger bulge formation scenario, provided there is sufficiently good age information available. Our simulations also show that stars formed during one of the merger events retain a systematically prograde rotation at the final time. This demonstrates that the orbit of the ancient merger that helped to form the bulge could still remain in the kinematics of bulge stars.

  9. 中等贫金属星的元素丰度分析%Abundance Analysis in the Mildly Metal-poor Stars

    Institute of Scientific and Technical Information of China (English)

    邱红梅; 赵刚; 新宇; 李宗伟

    2000-01-01

    We present here some observed data on 11 mildly metal-poor stars with -1.3 [Fe/H] -0.6. The model parameters and the abundances of 14 elements are determined. We also discuss the relation between the abundance ratio and the metallicity. The elements (Mg, Si, Ca, Ti) are overabundant relative to Fe with a varying scatter at each given metallicity. Most of the iron-peak elements (V, Cr, Ni, Cu) are also overabundant relative to Fe by amounts that are independent of [Fe/H], while [Mn/Fe] increases with increasing metallicity. [Na/Al] is overabundant in the sample with [Fe/H]>-1.1 and definitely overdeficient in the sample with [Fe/H]-1.1的样本星中表现超丰,在[Fe/H]<-1.1的样本中却明显过贫.

  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

    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.

  12. 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/...

  13. Enhanced methods for computing spectra from CO5BOLD models using Linfor3D. Molecular bands in metal-poor stars

    CERN Document Server

    Gallagher, A J; Caffau, E; Bonifacio, P; Ludwig, H -G; Freytag, B

    2016-01-01

    Molecular features such as the G-band, CN-band and NH-band are important diagnostics for measuring a star's carbon and nitrogen abundances, especially in metal-poor stars where atomic lines are no longer visible in stellar spectra. Unlike atomic transitions, molecular features tend to form in bands, which cover large wavelength regions in a spectrum. While it is a trivial matter to compute carbon and nitrogen molecular bands under the assumption of 1D, it is extremely time consuming in 3D. In this contribution to the 2016 CO5BOLD workshop we review the improvements made to the 3D spectral synthesis code Linfor3D, and discuss the new challenges found when computing molecular features in 3D.

  14. 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.

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

    Institute of Scientific and Technical Information of China (English)

    Jing Ren; Norbert Christlieb; Gang Zhao

    2012-01-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Constantino, Thomas; Campbell, Simon; Lattanzio, John [Monash Centre for Astrophysics, School of Mathematical Sciences, Monash University, Victoria 3800 (Australia); Gil-Pons, Pilar, E-mail: thomas.constantino@monash.edu [Department of Applied Physics, Polytechnic University of Catalonia, 08860 Barcelona (Spain)

    2014-03-20

    The vital importance of composition-dependent low-temperature opacity in low-mass (M ≤ 3 M {sub ☉}) 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 {sub ☉}) 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 {sub ☉} ≤ 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 {sub 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.

  17. 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.

  18. Metal-Poor, Strongly Star-Forming Galaxies in the DEEP2 Survey: The Relationship Between Stellar Mass, Temperature-Based Metallicity, and Star Formation Rate

    Science.gov (United States)

    Ly, Chun; Rigby, Jane R.; Cooper, Michael; Yan, Renbin

    2015-01-01

    We report on the discovery of 28 redshift (z) approximately equal to 0.8 metal-poor galaxies in DEEP2. These galaxies were selected for their detection of the weak [O (sub III)] lambda 4363 emission line, which provides a "direct" measure of the gas-phase metallicity. A primary goal for identifying these rare galaxies is to examine whether the fundamental metallicity relation (FMR) between stellar mass, gas metallicity, and star formation rate (SFR) holds for low stellar mass and high SFR galaxies. The FMR suggests that higher SFR galaxies have lower metallicity (at fixed stellar mass). To test this trend, we combine spectroscopic measurements of metallicity and dust-corrected SFR with stellar mass estimates from modeling the optical photometry. We find that these galaxies are 1.05 plus or minus 0.61 dex above the redshift (z) approximately 1 stellar mass-SFR relation and 0.23 plus or minus 0.23 dex below the local mass-metallicity relation. Relative to the FMR, the latter offset is reduced to 0.01 dex, but significant dispersion remains dex with 0.16 dex due to measurement uncertainties). This dispersion suggests that gas accretion, star formation, and chemical enrichment have not reached equilibrium in these galaxies. This is evident by their short stellar mass doubling timescale of approximately equal to 100 (sup plus 310) (sub minus 75) million years which suggests stochastic star formation. Combining our sample with other redshift (z) of approximately 1 metal-poor galaxies, we find a weak positive SFR-metallicity dependence (at fixed stellar mass) that is significant at 94.4 percent confidence. We interpret this positive correlation as recent star formation that has enriched the gas but has not had time to drive the metal-enriched gas out with feedback mechanisms.

  19. VVV Survey Observations of a Microlensing Stellar Mass Black Hole Candidate in the Field of the Globular Cluster NGC 6553

    CERN Document Server

    Minniti, D; Alonso-Garcia, J; Anguita, T; Catelan, M; Gran, F; Motta, V; Muro, G; Rojas, K; Saito, R K

    2015-01-01

    We report the discovery of a large timescale candidate microlensing event of a bulge stellar source based on near-infrared observations with the VISTA Variables in the Via Lactea Survey (VVV). The new microlensing event is projected only 3.5 arcmin away from the center of the globular cluster NGC 6553. The source appears to be a bulge giant star with magnitude Ks = 13.52, based on the position in the color-magnitude diagram. The foreground lens may be located in the globular cluster, which has well-known parameters such as distance and proper motions. If the lens is a cluster member, we can directly estimate its mass simply following Paczynski et al. (1996) which is a modified version of the more general case due to Refsdal. In that case, the lens would be a massive stellar remnant, with M = 1.5-3.5 Msun. If the blending fraction of the microlensing event appears to be small, and this lens would represent a good isolated black hole (BH) candidate, that would be the oldest BH known. Alternative explanations (w...

  20. FORS2/VLT survey of Milky Way globular clusters. II. Fe and Mg abundances of 51 Milky Way globular clusters on a homogeneous scale

    Science.gov (United States)

    Dias, B.; Barbuy, B.; Saviane, I.; Held, E. V.; Da Costa, G. S.; Ortolani, S.; Gullieuszik, M.; Vásquez, S.

    2016-05-01

    Context. Globular clusters trace the formation and evolution of the Milky Way and surrounding galaxies, and outline their chemical enrichment history. To accomplish these tasks it is important to have large samples of clusters with homogeneous data and analysis to derive kinematics, chemical abundances, ages and locations. Aims: We obtain homogeneous metallicities and α-element enhancement for 51 Galactic bulge, disc, and halo globular clusters that are among the most distant and/or highly reddened in the Galaxy's globular cluster system. We also provide membership selection based on stellar radial velocities and atmospheric parameters. The implications of our results are discussed. Methods: We observed R ~ 2000 spectra in the wavelength interval 456-586 nm for over 800 red giant stars in 51 Galactic globular clusters. We applied full spectrum fitting with the code ETOILE together with libraries of observed and synthetic spectra. We compared the mean abundances of all clusters with previous work and with field stars. We used the relation between mean metallicity and horizontal branch morphology defined by all clusters to select outliers for discussion. Results: [Fe/H], [Mg/Fe], and [α/Fe] were derived in a consistent way for almost one-third of all Galactic globular clusters. We find our metallicities are comparable to those derived from high-resolution data to within σ = 0.08 dex over the interval -2.5< [Fe/H] < 0.0. Furthermore, a comparison of previous metallicity scales with our values yields σ< 0.16 dex. We also find that the distribution of [Mg/Fe] and [α/Fe] with [Fe/H] for the 51 clusters follows the general trend exhibited by field stars. It is the first time that the following clusters have been included in a large sample of homogeneous stellar spectroscopic observations and metallicity derivation: BH 176, Djorg 2, Pal 10, NGC 6426, Lynga 7, and Terzan 8. In particular, only photometric metallicities were available previously for the first three

  1. DEEP CHANDRA MONITORING OBSERVATIONS OF NGC 4649. II. WIDE-FIELD HUBBLE SPACE TELESCOPE IMAGING OF THE GLOBULAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Strader, Jay [Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan, MI 48824 (United States); Fabbiano, Giuseppina; Luo, Bin; Kim, Dong-Woo; Fragos, Tassos [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Brodie, Jean P. [UCO/Lick Observatory, 1156 High Street, Santa Cruz, CA 95064 (United States); Gallagher, John S. [Department of Astronomy, University of Wisconsin, Madison, WI 53706-1582 (United States); Kalogera, Vassiliki [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); King, Andrew [Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom); Zezas, Andreas, E-mail: strader@pa.msu.edu [Physics Department, University of Crete, P.O. Box 2208, GR-710 03, Heraklion, Crete (Greece)

    2012-11-20

    We present g and z photometry and size estimates for globular clusters (GCs) in the massive Virgo elliptical NGC 4649 (M60) using a five-pointing Hubble Space Telescope/Advanced Camera for Surveys mosaic. The metal-poor GCs show a monotonic negative metallicity gradient of -0.43 {+-} 0.10 dex per dex in radius over the full radial range of the data, out to {approx}24 kpc. There is evidence for substantial color substructure among the metal-rich GCs. The metal-poor GCs have typical sizes {approx}0.4 pc larger than the metal-rich GCs out to large galactocentric distances ({approx}> 20 kpc), favoring an intrinsic explanation for the size difference rather than projection effects. There is no clear relation between half-light radius and galactocentric distance beyond {approx}15 kpc, suggesting that the sizes of GCs are not generically set by tidal limitation. Finally, we identify {approx}20 candidate ultracompact dwarfs that extend down to surprisingly faint absolute magnitudes (M{sub z} {approx} -8.5), and may bridge the gap between this class and 'extended clusters' in the Local Group. Three of the brighter candidates have published radial velocities and can be confirmed as bona fide ultracompact dwarfs; follow-up spectroscopy will determine the nature of the remainder of the candidates.

  2. The Giraffe Inner Bulge Survey (GIBS) II. Metallicity distributions and alpha element abundances at fixed Galactic latitude

    CERN Document Server

    Gonzalez, O A; Vasquez, S; Hill, V; Rejkuba, M; Valenti, E; Rojas-Arriagada, A; Renzini, A; Babusiaux, C; Minniti, D; Brown, T M

    2015-01-01

    High resolution (R$\\sim$22,500) spectra for 400 red clump giants, in four fields within $\\rm -4.8^{\\circ} \\lesssim b \\lesssim -3.4^{\\circ}$ and $\\rm -10^{\\circ} \\lesssim l \\lesssim +10^{\\circ}$, were obtained within the GIRAFFE Inner Bulge Survey (GIBS) project. To this sample we added another $\\sim$ 400 stars in Baade's Window, observed with the identical instrumental configuration. We constructed the metallicity distributions for the entire sample, as well as for each field individually, in order to investigate the presence of gradients or field-to-field variations in the shape of the distributions. The metallicity distributions in the five fields are consistent with being drawn from a single parent population, indicating the absence of a gradient along the major axis of the Galactic bar. The global metallicity distribution is well fitted by two Gaussians. The metal poor component is rather broad, with a mean at $\\rm =-0.31$ dex and $\\sigma=0.31$ dex. The metal-rich one is narrower, with mean $\\rm =+0.26$ a...

  3. Kinematics in the Galactic Bulge with APOGEE: II. High-Order Kinematical Moments and Comparison to Extragalactic Bar Diagnostics

    CERN Document Server

    Zasowski, G; Pérez, A E García; Martinez-Valpuesta, I; Johnson, J A; Majewski, S R

    2016-01-01

    Much of the inner Milky Way's (MW) global rotation and velocity dispersion patterns can be reproduced by models of secularly-evolved, bar-dominated bulges. More sophisticated constraints, including the higher moments of the line-of-sight velocity distributions (LOSVDs) and limits on the chemodynamical substructure, are critical for interpreting observations of the unresolved inner regions of extragalactic systems and for placing the MW in context with other galaxies. Here, we use SDSS-APOGEE data to develop these constraints, by presenting the first maps of the LOSVD skewness and kurtosis of metal-rich and metal-poor inner MW stars (divided at [Fe/H] = -0.4), and comparing the observed patterns to those that are seen both in N-body models and in extragalactic bars. Despite closely matching the mean velocity and dispersion, the models do not reproduce the observed LOSVD skewness patterns in different ways, which demonstrates that our understanding of the detailed orbital structure of the inner MW remains an im...

  4. The morphological details of globular keratohyalin granules.

    Science.gov (United States)

    Westerhof, W; Dingemans, K P

    1986-10-01

    In quickly dividing epithelia such as that of the tongue, keratohyalin formation takes place in globular keratohyalin granules (KHG). This is in contrast with the irregular KHG as seen in normal, slowly dividing epidermis. The morphogenesis of the globular KHG is explained in this study. In small KHG, dense aggregates of ribosomes can be seen at the site of blebs. It is suggested that these blebs framed with ribosomes are internalized giving rise to "dense homogeneous deposits" or "single granules". Lipid droplets occur in the upper spinous and horny layer. Globular KHG also contain variable amounts of lipids, and the lipid content seems to be inversely related to the protein content, dependent on the degree of cell differentiation or on the rate of cell turnover. It is suggested that in epithelia with a high cell turnover few rigid keratohyalin components are dispersed in lipids, which maintain a globular shape due to the surface tension.

  5. Globular Cluster X-ray Sources

    CERN Document Server

    Verbunt, F

    2004-01-01

    After a brief historical overview we discuss the luminous X-ray sources in globular clusters of our Galaxy. This is followed by an overview of the very luminous X-ray sources studied in globular clusters of 14 other galaxies, and a discussion of their formation and the relation to X-ray sources outside globular clusters. We describe the discovery and classification of low-luminosity X-ray sources, and end the review with some remarks on the formation and evolution of X-ray sources in globular clusters. Observational results are summarized in three tables. Comments are very welcome. Please send them to F.W.M.Verbunt@astro.uu.nl and lewin@mit.edu.

  6. Constraining the structure and formation of the Galactic bulge from a field in its outskirts. FLAMES-GIRAFFE spectra of $\\sim400$ red giants around $(l,b)=(0\\degr,-10\\degr)$

    CERN Document Server

    Uttenthaler, Stefan; Nataf, David M; Robin, Annie C; Lebzelter, Thomas; Chen, B

    2012-01-01

    The presence of two stellar populations in the Milky Way bulge has been reported recently. We aim at studying the abundances and kinematics of stars in the outer bulge, thereby providing additional constraints on models of its formation. Spectra of 401 red giant stars in a field at (l,b)=(0{\\deg},-10{\\deg}) were obtained with FLAMES at the VLT. Stars of luminosities down to below the two bulge red clumps (RCs) are included. From these spectra we measure general metallicities, abundances of Fe and the alpha-elements, and radial velocities (RV) of the stars. These measurements as well as photometric data are compared to simulations with the Besancon and TRILEGAL models of the Galaxy. We confirm the presence of two populations among our sample stars: i) a metal-rich one at [M/H] ~+0.3, comprising about 30% of the sample, with low RV dispersion and low alpha-abundance, and ii) a metal-poor population at [M/H] ~-0.6 with high RV dispersion and high alpha-abundance. The metal-rich population could be connected to t...

  7. Some Remarks on Extragalactic Globular Clusters

    CERN Document Server

    Richtler, T

    2005-01-01

    I comment (in a review fashion) on a few selected topics in the field of extragalactic globular clusters with strong emphasis on recent work. The topics are: bimodality in the colour distribution of cluster systems, young massive clusters, and the brightest old clusters. Globular cluster research, perhaps more than ever, has lead to important (at least to astronomers) progress and problems in galaxy structure and formation.

  8. Deep Infrared Array Imaging of Globular Clusters. IV. M22 (NGC 6656)

    Science.gov (United States)

    Davidge, T. J.; Harris, W. E.

    1996-05-01

    Moderately deep J and K' images, recorded during subarcsecond seeing conditions, are used to investigate the near-infrared color-magnitude diagram (CMD) of the heavily reddened metal-poor globular cluster M22 (NGC 6656). The CMD constructed from these data extends from K = 7 to K = 18, and includes the upper portions of the main sequence. The main-sequence turnoff (MSTO) occurs at K = 15.1 and J - K = 0.41 values that are well matched by metal-poor 12 Gyr isochrones from Bergbusch & VandenBerg and Straniero & Chieffi after adopting canonical values for the cluster distance and reddening. For comparison, 16 Gyr isochrones are unable to match the brightness and color of the MSTO, although we emphasize that uncertainties in our current knowledge of stellar structure and evolution make any estimate of absolute ages tentative. We also compare the M22 CMD with that obtained for M13 by Davidge & Harris. After correcting for differences in distance, reddening, and [Fe/H], we find that the brightnesses of the subgiant branch (SGB) and MSTO in M22 and M13 are not significantly different. However, the M22 giant branch is steeper than that in M13, a finding contrary to the relative metallicities of these clusters, but consistent with earlier optical observations by Hesser, Hart- wick, & McClure. In particular, the lower giant branch of M22 falls blueward of M13, although the upper giant branches coincide. We suggest that the overall giant branch slope at near-infrared wavelengths may be sensitive to parameters other than age and [Fe/H]. Finally, we investigate the mass function of stars with masses between 0.5 and 0.8 Msun. The data are consistent with a relatively flat mass function above 0.6 Msun, a result broadly consistent with what would be predicted based on the mean metallicity and location of M22 in the Galaxy.

  9. Pseudo bulges in galaxy groups: the role of environment in secular evolution

    Science.gov (United States)

    Mishra, Preetish K.; Wadadekar, Yogesh; Barway, Sudhanshu

    2017-01-01

    We examine the dependence of the fraction of galaxies containing pseudo bulges on environment for a flux limited sample of ˜5000 SDSS galaxies. We have separated bulges into classical and pseudo bulge categories based on their position on the Kormendy diagram. Pseudo bulges are thought to be formed by internal processes and are a result of secular evolution in galaxies. We attempt to understand the dependence of secular evolution on environment and morphology. Dividing our sample of disc+bulge galaxies based on group membership into three categories: central and satellite galaxies in groups and isolated field galaxies, we find that pseudo bulge fraction is almost equal for satellite and field galaxies. Fraction of pseudo bulge hosts in central galaxies is almost half of the fraction of pseudo bulges in satellite and field galaxies. This trend is also valid when only galaxies are considered only spirals or S0. Using the projected fifth nearest neighbour density as measure of local environment, we look for the dependence of pseudo bulge fraction on environmental density. Satellite and field galaxies show very weak or no dependence of pseudo bulge fraction on environment. However, fraction of pseudo bulges hosted by central galaxies decreases with increase in local environmental density. We do not find any dependence of pseudo bulge luminosity on environment. Our results suggest that the processes that differentiate the bulge types are a function of environment while processes responsible for the formation of pseudo bulges seem to be independent of environment.

  10. Chemical Abundances of the Highly Obscured Galactic Globular Clusters 2MASS GC02 and Mercer 5

    CERN Document Server

    Penaloza, Francisco; Vasquez, Sergio; Borissova, Jura; Kurtev, Radostin; Zoccali, Manuela

    2015-01-01

    We present the first high spectral resolution abundance analysis of two newly discovered Galactic globular clusters, namely Mercer 5 and 2MASS GC02 residing in regions of high interstellar reddening in the direction of the Galactic center. The data were acquired with the Phoenix high-resolution near-infrared echelle spectrograph at Gemini South (R~50000) in the 15500.0 A - 15575.0 A spectral region. Iron, Oxygen, Silicon, Titanium and Nickel abundances were derived for two red giant stars, in each cluster, by comparing the entire observed spectrum with a grid of synthetic spectra generated with MOOG. We found [Fe/H] values of -0.86 +/- 0.12 and -1.08 +/- 0.13 for Mercer 5 and 2MASS GC02 respectively. The [O/Fe], [Si/Fe] and [Ti/Fe] ratios of the measured stars of Mercer 5 follow the general trend of both bulge field and cluster stars at this metallicity, and are enhanced by > +0.3. The 2MASS GC02 stars have relatively lower ratios, but still compatible with other bulge clusters. Based on metallicity and abund...

  11. Fracture and springback on Double Bulge Tube Hydro-Forming

    Directory of Open Access Journals (Sweden)

    F. Djavanroodi

    2008-01-01

    Full Text Available This research aims to establish a basic understanding of Double Bulge Tube Hydro-Form processing of stainless steel deep drawn cups. The method is briefly reviewed by carrying out experimental tests and Finite element analysis. By measuring bulge height in both formed curves by Coordinate measuring machine (CMM and thickness variation specimen by Ulterasonic thickness measurment device (UTM, it has been shown that maximum thinness occured where the bending is maximized. A finite element model is constructed to simulate the Double Bulge Tube Hydro Forming process and asses the influence of friction cofficient, tube Material properties and springback. It has been shown that material hardening coefficient had the most significant influence on formability characteristics during double bulge tube hydroforming. Also it is shown that springback has significant effect on tolerances of formed tube. Finally fracture strain was estimated by analytical method and compared with simulation results, also fracture location was predicted on Double Bulge Tube Hydro-Forming (DBTHF by simulating the process.

  12. Bulge growth through disk instabilities in high-redshift galaxies

    CERN Document Server

    Bournaud, Frederic

    2015-01-01

    The role of disk instabilities, such as bars and spiral arms, and the associated resonances, in growing bulges in the inner regions of disk galaxies have long been studied in the low-redshift nearby Universe. There it has long been probed observationally, in particular through peanut-shaped bulges. This secular growth of bulges in modern disk galaxies is driven by weak, non-axisymmetric instabilities: it mostly produces pseudo-bulges at slow rates and with long star-formation timescales. Disk instabilities at high redshift (z>1) in moderate-mass to massive galaxies (10^10 to a few 10^11 Msun of stars) are very different from those found in modern spiral galaxies. High-redshift disks are globally unstable and fragment into giant clumps containing 10^8-10^9 Msun of gas and stars each, which results in highly irregular galaxy morphologies. The clumps and other features associated to the violent instability drive disk evolution and bulge growth through various mechanisms, on short timescales. The giant clumps can...

  13. Chemical composition and constraints on mass loss for globular clusters in dwarf galaxies: WLM and IKN

    Science.gov (United States)

    Larsen, Søren S.; Brodie, Jean P.; Forbes, Duncan A.; Strader, Jay

    2014-05-01

    Aims: We determine the metallicities of globular clusters (GCs) in the WLM and IKN dwarf galaxies, using VLT/UVES and Keck/ESI spectroscopy. These measurements are combined with literature data for field stars to constrain GC formation scenarios. For the WLM GC, we also measure detailed abundance ratios for a number of light, α, Fe-peak, and n-capture elements, which are compared with literature data for the Fornax dSph and the Milky Way. Methods: The abundances are derived by computing synthetic integrated-light model spectra and adjusting the input composition until the best fits to the observed spectra are obtained. Results: We find low metallicities of [Fe/H] = -2.0 and -2.1 for the WLM GC and the GC IKN-5, respectively. We estimate that 17%-31% of the stars with [Fe/H] ≤ -2 in WLM belong to the GC, and IKN-5 may even contain a similar number of metal-poor stars as the whole of the IKN dwarf itself. While these fractions are much higher than in the Milky Way halo, we have previously found a similarly high ratio of metal-poor GCs to field stars in the Fornax dSph. The overall abundance patterns in the WLM GC are similar to those observed for GCs in the Fornax dSph: the [Ca/Fe] and [Ti/Fe] ratios are super-Solar at about +0.3 dex, while [Mg/Fe] is less elevated than [Ca/Fe] and [Ti/Fe]. The [Na/Fe] ratio is similar to the averaged [Na/Fe] ratios in Milky Way GCs, but higher (by ~2σ) than those of Milky Way halo stars. Iron-peak (Mn, Sc, Cr) and heavy elements (Ba, Y, La) generally follow the trends seen in the Milky Way halo. Conclusions: The GCs in the WLM and IKN dwarf galaxies resemble those in the Fornax dSph by being significantly more metal-poor than a typical halo GC in the Milky Way and other large galaxies. They are also substantially more metal-poor than the bulk of the field stars in their parent galaxies. It appears that only a small fraction of the Milky Way GC system could have been accreted from galaxies similar to these dwarfs. The relatively

  14. 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

  15. THE DIVERSE ORIGINS OF NEUTRON-CAPTURE ELEMENTS IN THE METAL-POOR STAR HD 94028: POSSIBLE DETECTION OF PRODUCTS OF i-PROCESS NUCLEOSYNTHESIS

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U. [Department of Astronomy, University of Michigan, 1085 S. University Ave., Ann Arbor, MI 48109 (United States); Karakas, Amanda I. [Research School of Astronomy and Astrophysics, The Australian National University, Canberra ACT 2611 (Australia); Pignatari, Marco [E.A. Milne Centre for Astrophysics, Department of Physics and Mathematics, University of Hull, HU6 7RX (United Kingdom); Herwig, Falk, E-mail: iur@umich.edu, E-mail: amanda.karakas@monash.edu, E-mail: mpignatari@gmail.com, E-mail: fherwig@uvic.ca [Joint Institute for Nuclear Astrophysics and Center for the Evolution of the Elements (JINA-CEE) (United States)

    2016-04-10

    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.

  16. The Magellan PFS Planet Search Program: Radial Velocity and Stellar Abundance Analyses of the 360 au, Metal-poor Binary “Twins” HD 133131A & B

    Science.gov (United States)

    Teske, Johanna K.; Shectman, Stephen A.; Vogt, Steve S.; Díaz, Matías; Butler, R. Paul; Crane, Jeffrey D.; Thompson, Ian B.; Arriagada, Pamela

    2016-12-01

    We present a new precision radial velocity (RV) data set that reveals multiple planets orbiting the stars in the ˜360 au, G2+G2 “twin” binary HD 133131AB. Our six years of high-resolution echelle observations from MIKE and five years from the Planet Finder Spectrograph (PFS) on the Magellan telescopes indicate the presence of two eccentric planets around HD 133131A with minimum masses of 1.43 ± 0.03 and 0.63 ± 0.15 {{ M }}{{J}} at 1.44 ± 0.005 and 4.79 ± 0.92 au, respectively. Additional PFS observations of HD 133131B spanning five years indicate the presence of one eccentric planet of minimum mass 2.50 ± 0.05 {{ M }}{{J}} at 6.40 ± 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 the 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 parameters and measure a suite of 21 abundances across a wide range of condensation temperatures. The host stars are old (likely ˜9.5 Gyr) and metal-poor ([Fe/H] ˜ -0.30), and we detect a ˜0.03 dex depletion in refractory elements in HD 133131A versus B (with standard errors ˜0.017). This detection and analysis adds to a small but growing sample of binary “twin” exoplanet host stars with precise abundances measured, and represents the most metal-poor and likely oldest in that sample. Overall, the planets around HD 133131A and B fall in an unexpected regime in planet mass-host star metallicity space and will serve as an important benchmark for the study of long-period giant planets. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  17. Tidal tails around globular clusters: are they good tracers of cluster orbits?

    CERN Document Server

    Matteo, P D; Miocchi, P; Montuori, M

    2006-01-01

    In the last decade, observational studies have shown the existence of tidal streams in the outer part of many galactic globular clusters. The most striking examples of clusters with well defined tidal tails are represented by Palomar 5 and NGC 5466 (both observed in the framework of the Sloan Digital Sky Survey), which show structures elongated for 4 kpc and 1 kpc in length, respectively. Unfortunately, most of the observational studies about globular clusters (GCs) do not cover such a large field of the sky as the SDSS does. In this framework, by mean of a parallel, adaptive tree-code, we performed detailed N-body simulations of GCs moving in a realistic three-components (bulge, disk and halo) Milky Way potential, in order to clarify whether and to what extent tails in the clusters outer regions (few tidal radii) are tracers of the local orbits and, also, if some kind of correlation exists among the cluster orbital phase and the orientation of such streams.

  18. MCAO near-IR photometry of the Globular Cluster NGC 6388: MAD observations in crowded fields

    CERN Document Server

    Moretti, A; Arcidiacono, C; Milone, A P; Ragazzoni, R; Falomo, R; Farinato, J; Bedin, L R; Anderson, J; Sarajedini, A; Baruffolo, A; Diolaiti, E; Lombini, M; Brast, R; Donaldson, R; Kolb, J; Marchetti, E; Tordo, S

    2008-01-01

    Deep photometry of crowded fields, such as Galactic Globular Clusters, is severely limited by the actual resolution of ground-based telescopes. On the other hand, the Hubble Space Telescope does not provide the near-infrared (NIR) filters needed to allow large color baselines. In this work we aim at demonstrating how ground based observations can reach the required resolution when using Multi-Conjugated Adaptive Optic (MCAO) devices in the NIR, such as the experimental infrared camera (MAD) available on the VLT. This is particularly important since these corrections are planned to be available on all ground--based telescopes in the near future. We do this by combining the infrared photometry obtained by MAD/VLT with ACS/HST optical photometry of our scientific target, the bulge globular cluster NGC 6388, in which we imaged two fields. In particular, we constructed color-magnitude diagrams with an extremely wide color baseline in order to investigate the presence of multiple stellar populations in this cluster...

  19. The lack of carbon stars in the Galactic bulge

    Institute of Scientific and Technical Information of China (English)

    Zhu Chun-Hua; Lv Guo-Liang; Wang Zhao-Jun; Zhang Jun

    2008-01-01

    In order to explain the lack of carbon stars in the Galactic bulge, we have made a detailed study of thermal pulseasymptotic giant branch (TP-AGB) stars by using a population synthesis code. The effects of the oxygen overabundance and the mass loss rate on the ratio of the number of carbon stars to that of oxygen stars in the Galactic bulge are discussed. We find that the oxygen overabundance which is about twice as large as that in the solar neighbourhood (close to the present observations) is insufficient to explain the rareness of carbon stars in the bulge. We suggest that the large mass loss rate may serve as a controlling factor in the ratio of the number of carbon stars to that of oxygen stars.

  20. Near-Infrared Bulge-Disk Correlations of Lenticular Galaxies

    CERN Document Server

    Barway, Sudhanshu; Kembhavi, Ajit K; Mayya, Y D

    2008-01-01

    We consider the luminosity and environmental dependence of structural parameters of lenticular galaxies in the near-infrared K band. Using a two-dimensional galaxy image decomposition technique, we extract bulge and disk structural parameters for a sample of 36 lenticular galaxies observed by us in the K band. By combining data from the literature for field and cluster lenticulars with our data, we study correlations between parameters that characterise the bulge and the disk as a function of luminosity and environment. We find that scaling relations such as the Kormendy relation, photometric plane and other correlations involving bulge and disk parameters show a luminosity dependence. This dependence can be explained in terms of galaxy formation models in which faint lenticulars (M_T > -24.5) formed via secular formation processes that likely formed the pseudobulges of late-type disk galaxies, while brighter lenticulars (M_T < -24.5) formed through a different formation mechanism most likely involving maj...

  1. Galactic Rotation Described with Bulge+Disk Gravitational Models

    CERN Document Server

    Gallo, C F

    2008-01-01

    Observations reveal that mature spiral galaxies consist of stars, gases and plasma approximately distributed in a thin disk of circular shape, usually with a central bulge. The rotation velocities quickly increase from the galactic center and then achieve a constant velocity from the core to the periphery. The basic dynamic behavior of a mature spiral galaxy, such as the Milky Way, is well described by simple models balancing Newtonian gravitational forces against the centrifugal forces associated with a rotating thin axisymmetric disk. In this research, we investigate the effects of adding central bulges to thin disk gravitational models. Even with the addition of substantial central bulges, all the critical essential features of our thin disk gravitational models are preserved. (1) Balancing Newtonian gravitational and centrifugal forces at every point within the disk yields computed radial mass distributions that describe the measured rotation velocity profiles of mature spiral galaxies successfully. (2) T...

  2. The Metallicity Gradient of the Old Galactic Bulge Population

    CERN Document Server

    Fuentes, Sara Alejandra Sans

    2014-01-01

    Understanding the structure, formation and evolution of the Galactic Bulge requires the proper determination of spatial metallicity gradients in both the radial and vertical directions. RR Lyrae pulsators, known to be excellent distance indicators, may hold the key to determining these gradients. Jurcsik & Kovacs (1996) has shown that RR Lyrae light curves and the phase difference of their Fourier decomposition, {\\phi}31, can be used to estimate photometric metallicities. The existence of galactic bulge metallicity gradients is a currently debated topic that would help pinpoint the Galaxy's formation and evolution. A recent study of the OGLE-III Galactic Bulge RR Lyrae Population by Pietrukowicz et al. (2012) suggests that the spatial distribution is uniform. We investigate how small a gradient would be detectable within the current S/N levels of the present data set, given the random and systematic errors associated with the derivation of a photometric metallicity versus spatial position relationship.

  3. All quiet in Globular Clusters

    CERN Document Server

    Dobrotka, A; Menou, K; Dobrotka, Andrej; Lasota, Jean-Pierre; Menou, Kristen

    2006-01-01

    Cataclysmic Variables (CVs) should be present in large numbers in Globular Clusters (GCs). Numerous low-luminosity X-ray sources identified over the past few years as candidate CVs in GCs support this notion. Yet, very few "cataclysms," the characteristic feature of this class of objects in the field, have been observed in GCs. We address this discrepancy here, within the framework of the standard Disk Instability Model for CV outbursts. We argue that the paucity of outbursts in GCs is probably not a direct consequence of the donors' low metallicities. We present diagnostics based on outburst properties allowing tests of the hypothesis that rare cataclysms are entirely due to lower mass transfer rates in GCs relative to the field, and we argue against this explanation. Instead, we propose that a combination of low mass transfer rates (>~ 10^14-15 g/s) and moderately strong white dwarf magnetic moments (>~ 10^30 G cm^3) stabilize CV disks in GCs and thus prevent most of them from experiencing frequent outburst...

  4. 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...

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

    Science.gov (United States)

    Amarsi, A. M.; Lind, K.; Asplund, M.; Barklem, P. S.; Collet, R.

    2016-12-01

    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 overestimated 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 atmospheres; these differences go in the same direction as the non-LTE effects themselves. We make available grids of departure coefficients, equivalent widths and abundance corrections, calculated on 1D MARCS model atmospheres and horizontally and temporally averaged 3D STAGGER model atmospheres.

  6. 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...

  7. 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...

  8. The Binary Frequency of r-Process-Element Enhanced Metal-Poor Stars and its Implications: Chemical Tagging in the Primitive Halo of the Milky Way

    CERN Document Server

    Hansen, Terese; Nordström, Birgitta; Buchhave, Lars A; Beers, Timothy C

    2011-01-01

    A few rare halo giants in the range [Fe/H] $\\simeq -2.9\\pm0.3$ exhibit {\\it r}-process element abundances that vary as a group by factors up to [$r$/Fe] $\\sim80$, relative to those of the iron peak and below. Yet, the astrophysical production site of these {\\it r}-process elements remains unclear. We report initial results from four years of monitoring the radial velocities of 17 {\\it r}-process-enhanced metal-poor giants to detect and characterise binaries in this sample. We find three (possibly four) spectroscopic binaries with orbital periods and eccentricities that are indistinguishable from those of Population I binaries with giant primaries, and which exhibit no signs that the secondary components have passed through the AGB stage of evolution or exploded as supernovae. The other 14 stars in our sample appear to be single -- including the prototypical $r$-process-element enhanced star CS 22892-052, which is also enhanced in carbon, but not in {\\it s}-process elements. We conclude that the {\\it r}-proces...

  9. 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.

  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

    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.

  11. 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 ...

  12. 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...

  13. Keck Observations of the Young Metal-Poor Host Galaxy of the Super-Chandrasekhar-Mass Type Ia Supernova SN 2007if

    CERN Document Server

    Childress, M; Aragon, C; Antilogus, P; Bailey, S; Baltay, C; Bongard, S; Buton, C; Canto, A; Chotard, N; Copin, Y; Fakhouri, H K; Gangler, E; Kerschhaggl, M; Kowalski, M; Hsiao, E Y; Loken, S; Nugent, P; Paech, K; Pain, R; Pecontal, E; Pereira, R; Perlmutter, S; Rabinowitz, D; Runge, K; Scalzo, R; Thomas, R C; Smadja, G; Tao, C; Weaver, B A; Wu, C

    2011-01-01

    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 $m_g=23.15\\pm0.06$, which at the spectroscopically-measured redshift of $z_{helio}=0.07450\\pm0.00015$ corresponds to an absolute magnitude of $M_g=-14.45\\pm0.06$. Galaxy $g-r$ color constrains the mass-to-light ratio, giving a host stellar mass estimate of $\\log(M_*/M_\\odot)=7.32\\pm0.17$. Balmer absorption in the stellar continuum, along with the strength of the 4000\\AA\\ break, constrain the age of the dominant starburst in the galaxy to be $t_\\mathrm{burst}=123^{+165}_{-77}$ Myr, corresponding to a main-sequence turn-off mass of $M/M_\\odot=4.6^{+2.6}_{-1.4}$. Using the R$_{23}$ method of calculating metallicity from the fluxes of strong emission lines, we determine the host oxygen abundance to be $12+\\log(O/H)_\\mathrm{KK04}=8.01\\pm0.09$, significantly lower than any previously reported...

  14. First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements

    CERN Document Server

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

    2004-01-01

    We have investigated the poorly-understood origin of nitrogen in the early Galaxy by determining N abundances in 35 extremely metal-poor halo giants (22 stars have [Fe/H]<-3.0) using the C and O abundances determined in Paper V. Because any dredge-up of CNO processed material to the surface may complicate the interpretation of CNO abundances in giants, we have also measured the surface abundance of lithium. Our sample shows a clear dichotomy between two groups of stars. The first group shows evidence of C to N conversion through CN cycling and strong Li dilution, a signature of mixing. The second group shows no evidence for C to N conversion, and Li is only moderately diluted, and we conclude that their C and N abundances are very close to those of the gas from which they formed in the early Galaxy. These "unmixed" stars reflect the abundances in the early Galaxy: the [C/Fe] ratio is constant (about +0.2 dex) and the [C/Mg] ratio is close to solar at low metallicity, favouring a high C production by massiv...

  15. 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 ...

  16. 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...

  17. Oxygen and light element synthesis by neutron-capture reactions in metal-free and extremely metal-poor AGB stars

    CERN Document Server

    Nishimura, Takanori; Suda, Takuma; Fujimoto, Masayuki Y

    2009-01-01

    The metal-free (Pop. III) and extremely metal-poor (EMP) stars of low- and intermediate-masses experience mixing of hydrogen into the helium convection during the early TP-AGB phase, differently from the meal-rich stars. We study the nucleosynthesis in the helium convective zone with 13C formed from mixed protons as neutron source by using a nuclear network from H through S. In the absence or scarcity of the pristine metals, the neutron-recycling reactions, 12C(n,g)13C(a,n)16O and also 16O(n,g)17O(a,n)20Ne promote the synthesis of O and light elements, including their neutron-rich isotopes and the odd atomic number elements. Based on the results, we demonstrate that the peculiar abundance patterns of C through Al observed for the three most iron-deficient, carbon-rich stars can be reproduced in terms of the nucleosynthesis in Pop. III, AGB stars in the different mass range. We argue that these three stars were born as the low-mass members of Pop. III binaries and later subject to the surface pollution by the ...

  18. Observations of Binary Stars with the Differential Speckle Survey Instrument. V. Toward an Empirical Metal-Poor Mass-Luminosity Relation

    CERN Document Server

    Horch, Elliott P; Demarque, Pierre; Howell, Steve B; Everett, Mark E; Ciardi, David R; Teske, Johanna K; Henry, Todd J; Winters, Jennifer G

    2015-01-01

    In an effort to better understand the details of the stellar structure and evolution of metal poor stars, the Gemini North telescope was used on two occasions to take speckle imaging data of a sample of known spectroscopic binary stars and other nearby stars in order to search for and resolve close companions. The observations were obtained using the Differential Speckle Survey Instrument, which takes data in two filters simultaneously. The results presented here are of 90 observations of 23 systems in which one or more companions was detected, and 6 stars where no companion was detected to the limit of the camera capabilities at Gemini. In the case of the binary and multiple stars, these results are then further analyzed to make first orbit determinations in five cases, and orbit refinements in four other cases. Mass information is derived, and since the systems span a range in metallicity, a study is presented that compares our results with the expected trend in total mass as derived from the most recent Ya...

  19. 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...

  20. 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...