Examinando por Autor "Worley, C."

Mostrando 1 - 7 de 7
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    Gaia-ESO Survey: Gas dynamics in the Carina nebula through optical emission lines
    (EDP SCIENCES, 2016-06) Damiani, F.; Bonito, R.; Magrini, L.; Prisinzano, L.; Mapelli, M.; Micela, G.; Kalari, V.; Maíz Apellániz, J.; Gilmore, G.; Randich, S.; Alfaro, E.; Flaccomio, E.; Koposov, S.; Klutsch, A.; Lanzafame, A. C.; Pancino, E.; Sacco, G. G.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Lardo, C.; Lewis, J.; Monaco, L.; Morbidelli, L.; Worley, C.; Zaggia, S.; Zwitter, T.; Dorda, R.
    Aims. We present observations from the Gaia-ESO Survey in the lines of Hα, [N II], [S II], and He I of nebular emission in the central part of the Carina nebula. Methods. We investigate the properties of the two already known kinematic components (approaching and receding), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV >50 km s-1) gas emission. Results. We show that gas giving rise to Hα and He I emission is dynamically well correlated with but not identical to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arise from several distinct shell-like expanding regions, the most evident found around η Car, the Trumpler 14 core, and the star WR25. These “shells” are non-spherical and show distortions probably caused by collisions with other shells or colder, higher-density gas. Some of them are also partially obscured by foreground dust lanes, while very little dust is found in their interior. Preferential directions, parallel to the dark dust lanes, are found in the shell geometries and physical properties, probably related to strong density gradients in the studied region. We also find evidence that the ionizing flux emerging from η Car and the surrounding Homunculus nebula varies with polar angle. The high-velocity components in the wings of Hα are found to arise from expanding dust reflecting the η Car spectrum.
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    The Gaia -ESO Survey: The origin and evolution of s -process elements
    (EDP Sciences, 2018-09) Magrini, L.; Spina, L.; Randich, S.; Friel, E.; Kordopatis, G.; Worley, C.; Pancino, E.; Bragaglia, A.; Donati, P.; Tautvaišienė, G.; Bagdonas, V.; Delgado-Mena, E.; Adibekyan, V.; Sousa, S.G.; Jiménez-Esteban, F.M.; Sanna, N.; Roccatagliata, V.; Bonito, R.; Sbordone, L.; Duffau, S.; Gilmore, G.; Feltzing, S.; Jeffries, R.D.; Vallenari, A.; Alfaro, E.J.; Bensby, T.; Francois, P.; Koposov, S.; Korn, A.J.; Recio-Blanco, A.; Smiljanic, R.; Bayo, A.; Carraro, G.; Casey, A.R.; Costado, M.T.; Damiani, F.; Franciosini, E.; Frasca, A.; Hourihane, A.; Jofré, P.; De Laverny, P.; Lewis, J.; Masseron, T.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sacco, G.; Zaggia, S.
    Context. Several works have found an increase of the abundances of the s-process neutron-capture elements in the youngest Galactic stellar populations. These trends provide important constraints on stellar and Galactic evolution and they need to be confirmed with large and statistically significant samples of stars spanning wide age and distance intervals. Aims. We aim to trace the abundance patterns and the time evolution of five s-process elements - two belonging to the first peak, Y and Zr, and three belonging to the second peak, Ba, La, and Ce - using the Gaia-ESO IDR5 results for open clusters and disc stars. Methods. From the UVES spectra of cluster member stars, we determined the average composition of clusters with ages >0.1 Gyr. We derived statistical ages and distances of field stars, and we separated them into thin and thick disc populations. We studied the time-evolution and dependence on metallicity of abundance ratios using open clusters and field stars whose parameters and abundances were derived in a homogeneous way. Results. Using our large and homogeneous sample of open clusters, thin and thick disc stars, spanning an age range larger than 10 Gyr, we confirm an increase towards young ages of s-process abundances in the solar neighbourhood. These trends are well defined for open clusters and stars located nearby the solar position and they may be explained by a late enrichment due to significant contribution to the production of these elements from long-living low-mass stars. At the same time, we find a strong dependence of the s-process abundance ratios on the Galactocentric distance and on the metallicity of the clusters and field stars. Conclusions. Our results, derived from the largest and most homogeneous sample of s-process abundances in the literature, confirm the growth with decreasing stellar ages of the s-process abundances in both field and open cluster stars. At the same time, taking advantage of the abundances of open clusters located in a wide Galactocentric range, these results offer a new perspective on the dependence of the s-process evolution on the metallicity and star formation history, pointing to different behaviours at various Galactocentric distances. © 2018 ESO.
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    THE GAIA-ESO SURVEY: METAL-RICH BANANAS IN THE BULGE
    (IOP PUBLISHING, 2016-06) 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.
    We analyze the kinematics of similar to 2000 giant stars in the direction of the Galactic bulge, extracted from the Gaia-ESO survey in the region -10 degrees less than or similar to l less than or similar to 10 degrees and -11 degrees less than or similar to b less than or similar to -3 degrees. We find distinct kinematic trends in the metal-rich ([M/H] > 0) and metal-poor ([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 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.
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    The Gaia-ESO Survey: pre-main-sequence stars in the young open cluster NGC 3293
    (OXFORD UNIV PRESS, 2016-05) Delgado, A. J.; Sampedro, L.; Alfaro, E. J.; Costado, M. T.; Yun, J. L.; Frasca, A.; Lanzafame, A. C.; Drew, J. E.; Eislöffel, J.; Blomme, R.; Morel, T.; Lobel, A.; Semaan, T.; Randich, S.; Jeffries, R. D.; Micela, G.; Vallenari, A.; Kalari, V.; Gilmore, G.; Flaccomio, E.; Carraro, G.; Lardo, C.; Monaco, L.; Prisinzano, L.; Sousa, S. G.; Morbidelli, L.; Lewis, J.; Koposov, S.; Hourihane, A.; Worley, C.; Casey, A.; Franciosini, E.; Sacco, G.; Magrini, L.
    The young open cluster NGC3293 is included in the observing program of the Gaia-ESO survey (GES). The radial velocity values provided have been used to assign cluster membership probabilities by means of a single-variable parametric analysis. These membership probabilities are compared to the results of the photometric membership assignment of NGC3293, based on UBVRI photometry. The agreement of the photometric and kinematic member samples amounts to 65 per cent, and could increase to 70 per cent as suggested by the analysis of the differences between both samples. A number of photometric PMS candidate members of spectral type F are found, which are confirmed by the results from VPHAS photometry and SED fitting for the stars in common with VPHAS and GES data sets. Excesses at mid- and near-infrared wavelengths, and signs of Hα emission, are investigated for them. Marginal presence of Hα emission or infilling is detected for the candidate members. Several of them exhibit moderate signs of U excess and weak excesses at mid-IR wavelengths. We suggest that these features originate from accretion discs in their last stages of evolution.
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    The Gaia-ESO Survey: the most metal-poor stars in the galactic bulge
    (Oxford University Press, 2014-09) Howes, L.M.; Asplund, M.; 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.; Allende Prieto, C.; 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.
    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 utilizes 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 [α/Fe] ratios.
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    The Gaia-ESO Survey: The most metal-poor stars in the Galactic bulge
    (2014) Howes, L.M.; Asplund, M.; 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.
    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 utilizes 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 [a/Fe] ratios. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
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    The Gaia-ESO survey: the non-universality of the age–chemical-clocks–metallicity relations in the Galactic disc
    (EDP Sciences, 2020-07) Casali, G.; Spina, L.; Magrini, L.; Karakas, A. I.; Kobayashi, C.; Feltzing, S.; Van der Swaelmen, M.; Tsantaki, M.; Jofré, P.; Bragaglia, A.; Feuille, D.; . Bensby, T; Biazzo, K.; Gonneau, A; Tautvaišiene˙, G.; Baratella, M; Roccatagliata, V.; Pancino, E.; Sousa, S.; Adibekyan, V.; Martell, S; Bayo, A.; Jackson, R. J.; Jeffries, R. D.; Gilmore, G.; Randich, S.; Alfaro, E.; Koposov, S. E.; Korn, A. J.; Recio-Blanco, A.; Smiljanic, R; . Franciosini, E; Hourihane, A.; Monaco, L.; Morbidelli, L.; Sacco, G.; Worley, C.; Zaggia, S.
    Context. In the era of large spectroscopic surveys, massive databases of high-quality spectra coupled with the products of the Gaia satellite provide tools to outline a new picture of our Galaxy. In this framework, an important piece of information is provided by our ability to infer stellar ages, and consequently to sketch a Galactic timeline. Aims. We aim to provide empirical relations between stellar ages and abundance ratios for a sample of stars with very similar stellar parameters to those of the Sun, namely the so-called solar-like stars. We investigate the dependence on metallicity, and we apply our relations to independent samples, that is, the Gaia-ESO samples of open clusters and of field stars. Methods. We analyse high-resolution and high-signal-to-noise-ratio HARPS spectra of a sample of solar-like stars to obtain precise determinations of their atmospheric parameters and abundances for 25 elements and/or ions belonging to the main nucleosynthesis channels through differential spectral analysis, and of their ages through isochrone fitting. Results. We investigate the relations between stellar ages and several abundance ratios. For the abundance ratios with a steeper dependence on age, we perform multivariate linear regressions, in which we include the dependence on metallicity, [Fe/H]. We apply our best relations to a sample of open clusters located from the inner to the outer regions of the Galactic disc. Using our relations, we are able to recover the literature ages only for clusters located at RGC > 7 kpc. The values that we obtain for the ages of the inner-disc clusters are much greater than the literature ones. In these clusters, the content of neutron capture elements, such as Y and Zr, is indeed lower than expected from chemical evolution models, and consequently their [Y/Mg] and [Y/Al] are lower than in clusters of the same age located in the solar neighbourhood. With our chemical evolution model and a set of empirical yields, we suggest that a strong dependence on the star formation history and metallicity-dependent stellar yields of s-process elements can substantially modify the slope of the [s/α]–[Fe/H]–age relation in different regions of the Galaxy. Conclusions. Our results point towards a non-universal relation [s/α]–[Fe/H]–age, indicating the existence of relations with different slopes and intercepts at different Galactocentric distances or for different star formation histories. Therefore, relations between ages and abundance ratios obtained from samples of stars located in a limited region of the Galaxy cannot be translated into general relations valid for the whole disc. A better understanding of the s-process at high metallicity is necessary to fully understand the origin of these variations