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

Siqueira-Mello, C.; Chiappini, C; Barbuy, Beatriz; Freeman, Kenneth; Ness, M; Depagne, E.; Cantelli, E.; Pignatari, Marco; Hirschi, Raphael; Frischknecht, U.; Meynet, G.; Maeder, A.

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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 [α/Fe] ratios,...[Show more]

dc.contributor.authorSiqueira-Mello, C.
dc.contributor.authorChiappini, C
dc.contributor.authorBarbuy, Beatriz
dc.contributor.authorFreeman, Kenneth
dc.contributor.authorNess, M
dc.contributor.authorDepagne, E.
dc.contributor.authorCantelli, E.
dc.contributor.authorPignatari, Marco
dc.contributor.authorHirschi, Raphael
dc.contributor.authorFrischknecht, U.
dc.contributor.authorMeynet, G.
dc.contributor.authorMaeder, A.
dc.date.accessioned2018-11-29T22:51:59Z
dc.date.available2018-11-29T22:51:59Z
dc.identifier.issn0004-6361
dc.identifier.urihttp://hdl.handle.net/1885/152042
dc.description.abstractContext. 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 [α/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 α-elements O, Mg, Si, Ca, and Ti, the odd-Z elements Na and Al, the neutron-capture s-process dominated elements Y, Zr, La, and Ba, and the r-element Eu. Methods. High-resolution spectra of five field giant stars were obtained at the 8 m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. Spectroscopic parameters were derived based on the excitation and ionization equilibrium of Fe i and Fe ii. The abundance analysis was performed with a MARCS LTE spherical model atmosphere grid and the Turbospectrum spectrum synthesis code. Results. We confirm that the analysed stars are moderately metal-poor (−1.04 ≤ [Fe/H] ≤−0.43), non-carbon-enhanced (non-CEMP) with [C/Fe] ≤ + 0.2, and α-enhanced. We find that our three most metal-poor stars are nitrogen enhanced. The α-enhancement suggests that these stars were formed from a gas enriched by core-collapse supernovae, and that the values are in agreement with results in the literature for bulge stars in the same metallicity range. No abundance anomalies (Na − O, Al − O, Al − Mg anti-correlations) were 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.
dc.format.mimetypeapplication/pdf
dc.publisherSpringer
dc.sourceAstronomy and Astrophysics
dc.titleLooking for imprints of the first stellar generations in metal-poor bulge field stars
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume593
dc.date.issued2016
local.identifier.absfor020100 - ASTRONOMICAL AND SPACE SCIENCES
local.identifier.ariespublicationa383154xPUB4378
local.type.statusPublished Version
local.contributor.affiliationSiqueira-Mello, C., Universidade de São Paulo
local.contributor.affiliationChiappini, C, Leibniz-Institut fur Astrophysik Potsdam
local.contributor.affiliationBarbuy, Beatriz, Universidade de Sao Paulo
local.contributor.affiliationFreeman, Kenneth, College of Science, ANU
local.contributor.affiliationNess, M, Max-Planck-Institut
local.contributor.affiliationDepagne, E., South African Astronomical Observatory
local.contributor.affiliationCantelli, E., Universidade de São Paulo
local.contributor.affiliationPignatari, Marco, University of Hull
local.contributor.affiliationHirschi, Raphael, University of Tokyo
local.contributor.affiliationFrischknecht, U., Keele University
local.contributor.affiliationMeynet, G., Observatoire de Genève
local.contributor.affiliationMaeder, A., Observatoire de Genève
local.bibliographicCitation.issueA79
local.identifier.doi10.1051/0004-6361/201628104
local.identifier.absseo970102 - Expanding Knowledge in the Physical Sciences
dc.date.updated2018-11-29T07:42:27Z
local.identifier.scopusID2-s2.0-84989271251
local.identifier.thomsonID000385820100039
dcterms.accessRightsOpen Access
CollectionsANU Research Publications

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