Examinando por Autor "Allende Prieto C."
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Ítem A Perspective on the Milky Way Bulge Bar as Seen from the Neutron-capture Elements Cerium and Neodymium with APOGEE(Institute of Physics, 2024-04-01) Sales-Silva J.V.; Cunha K.; Smith V.V.; Daflon S.; Souto D.; Guerço R.; Queiroz A.; Chiappini C.; Hayes C.R.; Masseron T.; Hasselquist, Sten; Horta D.; Prantzos N.; Zoccali M.; Allende Prieto C.; Barbuy B.; Beaton R.; Bizyaev D.; Fernández-Trincado J.G.; Frinchaboy P.M.; Holtzman J.A.; Johnson J.A.; Jönsson, Henrik; Majewski S.R.; Minniti D.; Nidever D.L.; Schiavon R.P.; Schultheis M.; Sobeck J.; Stringfellow G.S.; Zasowski G.This study probes the chemical abundances of the neutron-capture elements cerium and neodymium in the inner Milky Way from an analysis of a sample of ∼2000 stars in the Galactic bulge bar spatially contained within ∣X Gal∣ < 5 kpc, ∣Y Gal∣ < 3.5 kpc, and ∣Z Gal∣ < 1 kpc, and spanning metallicities between −2.0 ≲ [Fe/H] ≲ +0.5. We classify the sample stars into low- or high-[Mg/Fe] populations and find that, in general, values of [Ce/Fe] and [Nd/Fe] increase as the metallicity decreases for the low- and high-[Mg/Fe] populations. Ce abundances show a more complex variation across the metallicity range of our bulge-bar sample when compared to Nd, with the r-process dominating the production of neutron-capture elements in the high-[Mg/Fe] population ([Ce/Nd] < 0.0). We find a spatial chemical dependence of Ce and Nd abundances for our sample of bulge-bar stars, with low- and high-[Mg/Fe] populations displaying a distinct abundance distribution. In the region close to the center of the MW, the low-[Mg/Fe] population is dominated by stars with low [Ce/Fe], [Ce/Mg], [Nd/Mg], [Nd/Fe], and [Ce/Nd] ratios. The low [Ce/Nd] ratio indicates a significant contribution in this central region from r-process yields for the low-[Mg/Fe] population. The chemical pattern of the most metal-poor stars in our sample suggests an early chemical enrichment of the bulge dominated by yields from core-collapse supernovae and r-process astrophysical sites, such as magnetorotational supernovae.Ítem Baade's window and APOGEE: Metallicities, ages, and chemical abundances(2017-04) Schultheis M.; Rojas-Arriagada A.; García Pérez A.E.; Jönsson H.; Hayden M.; Nandakumar G.; Cunha K.; Allende Prieto C.; Holtzman J.A.; Beers T.C.; Bizyaev D.; Brinkmann J.; Carrera R.; Cohen R.E.; Geisler D.; Hearty F.R.; Fernandez-Tricado J.G.; Maraston C.; Minnitti D.; Nitschelm C.; Roman-Lopes A.; Schneider D.P.; Tang B.; Villanova S.; Zasowski G.; Majewski S.R.Context. Baade's window (BW) is one of the most observed Galactic bulge fields in terms of chemical abundances. Owing to its low and homogeneous interstellar absorption it is considered the perfect calibration field for Galactic bulge studies. Aims. In the era of large spectroscopic surveys, calibration fields such as BW are necessary for cross calibrating the stellar parameters and individual abundances of the APOGEE survey. Methods. We use the APOGEE BW stars to derive the metallicity distribution function (MDF) and individual abundances for α-and iron-peak elements of the APOGEE ASPCAP pipeline (DR13), as well as the age distribution for stars in BW. Results. We determine the MDF of APOGEE stars in BW and find a remarkable agreement with that of the Gaia-ESO survey (GES). Both exhibit a clear bimodal distribution. We also find that the Mg-metallicity planes of the two surveys agree well, except for the metal-rich part ([Fe/H] > 0.1), where APOGEE finds systematically higher Mg abundances with respect to the GES. The ages based on the [C/N] ratio reveal a bimodal age distribution, with a major old population at ~ 10 Gyr, with a decreasing tail towards younger stars. A comparison of stellar parameters determined by APOGEE and those determined by other sources reveals detectable systematic offsets, in particular for spectroscopic surface gravity estimates. In general, we find a good agreement between individual abundances of O, Na, Mg, Al, Si, K, Ca, Cr, Mn, Co, and Ni from APOGEE with that of literature values. Conclusions. We have shown that in general APOGEE data show a good agreement in terms of MDF and individual chemical abundances with respect to literature works. Using the [C/N] ratio we found a significant fraction of young stars in BW. © ESO, 2017.Ítem The gaia -ESO survey: Calibration strategy(EDP Sciences, 2017-02) Pancino E.; Lardo C.; Altavilla G.; Marinoni S.; Ragaini S.; Cocozza G.; Bellazzini M.; Sabbi E.; Zoccali M.; Donati P.; Heiter U.; Koposov S.E.; Blomme R.; Morel T.; Símon-Díaz S.; Lobel A.; Soubiran C.; Montalban J.; Valentini M.; Casey A.R.; Blanco-Cuaresma S.; Jofré P.; Worley C.C.; Magrini L.; Hourihane A.; François P.; Feltzing S.; Gilmore G.; Randich S.; Asplund M.; Bonifacio P.; Drew J.E.; Jeffries R.D.; Micela G.; Vallenari A.; Alfaro E.J.; Allende Prieto C.; Babusiaux C.; Bensby T.; Bragaglia A.; Flaccomio E.; Hambly N.; Korn A.J.; Lanzafame A.C.; Smiljanic R.; Van Eck S.; Walton N.A.; Bayo A.; Carraro G.; Costado M.T.; Damiani F.; Edvardsson B.; Franciosini E.; Frasca A.; Lewis J.; Monaco L.; Morbidelli L.; Prisinzano L.; Sacco G.G.; Sbordone L.The Gaia-ESO survey (GES) is now in its fifth and last year of observations and has produced tens of thousands of high-quality spectra of stars in all Milky Way components. This paper presents the strategy behind the selection of astrophysical calibration targets, ensuring that all GES results on radial velocities, atmospheric parameters, and chemical abundance ratios will be both internally consistent and easily comparable with other literature results, especially from other large spectroscopic surveys and from Gaia. The calibration of GES is particularly delicate because of (i) the large space of parameters covered by its targets, ranging from dwarfs to giants, from O to M stars; these targets have a large wide of metallicities and also include fast rotators, emission line objects, and stars affected by veiling; (ii) the variety of observing setups, with different wavelength ranges and resolution; and (iii) the choice of analyzing the data with many different state-of-the-art methods, each stronger in a different region of the parameter space, which ensures a better understanding of systematic uncertainties. An overview of the GES calibration and homogenization strategy is also given, along with some examples of the usage and results of calibrators in GES iDR4, which is the fourth internal GES data release and will form the basis of the next GES public data release. The agreement between GES iDR4 recommended values and reference values for the calibrating objects are very satisfactory. The average offsets and spreads are generally compatible with the GES measurement errors, which in iDR4 data already meet the requirements set by the main GES scientific goals. © ESO, 2017.Ítem The Gaia-ESO Survey: Low-α element stars in the Galactic bulge(EDP Sciences, 2017-07) Recio-Blanco A.; Rojas-Arriagada A.; De Laverny P.; Mikolaitis S.; Hill V.; Zoccali M.; Fernández-Trincado J.G.; Robin A.C.; Babusiaux C.; Gilmore G.; Randich S.; Alfaro E.; Allende Prieto C.; Bragaglia A.; Carraro G.; Jofré P.; Lardo C.; Monaco L.; Morbidelli L.; Zaggia S.We take advantage of the Gaia-ESO Survey iDR4 bulge data to search for abundance anomalies that could shed light on the composite nature of the Milky Way bulge. The α-element (Mg, Si, and whenever available, Ca) abundances, and their trends with Fe abundances have been analysed for a total of 776 bulge stars. In addition, the aluminum abundances and their ratio to Fe and Mg have also been examined. Our analysis reveals the existence of low-α element abundance stars with respect to the standard bulge sequence in the [α/ Fe] versus [Fe/H] plane. Eighteen objects present deviations in [α/ Fe] ranging from 2.1 to 5.3σ with respect to the median standard value. Those stars do not show Mg-Al anti-correlation patterns. Incidentally, this sign of the existence of multiple stellar populations is reported firmly for the first time for the bulge globular cluster NGC 6522. The identified low-α abundance stars have chemical patterns that are compatible with those of the thin disc. Their link with massive dwarf galaxies accretion seems unlikely, as larger deviations in α abundance and Al would be expected. The vision of a bulge composite nature and a complex formation process is reinforced by our results. The approach used, which is a multi-method and model-driven analysis of high resolution data, seems crucial to reveal this complexity. © ESO, 2017.