Examinando por Autor "Mucciarelli A."
Mostrando 1 - 5 de 5
Resultados por página
Opciones de ordenación
Ítem Chemical abundances in the nucleus of the Sagittarius dwarf spheroidal galaxy(EDP Sciences, 2017-09) Mucciarelli A.; Bellazzini M.; Ibata R.; Romano D.; Chapman S.C.; Monaco L.We present iron, magnesium, calcium, and titanium abundances for 235 stars in the central region of the Sagittarius dwarf spheroidal galaxy (within 9:00∼70 pc from the centre) from medium-resolution Keck/Deep Imaging Multi-Object Spectrograph spectra. All the considered stars belong to the massive globular cluster M 54 or to the central nucleus of the galaxy (Sgr, N). In particular we provide abundances for 109 stars with [Fe/H] ≥-1:0, more than doubling the available sample of spectroscopic metallicity and-elements abundance estimates for Sgr dSph stars in this metallicity regime.We find for the first time a metallicity gradient in the Sgr,N population, whose peak iron abundance goes from [Fe/H] =-0:38 for R ≤2:50 to [Fe/H] =-0:57 for 5:0 < R 9:0. On the other hand, the trends of [Mg/Fe], [Ca/Fe], and [Ti/Fe] with [Fe/H] are the same over the entire region explored by our study.We reproduce the observed chemical patterns of the Sagittarius dwarf spheroidal as a whole with a chemical evolution model which implies that a high mass progenitor (MDM = 6 1010 M) and a significant event of mass-stripping occurred a few Gyr ago, presumably starting at the first peri-Galactic passage after infall.Ítem MINCE: II. Neutron capture elements(EDP Sciences, 2024-06) François P.; Cescutti G.; Bonifacio P.; Caffau E.; Monaco L.; Steffen M.; Puschnig J.; Calura F.; Cristallo S.; Di Marcantonio P.; Dobrovolskas V.; Franchini M.; Gallagher A.J.; Hansen C.J.; Korn A.; Kučinskas A.; Lallement R.; Lombardo L.; Lucertini F.; Magrini L.; Matas Pinto A.M.; Matteucci F.; Mucciarelli A.; Sbordone L.; Spite M.; Spitoni E.; Valentini M.Context. Most of the studies on the determination of the chemical composition of metal-poor stars have been focused on the search of the most pristine stars, searching for the imprints of the ejecta of the first supernovae. Apart from the rare and very interesting r-enriched stars, few elements are measurable in the very metal-poor stars. On the other hand, a lot of work has been done also on the thin-disc and thick-disc abundance ratios in a metallicity range from [Fe/H]> -1.5 dex to solar. In the available literature, the intermediate metal-poor stars (-2.5<[Fe/H]< -1.5) have been frequently overlooked. The MINCE (Measuring at Intermediate metallicity Neutron-Capture Elements) project aims to gather the abundances of neutron-capture elements but also of light elements and iron peak elements in a large sample of giant stars in this metallicity range. The missing information has consequences for the precise study of the chemical enrichment of our Galaxy in particular for what concerns neutron-capture elements and it will be only partially covered by future multi object spectroscopic surveys such as WEAVE and 4MOST. Aims. The aim of this work is to study the chemical evolution of galactic sub-components recently identified (i.e. Gaia Sausage Enceladus (GSE), Sequoia). Methods. We used high signal-to-noise ratios, high-resolution spectra and standard 1D LTE spectrum synthesis to determine the detailed abundances. Results. We could determine the abundances for up to 10 neutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm and Eu) in 33 stars. The general trends of abundance ratios [n-capture element/Fe] versus [Fe/H] are in agreement with the results found in the literature. When our sample is divided in sub-groups depending on their kinematics, we found that the run of [Sr/Ba] versus [Ba/H] for the stars belonging to the GSE accretion event shows a tight anti-correlation. The results for the Sequoia stars, although based on a very limited sample, shows a [Sr/Ba] systematically higher than the [Sr/Ba] found in the GSE stars at a given [Ba/H] hinting at a different nucleosynthetic history. Stochastic chemical evolution models have been computed to understand the evolution of the GSE chemical composition of Sr and Ba. The first conclusions are that the GSE chemical evolution is similar to the evolution of a dwarf galaxy with galactic winds and inefficient star formation. Conclusions. Detailed abundances of neutron-capture elements have been measured in high-resolution, high signal-to-noise spectra of intermediate metal-poor stars, the metallicity range covered by the MINCE project. These abundances have been compared to detailed stochastic models of galactic chemical evolution.Ítem The central velocity dispersion of the Milky Way bulge(EDP Sciences, 2018) Valenti E.; Zoccali M.; Mucciarelli A.; González O.A.; Surot F.; Minniti D.; Rejkuba M.; Pasquini L.; Fiorentino G.; Bono G.; Rich R.M.; Soto M.Context: Current spectroscopic and photometric surveys are providing a comprehensive view of the Milky Way bulge stellar population properties with unprecedented accuracy. This in turn allows us to explore the correlation between kinematics and stellar density distribution, crucial to constrain the models of Galactic bulge formation. Aims. The Giraffe Inner Bulge Survey (GIBS) revealed the presence of a velocity dispersion peak in the central few degrees of the Galaxy by consistently measuring high velocity dispersion in the three central most fields. Due to the suboptimal distribution of these fields, all being at negative latitudes and close to each other, the shape and extension of the sigma peak is poorly constrained. In this study we address this by adding new observations distributed more uniformly and in particular including fields at positive latitudes that were missing in GIBS. Methods. Observations with Multi Unit Spectroscopic Explorer (MUSE) were collected in four fields at (l, b) = (0◦, +2◦), (0◦, −2◦), (+1◦, −1◦), and (−1◦, +2◦). Individual stellar spectra were extracted for a number of stars comprised between ∼500 and ∼1200, depending on the seeing and the exposure time. Velocity measurements are done by cross-correlating observed stellar spectra in the CaT region with a synthetic template, and velocity errors are obtained through Monte Carlo simulations, cross-correlating synthetic spectra with a range of different metallicities and different noise characteristics. Results. We measure the central velocity dispersion peak within a projected distance from the Galactic center of ∼280 pc, reaching σVGC ∼ 140 km s−1 at b = −1◦. This is in agreement with the results obtained previously by GIBS at negative longitude. The central sigma peak is symmetric with respect to the Galactic plane, with a longitude extension at least as narrow as predicted by GIBS. As a result of the Monte Carlo simulations we present analytical equations for the radial velocity measurement error as a function of metallicity and signal-to-noise ratio for giant and dwarf stars. © ESO 2018.Ítem The Gaia -ESO Survey: Lithium enrichment histories of the Galactic thick and thin disc(EDP Sciences, 2018-02) Fu X.; Romano D.; Bragaglia A.; Mucciarelli A.; Lind K.; Delgado Mena E.; Sousa S.G.; Randich S.; Bressan A.; Sbordone L.; Martell S.; Korn A.J.; Abia C.; Smiljanic R.; Jofré P.; Pancino E.; Tautvaišiene G.; Tang B.; Magrini L.; Lanzafame A.C.; Carraro G.; Bensby T.; Damiani F.; Alfaro E.J.; Flaccomio E.; Morbidelli L.; Zaggia S.; Lardo C.; Monaco L.; Frasca A.; Donati P.; Drazdauskas A.; Chorniy Y.; Bayo A.; Kordopatis G.Lithium abundance in most of the warm metal-poor main sequence stars shows a constarnt plateau (A(Li) ~ 2.2 dex) and then the upper envelope of the lithium vs. metallicity distribution increases as we approach solar metallicity. Meteorites, which carry information about the chemical composition of the interstellar medium (ISM) at the solar system formation time, show a lithium abundance A(Li) ~ 3.26 dex. This pattern reflects the Li enrichment history of the ISM during the Galaxy lifetime. After the initial Li production in big bang nucleosynthesis, the sources of the enrichment include asymptotic giant branch (AGB) stars, low-mass red giants, novae, type II supernovae, and Galactic cosmic rays. The total amount of enriched Li is sensitive to the relative contribution of these sources. Thus different Li enrichment histories are expected in the Galactic thick and thin disc. We investigate the main sequence stars observed with UVES in Gaia-ESO Survey iDR4 catalogue and find a Li-anticorrelation independent of [Fe/H], Teff, and log(g). Since in stellar evolution different α enhancements at the same metallicity do not lead to a measurable Li abundance change, the anticorrelation indicates that more Li is produced during the Galactic thin disc phase than during the Galactic thick disc phase. We also find a correlation between the abundance of Li and s-process elements Ba and Y, and they both decrease above the solar metallicity, which can be explained in the framework of the adopted Galactic chemical evolution models. © ESO 2018.Ítem The true nature of HE 0057-5959, the most metal-poor, Li-rich star(EDP Sciences, 2024-09) Mucciarelli A.; Bonifacio P.; Monaco L.; Salaris M.; Matteuzzi M.The Li-rich stars are a class of rare objects with a surface lithium abundance, A(Li), that exceeds that of other stars in the same evolutionary stage. The origin of these stars is still debated, and valuable routes to look at include the Cameron-Fowler mechanism, a mass-Transfer process in a binary system, or the engulfment of rocky planets or brown dwarfs. Metal-poor ([Fe/H]