Examinando por Autor "Caffau, Elisabetta"
Mostrando 1 - 4 de 4
Resultados por página
Opciones de ordenación
Ítem Detailed investigation of two high-speed evolved Galactic stars(John Wiley and Sons Inc, 2022-03) Matas Pinto, Aroa del Mar; Caffau, Elisabetta; François, Patrick; Spite, Monique; Bonifacio, Piercarlo; Wanajo, Shinya; Aoki, Wako; Monaco, Lorenzo; Suda, Takuma; Spite, François; Sbordone, Luca; Lombardo, Linda; Mucciarelli, AlessioThe study of metal poor stars provides clarification and knowledge about the primordial Universe. Specially, halo stars provide explanations of the nature of the first generations of stars and the nucleosynthesis in the metal-poor regime. We present a detailed chemical analysis and determination of the kinematic and orbital properties of two stars characterized by high speed with respect to the Sun. We analyzed two high-resolution Subaru spectra employing the MyGIsFOS code, which allows to derive the detailed chemical abundances for 28 elements (C, N, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu), and abundance from two ionization states in the case of four elements (Ti, Cr, Fe, and Zr). TYC 622–742–1 and TYC 1193–1918–1 are metal-poor stars ([Fe/H] of −2.37 and −1.60), they are similar in the chemical pattern with respect to Fe, they are (Formula presented.) enhanced and show a slight excess in Eu abundance. Both giant stars are poor in C and rich in N, as expected for evolved stars, and this fact is supported by the low (Formula presented.) isotopic ratio in TYC 1193–1918–1. Nevertheless, the C abundance of TYC 622–742–1 is particularly low. TYC 622–742–1 and TYC 1193–1918–1 have a similar chemical composition to the other Galactic halo stars of comparable metallicity. According to their kinematics, both stars belong to the Galactic halo, but they are not a part of the Gaia-Sausage-Enceladus structure. © 2021 Wiley-VCH GmbHÍtem Sulfur abundances in the milky way major components(Universidad Andrés Bello, 2023) Lucertini, Francesca; Monaco, Lorenzo; Caffau, Elisabetta; Sbordone, Luca; Bonifacio, Piercarlo; Francois, Patrick; Facultad de Ciencias ExactasThe measurements of chemical abundances and their ratios are a powerful diagnostic to put con straints on both stellar nucleosynthesis and galaxy formation history. For instance, the ratio between elements produced on different timescales, such as α-elements (produced by Supernovae Type-II after ∼30 Myr) and iron (produced by Supernovae Type-Ia on longer timescales), can be used as cosmic clocks. Sulfur is an α-element produced in the final stage of the evolution of massive stars by oxygen convective shell burning and explosive oxygen burning. Moreover, it is moderately volatile so, unlike other α-elements, its abundance measured in stars in the Local Group galaxies can be directly compared to the abundance measured in the gaseous phase in the far Universe, as extra-galactic H II regions or damped Ly-α systems. For these reasons sulfur abundances provide clues on star forma tion history and properties of the interstellar medium, connecting the local and distant Universe. Despite the great potential of this element, most of the available stellar abundances of sulfur come from Galactic stars. Only in the latest years, this analysis was expanded to stars outside the Milky Way. Our view of the behavior of Sulphur in the Milky Way and its satellite is, thus, far from complete. I ran a series of experiments to define the top level requirements needed to measure sulfur abun dances, and I explored the ESO archive looking for available data in a setup adequate for my goal. I identified several interesting public datasets. I focused on the Milky Way major components and, in particular, I found useful data for the Galactic bulge and disk, and a few clusters likely residual of accretion events in the Milky Way (like ω Cen, M 54 and Rup 106). Furthermore, the collaboration with the MINCE project gave me access to high-quality spectra of giant stars at intermediate metallicities in the Milky Way halo. The analysis of this dataset provides important clues about the evolution of Sulphur within the Milky Way. It provides a homogeneous database useful to compare the Milky Way major components with distant systems.Ítem The metallicity distribution in the core of the Sagittarus dwarf spheroidal: Minimising the metallicity biases(EDP Sciences, 2023-01) Minelli, Alice; Bellazzini, Michele; Mucciarelli, Alessio; Bonifacio, Piercarlo; Ibata, Rodrigo; Romano, Donatella; Monaco, Lorenzo; Caffau, Elisabetta; Dalessandro, Emanuele; Pascale, RaffaeleWe present the metallicity and radial velocity for 450 bona fide members of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy, measured from high-resolution spectra (R ' 18 000) obtained with FLAMES at the VLT. The targets were carefully selected (a) to sample the core of the main body of Sgr dSph while avoiding contamination from the central stellar nucleus, and (b) to prevent any bias on the metallicity distribution by selecting targets based on their Gaia parallax and proper motions. All the targets selected in this way were confirmed as radial velocity members. We used this sample to derive the first metallicity distribution of the core of Sgr dSph, which is virtually unaffected by metallicity biases. The observed distribution ranges from [Fe=H] ≃-2:3 to [Fe=H] ≃0:0, with a strong, symmetric, and relatively narrow peak around [Fe=H] ' -0:5 and a weak and extended metal-poor tail, in which only 13:8 ±1:9% of the stars have [Fe=H] < -1:0. We confirm previous evidence of correlations between chemical and kinematical properties of stars in the core of Sgr. In our sample, stars with [Fe=H] ≥ -0:6 display a lower velocity dispersion and a higher rotation amplitude than those with [Fe=H] < -0:6, confirming previous suggestions of disk/halo structure for the progenitor of the system. © The Authors 2023.Ítem Young giants of intermediate mass: Evidence of rotation and mixing(EDP Sciences, 2021-12) Lombardo, Linda; François, Patrick; Bonifacio, Piercarlo; Caffau, Elisabetta; Del Mar Matas Pinto, Aroa; Charbonnel, Corinne; Meynet, Georges; Monaco, Lorenzo; Cescutti, Gabriele; Mucciarelli, AlessioContext. In the search of a sample of metal-poor bright giants using Strömgren photometry, we serendipitously found a sample of 26 young (ages younger than 1 Gyr) metal-rich giants, some of which have high rotational velocities. Aims. We determined the chemical composition and rotational velocities of these stars in order to compare them with predictions from stellar evolution models. These stars where of spectral type A to B when on the main sequence, and we therefore wished to compare their abundance pattern to that of main-sequence A and B stars. Methods. Stellar masses were derived by comparison of the position of the stars in the colour-magnitude diagram with theoretical evolutionary tracks. These masses, together with Gaia photometry and parallaxes, were used to derive the stellar parameters. We used spectrum synthesis and model atmospheres to determine chemical abundances for 16 elements (C, N, O, Mg, Al, Ca, Fe, Sr, Y, Ba, La, Ce, Pr, Nd, Sm, and Eu) and rotational velocities. Results. The age-metallicity degeneracy can affect photometric metallicity calibrations. We identify 15 stars as likely binary stars. All stars are in prograde motion around the Galactic centre and belong to the thin-disc population. All but one of the sample stars present low [C/Fe] and high [N/Fe] ratios together with constant [(C+N+O)/Fe], suggesting that they have undergone CNO processing and first dredge-up. The observed rotational velocities are in line with theoretical predictions of the evolution of rotating stars.