Browsing by Author "Minchev, I."
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- ItemConstraining the formation of the Milky Way: Ages(Les Ulis : EDP Sciences, 2013) Chiappini, C.; Minchev, I.; Martig, M.We present a new approach for studying the chemodynamical evolution of the Milky Way, which combines a thin disk chemical evolution model with the dynamics from N-body simulation of a galaxy with properties similar to those of our Galaxy. A cosmological re-simulation is used as a surrogate in order to extract ∼11 Gyrs of self-consistent dynamical evolution. We are then in a position to quantify the impact of radial migration at the Solar Vicinity. We find that the distribution of birth radii, r0, of stars ending up in a solar neighborhood-like location after ∼11 Gyr of evolution peaks around r0 = 6 kpc due to radial migration. A wide range of birth radii is seen for different age groups. The strongest effect from radial migration is found for the oldest stars and it is connected to an early merger phase typical from cosmological simulations. We find that while the low-end in our simulated solar vicinity metallicity distribution is composed by stars with a wide range of birth radii, the tail at larger metallicities (0.25 <[Fe/H]< 0.6) results almost exclusively from stars with 3 < r0< 5 kpc. This is the region just inside the bar's corotation (CR), which is where the strongest outward radial migration occurs. The fraction of stars in this tail can, therefore, be related to the bar's dynamical properties, such as its strength, pattern speed and time evolution/formation. We show that one of the main observational constraints of this kind of models is the time variation of the abundance gradients in the disk. The most important outcome of our chemodynamical model is that, although we used only a thin-disc chemical evolution model, the oldest stars that are now in the solar vicinity show several of the properties usually attributed to the Galactic thick disc. In other words, in our model the MW "thick disc" emerges naturally from stars migrating from the inner disc very early on due to strong merger activity in the first couple of Gyr of disc formation, followed by further radial migration driven by the bar and spirals at later times. These results will be extended to other radius bins and more chemical elements in order to provide testable predictions once more precise information on ages and distances would become available (with Gaia, asteroseismology and future surveys such as 4MOST).
- ItemStellar Population Astrophysics (SPA) with the TNG: α-elements, lithium, sodium and aluminum in 16 open clusters(Les Ulis : EDP Sciences, 2022) Zhang, R.; Lucatello, S.; Bragaglia, A.; Alonso-Santiago, J.; Andreuzzi, G.; Casali, G.; Carrera, R.; Carretta, E.; D’Orazi, V.; Frasca, A.; Fu, X.; Magrini, L.; Minchev, I.; Origlia, L.; Spina, L.; Vallenari, A.Context. Exploring the Galactic chemical evolution and enrichment scenarios with open clusters (OCs) allows us to understand the history of the Milky Way disk. High-resolution spectra of OCs are a crucial tool, as they provide precise chemical information, to combine with precise distances and ages. Aims. The aim of the Stellar Population Astrophysics (SPA) project is to derive homogeneous and accurate comprehensive chemical characterization of a number of poorly studied OCs. Methods. Using the HARPS-N echelle spectrograph at the Telescopio Nazionale Galileo (TNG), we obtained high-resolution spectra of giant stars in 18 OCs, 16 of which are chemically characterized for the first time, and two of which are well studied for comparison. The OCs in this sample have ages from a few tens of Myr to 4 Gyr, with a prevalence of young clusters. We already presented the radial velocities and atmospheric parameters for them in a previous SPA paper. Here, we present results for the α-elements O, Mg, Si, Ca and Ti, and the light elements Na and Al, all determined by the equivalent width method. We also measured Li abundance through the synthesis method. Results. We discuss the behaviors of lithium, sodium and aluminum in the context of stellar evolution. For Na and Al, we compare our findings with models to investigate their behaviors as a function of mass, suggesting that Na mixing to the surface might start in masses as low as 2 M·. We study the radial, vertical, and age trends for the measured abundance ratios in a sample that combines our results and recent literature for OCs, finding significant (positive) gradients only for [Mg/Fe] and [Ca/Fe] in all cases. Finally, we compare O and Mg in the combined sample with chemo-dynamical models, finding a good agreement for intermediate-Age and old clusters. There is a sharp increase in the abundance ratios measured among very young clusters (age < 300 Myr), accompanied by a poorer fit with the models for O and Mg, likely related to the inadequacy of traditional model atmospheres and methods in the derivation of atmospheric parameters and abundance ratios for stars of such young ages.