Browsing by Author "Romano, D."
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- ItemThe Gaia-ESO survey: Mapping the shape and evolution of the radial abundance gradients with open clusters(Les Ulis : EDP Sciences, 2023) Magrini, L.; Viscasillas Vázquez, C.; Spina, L.; Randich, S.; Romano, D.; Franciosini, E.; Recio-Blanco, A.; Nordlander, T.; D'orazi, V.; Baratella, M.; Smiljanic, R.; Dantas, M.L.L.; Pasquini, L.; Spitoni, E.; Casali, G.; Van Der Swaelmen, M.; Bensby, T.; Stonkute, E.; Feltzing, S.; Sacco, G.G.; Bragaglia, A.; Pancino, E.; Heiter, U.; Biazzo, K.; Gilmore, G.; Bergemann, M.; Tautvaišienė, G.; Worley, C.; Hourihane, A.; Gonneau, A.; Morbidelli, L.Context. The spatial distribution of elemental abundances and their time evolution are among the major constraints to disentangling the scenarios of formation and evolution of the Galaxy. Aims. In this paper we used the sample of open clusters available in the final release of the Gaia-ESO survey to trace the Galactic radial abundance and abundance-to-iron ratio gradients, and their time evolution. Methods. We selected member stars in 62 open clusters, with ages from 0.1 to about 7 Gyr, located in the Galactic thin disc at galactocentric radii (RGC) from about 6 to 21 kpc. We analysed the shape of the resulting [Fe/H] gradient, the average gradients [El/H] and [El/Fe] combining elements belonging to four different nucleosynthesis channels, and their individual abundance and abundance ratio gradients. We also investigated the time evolution of the gradients dividing open clusters in three age bins. Results. The [Fe/H] gradient has a slope of −0.054 dex kpc−1. It can be better approximated with a two-slope shape, steeper for RGC ≤ 11.2 kpc and flatter in the outer regions. We saw different behaviours for elements belonging to different channels. For the time evolution of the gradient, we found that the youngest clusters (age < 1 Gyr) in the inner disc have lower metallicity than their older counterparts and that they outline a flatter gradient. We considered some possible explanations, including the effects of gas inflow and migration. We suggest that the most likely one may be related to a bias introduced by the standard spectroscopic analysis producing lower metallicities in the analysis of low-gravity stars. Conclusions. To delineate the shape of the ‘true’ gradient, we should most likely limit our analysis to stars with low surface gravity log g > 2.5 and microturbulent parameter ξ < 1.8 km s−1. Based on this reduced sample, we can conclude that the gradient has minimally evolved over the time-frame outlined by the open clusters, indicating a slow and stationary formation of the thin disc over the last 3 Gyr. We found a secondary role of cluster migration in shaping the gradient, with a more prominent role of migration for the oldest clusters.
- ItemThe Gaia-ESO Survey: Probing the lithium abundances in old metal-rich dwarf stars in the solar vicinity(Les Ulis : EDP Sciences, 2022) Dantas, M.L.L.; Guiglion, G.; Smiljanic, R.; Romano, D.; Magrini, L.; Bensby, T.; Chiappini, C.; Franciosini, E.; Nepal, S.; Tautvaišienė, G.; Gilmore, G.; Randich, S.; Lanzafame, A.C.; Heiter, U.; Morbidelli, L.; Prisinzano, L.; Zaggia, S.Context. Lithium (Li) is a fragile element that is produced in a variety of sites but can also be very easily depleted in stellar photospheres. Radial migration has been reported to explain the decrease in the upper envelope of Li measurements observed for relatively old metal-rich dwarf stars in some surveys. Aims. We test a scenario in which radial migration could affect the Li abundance pattern of dwarf stars in the solar neighbourhood. This may confirm that the Li abundances in these stars cannot serve as a probe for the Li abundance in the interstellar medium (ISM). In other words, to probe the evolution of the Li abundance in the local ISM, it is crucial that stellar intruders be identified and removed from the adopted sample. Methods. We used the high-quality data (including Li abundances) from the sixth internal Data Release of the Gaia-ESO survey. In this sample we grouped stars by similarity in chemical abundances via hierarchical clustering. Our analysis treats both measured Li abundances and upper limits. Results. The Li envelope of the previously identified radially migrated stars is well below the benchmark meteoritic value (<3.26 dex); the star with the highest detected abundance has A(Li) = 2.76 dex. This confirms the previous trends observed for old dwarf stars (median ages ~ 8 Gyr), where Li decreases for [Fe/H] ≳ 0. Conclusions. This result is supporting evidence that the abundance of Li measured in the upper envelope of old dwarf stars should not be considered a proxy for the ISM Li. Our scenario also indicates that the stellar yields for [M/H] >0 should not be decreased, as recently proposed in the literature. Our study backs recent studies that claim that old dwarfs on the hot side of the dip are efficient probes of the ISM abundance of Li, provided atomic diffusion does not significantly lower the initial Li abundance in the atmospheres of metal-rich objects.