The Gaia-ESO Survey: radial distribution of abundances in the Galactic disc from open clusters and young-field stars

L. Magrini, S. Randich, G. Kordopatis, N. Prantzos, D. Romano, A. Chieffi, M. Limongi, P. Francois, E. Pancino, E. Friel, A. Bragaglia, G. Tautvaisiene, L. Spina, J. Overbeek, T. Cantat-Gaudin, P. Donati, A. Vallenari, R. Sordo, F. M. Jimenez-Esteban, B. Tang, A. Drazdauskas, S. Sousa, S. Duffau, P. Jofre, G. Gilmore, S. Feltzing, E. Alfaro, T. Bensby, E. Flaccomio, S. Koposov, A. Lanzafame, R. Smiljanic, A. Bayo, G. Carraro, A. R. Casey, M. T. Costado, F. Damiani, E. Franciosini, A. Hourihane, C. Lardo, J. Lewis, L. Monaco, L. Morbidelli, G. Sacco, L. Sbordone, C.C. Worley, S. Zaggia. 2017. The Gaia-ESO Survey: radial distribution of abundances in the Galactic disc from open clusters and young-field stars. Astronomy and Astrophysics 603, DOI: 10.1051/0004-6361/201630294

The spatial distribution of elemental abundances in the disc of our Galaxy gives insights both on its assembly process and subsequent evolution, and on the stellar nucleogenesis of the different elements. Gradients can be traced using several types of objects as, for instance, (young and old) stars, open clusters, HII regions, planetary nebulae.

Aims. We aim to trace the radial distributions of abundances of elements produced through different nucleosynthetic channels – the alpha-elements O, Mg, Si, Ca and Ti, and the iron-peak elements Fe, Cr, Ni and Sc – by use of the Gaia-ESO IDR4 results for open clusters and young-field stars.

Methods. From the UVES spectra of member stars, we have determined the average composition of clusters with ages > 0.1 Gyr. We derived statistical ages and distances of field stars. We traced the abundance gradients using the cluster and field populations and compared them with a chemo-dynamical Galactic evolutionary model.

Results. The adopted chemo-dynamical model, with the new generation of metallicity-dependent stellar yields for massive stars, is able to reproduce the observed spatial distributions of abundance ratios, in particular the abundance ratios of [O/Fe] and [Mg/Fe] in the inner disc (5 kpc < R-GC < 7 kpc), with their differences, that were usually poorly explained by chemical evolution models.

Conclusions. Oxygen and magnesium are often considered to be equivalent in tracing alpha-element abundances and in deducing, for example, the formation timescales of different Galactic stellar populations. In addition, often [alpha/Fe] is computed combining several alpha-elements. Our results indicate, as expected, a complex and diverse nucleosynthesis of the various alpha-elements, in particular in the high metallicity regimes, pointing towards a different origin of these elements and highlighting the risk of considering them as a single class with common features.

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