Nucleosynthetic history of elements in the Galactic disk

[X/Fe]–age relations from high-precision spectroscopy^⋆

¹ Universidade de São Paulo, IAGDepartamento de Astronomia, Rua do Matão 1226, 05509-900 São Paulo, Brasil
e-mail: lspina@usp.br
² Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, 3800 Victoria, Australia
³ Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205, USA
⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁵ Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, 2611 Canberra, Australia

Received: 18 March 2016
Accepted: 15 June 2016

Abstract

Context. The chemical composition of stars is intimately linked to the formation and evolution of the Galaxy.

Aims. We aim to trace the chemical evolution of the Galactic disk through the inspection of the [X/Fe]–age relations of 24 species from C to Eu.

Methods. Using high-resolution and high signal-to-noise UVES spectra of nine solar twins, we obtained precise estimates of stellar ages and chemical abundances. These determinations have been integrated with additional accurate age and abundance determinations from recent spectroscopic studies of solar twins existing in the literature, comprising superb abundances with 0.01 dex precision. Based on this data set, we outlined the [X/Fe]–age relations over a time interval of 10 Gyr.

Results. We present the [X/Fe] – age relations for 24 elements (C, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Ba, La, Ce, Nd, and Eu). Each different class of elements showed a distinct evolution with time that relies on the different characteristics, rates, and timescales of the nucleosynthesis sites from which they are produced. The α-elements are characterized by a [X/Fe] decrease with time. Strikingly, the opposite behavior is observed for Ca. The iron-peak elements show an early [X/Fe] increase followed by a decrease towards the youngest stars. The [X/Fe] for the n-capture elements decrease with age. We also found that both [Mg/Y] and [Al/Y] are precise stellar clocks, with [Al/Y] showing the steepest dependence on age.

Conclusions. Knowledge of the [X/Fe]-age relations is a gold mine from which we can achieve a great understanding of the processes that governed the formation and evolution of the Milky Way. Through the reverse engineering of these relations we will be able to put strong constraints on the nature of the stellar formation history, the SNe rates, the stellar yields, and the variety of the SNe progenitors.