Tracing the evolution of the Galactic bulge with chemodynamical modelling of alpha-elements ^⋆

Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, Brazil

Received: 21 October 2016
Accepted: 30 November 2016

Abstract

Context. Galactic bulge abundances can be best understood as indicators of bulge formation and nucleosynthesis processes by comparing them with chemo-dynamical evolution models.

Aims. The aim of this work is to study the abundances of alpha-elements in the Galactic bulge, including a revision of the oxygen abundance in a sample of 56 bulge red giants.

Methods. Literature abundances for O, Mg, Si, Ca and Ti in Galactic bulge stars are compared with chemical evolution models. For oxygen in particular, we reanalysed high-resolution spectra obtained using FLAMES+UVES on the Very Large Telescope, now taking each star’s carbon abundances, derived from CI and C₂ lines, into account simultaneously.

Results. We present a chemical evolution model of alpha-element enrichment in a massive spheroid that represents a typical classical bulge evolution. The code includes multi-zone chemical evolution coupled with hydrodynamics of the gas. Comparisons between the model predictions and the abundance data suggest a typical bulge formation timescale of 1–2 Gyr. The main constraint on the bulge evolution is provided by the O data from analyses that have taken the C abundance and dissociative equilibrium into account. Mg, Si, Ca and Ti trends are well reproduced, whereas the level of overabundance critically depends on the adopted nucleosynthesis prescriptions.