Group: Gr. Estrutura e Evolução Galáctica (OV-UFRJ) - Matteucci:F [4 articles]

Abstract

Chromospheric activity is widely used as an age indicator for solar-type stars based on the early evidence that there is a smooth evolution from young and active to old and inactive stars. We analysed chromospheric activity in five solar-type stars in two open clusters, in order to study how chromospheric activity evolves with time. We took UVES high-resolution, high S/N ratio spectra of 3 stars in IC 4756 and 2 in NGC 5822, which were combined with a previously studied data-set and reanalysed here. The emission core ...

Abstract

We aim at studying the abundance gradients along the Galactic disk and their dependence upon several parameters: a threshold in the surface gas density regulating star formation, the star formation efficiency, the timescale for the formation of the thin disk and the total surface mass density of the stellar halo. We test a model which considers a cosmological infall law. This law does not predict an inside-out disk formation, but it allows to well fit the properties of the solar vicinity. We study several cases. We find ...

Abstract

Oxygen to iron abundance ratios of metal-poor stars provide information on nucleosynthesis yields from massive stars that end in Type II supernova (SN II) explosions. Using a standard model of chemical evolution of the Galaxy we have reproduced the solar neighborhood abundance data and estimated the oxygen and iron yields of genuine SN II origin. The estimated yields are compared with the theoretical yields to derive the relation between the lower and upper mass limits in each generation of stars and the initial mass function (IMF) slope. Independent of ...

Abstract

The time-scales of chemical enrichment are fundamental to understand the evolution of abundances and abundance ratios in galaxies. In particular, the time-scales for the enrichment by SNe II and SNe Ia are crucial in interpreting the evolution of abundance ratios such as [alpha/Fe]. In fact, the alpha-elements are produced mainly by SNe II on time-scales of the order of 3 to 30 Myr, whereas the Fe is mainly produced by SNe Ia on a larger range of time-scales, going from 30 Myr to a Hubble time. This ...