On the validity of the spectroscopic age indicators [Y/Mg], [Y/Al], [Y/Si], [Y/Ca], and [Y/Ti] for giant stars

Abstract

ABSTRACT The abundance ratios [Y/Mg], [Y/Al], [Y/Si], [Y/Ca], and [Y/Ti] have been suggested as chemical clocks for solar-metallicity dwarf stars in the field as well as for giant stars in open clusters. To verify this last hypothesis, we derive these abundances ratios of 50 giant stars belonging to seven open clusters. To calculate the abundances, we analyse FEROS spectra assuming the LTE-hypothesis. We confirm that [Y/Mg], [Y/Al], [Y/Si], [Y/Ca], and [Y/Ti] work as chemical clocks for field dwarf stars at the local region (d < 1 kpc) whereas for the field giants the [Y/Mg], [Y/Al], and [Y/Si] also present trends with the ages but high scattering. [Y/Ca] and [Y/Ti] do not present any correlation with ages in the field giants. In our open clusters, the behaviour is similar, [Y/Mg], [Y/Al], and [Y/Si] present evident trends, whereas [Y/Ca] versus ages is a flat and [Y/Ti] versus ages is less steep. We also confirm that the chemical clocks have high scatter at the early ages. In the case of the compiled sample, the chemical clocks are similar to our results but in some situations there are important differences. Several relations between abundance ratios and ages may be obtained when dwarfs and giants are analysed, confirming the non-universality of the spectroscopic age indicators.